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Self-imaging of tailored vortex pulse arrays andspectral Gouy rotation echoes

Max Liebmann, Alexander Treffer, Martin Bock, Thomas Seiler, Jürgen Jahns, Thomas Elsaesser, and Ruediger Grunwald

Doc ID: 351594 Received 14 Nov 2018; Accepted 18 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: Self-imaging of femtosecond pulses with orbital angularmomentum is studied in spectral domain by illuminatingorthogonal arrays of spiral gratings. Spectral Gouyrotation, i.e., the characteristic circulation of extremalregions near phase singularities in spatial spectral maps,is found to partially reappear at discrete distances. Selfimagingof co-rotating and counter-rotating vortices iscompared in intensity and spectral behavior. Highselectivitypattern recognition from weakly modulatedspectral maps is demonstrated by analyzing spectralmoments. By our experiments, the classical Talbot effectis extended to polychromatic pulsed vortex arrays withcontrolled maps of rotation sign.

Orbital angular momentum generation in two modefiber based on the modal interference principle

Guolu Yin, Liang Chuancan, IROEGBU PAUL Ikechukwu, Ming Deng, leilei shi, Qinjiang Fu, Tao Zhu, and Lin Zhang

Doc ID: 355047 Received 13 Dec 2018; Accepted 18 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: In this paper, we demonstrated a novel method togenerate orbital angular momentum based on theprinciple of the modal interference in a two mode fiber.At the interference dips, the left- or right-handed circularpolarized HE11 modes can be ideally converted into the ±1order OAM beam. To verify this concept, we employed thefemtosecond laser micro-processing technology to writemicro-waveguides in the two mode fiber, and hencerealized the in-line modal interferometer. To enhance themode conversion efficiency at the dips, we optimized thewaveguide parameters both theoretically andexperimentally. The interference spectrum and spiral/forkpatterns confirm the OAM beam generation with efficiencyhigh up to 99%.

Diagnosing plasmas with wideband THz pulses

Alessandro Curcio and massimo petrarca

Doc ID: 357248 Received 09 Jan 2019; Accepted 17 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: A diagnostic method for the electron plasma densityand temperature based on the exploitation of widebandTHz pulses is presented. The model accompanyingthe diagnostic method is described and it is shownuseful to characterize the plasma density and temperatureprofile along a symmetry axis. This diagnosticsis particularly interesting for plasma-accelerationschemes or laser-produced plasma channels.

Are Graphene-Bi2Te3 van der Waalsheterostructure based saturable absorberspromising for solid-state Q-switched lasers?

junpeng qiao, Wei-heng Sung, Jia Lan, YuanYao Lin, Meng Yu Wu, Ranran Fan, Yufei Li, Wenchao Qiao, Hong Liu, Shengzhi Zhao, and Chao-Kuei Lee

Doc ID: 354610 Received 05 Dec 2018; Accepted 17 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: This study compared the absorption characteristics of ahomemade graphene-Bi2Te3 (G-B) van der Waalsheterostructure to a Bi2Te3 topological insulator (TI)with a similar preparation method and number of layers.The results indicate that the G-B heterostructure cantremendously enhance the modulation depth andsaturable intensity. In addition, a passively Q-switchedlaser at 1.06 μm with a G-B heterostructure as asaturable absorber was demonstrated for the first time.Compared to Bi2Te3 TI, the G-B heterostructure Qswitchedlaser had better laser performance, indicatingthat a G-B heterostructure is a promising saturableabsorber candidate for a 1 μm laser.

Exploring elliptical vortex beams with the spatial damping effect

Yung-Fu Chen, M. X. Hsieh, Y. H. Lai, Y. H. Hsieh, C. W. Tu, Hsing-Chih Liang, and K. F. Huang

Doc ID: 356537 Received 02 Jan 2019; Accepted 17 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: A general integral formula is analytically derived to represent the wave function of elliptical vortex modes. The derived formula can be straightforwardly employed to take account of the spatial damping to explore the vortex structure. The spatial damping is found to cause the central degenerate singularity of the circular vortex mode to be split into several singularities with different topological charges. For the non-circular vortex beam, the influence of the spatial damping on the distribution of the singularities is not significant. The theoretical analyses are confirmed to agree very well with the experimental measurements.

Polarization-maintaining nonlinear-amplifying-loop-mirror mode-locked fiber laser based on a 3x3 coupler

Dohyun Kim, Dohyeon Kwon, Bongwan Lee, and Jungwon Kim

Doc ID: 354823 Received 07 Dec 2018; Accepted 17 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: We demonstrate a robust and low-noise all-polarization-maintaining (PM) nonlinear-amplifying-loop-mirror (NALM) mode-locked Er-fiber laser based on a 3x3 coupler. Since the 3x3 coupler generates 120-degree phase bias, the 3x3 PM-NALM laser can easily acquire mode-locked state even without any additional phase biasing components. In our experiment, the initiation of mode-locking required at least 1.5 times less pump power compared to the similar-structured 2x2 PM-NALM laser. The minimum RIN level reaches -156 dB/Hz with integrated rms RIN of 0.0043% [10 Hz – 1 MHz], which corresponds to one of the lowest integrated RINs from any free-running mode-locked lasers. The laser also features very robust operation against mechanical vibrations. Stable mode-locked operation is maintained for more than 60 minutes even in continuous 1.5g(rms) vibrations.

Low-index second-order metagratings for large-angle anomalous reflection

Xipu Dong, Jie -Rong Cheng, Fei Fan, and Shengjiang Chang

Doc ID: 355142 Received 12 Dec 2018; Accepted 17 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: A large-angle anomalous reflector based on low-index polylactic acid metagratings is designed around 140 GHz. By breaking the limit of fixed bar-to-bar distance and directing the beam into the second diffraction order through the optimization of the 4π phase supercell, the efficiencies for 70° and 80° reflection under normal excitation both reaches 0.82 with wide bandwidth. In contrast, the efficiency is less than 0.2 in conventional designs. The success of the second-order low-index metagrating for large angle deflection originates from the appropriate number of Bloch modes with well-engineered mode interactions and couplings. The design can be potentially fabricated by 3D printing, with promising applications in designing flat lenses of high numerical aperture, and extending the material system of metadevices.

Stable interferometric platform for phase modulation of FEL seed lasers

Andreas Wituschek, M Danailov, Alexander Demidovich, Jergus Strucka, Lukas Bruder, Lars-Stephan Klein, and Frank Stienkemeier

Doc ID: 355345 Received 13 Dec 2018; Accepted 17 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: We present a compact phase modulation setup designed for high laser intensities sufficient to drive highly nonlinear processes, such as high gain harmonic generation (HGHG) in seeded free-electron lasers (FELs). This paves the way for all-XUV coherent nonlinear spectroscopy. The high linearity, phase stability and sensitivity of the setup are demonstrated by probing quantum beats of weak electronic sodium transitions in the deep ultra violet region (268 nm) combined with photoion time-of-flight mass spectrometry.

Tailoring focused optical vortices by using spiral forked plates

Changqing Xie, Yonghao Liang, Hailiang Li, and Enliang Wang

Doc ID: 355417 Received 14 Dec 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: We propose and experimentally demonstrate a single optical element, termed as spiral forked plates (SFPs), to simultaneously generate two tightly focused optical vortices (OVs). The key idea is to combine the advantages of a spiral zone plate (SZP) and a forked grating (FG) through a logic XOR operation. Both theoretical and experimental results demonstrate that SFPs not only can completely suppress the undesirable zeroth (central) order diffraction, but also can further manipulate the topological charges (TCs) of two resultant focused OVs by varying the TCs of the SZP and FG. Thus, SFPs show promising potential for advancing the shrinking and integrating applications of orbital angular momentum superpositions.

Analog of giant magnetoimpedance in magnetized ε-near-zero plasma

Lian Shen, Xiao Lin, Bin Zheng, Muhiddeen Yahaya, Zhiwei Xu, Xiaohong zhang, and Huaping Wang

Doc ID: 352399 Received 23 Nov 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: In this Letter we show that magnetized plasma with proper designed parameters at the plasma frequency suffers large magnetoimpedance change under a moderate external magnetic field. Such an interesting feature can be described as the analog of giant magnetoimpedance (GMI), which is confirmed by detailed calculation. GMI devices based on magnetized ε-near-zero plasma do not require microfabrication and they are capable of working at tunable frequency, even in terahertz frequency range; more importantly, they can be dynamically controlled by the environmental parameters such as temperature and pressure.

Holographic multi-parameter imaging of dynamic phenomena with visual and audio features

Sudheesh Rajput, Osamu Matoba, and Yasuhiro Awatsuji

Doc ID: 352716 Received 26 Nov 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: In this Letter, a concept of new multi-parameter imaging which can acquire visual and audio data of dynamic object phenomena simultaneously by holographic technique is proposed. Temporal intensity distributions give us the visual information of the dynamic events. Temporal profile of the phase distribution can give another different information of the dynamic events such as audio data. These two physical data can express the dynamic events with multi-parameter in various dimensions. The proposed imaging approach has potential in several applications in physics and life science research. Two experimental demonstrations such as static object and broken glass with visual and sound features are provided to show the effectiveness of the proposed concept.

Integration of crescent laser beams into dark-field microscopes for enhancing the Raman characterization of micro/nano particles

Chien-Chung Jeng, Yi-Cheng Wang, Ying-Yu Chen, and Shiuan-Yeh Chen

Doc ID: 352870 Received 27 Nov 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: Dark-field microscopy is widely used to image micro/nano particles or characterize their optical response (scattering spectrum). If laser excitation is incorporated into the microscope, the microscope can further probe chemical (molecular) properties of these objects through Raman scattering. However, when the size of the particles is comparable to or smaller than the characteristic sizes of the laser beam, the conventional setup using on-axis excitation usually suffers from undesired background signals produced by illuminated substrates below the target particles. Therefore, a crescent laser beam possessing a stable shape along the propagation direction is generated by a pair of shifted axicons and then integrated into a dark-field microscope for large oblique angle (i.e., off-axis) excitation. Under this excitation setup, the contrast between Raman and background fluorescence spectra is enhanced by a factor of 4 for a 1 um polystyrene particle sitting on a glass slide, compared to the conventional excitation configuration. This off-axis excitation based on the crescent beam integrates dark-field imaging with Raman spectroscopy and improves Raman characterization of micro/nano particles.

Unipolar subcycle pulse-driven nonresonant excitation of quantum systems

Anton Pakhomov, Rostislav Arkhipov, Ihar Babushkin, Mikhail Arkhipov, Nikolay Rosanov, Ayhan Demircan, and Uwe Morgner

Doc ID: 353270 Received 30 Nov 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: The interaction of subcycle pulses with quantum systems is considered when the pulse duration becomes much smaller than the timescales of electron oscillations. We show analytically that the interaction process in this case is governed by the so called electric pulse area. The efficient nonresonant excitation of quantum system by subcycle pulses with high degree of unipolarity is demonstrated. Obtained results are confirmed by direct numerical solution of multi-level Bloch equations.

Polarization-independent and high-efficiency broadband optical absorber in visible light based on nanostructured germanium arrays

Jiancun Zhao, Xiaochang Yu, Xiaoming Yang, Clarence Augustine TH Tee, Weizheng Yuan, and Yiting Yu

Doc ID: 357467 Received 14 Jan 2019; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: A broadband optical absorber based on the nanostructured germanium (Ge) film composed of single-sized circular nanodisk-nanohole arrays is proposed, which demonstrates high efficiency, strong polarization independence and large viewing angle. Due to the electric and magnetic resonance absorption modes excited by the nanostructure arrays in highly lossy Ge film, the absorber obtains a high absorptivity reaching above 90% over the full visible wavelength, and it can be maintained well at a large viewing angle over ±50°. Based on the geometrical symmetry, the absorber is proved to be polarization independent. Moreover, the simple single-sized nanostructure within a certain size tolerance decreases the design and fabrication complexity. And the structural configuration with a slight Ge sidewall formed in the nanofabrication process could enhance the overall light absorption. These results indicate that the proposed broadband absorber has great potential in various applications such as anti-reflective coating, and perfect cloaking.

Cost-efficient half-duplex 10-Gbit/s all-optical indoor optical wireless communication enabled by a low-cost Fabry-Perot laser/photodetector

Chao Li, Xuebing Zhang, Eduward Tangdiongga, Xiaoyu Dai, Cheng-Ting Tsai, Huai-Yung Wang, Yuanjiang Xiang, Gong-Ru Lin, Zizheng Cao, and Ton Koonen

Doc ID: 354706 Received 06 Dec 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: To develop an indoor optical wireless communication (OWC) system, both the system complexity/cost and data rate need to be taken into consideration. In this letter, a cost-efficient half-duplex OWC system for photonic home area network applications is proposed and experimentally demonstrated. A low-cost Fabry-Perot laser diode (FP-LD) is proposed to be employed as both the downlink receiver (Rx) and uplink transmitter (Tx) at the user side. Enabled by the Fabry-Perot transceiver (FP-TRx), the indoor transmission of 10-Gbit/s 4-level pulse-amplitude-modulation (PAM-4) signal for both down- and uplink is experimentally achieved over 1.7-km SMF and 1.1-m free space. Moreover, the proposed scheme also enables to operate orthogonal frequency division multiplexing (OFDM) signal. The BER levels of multi-gigabit OFDM data for both down- and uplink over 10-hour measurement are all under 7% forward error correction (FEC) limit of 3.8×10-3, which indicates the proposed system is robust, thus can provide a promising solution for high-speed low-cost home area OWC networks.

Multi-microjoule GaSe-based mid-infrared optical parametric amplifier with an ultra-broad idlerspectrum covering 4.2-16 μm

Kun Liu, Houkun Liang, Lifeng Wang, Shizhen Qu, Tino Lang, hao Li, Qijie Wang, and Ying Zhang

Doc ID: 356851 Received 04 Jan 2019; Accepted 16 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: We report a multi-microjoule, ultra-broadband mid- infrared optical parametric amplifier based on a GaSe nonlinear crystal pumped at ~2 μm. The generated idler pulse has a flat spectrum spanning from 4.5 to 13.3 μm at-3 dB and 4.2 to 16 μm in the full spectral range, with a central wavelength of 8.8 μm. The proposed scheme supports a sub-cycle Fourier-transform-limited pulse width. A (2+1)-dimensional numerical simulation is employed to reproduce the obtained idler spectrum. To our best knowledge, this is the broadest -3 dB spectrum ever obtained by optical parametric amplifiers in this spectral region. The idler pulse energy is ~3.4 μJ with a rsion efficiency of ~2% from the ~2 μm pump to theidler pulse.

Abruptly autofocused and rotated circular chirp Pearcey Gaussian vortex beams

Xingyu Chen, Dongmei Deng, Guanghui Wang, Xiangbo Yang, and Hongzhan Liu

Doc ID: 340893 Received 27 Jul 2018; Accepted 16 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: In this letter, we introduce a new class of abruptly autofocued and rotated circular chirp Pearcey Gaussian vortex beams (AARCCPGVBs) which tend to abruptly autofocused circular chirp Pearcey vortex beams or chirp Gaussian vortex beams by adjusting the spatial distribution factors. Different from other rotated beams [Opt. Lett. 31, 694 (2006) and Opt. Lett. 31, 2199 (2006)], the AARCCPGVBs are autofocused abruptly, and maintain a low rotating speed before the focal point and rotate abruptly and quickly in the focal point. Further, the position of the focal point in propagating direction can also be controlled by adjusting the chirp factor.

Accumulation-layer hybridized surface plasmon polaritions at ITO/LiNbO₃ interface

Yingce Wang, Hua Zhao, Dewang Huo, Hang Su, Chao Wang, and Jingwen Zhang

Doc ID: 349971 Received 05 Nov 2018; Accepted 16 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: The inherent large dissipative loss associated with the use of noble metallic materials in conventional plasmonic structures poses a great limitation to their broad practical applications. As an alternative low-loss plasmonic structures, electrostatic modification based surface plasmon polarition (SPP) supporting systems have drawn growing attentions, especially indium-tin-oxide (ITO). Furthermore, the screening of spontaneous polarization and photovoltaic electric fields results in electron confinement, pushing the local plasma frequency of ITO up to the visible region, ideal for long-range SPP excitation and propagation. In addition, the anisotropy of dielectric LiNbO₃ (LN) is considered in supporting hybridized SPPs. This physical picture agrees well to the 2D diffraction patterns observed out of phase gratings written with either two coherent, pure-extraordinary or pure-ordinary or mixed polarized laser beams. This platform of ITO/LN is promising in designing hybridized SPPs based devices, in which the parasitic scattering of surface waves may be suppressed greatly.

Broadband optical switch for multiple spatial modes based on silicon densely packed waveguide array

Kaixuan Chen, Jialin Yan, Sailing He, and Liu Liu

Doc ID: 351514 Received 12 Nov 2018; Accepted 16 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: A broadband thermo-optic 2×2 Mach–Zehnder switch, which can control two spatial modes on a silicon chip simultaneously, is demonstrated. A broadband multimode 3 dB coupler is first realized based on symmetrically coupled waveguides with a sub-wavelength structure. The length of the coupler is only 24.2 μm. Employing such a multimode 3 dB coupler together with symmetrical delay arms, optical switching functionality is realized experimentally with excess losses of <1.3 dB and crosstalks of <-15 dB over 60 nm bandwidth for two spatial modes. Arbitrary splitting ratio at two output ports for two modes simultaneously is also demonstrated when applying different currents on the heater.

Synthetic subaperture based angle independentDoppler flow measurements using single beam linefield OCT in-vivo

Laurin Ginner, Andreas Wartak, Matthias Salas, Marco Augustin, Michael Niederleithner, Lara Wurster, and Rainer Leitgeb

Doc ID: 351596 Received 14 Nov 2018; Accepted 15 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: We demonstrate a synthetic subaperture based angleindependent Doppler flow calculation, using a line fieldSD-OCT system. The high speed of the system features ahigh phase stability over the volume, which is necessaryto apply synthetic subapertures in the aperture plane.Thus, the flow component for each subaperture can bereconstructed in post processing. Capillary phantom andin-vivo retinal imaging experiments were performed tovalidate and demonstrate angle independent Dopplerflow calculation.

High-performance solution-processed white organiclight-emitting diodes based on silica coated silvernanocubes

Deng Lingling, Jiaqi Yang, Nan Zhan, Tianyan Yu, Hongtao Yu, and Shufen Chen

Doc ID: 355034 Received 11 Dec 2018; Accepted 15 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: Solution-processed white organic light-emitting diodes(WOLEDs) with silica coated silver nanocubes (Ag@SiO2NCs) incorporated at the interface of hole transportinglayer and emission layer are studied. The concentration ofAg@SiO2 NCs is varied to investigate the effect ofAg@SiO2 NCs on the performances of WOLEDs. Owingto the sharp edges and corners, Ag NCs greatly improvethe radiative rate and emission intensity of nearby blueexcitons. The blue emission at different Ag@SiO2 NCsconcentration determines the performance of theWOLEDs. For the orange excitons, their emission isstrengthened by the high concentration of Ag@SiO2 NCs,which slightly influences the device performance. On theother hand, the SiO2 shell and some SiO2 nanospherescoexisted with Ag NCs reduce the hole transporting,improving the carrier balance in the WOLEDs.Experimental and simulated results also show thatexcessive Ag@SiO2 NCs may cause rough film surface,unbalanced carrier injection, and fluorescence quenching,which decreases the device performance. The optimizedWOLED with a proper concentration of Ag@SiO2 NCshas a peak current efficiency of 53.9 cd/A, acquiring asignificant enhancement factor of 77.3% compared to thecontrol device without Ag@SiO2 NCs.

Improving the color-rendering index of tandemwarm white organic light-emitting device byemploying simple fabrication process

yu ye, cao chen, z j wu, qihui wu, Wenyan Lin, xuekang peng, Yu Jin, Xining Zhang, huishan yang, and qingxiao Tong

Doc ID: 355409 Received 17 Dec 2018; Accepted 15 Jan 2019; Posted 16 Jan 2019  View: PDF

Abstract: We realized an efficient spectra-stable tandem whiteorganic light-emitting device (WOLED) with pleasurablewarm-white emission and extremely high colorrenderingindex (CRI) simultaneously by connecting afluorescent blue unit and a phosphorescent dual-colorunit via an easy-fabrication charge generation unit (CGU).Over a wide range of driving current density, the tandemwarm-white OLED exhibited general CRI (Ra) valueexceeding 85 and special CRI (R9) value close to 57. Inaddition, the Duvs are within the tolerance for CRImeasurement, ensuring validity and logicality of thecalculated results concerning Ra and R9. The obtainedtandem OLED showed the maximum efficiencies of 38cd/A and 22.9 lm/W and still maintained high efficienciesof 35.5 cd/A and 17.2 lm/W at the luminance of 1000cd/m2. Moreover, we studied the origins of both extremecolor stability in dual-color OLED and superiorly efficientelectron injection within CGU. To the best of ourknowledge, it is the first report regarding quantitativevalues of both R9 and Duv for high-Ra tandem WOLED.

Nanometric sensing with laser feedback interferometry

Daeyoung Choi, Michael Wishon, Evgeny Viktorov, David Citrin, and Alexandre Locquet

Doc ID: 348217 Received 24 Oct 2018; Accepted 15 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We demonstrate a nanometric sensor based on feedback interferometry in a DFB laser by using a measurement of either the optical frequency or laser voltage. We find that in an optimal range of optical feedback, the sensor operates reliably down to an extrapolated 12 nm; for the sensor demonstrated here at ~1550 nm, this provides a minimum detectible displacement of λ/130.

High-confinement gallium nitride-on-sapphire waveguides for integrated nonlinear photonics

Erik Stassen, Minhao Pu, Elizaveta Semenova, Evgeniy Zavarin, Wsevolod Lundin, and Kresten Yvind

Doc ID: 351461 Received 09 Nov 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We demonstrate a high effective nonlinearity of 6.2 W^−1m^−1 in a high-confinement gallium nitride-on-sapphire waveguide by performing four-wave mixing characterization at telecom wavelengths. Benefitting from a high-index-contrast waveguide layout, we can engineer the device dispersion efficiently and achieve broadband four-wave mixing operation over more than 100 nm. The intrinsic material nonlinearity of gallium nitride is extracted. Furthermore, we fabricate microring resonators with quality factors above 100,000, which will be promising for various nonlinear applications.

Wideband chaos from a laser diode with phase-conjugate feedback

Guillaume Bouchez, Brice Macias, Chi-Hak UY, Delphine Wolfersberger, and Marc Sciamanna

Doc ID: 352241 Received 18 Nov 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We analyze experimentally and theoretically the chaotic dynamics generated by a laser diode subjected to phase-conjugate feedback.Phase-conjugation is obtained from four-wave mixing in a BaTiO₃ photorefractive crystal. We demonstrate that the chaos bandwidth first increases linearly with the feedback ratio but then saturates to relatively high values. A chaos bandwidth up to about 18 GHz is achieved, which is more than five times larger than the free-running laser diode relaxation oscillation frequency. Numerical simulations confirm our experimental observations and unveil that the finite depth penetration into the crystal is responsible for the observed saturation.

Phase transfer between three visible lasers for coherent population trapping

Mathieu Collombon, Gaëtan HAGEL, Cyril Chatou, Didier GUYOMARC’H, Didier Ferrand, Marie HOUSSIN, Caroline CHAMPENOIS, and Martina Knoop

Doc ID: 352953 Received 29 Nov 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: Stringent conditions on the phase relation of multiple photons are a prerequisite for novel protocols of high-resolution coherent spectroscopy. In a recent experiment we have implemented an interrogation process of a Ca$^+$-ion cloud based on three-photon coherent population trapping, with the potential to serve as a frequency reference in the THz-range. This high-resolution interrogation has been made possible by phase-locking both laser sources for cooling and repumping of the trapped ions to a clock laser at 729~nm by means of an optical frequency comb. The clock laser, a titanium-sapphire laser built in our lab locked onto its high-finesse cavities reaches a linewidth of a few Hertz and a frequency stability below 10$^{-14}$ at one second, performances which can be copied onto the two other sources. In this paper we discuss the performances of the phase-transfer between the three involved lasers via the optical frequency comb.

A femtosecond fiber Mamyshev oscillator at 1550 nm

Michel Olivier, Vincent Boulanger, Félix Guilbert-Savary, Pavel Sidorenko, Frank Wise, and Michel Piche

Doc ID: 353177 Received 29 Nov 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We investigated the possibility to reach nanojoule-level pulse energies in a femtosecond erbium-doped fiber Mamyshev oscillator at 1550 nm. Experiments exhibit a stable pulse train with transform-limited pulse duration of 57 fs and energy of 31.3 nJ, comparable to the best pulse energies from prior ultrafast erbium fiber lasers. However, the pulse duration obtained from a grating compressor is around 100 fs and, as the pulse energy is increased, the compressed pulse quality degrades significantly with a substantial fraction of the energy going into a picosecond pedestal on the autocorrelation trace. Numerical simulations agree with the experimental observations, and allow us to identify the limited gain bandwidth combined with the excessive nonlinearity of the erbium-doped fibers as a challenge to the operation of such oscillators at high pulse energy.

Passively Q-switched fiber lasers based on pure water as saturable absorber

Li Zhan, Tianhao Xian, Li-Run Gao, Wenyan Zhang, and chao zhang

Doc ID: 353331 Received 30 Nov 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We propose and demonstrate a passively Q-switched Er-doped fiber laser (EDFL) based on water as saturable absorber (SA). The SA is made of two optical ferrules matching with a cannula, with the gap between the end-facets filled with pure water. The nonlinear response of this SA has been characterized and stable Q-switching operation has been achieved. The maximum output power is 21.1 mW for 65.0 kHz repetition rate. The pulse energy reaches to 324.8 nJ, and the pulse duration is 1.44μs. To the best of our knowledge, this is the first demonstration on the passively Q-switched laser based on pure water as SA. This provides a further evidence on the possibility of liquid as effective SA for pulsed lasers.

3D-Printed Chiral Metasurface as a Dichroic Dual-Band Polarization Converter

Shengzhe Wu, Su Xu, Tatiana Zinenko, Vladimir Yachin, Sergey Prosvirnin, and Vladimir Tuz

Doc ID: 354896 Received 07 Dec 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We propose a novel design of a true 3D chiral metasurface behaving as a spatial polarization converter with asymmetric transmission. The metasurface is made of a lattice of metallic sesquialteral (one and a half pitch) helical particles. The proposed metasurface exhibits a dual-band asymmetric transmission accompanied by the effect of a complete polarization conversion. Regarding circularly polarized waves the metasurface demonstrates a strong circular dichroism. A prototype of the metasurface is manufactured for the quasi-optic experiment by using 3D-printing technique utilizing Cobalt-Chromium alloy, which exhibits good performances against thermal fatigue and corrosion at high temperatures.

Plasmonic Metamaterial Based Filtering Structures with Dynamic Tunability

Nagendra Pathak, Nidhi Pandit, and Rahul Jaiswal

Doc ID: 354689 Received 06 Dec 2018; Accepted 14 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: In this letter, we report the design, analysis and characterization of the plasmonic metamaterial based multi-mode filtering structures. Further, electronic adaptivity in filters transfer functions is introduced and characterized. First, the basic operating principle of the engineered multi-mode resonator based band-pass filter (BPF) is presented. Then, the concept is extended by introducing electronic (dynamic) tuning of the bandwidth using semiconductor varactor diodes. Afterwards, to enhance the selectivity and out of band filtering response, second order multi-mode designs are realized. For practical demonstration, hardware prototype is fabricated and characterized using Keysight Field-Fox analyzer N9918A. The designed filtering structure will pave important role in tunable plasmonic circuits and systems.

Rapid phase retrieval of ultrashort pulses fromdispersion scan traces using deep neural networks

Sven Kleinert, Ayhan Tajalli, Tamas Nagy, and Uwe Morgner

Doc ID: 355275 Received 14 Dec 2018; Accepted 14 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: The knowledge of the temporal shape of femtosecond pulses is of major interest for all their applications. The reconstruction of the temporal shape of these pulses is an inverse problem for characterization techniques, which benefit from an inherent redundancy in the measurement. Conventionally, time-consuming optimization algorithms are used to solve the inverse problems. Here, we demonstrate the reconstruction of ultrashort pulses from dispersion scan traces employing a deep neural network. The network is trained with a multitude of artificial and noisy dispersion scan traces from randomly shaped pulses. The retrieval takes only 16 ms enabling video-rate reconstructions. This approach reveals a great tolerance against noisy conditions, delivering reliable retrievals from traces with signal-to-noise ratios down to 5.

Three-dimensional Isotropic Metacrystals with Broadband Diamagnetic Response and Negative Index of Refraction

Su Xu, Jian-Bin Liu, Hao Wang, Ci-Kang Su, and Hong-Bo Sun

Doc ID: 347939 Received 16 Oct 2018; Accepted 14 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: Metamaterials (MM) and photonic crystals (PhC) exhibiting artificially engineered physical properties have been widely studied in the past decade. However, abnormal properties could only be proposed under a limited range of polarization and directions in the most of previous researches. It is still a challenge to realize an isotropic artificial material with multiple exotic electromagnetic properties. Here, we report a three-dimensional isotropic metacrystal supporting full polarization and omni-directional incidence. The center-symmetric unit cell consists of non-resonant closed metallic loops on each surface of the dielectric cube. With the cross-scale dispersion engineering, the metacrystal can exhibit diamagnetic response and negative index of refraction simultaneously at the opposite sides of the MM-PhC transition region. Additional numerical analysis shows the good performance in Terahertz and mid-infrared frequencies, which indicates its potential applications on multi-funcational optical components with wide polarization-and-direction allowance.

Undersampling for fiber distributed acoustic sensing based on coherent phase-OTDR

Fei Jiang, Honglang Li, Zhenhai Zhang, Zhewen Hu, Yanzhu Hu, yixin zhang, and Xuping Zhang

Doc ID: 351919 Received 14 Nov 2018; Accepted 14 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: Phase-sensitive optical time-domain reflectometry (φ-OTDR) based on coherent detection is one of the most widely used schemes to achieve fiber distributed acoustic sensing. In previous studies, a fairly high data acquisition speed is essential for the phase-measuring coherent φ-OTDR, thus leading to severe computational burden. In this Letter, we first analyze the spectrum of the beat signal and then propose the use of undersampling theory to reduce the need for high sampling frequency. Then we give the principle of selecting matched sampling frequency and bandpass filter bandwidth so that the beat signal can be sampled without aliasing. The experimental results show that, when the central frequency of the beat signal is 200 MHz, its phase signal can be correctly demodulated even using a sampling rate as low as 71 MSa/s. This method can be extended to all existing coherent φ-OTDR systems with no or only a few modifications on them.

High-resolution femtosecond laser beam shaping via digital holography

Qinglei Hu, Yu Wang, Yiming Guo, Xiaohua Lv, and Shaoqun Zeng

Doc ID: 354478 Received 05 Dec 2018; Accepted 14 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: We propose a method to achieve high-resolution femtosecond laser beam shaping (HR-FLBS) via digital holography based on digital mirror device (DMD) and optimized optical design. By programming the hologram on the DMD, we captured several patterns, such as, light spots, decorated letters of ‘HUST’, and a series of concentric annuli, whose fine structure approaches the optical diffraction limit. The experimental results confirm that the proposed method can shape the amplitude and phase of a femtosecond laser arbitrarily with high resolution.

Low-power optical beam steering by microelectromechanical waveguide gratings

Carlos Errando-Herranz, Nicolas Le Thomas, and Kristinn Gylfason

Doc ID: 352248 Received 23 Nov 2018; Accepted 13 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: Optical beam steering is key for optical communications, laser mapping (LIDAR), and medical imaging.For these applications, integrated photonics is an enabling technology that can provide miniaturized, lighter, lower cost, and more power efficient systems.However, common integrated photonic devices are too power demanding. Here, we experimentally demonstrate, for the first time, beam steering by microelectromechanical (MEMS) actuation of a suspended silicon photonic waveguide grating.Our device shows up to 5.6º beam steering with 20 V actuation and a power consumption below the μW level, i.e. more than 5 orders of magnitude lower power consumption than previous thermo-optic tuning methods.The novel combination of MEMS with integrated photonics presented in this work lays ground for the next generation of power-efficient optical beam steering systems.

Demonstration of a Tilted-Pulse-Front Pumped Plane-Parallel Slab Terahertz Source

Priyo Nugraha, Gergő Krizsán, Csaba Lombosi, László Pálfalvi, Gyorgy Toth, Gabor Almasi, Jozsef Fulop, and Janos Hebling

Doc ID: 351457 Received 23 Nov 2018; Accepted 12 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a LiNbO3 plane-parallel slab with an echelon structure on its input surface. Single-cycle pulses of 1 µJ energy and 0.30 THz central frequency have been generated with 5×10–4 efficiency from such a source. One order-of-magnitude increase in efficiency is expected by pumping a cryogenically cooled echelon of increased size and thickness with a Ti:sapphire laser. The use of a plane-parallel nonlinear optical crystal slab enables straightforward scaling to high THz pulse energies and to produce a symmetric THz beam with uniform pulse shape for good focusability and high field strength.

Subtraction imaging by the combination of higher-order vector beams for enhanced spatial resolution

Mio Yoshida, Yuichi Kozawa, and Shunichi Sato

Doc ID: 355923 Received 20 Dec 2018; Accepted 12 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: We demonstrate that the spatial resolution in confocal laser scanning microscopy is remarkably improved by simple image subtraction between images acquired by higher-order transverse modes of cylindrical vector beam, referred to as radially and azimuthally polarized Laguerre-Gaussian mode beams. Two types of combinations of vector mode beams suitable for subtraction imaging are derived by a systematical study based on numerical calculation. The spatial resolution of about 100 nm is experimentally achieved without degradation of image quality.

Broadband metamaterial absorber with an in-band metasurface function

Yungui Ma, Wenjie Chen, Rui Chen, and Yi Zhou

Doc ID: 349618 Received 30 Oct 2018; Accepted 12 Jan 2019; Posted 18 Jan 2019  View: PDF

Abstract: Metamaterials (MMs) have received wide attentions due to their strong ability to control wave propagation. Here we propose a thin MM which can realize broadband absorption as well as in-band phase-controlled reflection. It absorbs more than 90% energy of the incident circularly polarized (CP) light between 7.94~9.76 GHz and 10.99~12.26 GHz, and meanwhile works as a half-wave plate near 10.35 GHz. The schemes based on both natural and artificial magnetic materials have been discussed to produce the anisotropic phase. A reflection beam steering metasurface is proposed using the absorption-selective MM. The metasurface-integrated MM absorber may have important applications in aerospace technologies like radome.

Fluorescence characterization of heavily Eu3+-doped lanthanum gallate glass spheres with high quenching concentration

Kohei Yoshimoto, Yoshinobu Ezura, Motoi Ueda, Atsunobu Masuno, Hiroyuki Inoue, and Masafumi Mizuguchi

Doc ID: 354883 Received 11 Dec 2018; Accepted 11 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: Highly Eu₂O₃-doped (up to 30 mol%) La₂O₃–Ga₂O₃ glasses were synthesized by an aerodynamic levitation technique. The red emission associated with ⁵D₀ level of Eu3+ was most intense at 20 mol% Eu₂O₃ indicating a small effect of concentration quenching even at high Eu concentration. The fluorescence decay curves indicated that the dominant transition mechanism at high Eu concentration was fast energy migration among the Eu3+ ions which averaged the environment of the Eu, yielding a nearly single-exponential decay of ⁵D₀ → ⁷F₂ emission. Lifetime of the ⁵D₀ level gradually decreased with Eu₂O₃ over the 5–25 mol% and rapidly decreased at 30 mol%, well consistent with the observed emission spectra.

Chromatic-dispersion-induced power fading suppression technique for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission

Wei Li, Sha Zhu, Ming Li, and Ninghua Zhu

Doc ID: 355944 Received 21 Dec 2018; Accepted 11 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: We report a technique to overcome chromatic-dispersion-induced power fading (CDIP) for bandwidth-quadrupling dual-chirp microwave signals over fiber transmission. Normally, dual-chirp microwave signals are generated using double-sideband (DSB) modulation. However, DSB modulation suffers from CDIP significantly. We propose a carrier-frequency shift (CFS) method to suppress the CDIP based on a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). In addition, the bandwidth of the dual-chirp signal can be quadrupled by properly setting the biases of the modulator. The proposed technique is theoretically analyzed and experimentally verified. Our technique is promising for improving the range-Doppler resolution of radars for one-to-multi base stations transmission.

Model for computing optical caustic partitions for the primary rainbow from tilted spheriodal drops

Haitao Yu, Jianqi Shen, Cameron Tropea, and Feng Xu

Doc ID: 356699 Received 03 Jan 2019; Accepted 11 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: A model is proposed to compute the salient optical caustic partitions occurring in the primary rainbow for oblate spheriodal drops. By computing the boundary limits of outgoing rays, the optical caustic structures (termed rainbow and hyperbolic umbilic fringes) for tilted drops are calculated and compared with that for aligned (untilted) drops. The curvature of the rainbow fringe and the shifts of cusp caustics are discussed as well. The observed properties of the caustics can potentially be used for drop measurements. The model could also be applied to compute the optical caustics for drops with arbitrary shape, arbitrary orientation, and shaped beam illumination.

Robust full Stokes imaging polarimeter with dynamic calibration

Shuhei Shibata, Nathan Hagan, and Yukitoshi Otani

Doc ID: 349490 Received 05 Nov 2018; Accepted 11 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: We present a full Stokes imaging polarimeter using a rotating retarder in combination with a polarization camera—a detector array on which a pixelated polarizer array is attached. By itself, a polarization camera cannot capture the full Stokes parameters, but we add a rotating retarder in front and show how it can be used to provide full Stokes images. In addition, we demonstrate the advantage that it can be recalibrated dynamically while taking measurements, allowing accurate measurements even in environments where the retardance in changing.

Generation of narrowband pulses from chirped broadband pulse frequency mixing

Christopher Kliewer, Trevor Courtney, Mark Linne, Brian Patterson, and Torge Mecker

Doc ID: 352276 Received 18 Nov 2018; Accepted 10 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: We extend an approach based upon sum-frequency generation of oppositely chirped pulses to narrow the bandwidths of broadband femtosecond pulses. We generate near transform-limited picosecond pulses by reducing the pulse bandwidth by a factor of 120, which is more than twice the reduction reported in previous literature, while maintaining comparably high throughput efficiency. Such extreme bandwidth narrowing of a broadband pulse enhances the effects of dispersion nonlinearities. Precise chirp control enables us to characterize the efficacy of frequency mixing broadband pulses with nonlinear temporal chirps. We demonstrate the use of these narrowband pulses as probes in coherent anti-Stokes Raman spectroscopy.

Working-distance-extended plasmonic nanolithography using bowtie aperture combined with metal-insulator-metal structure

Liang Wang, Zhongjun Jiang, Huiwen Luo, and songpo guo

Doc ID: 352845 Received 28 Nov 2018; Accepted 10 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: In this letter, working-distance-extended plasmonic nanolithography using bowtie aperture incorporated with metal-insulator-metal (MIM) structure is studied numerically and experimentally. Results show that with a 20nm index-matching layer, enhanced and confined light field penetrates into 40nm-thick photoresist by using MIM configuration. Imaging contrast calculation indicates that sub-45nm resolution with exposure depth in the order of tens of nanometers is achievable, which is also confirmed by the experimental results. Therefore, high-resolution complex patterns can be obtained using this technique via scanning. This brings plasmonic nanolithography using bowtie aperture one step closer to practical applications.

Combined photoacoustic imaging to delineate the internal structure of paintings

Alice Dal Fovo, George Tserevelakis, ATHANASIA PAPANIKOLAOU, Giannis Zacharakis, and raffaella fontana

Doc ID: 352938 Received 28 Nov 2018; Accepted 10 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: In this work, we present a combined photoacoustic imaging method, based on consecutive excitation using either the fundamental or the second harmonic wavelength of a pulsed Nd:YAG laser for the stratigraphy of painted artworks. Near infrared excitation was employed for the imaging of hidden underdrawings in mock up samples, whereas visible light for the thickness mapping of the overlying paint through the detection of photoacoustic signal attenuation. The proposed methodology was proven effective in measuring thick and strongly absorbing layers, which would not be possible by means of other pure optical techniques, while also enabling the visualization of features underneath the painted surface. Such an implementation expands significantly the applicability of the previously presented photoacoustic technique, which was limited to point-measurements, and paves the way for novel application in historical and technical studies, as well as in documenting restoring operations.

Beam shaping of a broad-area laser diode using 3D integrated optics

Simon Gross, David Coutts, Mark Dubinskii, and Michael Withford

Doc ID: 354672 Received 06 Dec 2018; Accepted 10 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: Typical high power broad-area semiconductor lasers exhibit a highly astigmatic beam profile. However, many applications require a homogenous and circular symmetric beam. Thus coupling into circular multimode optical fibers is often employed. The strip-like astigmatic output of the diode laser underfills the circular multimode fiber, thus a decrease in beam quality occurs after fiber coupling due to mode mixing inside the optical fiber. This paper presents a 3D integrated optics approach to shape the output of a broad-area laser diode. Ultrafast laser inscription is utilized to create a pair of photonic lanterns connected back to back inside a glass chip that captures and shapes the output of a commercial 976 nm wavelength broad area laser diode with 95 μm emitter width. Compared to coupling to a 105 μm diameter, 0.15 numerical aperture step-index multimode fiber, the photonic chip based approach results in a 13× higher beam quality and 7× greater brightness.

Resonant Response and Mode Conversion of Microsphere Coupled with Microfiber Coupler

Ke Liu, Yang He, Ao Yang, Lei Shi, Liangjin Huang, Pu Zhou, Fufei Pang, Tingyun Wang, and Xianglong Zeng

Doc ID: 355217 Received 13 Dec 2018; Accepted 09 Jan 2019; Posted 15 Jan 2019  View: PDF

Abstract: We experimentally investigate the resonant response in a microsphere coupled with a biconical microfiber coupler (MFC) composing of single (few) mode fibers. The evolution between Lorentz and Fano resonances dependent on the phase difference of the supermodes is demonstrated along the coupling region of the MFC. A flexible narrow-linewidth add/drop filter can be simultaneously achieved with the advantage of easy alignment and efficiently evanescent coupling. In addition, the mode conversion process of the microsphere is demonstrated and the purity of LP11 mode in coupler at the WGM resonance is analyzed. The proposed MFC coupling system holds great promising applications in the optical filtering and sensing, mode-switching and micro-resonator based combs.

Single Frequency 620 nm Diamond Laser at High Power, Stabilized via Harmonic Self-Suppression and Spatial-Hole-Burning-Free Gain

Xuezong Yang, Ondrej Kitzler, David Spence, Robert Williams, Zhenxu Bai, Soumya Sarang, Lei Zhang, Yan Feng, and Richard Mildren

Doc ID: 355814 Received 19 Dec 2018; Accepted 09 Jan 2019; Posted 09 Jan 2019  View: PDF

Abstract: Single longitudinal mode (SLM) operation of a 620 nm diamond Raman laser is demonstrated in a standing-wave cavity that includes a second harmonic generation element. Mode competition provided by the harmonic mixing is shown to greatly increase mode stability in addition to the benefits of the spatial hole burning-free gain medium. Using a multi-longitudinal mode 1064 nm Nd:YAG pump laser of power 321 W and linewidth 3.3 GHz, SLM powers of 38 W at 620 nm and 11.8 W at 1240 nm were obtained. The results indicate that simple standing-wave oscillators pumped by multimode Yb or Nd pumps comprise a promising practical route towards generation of high power SLM beams in the yellow – red part of the spectrum.

Highly efficient upconversion luminescence of Er heavily doped nanocrystals through 1530 nm excitation

Lu Liu, lei Lu, li Xu, DongYang Tang, Chao Liu, Muhammud Khuram Shahzad, dong yan, Fahim Khan, Enming Zhao, and Hanyang Li

Doc ID: 349177 Received 25 Oct 2018; Accepted 09 Jan 2019; Posted 10 Jan 2019  View: PDF

Abstract: Improving the luminescence efficiency is of vital importance for the applications of rare earth doped upconversion materials. Herein, we presented highly efficient upconversion nanocrystal, which is brighter than the state-of-the-art Er3+/Yb3+ co-doped core-shell material, through the Er3+ heavily doping and 1530 nm excitation. Moreover, upconversion characteristics and mechanisms of Er3+ heavily doped core nanocrystals and their core-shell counterparts are investigated intensely.

Fast and large-area fabrication of plasmonic reflection color filters by achromatic Talbot lithography

Qingjun Wu, Huijuan Xia, Hao Jia, Hao Wang, Cheng Jiang, Liansheng Wang, Jun Zhao, Renzhong Tai, Sanshui Xiao, Dongxian Zhang, Shumin Yang, and Jianzhong Jiang

Doc ID: 353114 Received 29 Nov 2018; Accepted 08 Jan 2019; Posted 10 Jan 2019  View: PDF

Abstract: To overcome the limits of traditional technologies which cannot achieve high resolution and high throughput simultaneously, here we propose a novel method, i.e., achromatic Talbot lithography, to fabricate large-area nanopatterns fast and precisely. We successfully demonstrate reflection color filters with maximum size of about 0.72 x 0.72 mm² with a time of only 20 seconds, which have colors similar to simulations and small area devices fabricated by electron beam lithography. These results indicate the possibility of large-scale fabrication of plasmonic color filters with high resolution efficiently by the achromatic Talbot lithography method.

Propagation formulae and characteristics of partially coherent laser beams in nonlinear media

Xiaoling Ji, HUAN WANG, Hao Zhang, Xiaoqing Li, and YU DENG

Doc ID: 349501 Received 29 Oct 2018; Accepted 08 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: Analytical propagation formulae of partially coherent beams (PCBs) in nonlinear media are derived. It is proved that the ABCD law is valid if a new complex beam parameter is adopted, which presents a simple method to study the propagation of PCBs through an optical system in nonlinear media. In self-focusing media, the spatial coherence for the beam spreading case is better than that for the beam self-focusing case when the propagation distance is longer than the inversion coherence distance. An optimal beam will necessarily involve a trade-off between collimation and spatial coherence when PCBs propagate in self-focusing media.

Optical Angular Momentum manipulations in a Four Wave Mixing process

Nikunj Prajapati, Nathan Super, R Lanning, Jonathan Dowling, and Irina Novikova

Doc ID: 347779 Received 10 Oct 2018; Accepted 08 Jan 2019; Posted 08 Jan 2019  View: PDF

Abstract: We investigate the spatial and quantum intensity correlations between the probe and Stokes optical fields produced via four-wave mixing in a double-Λ configuration, when both incoming probe and control fields carry non-zero optical orbital angular momentum (OAM). We observed that the topological charge of the generated Stokes field obeyed the OAM conservation law. However, the maximum values and optimal conditions for the intensity squeezing between the probe and Stokes fields were largely independent of the angular momenta of the beams, even when these two fields had significantly different OAM charges. We also investigated the case of a composite-vortex pump field, containing two closely-positioned optical vortices, and showed that the generated Stokes field carried the OAM corresponding to the total topological charge of the pump field, further expanding the range of possible OAM manipulation techniques.

Telecom InP/InGaAs Nano-Laser Array Directly Grown on (001) Silicon-on-Insulator

Yu Han, Wai Kit Ng, Ying Xue, Qiang Li, Kam Sing Wong, and Kei May Lau

Doc ID: 349936 Received 01 Nov 2018; Accepted 07 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: A compact, efficient and monolithically grown III-V laser source provides an attractive alternative to bonding off-chip lasers for Si photonics research. Although recent demonstrations of micro-lasers on (001) Si wafers using thick metamorphic buffers are encouraging, scaling down the laser footprint to nano-scale and operating the nano-lasers at telecom wavelengths remain a significant challenge. Here, we report monolithically integrated in-plane InP/InGaAs nano-laser array on (001) silicon-on-insulator (SOI) platforms with emission wavelengths covering the entire C-band (1.55 µm). Multiple InGaAs quantum wells are embedded in high-quality InP nano-ridges by selective-area growth on patterned (001) SOI. Combined with air-surrounded InP/Si optical cavities, room-temperature operation at multiple telecom bands is obtained by defining different cavity lengths with lithography. The demonstration of telecom-wavelength monolithic nano-lasers on (001) SOI platforms presents an important step towards fully integrated Si photonics circuits.

Improve polarization topological order sorting with diffractive splitting method

Shuiqin Zheng, Xuanke Zeng, HUANGCHENG SHANGGUAN, Yi Cai, XinJian Pan, Shixiang Xu, Xiaocong Yuan, and Dianyuan Fan

Doc ID: 355048 Received 11 Dec 2018; Accepted 07 Jan 2019; Posted 09 Jan 2019  View: PDF

Abstract: Vector beams with different polarization topological orders (PTOs) are the eigenmodes of traditional optical fibers, and orthogonal to each other, so PTO multiplexing channel is a promising candidate for oncoming generation of optical communication. Here we demonstrate experimentally a PTO sorting system with high separation resolution basing on diffractive splitting (DS) method. Our experiments show that our design with DS method helps to enhance the separation resolution to 77.5% from 58% compared that without applying DS method. Theoretically, to increase the copy number can promote the separation resolution further. This work provides a high-resolution way to decode information from PTO division multiplexing.

Compression optical coherence elastography with two-dimensional displacement measurement and local deformation visualization

Yoshiaki Yasuno, En Li, Shuichi Makita, Shinnosuke Azuma, and Arata Miyazawa

Doc ID: 353242 Received 30 Nov 2018; Accepted 07 Jan 2019; Posted 11 Jan 2019  View: PDF

Abstract: Current compression-based optical coherence elastography (OCE) only measures axial displacement of a tissue, although the tissue also undergoes lateral displacement and microstructural alteration by the compression. In this study, we demonstrate a new compression-based OCE method that visualizes not only axial displacement, but also lateral displacement and microstructural decorrelation. This method employs complex correlation-based displacement and microstructural decorrelation measurements. It is implemented in a swept-source optical coherence tomography system with an active submicrometer compression. The performance of the method was demonstrated by measuring the porcine carotid artery and esophagus. The results showed significant axial and lateral displacements in the tissues by compression. A microstructural decorrelation map demonstrates high contrast mechanical-property imaging.

A ray mapping method for off-axis and non-paraxial freeform illumination lens design.

Karel Desnijder, Peter Hanselaer, and Youri Meuret

Doc ID: 351940 Received 15 Nov 2018; Accepted 06 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: The ray mapping method for freeform illumination design is an easy and flexible method, but only in the paraxial regime does it results in surface normal fields that are directly integrable into continuous freeform surfaces that provide the desired illuminance distribution. A new mapping scheme is proposed to alter an initial source-target mapping via a symplectic flow of an equi-flux parametric coordinate system. The resulting mapping provides integrable surface normal vector fields for complex off-axis and non-paraxial illumination problems as demonstrated by two freeform lens examples.

Compensating spatially-dependent dispersion in visible light OCT

Aaron Kho and Vivek Srinivasan

Doc ID: 351962 Received 29 Nov 2018; Accepted 06 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: Visible light Optical Coherence Tomography (OCT) has recently emerged in retinal imaging, with claims of micron-scale axial resolution and multi-color (sub-band) imaging. Here, we show that the large dispersion of optical glass and aqueous media, together with broad optical bandwidths often used in visible light OCT, compromises both of these claims. To rectify this, we introduce the notion of spatially-dependent (i.e. depth and transverse position-dependent) dispersion. We use a novel sub-band, sub-image correlation algorithm to estimate spatially-dependent dispersion in our 109 nm bandwidth visible light OCT mouse retinal imaging system. After carefully compensating spatially-dependent dispersion, we achieve delineation of fine outer retinal bands in mouse strains of varying pigmentation. Spatially-dependent dispersion correction is even more important for broader bandwidths and shorter visible light OCT wavelengths.

Three-dimensional magnetization needle arrays with controllable orientation

Jianjun Luo, HENWEN ZHANG, Sicong Wang, Liu Shi, Zhuqing Zhu, Gu Bing, Xiaolei Wang, and Xiangping Li

Doc ID: 347759 Received 11 Oct 2018; Accepted 06 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: Based on the Richard-Wolf vectorial diffraction theory and the inverse Faraday effect, we first propose a scheme to generate three-dimensional magnetization needle arrays with arbitrary orientation for each individual needle and controllable spatial position and number through reversing the electric dipole array radiation. To achieve this, each unit of the electric dipole array has two electric dipoles with orthogonal oscillation directions and quadrature phase, and is located in mirror-symmetric with respect to the focal plane of the high numerical aperture (NA) lens. Uniformly distributed magnetization needles with a subwavelength lateral size of 0.44λ and a longitudinal depth of 5.36λ with four different orientations are obtained by optimized arrangement for 2N (here N=2) units of the electric dipole array. The corresponding purity of magnetization needle is also discussed in detail. Furthermore, two combinations of magnetization needle arrays with orthogonal orientation are emphatically exploited in the hybrid bit-patterned media (BPM) recording. The results illustrate the richness of the proposed methods to locally control the particular orientation properties of the magnetization needle and find many potential applications in multichannel/ multilayer magneto-optical storage, information security, and spintronics.

A resource-saving realization of apolarization-independentorbital-angular-momentum-preserving tunable beamsplitter

Li Yaping, Fang-Xiang Wang, Wei Chen, Guo-Wei Zhang, Zhen-Qiang Yin, De-Yong He, Shuang Wang, Guang-can Guo, and Zhen-fu Han

Doc ID: 349611 Received 05 Nov 2018; Accepted 06 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: The tunable beam splitter (TBS) is a fundamental component used in optical experiments. A TBS which can preserve the orbital angular momentum (OAM) sates as well as the polarization states of photons will be valuable for some particular experiments, such as high-dimensional quantum information processing. We realized such a TBS with a self-designed compact structure based on modified polarization beam splitters and half-wave plates. Comparing with existing works, the TBS can reduce the device number required and make its simpleness. The verification experiments show that the dynamic range of the transmissivity can exceed 30 dB, meanwhile, the extinction ratio to evaluate the polarization and the OAM preservation are both over 20 dB. Furthermore, a Sagnac interferometer with a mean visibility greater than 99% has been implemented using the proposed TBS, which demonstrate its potential application value for optical information processing.

Axially-shifted pattern illumination for macroscale turbidity suppression and virtual volumetric confocal imaging without axial scanning

Shaowei Jiang, Jun Liao, Zichao Bian, Pengming Song, Garrett Soler, Kazunori Hoshino, and Guoan Zheng

Doc ID: 355475 Received 14 Dec 2018; Accepted 06 Jan 2019; Posted 08 Jan 2019  View: PDF

Abstract: Structured illumination has been widely used for optical sectioning and 3D surface recovery. In a typical implementation, multiple images under non-uniform pattern illumination are used to recover a single object section. Axial scanning of the sample or the objective lens is needed for acquiring the 3D volumetric data. Here we demonstrate the use of axially-shifted pattern illumination (asPI) for virtual volumetric confocal imaging without axial scanning. In the reported approach, we project illumination patterns at a tilted angle with respect to the detection optics. As such, the illumination patterns shift laterally at different z sections and the sample information at different z-sections can be recovered based on the captured 2D images. We demonstrate the reported approach for virtual confocal imaging through a diffusing layer and underwater 3D imaging through diluted milk. We show that we can acquire the entire confocal volume in ~1s with a throughput of 420 megapixels per second. Our approach may provide new insights for developing confocal light ranging and detection systems in degraded visual environments.

Full-field characterization of breather dynamics over the whole length of an optical fiber

Corentin Naveau, Pascal Szriftgiser, Alexandre Kudlinski, Matteo Conforti, Stefano Trillo, and Arnaud Mussot

Doc ID: 349626 Received 05 Nov 2018; Accepted 05 Jan 2019; Posted 08 Jan 2019  View: PDF

Abstract: Full-field longitudinal characterization of picosecond pulse train formation in optical fibers is reported. The spatio-temporal evolution is obtained via fast and non-invasive distributed measurements in phase and intensity of the main spectral components of the pulses. To illustrate the performance of the setup, we report the first time-domain experimental observation of the symmetry breaking of Fermi-Pasta-Ulam recurrences. Experimental results are in good agreement with numerical simulations.

Employing Covert Communications-based Information Reconciliation and Multiple Spatial Modes to Polarization Entanglement QKD

John Gariano and Ivan Djordjevic

Doc ID: 348546 Received 18 Oct 2018; Accepted 05 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: The information that is leaked to an eavesdropper during the error reconciliation phase of QKD protocols limits the maximum bit error rate of a system. In a standard QKD protocol, parity bits are transmitted over an authenticated noiseless channel, to which Eve has access to. This work presents the concept of using a covert classical communication channel to transmit the parity bits between Alice and Bob without Eve gaining information of the transmitted parity bits. This allows for higher secure key generation rates and operation of QKD system where the bit error rate exceeds the limit of the standard protocol. This concept is then applied to a practical free-space optical system that contains multiple parallel channels, where channel loss, crosstalk, atmospheric turbulence effects, and noise are considered.

Laser Direct Writing Electrode for Rapid Customization of Photodetector

Jun Chen, Wei Yi, Hanibo Zeng, Xiufeng Song, and Yu Gu

Doc ID: 355320 Received 14 Dec 2018; Accepted 05 Jan 2019; Posted 09 Jan 2019  View: PDF

Abstract: Interdigital Ag electrode is fabricated via a simple and fast approach called laser direct writing(LDW). The morphology and conductivity of electrode fingers are investigated systematically under different experimental parameters, including laser spot size, laser power and scanning speed. “Dose” is defined to describe the combined influence of these experimental parameters. It is found that over-dose results in net-shape and dot-shape hollows in the middle of Ag line due to the sintering degree and complex flow dynamics, which reduced conductivity of the Ag lines. Based on the printed Ag electrodes with best conductivity, a photodetector is customized further, which can detect the offset of the line-shape laser easily. Moreover, it is the first time the printed Ag electrodes are applied to photodetectors, which can be highly valuable for developing all-printed electronic devices by LDW in future.

Performance-enhanced silicon thermo-optic Mach-Zehnder switch using laterally supported suspended phase arms and efficient electrodes

Yonglin Yu, Kai Chen, and Fei Duan

Doc ID: 352690 Received 26 Nov 2018; Accepted 04 Jan 2019; Posted 14 Jan 2019  View: PDF

Abstract: We report a silicon thermo-optic Mach-Zehnder switch (MZS) with a broad band, low switching power and fast response. A broadband 3 dB directional coupler is used to act as a power splitter. Laterally supported suspended phase arms are employed to substantially reduce the switching power without sacrificing too much on temporal response. Furthermore, two metallization steps are utilized to further decrease the power consumption. We experimentally obtain a switching power as low as 1.1 mW, as well as a fast response of 76 μs and 48 μs for rise time and fall time, respectively. The demonstrated device also has a relatively high mechanical strength and compact size, making it promising to be applied in silicon photonic integrated circuits (PICs).

In-line reflective Mach-Zehnder interferometer based on tilted in-fiber beam splitter

Dongning Wang and Hua Zhang

Doc ID: 354750 Received 10 Dec 2018; Accepted 04 Jan 2019; Posted 08 Jan 2019  View: PDF

Abstract: A fiber in-line reflective Mach-Zehnder interferometer is proposed and experimentally demonstrated, which is based on a tilted in-fiber beam splitter inscribed by femtosecond laser. The beam splitter splits the incident light beam into two parts, one is directed to the fiber cladding-air interface, where it experiences total internal reflection and is directed to the fiber core. The other part of light beam keeps traveling in the fiber core. The two parts of light beams are recombined in the fiber core to generate interference before being reflected at the fiber cut end face. The device proposed is compact in size, robust in mechanical strength, easy in fabrication, and can be used for environmental refractive index sensing in a convenient manner.

Mode evolution based silicon-on-insulator 3 dB coupler using the fast quasiadiabatic dynamics

Yung-Jr Hung, Zhong-Ying Li, Hung-Ching Chung, Fu-Chieh Liang, Ming-Yang Jung, Tzu-Hsiang Yen, and Shuo-Yen Tseng

Doc ID: 355150 Received 12 Dec 2018; Accepted 04 Jan 2019; Posted 08 Jan 2019  View: PDF

Abstract: We report a 2×2 broadband and fabrication tolerant mode evolution based 3 dB coupler based on silicon-on-insulator (SOI) rib waveguides. The operating principle of the coupler is based on the adiabatic evolution of the local eigenmodes. The key element of the device is an adiabatically tapered mode evolution region, which converts two dissimilar waveguides into two identical waveguides. Contrary to conventional designs using a linear taper function where the device adiabaticity is uneven during the evolution, we use the fast quasiadiabatic approach to homogenize the adiabaticity of the device, leading to a shortcut to adiabaticity. Devices with an optimized taper region of 26.3 μm are designed and fabricated in a complimentary metal-oxide-semiconductor (CMOS) compatible process with 193-nm deep ultraviolet lithography. The measured devices exhibit a broadband 3 dB±0.5 dB splitting within a bandwidth of 100 nm, uniformly across an 8-inch wafer, showing good tolerance against fabrication variations.

High repetition rate 102 W middle infrared ZnGeP2 MOPA system with thermal lens compensation

Chuanpeng Qian, baoquan yao, Benrui Zhao, gaoyou liu, Xiaoming Duan, Tongyu Dai, Youlun Ju, and Yuezhu Wang

Doc ID: 354466 Received 03 Dec 2018; Accepted 04 Jan 2019; Posted 09 Jan 2019  View: PDF

Abstract: We demonstrate a 102W middle infrared ZnGeP2 (ZGP) optical parametric amplifier (OPA) pumped by a 2097-nm Q-switched Ho:YAG laser at pulse repetition frequency of 10 kHz. The seed middle infrared laser was produced by a ZGP OPO. Its average power was 28.4 W pumped by 50 W 2097-nm laser. By thermal lens compensation, the beam factor M2 reduced from 3.1 to 2.1. When the incident Ho pump power was 120 W, the middle infrared ZGP OPA yielded the maximum average output power of 102 W and slope efficiency of 61.7%. The overall optical conversion efficiency of 60% from Ho to middle infrared was obtained for whole middle infrared laser system. In addition, at the maximum average output power, the beam quality factors of middle infrared ZGP OPA were measured to be about 2.7 and 2.8 for horizontal and vertical directions, respectively.

Highly Efficient Cladding-pumped Single-mode Three-level Yb All-solid Photonic Bandgap Fiber Lasers

Turghun Matniyaz, Wensong Li, Monica Kalichevsky-Dong, Thomas Hawkins, Joshua Parsons, Guancheng Gu, and Liang Dong

Doc ID: 354805 Received 10 Dec 2018; Accepted 03 Jan 2019; Posted 03 Jan 2019  View: PDF

Abstract: Efficient cladding-pumped three-level Yb fiber lasers are difficult to achieve due to the competing four-level system and necessary high inversions. We demonstrate an efficiency of ~62.7% versus coupled pump, a record for cladding-pumped fiber lasers with a single-pass pump. 84W at ~978nm with ~1.12 M2 was achieved, record power for flexible fibers. ASE was suppressed by >40dB. The efficiency is quantum-limited ~94% versus absorbed pump. This is made possible by the use of a photo-darkening-free Yb phosphosilicate core and recent progress in single-mode large-core all-solid photonic bandgap fiber designs, which provide the necessary large core-to-cladding ratio and suppression of the four-level system.

Effect of pump wavelength and temperature on the spectral performance of BAC-Al in bismuth doped aluminosilicate fibers

Zhao Qiancheng, Yanhua Luo, Yutang Dai, and Gang-Ding Peng

Doc ID: 355344 Received 20 Dec 2018; Accepted 02 Jan 2019; Posted 03 Jan 2019  View: PDF

Abstract: The NIR luminescence of Bi-doped aluminosilicate fiber, within pump wavelength between 710 and 990 nm and under varying pump power and operation temperature, has been investigated systematically. It’s revealed that there exist two emission bands peaking around 1120 nm and at 1300 nm, which are believed to be associated with two different aluminum-related bismuth active centers (BAC-Al1 and BAC-Al2), the BAC-Al2 is found to be more efficiently excited at a lower temperature within the spectral range 790-850 nm. This is the first time that two sub-bands of BAC-Al are identified. The thermal annealing effect on the luminescence of BACs is also studied under 830 nm pumping. In contrast to the quenching of BAC-Si, the luminescence intensity of BAC-Al1 is enhanced by 1.5 times after 500 °C heating and subsequent cooling. The results demonstrate an effective strategy for tuning the emission scheme in the range 1100-1400 nm by adjusting the excitation wavelength and operation temperature.

Determination of geometry-induced positional distortion of ultrafast laser-inscribed circuits in a cylindrical optical fiber

Sang-Shin Lee, PENG JI, Young-Eun Im, and Younghee Choi

Doc ID: 352381 Received 19 Nov 2018; Accepted 02 Jan 2019; Posted 03 Jan 2019  View: PDF

Abstract: The positional distortion is a defocusing phenomenon in ultrafast laser inscription of fiber optic circuits due to the cylindrical geometry of an optical fiber. In this paper, a study on the positional distortion for ultrafast laser-processing assisted by tightly focusing optics is conducted. We pay attention to the effect of numerical aperture (NA) of the focusing optics and location of the laser-writing plane. It is observed a convex positional distortion is formed, which decreases with the NA, in an array of laser-inscribed optical tracks when scanning across the fiber, exhibiting a maximum distortion of 28.9 μm and .8 μm in the center plane of the fiber for the 0.42-NA and 0.85-NA dry objective lenses, respectively. Further, a negligible positional distortion is induced for the track array written in an off-center plane.

Phase retrieval by an array of overlapping time-lenses

Hamootal Duadi, tomer yaron, avi Klein, sara meir, and Moti Fridman

Doc ID: 354634 Received 05 Dec 2018; Accepted 02 Jan 2019; Posted 07 Jan 2019  View: PDF

Abstract: Temporal imaging of both the intensity and the phase is important for investigating ultra-short events such as rogue waves or mode-locked lasers dynamics in a record high resolution. We developed temporal phase retrieval scheme based on several overlapping time-lens where all the time-lenses are using the same fibers and detectors leading to high stability and low noise levels. We show that our phase retrieval technique converges faster than techniques which resort to a single time-lens together with the Fourier transform of the signal.

Tailoring ΡΤ-symmetric soliton switch

Govindarajan Arjunan, Amarendra Sarma, and Lakshmanan Muthusamy

Doc ID: 346572 Received 21 Sep 2018; Accepted 02 Jan 2019; Posted 02 Jan 2019  View: PDF

Abstract: We theoretically demonstrate soliton steering in ΡΤ-symmetric coupled nonlinear dimers. We show that if the length of the ΡΤ-symmetric system is set to 2π contrary to the conventional one which operates satisfactorily well only at the half-beat coupling length, the ΡΤ dimer remarkably yields an ideal soliton switch exhibiting almost 99.99% energy efficiency with an ultra-low critical power.

Transverse single-mode operation in a passive large pitch fiber with more than 200 µm mode-field diameter

Albrecht Steinkopff, Cesar Jauregui, Fabian Stutzki, Johannes Nold, Christian Hupel, Nicoletta Haarlammert, Joerg Bierlich, Andreas Tünnermann, and Jens Limpert

Doc ID: 349640 Received 05 Nov 2018; Accepted 02 Jan 2019; Posted 02 Jan 2019  View: PDF

Abstract: In this work we present the largest effective single-mode fiber reported to date. The employed waveguide is a passive large pitch fiber (LPF), which shows the core area scaling potential of such a fiber structure. In particular, we achieved stable single-transverse-mode transmission at a wavelength of 1.03 µm through a straight passive LPF with pitch of 140 µm resulting in a measured mode field diameter of 205 µm.

A novel model of acousto-optic interaction in optical fibers endowed with flexural wave

Maxim Yavorsky, Dmitriy Vikulin, Elena Barshak, Boris Lapin, and C. Alexeyev

Doc ID: 351890 Received 14 Nov 2018; Accepted 02 Jan 2019; Posted 02 Jan 2019  View: PDF

Abstract: We propose a novel model of the acousto-optic interaction (AOI) in circular fibers endowed with the lowest-order flexural acoustic wave (FAW) that is based on the actual distribution of the acoustically-induced displacement vector. The corresponding expression for the fiber's permittivity is derived and compared with the commonly-used one. The resonance optical fiber modes and the propagation constants are found. It is predicted that the lengths of the well-known acoustically-driven mode conversion LP_0->LP_1 should be slightly different for the x- and y-polarized incident fundamental mode. Moreover, we unveil a new polarization-dependent mode conversion, in which the azimuthal mode number l as well as the optical frequency of the generated standard fiber mode LP_l are governed by the linear polarization direction of the incident zero-order beam LP_0.

Narrow-band, polarization-independent, transmission filter in a silicon-on-insulator strip waveguide

Han Yun, Lukas Chrostowski, and Nicolas Jaeger

Doc ID: 353365 Received 03 Dec 2018; Accepted 31 Dec 2018; Posted 09 Jan 2019  View: PDF

Abstract: We report on a narrow-band, polarization-independent, transmission filter using phase-shifted, polarization-rotating Bragg gratings (PRBGs) in a silicon-on-insulator strip waveguide. In our device, phase-shifted PRBGs provide narrow transmission peaks for the transverse electric (TE) and transverse magnetic (TM) modes, both at the same wavelength. We present results for a 330.6 µm long device that has transmission peaks centered at 1556.36 nm, 3 dB bandwidths of 0.26 nm, and extinction ratios of 19 dB for both the TE and TM modes. We also integrated a heater onto our device and obtained a wavelength tuning efficiency of 0.028 nm/mW for both the TE and TM modes.

Reconstruction of Underwater Scattered Image via Incoherent Modulation Instability

Jing Han, Qinfeng Xu, jiannong chen, Linwei Zhu, and Zhigang Li

Doc ID: 351763 Received 13 Nov 2018; Accepted 31 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: A technology of reconstructing scattered image from turbid underwater is proposed, which is via stochastic resonance based on incoherent modulation instability in noninstantaneous nonlinear medium. When intensity-dependent nonlinearity exceeds the threshold imposed by attenuation and scattering, instability preferentially reinforce the underlying signal modes at the expense of neighbor highly-incoherent noise modes. Due to the directional energy transfer, noise-hidden signal image are effectively reconstructed with a cross-correlation gain high to 3.56. Results in turbid suspension demonstrated the wide applications of image detection in various dynamic scattering environments.

Effective metrology and standard of the surface roughness of micro/nanoscale waveguides with confocal laser scanning microscopy

DeGui Sun and Hongpeng Shang

Doc ID: 349190 Received 29 Oct 2018; Accepted 31 Dec 2018; Posted 07 Jan 2019  View: PDF

Abstract: Surface-roughness caused scattering loss is one of the important parameters affecting the optical performance of dielectric waveguides, so enormous interests for the surface roughness dependences of the optical losses of waveguides have led to the rebirth of researches, but much less attention is led to the study for an accurate metrology and standard of surface roughness. In this letter, we investigate an efficient metrology of waveguide surface roughness measurements using a confocal laser scanning microscopy (CLSM) first, for which a matching standard of surface roughness is defined based on the peak-to-valley (P-V) deviations. Then, the two- and three-dimensional statistics of multiple roughness measurements for the top and sidewall surfaces of waveguide are employed to reach the highly accurate results of roughness values. Finally, as the illustrations, for the 10m x 6m silica waveguides the two-dimensional average results of the top surface roughness of 0.478m and the sidewall surface roughness of 0.582m are measured with the CLSM metrology and their distributions are analyzed. In addition, the SEM measurement values of 01-0.2m are also obtained for the same sample, so there is a difference between these two metrologies.

Modal approach to optical forces between waveguides as derived by transformation optics formalism

Hideo Iizuka and Shanhui Fan

Doc ID: 352688 Received 23 Nov 2018; Accepted 30 Dec 2018; Posted 14 Jan 2019  View: PDF

Abstract: Optical force between two lossless waveguides has been described by two approaches. One approach is the explicit description of the force by Maxwell stress tensor. Another approach is to describe the modal force in terms of the derivative of the eigenmode frequency with respect to the distance variation. Here, we analytically prove the equivalence of these two approaches for lossless waveguides having arbitrary cross sections through the use of transformation optics formalism. Our derivation is applicable to both pressure and shear forces. We also show that these two approaches are not equivalent in the presence of loss.

Mass sensing by quantum-criticality

Shang-Wu Bin, Xin Lu, Tai-Shuang Yin, Gui Zhu, Qian Bin, and Ying Wu

Doc ID: 353089 Received 29 Nov 2018; Accepted 29 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: The mass sensing connects the mass variation to a frequency shift on mechanical oscillator, whose limitation is determined by mechanical frequency resolution. Here, we propose a method to enlarge a minute mechanical frequency shift, which is smaller than the linewidth of mechanical oscillator, into a huge frequency shift of the normal mode. Explicitly, a frequency shift about 20 Hz of the mechanical oscillator would be magnified to be 1 MHz frequency shift in the normal mode, which increases five orders of magnitudes. This enhancement relies on the sensibility appearing near the quantum critical point of the electromechanical system. As an example, we show that a mechanical frequency shift of 1 Hz could be resolved with mechanical resonance frequency $\omega_b $= 11× 2π MHz. Namely, ultrasensitive mechanical mass sensor of the resolution $\Delta m /m \backsim 2\Delta \omega_b/\omega_b\backsim$ 10¯⁸ is achieved. Our method may have great potential application in mass sensing and other techniques based on the frequency shift of mechanics oscillator.

Quantitative 2-D OH thermometry using spectrally-resolved planar laser-induced fluorescence

Shengkai Wang and Ronald Hanson

Doc ID: 351183 Received 07 Nov 2018; Accepted 28 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: A novel method is presented for quantitative two-dimensional temperature measurement in combustion gases. This method, namely spectrally-resolved planar laser-induced fluorescence (SR-PLIF) thermometry, utilizes a high-power, wavelength-tunable and narrow-linewidth CW laser to access the spectral lineshapes of a key combustion intermediate, the hydroxyl radical (OH), and enables high-fidelity and calibration-free quantification of non-uniform temperature fields in complex reacting flows. Specifically, the R₁(11)/R₁(7) line pair of the OH A²Σ – X²Π (0,0) rovibronic band was probed with laser radiation near 306.5 nm, and their fluorescence ratio was used to infer temperature. Preliminary demonstrations of this thermometry method were performed in a series of burner-stabilized CH₄-air flames.

Dirac Semimetal Saturable Absorber with Actively Tunable Modulation Depth

Yue Sun, Yafei Meng, Hongzhu Jiang, Qin Shuchao, yunkun yang, Faxian Xiu, Yi Shi, Shining Zhu, and Frank (Fengqiu) Wang

Doc ID: 351184 Received 06 Nov 2018; Accepted 28 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: In this Letter, we demonstrate an electrically-contacted saturable absorber (SA) device based on topological Dirac semimetal Cd3As2. With current-induced temperature change in the range 297-336 K, the modulation depth of the device is found to be significantly altered in the range of 33-76 %, under the irradiation of a 1560 nm femtosecond laser. The broad tuning of the modulation depth is attributed to the strong temperature-dependence of carrier concentration close to room temperature. The simple tuning mechanism uncovered here together with the compatibility with III-V compounds substrate point to the potential of fabricating electrically-tunable, SESAM-like devices based on emerging Dirac materials.

On the giant enhancement of light in plasmonic or all-dielectric gratings comprising nano-voids

Jérôme Le Perchec

Doc ID: 351453 Received 09 Nov 2018; Accepted 28 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: We report the possibility to generate tremendous light-field enhancements within shallow nano-trenches made in a high index dielectric material, because of resonant behaviours which are reminiscent of what we get with sub-wavelength plasmonic cavities. High quality factors are explained through a modal analysis which gives explicit design rules. The thin dielectric void gratings could be a relevant alternative to plasmon-based devices for chemical sensing, or could inspire novel efficient wavelength-selective photo-absorbers by taking weakly absorbing materials.

Fano resonance arising due to direct interaction of plasmonic and lattice modes in a mirrored array of split ring resonators

Dalius Seliuta, Gediminas Šlekas, Gintaras Valušis, and Žilvinas Kancleris

Doc ID: 349831 Received 31 Oct 2018; Accepted 28 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: It is demonstrated that the direct interaction of plasmonic and lattice modes leads to the Fano-type resonance in a mirrored array of simple split-ring resonators. Physics behind the effect is overlapping of the frequencies of the lowest lattice mode and the broadband plasmonic mode, which plays a role of “continuum”, whereas the lattice mode manifests itself as a "discrete state". The overlapping is achieved by mirror symmetric orientation of two adjacent split-ring resonators what increases the lattice period twice. We demonstrate that a further increase in the period of the modified array leads to a shift of the Fano resonance to a lower frequency. High quality factor of Fano resonance, around 100, is evidenced experimentally.

Brunel harmonics generated from ionizing clusters by few-cycle laser pulses

Xiaohui Gao, Bonggu Shim, and Michael Downer

Doc ID: 352803 Received 27 Nov 2018; Accepted 28 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: We study theoretically harmonic generation from ionizing nano-clusters irradiated by intense few-cycle laser pulses and identify a Brunel-type harmonic generation mechanism that originates from subcycle ionization dynamics in clusters. Compared to Brunel harmonics in gases, the spectra are shifted toward odd-order harmonics of Mie frequency ω_M due to efficient excitation of Mie oscillation. Considering the appreciable single-cluster harmonic yield and the relaxed phase-matching condition in overdense clustered plasmas, clusters driven by few-cycle laser pulses can be a promising source of vacuum-ultraviolet radiation.

Alpha-phase indium selenide saturable absorber for femtosecond all-solid-state laser

Xiaoli Sun, Jingliang He, bing nan shi, Baitao Zhang, Kejian Yang, chengqian zhang, and ruihua Wang

Doc ID: 355447 Received 17 Dec 2018; Accepted 28 Dec 2018; Posted 07 Jan 2019  View: PDF

Abstract: We successfully fabricated the high quality few-layered α-In2Se3 and investigated its carrier dynamics and nonlinear optical absorption properties by pump-probe and open-aperture Z-scan technologies. Intra- and inter-band relaxation time are determined to be 7.2 and 270 ps. And the effective nonlinear absorption coefficient was measured as βeff=-3.9×103 cm/GW (1064 nm). Based on α-In2Se3 saturable absorber, a continuous wave mode-locking operation was realized. Pulse duration, repetition rate and maximum output power were measured to be 352 fs, 42.4 MHz, and 0.56 W, corresponding to pulse energy of 13.2 nJ and peak power of 37.5 kW. To the best of our knowledge, this is the first demonstration of non-transition metal chalcogenides applied in ultrafast all-solid-state bulk lasers. This work well verified that α-In2Se3 should be a promising optical modulator candidate for all-solid-state laser.

Edge and bulk dissipative solitons in modulated PT-symmetric waveguide arrays

Yaroslav Kartashov and Victor Vysloukh

Doc ID: 353388 Received 03 Dec 2018; Accepted 28 Dec 2018; Posted 08 Jan 2019  View: PDF

Abstract: We address dissipative soliton formation in modulated PT-symmetric waveguide arrays composed from waveguides with amplifying and absorbing sections, whose density gradually increases (due to decreasing separation between waveguides) either towards the center of the array or towards its edges. In such a structure the level of gain/loss at which PT-symmetry gets broken depends on the direction of increase of the waveguide density. Breakup of the PT-symmetry occurs when eigenvalues of modes localized in the region, where waveguide density is largest, collide and move into complex plane. In this regime of broken symmetry the inclusion of focusing Kerr-type nonlinearity of the material and weak two-photon absorption allows to arrest the growth of the amplitude of amplified modes and may lead to the appearance of stable attractors either in the center or at the edge of the waveguide array, depending on the type of array modulation. Such solitons can be stable, they acquire specific triangular shapes and notably broaden with increase of gain/loss level. Our results illustrate how spatial array modulation that breaks PT-symmetry “locally” can be used to control specific location of dissipative solitons forming in the array.

Optomechanical properties of optically self-arranged colloidal waveguides

Oto Brzobohaty, Lukas Chvatal, and Pavel Zemanek

Doc ID: 348600 Received 17 Oct 2018; Accepted 27 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: When a suspension of wavelength-sized polystyrene spheres is illuminated with non-interfering counter-propagating Gaussian beams, the particles self-arrange into a colloidal waveguide. Mutual force interaction among particles is mediated by scattered light, referred to as the optical binding. We analyzed the longitudinal and lateral motion of particles in such colloidal waveguides made of increasing number of particles of either diameters 520 nm or 657 nm. We observed enhancement of the binding stiffness of neighboring particles by more than an order of magnitude. This enhancement is done by optical means, mainly due to local increase of optical intensity due to multiple light scattering in optically bound structure.

A Coherent Optical Wireless Communication Link employing Orbital-Angular-Momentum Multiplexing in a Ballistic and Diffusive Scattering Medium

Runzhou Zhang, Long Li, Zhe Zhao, Guodong Xie, Giovanni Milione, Hao Song, Peicheng Liao, Cong Liu, haoqian song, Kai Pang, Ari Willner, Brittany Lynn, Robert Bock, Moshe Tur, and Alan Willner

Doc ID: 348840 Received 26 Oct 2018; Accepted 26 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: We experimentally investigate the scattering effect on an 80-Gbit/s orbital-angular-momentum (OAM) multiplexed optical wireless communication (OWC) link. The power loss, mode purity, crosstalk, and bit-error-rate (BER) performance are measured and analyzed for different OAM modes under scattering levels from ballistic to diffusive regions. Results show that (i) power loss is the main impairment in the ballistic scattering, while the mode purities of different OAM modes are not significantly affected; (ii) in the diffusive scattering, however, the performance of an OAM-multiplexed link further suffers from the increased crosstalk between the different OAM modes.

Ultrashort infrared 2.5-11μm pulses: spatiotemporal profiles and absolute nonlinear response of air constituents

Howard Milchberg, Sina Zahedpour Anaraki, and Scott Hancock

Doc ID: 352557 Received 20 Nov 2018; Accepted 26 Dec 2018; Posted 07 Jan 2019  View: PDF

Abstract: We measure the detailed spatiotemporal profiles of femtosecond laser pulses in the infrared wavelength range λ=2.5-11μm, and the absolute nonlinear response of major air constituents (N2, O2, and Ar) over this range. The spatiotemporal measurements reveal wavelength-dependent pulse front tilt and temporal stretching in the infrared pulses.

Doppler-free coherent detection using period-one nonlinear dynamics of semiconductor lasers for OFDM-RoF links

Yu-Han Hung, Jhih-Heng Yan, Kai-Ming Feng, and Sheng-Kwang Hwang

Doc ID: 352026 Received 15 Nov 2018; Accepted 26 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: This study investigates coherent detection that is free from the Doppler frequency shift effect for orthogonal frequency division multiplexing radio-over-fiber (OFDM-RoF) links using period-one (P1) nonlinear dynamics of semiconductor lasers. Even under a dynamically time-varying Doppler frequency shift of up to 100 kHz, corresponding to a relative motion between a transmitter and a receiver with a velocity of more than 3850 km/hr at 28 GHz, the microwave carrier of a received OFDM-RoF signal can be well-regenerated instantaneously and uninterruptedly with its phase highly preserved through the P1 dynamics. No carrier frequency offset due to the Doppler frequency shift effect happens if the regenerated microwave carrier is used as a microwave local oscillator for coherent detection of the received OFDM-RoF signal. As a result, a bit-error ratio of around 10^{-9} is achieved for coherent detection of a 28-GHz OFDM-RoF signal carrying 4 Gb/s 16-quadrature amplitude modulation data. No digital signal processing, either photonic or electronic, is thus required to compensate for such a carrier frequency offest. This all-optical system is capable of operation up to at least 100 GHz.

Spatial mode detection by frequency up-conversion

Bereneice Sephton, Adam Vallés, Fabian Steinlechner, Thomas Konrad, Juan P. Torres, Filippus Roux, and Andrew Forbes

Doc ID: 351373 Received 09 Nov 2018; Accepted 25 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: The efficient creation and detection of spatial modes of light has become topical of late, driven by the need to increase photon-bit-rates in classical and quantum communications. Such mode creation/detection is traditionally achieved with tools based on linear optics. Here we put forward a new spatial mode detection technique based on the nonlinear optical process of sum-frequency generation. We outline the concept theoretically and demonstrate it experimentally with intense laser beams carrying orbital angular momentum and Hermite-Gaussian modes. Finally, we show that the method can be used to transfer an image from the infrared band to the visible, which implies the efficient conversion of many spatial modes.

Femtosecond written fiber Bragg gratings in Ytterbium doped fibers for fiber lasers in the kilowatt regime

Ria G. Krämer, Christian Matzdorf, Andreas Liem, Victor Bock, Wilko Middents, Thorsten A. Goebel, Maximilian Heck, Daniel Richter, Thomas Schreiber, Andreas Tünnermann, and Stefan Nolte

Doc ID: 346975 Received 27 Sep 2018; Accepted 25 Dec 2018; Posted 08 Jan 2019  View: PDF

Abstract: We investigate the high power durability of fiber Bragg gratings written directly into an Ytterbium doped large mode area fiber using ultrashort laser pulses. The gratings were successfully integrated as a high reflector into an oscillator setup reaching up to 1.9 kW signal output power with an efficiency of 87%. Defect states induced during the inscription process could be drastically reduced by a self-annealing process resulting in a stable laser performance.

Generation of aerosol-particle light-scattering patterns from digital holograms

Ramesh Giri, Claudia Morello, Yuli Heinson, Osku Kemppinen, Gorden Videen, and Matthew Berg

Doc ID: 355785 Received 19 Dec 2018; Accepted 24 Dec 2018; Posted 07 Jan 2019  View: PDF

Abstract: The similarity between the light-scattering pattern of a particle in the near-forward direction and diffraction from the particle’s silhouette is investigated. Images of irregularly shaped free-flowing aerosol particles are obtained from digital hologram measurements, which are then binarized to yield a silhouette. Application of Huygens’s and Babinet’s principles to the silhouette generates an approximate scattering pattern, which when compared to the true measured pattern shows a high level of agreement for particles much larger than the wavelength of light.

Impact-ionization mediated self-focusing of long-wavelength infrared pulses in gases

Xiaohui Gao and Bonggu Shim

Doc ID: 355007 Received 11 Dec 2018; Accepted 24 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: We numerically investigate the propagation dynamics of intense long-wavelength infrared pulses in a weakly ionized argon gas and show that the pulses undergo self-focusing due to the transverse variations of electron-impact ionization caused by quivering electrons. We demonstrate this plasma-induced self-focusing at a power much lower than the critical power for Kerr self-focusing and find it can be controlled by the initial electron density and pulse duration.

Generation of terahertz vortex pulses without any need of manipulation in terahertz region

QINGGANG LIN, Shuiqin Zheng, QIYING SONG, Xuanke Zeng, Yi Cai, Ying Li, Zhenkuan Chen, LANG ZHA, XinJian Pan, and Shixiang Xu

Doc ID: 352224 Received 18 Nov 2018; Accepted 24 Dec 2018; Posted 04 Jan 2019  View: PDF

Abstract: Obviously, converting a traditional Gaussian mode to a vortex beam is much more inconvenient in terahertz (THz) than in the near-infrared (NIR) region due to the underdevelopment of THz components and the strong THz diffraction. This paper reports a direct generation of THz vortex pulses by optical difference-frequency between a pair of NIR chirped pulses with different topological charges (TCs). By designing an all-passive and all-transmissive device for a collinear NIR pulse pair with conjugated TCs, we have got experimentally stable THz vortex pulses with a TC value of 2, exchangeable into -2 by rotating simply a quarter waveplate. This work avoids any need of THz components, so can be realized flexibly and have promising applications in THz field.

The photoluminescence enhancement in wide spectral range excitation in CsPbBr3 nanocrystal/Ag nanostructure via surface plasmon coupling

Chunfeng Cai, wang xiaoyu, Li Ling, Gang Bi, Zhousu Xu, and Huizhen Wu

Doc ID: 353074 Received 28 Nov 2018; Accepted 24 Dec 2018; Posted 03 Jan 2019  View: PDF

Abstract: This work demonstrates the SP-exciton coupling effect on the PL enhancement in CsPbBr3 NC/Ag NS heterostructure. The spectra dependent TRPL measurement reveals that the emission photons are from the recombination of localized excitons and the PL enhancement can be attributed to the near-field effect, which is also supported by evidence that the enhancements are nearly the same in the whole excitation wavelength. The non-spectral dependence of enhancement factor indicates that there is the same dynamic process of hot electrons in CsPbBr3 NC in multiphoton excitation. The hot electrons will relax into localized exciton states and the near field generated by SPs will enhance the radiative recombination of excitons. Thus the SP coupling will enhance the radiative recombination of excitons but have no influence on the photon absorption and hot electron relaxing processes. This work will have benefits on revealing the inner mechanism of dynamics of hot electrons relaxing and interactions of multi-photons absorption.

Coherent combining of mid-infrared difference frequency generators

Alice Odier, Rodwane CHTOUKI, Pierre Bourdon, Jean-Michel Melkonian, Laurent Lombard, Michel Lefebvre, and Anne Durécu

Doc ID: 349731 Received 06 Nov 2018; Accepted 24 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: We report what is, to the best of our knowledge, the first experimental demonstration of coherent combining of two mid-infrared difference frequency generators by active phase control in continuous-wave regime. Using the phase relation that is inherent to the nonlinear process, we are able to phase-lock and combine the idler waves by the sole phase control of one of the pump waves. This control is done by an all fiber electro-optic modulator. Combining is achieved with an excellent efficiency with a residual phase error of λ/28.

Next generation frequency domain diffuse optical imaging systems using silicon photomultipliers

vincent kitsmiller and Thomas O'Sullivan

Doc ID: 348181 Received 16 Oct 2018; Accepted 23 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: Diffuse optical imaging of biological tissue is a well-established methodology used to measure functional information from intrinsic contrast due to hemoglobin, water, and lipid. This information is exploited in frequency domain diffuse optical spectroscopy (FD-DOS) systems which have been used to investigate chemotherapy response, optical mammography, and brain imaging. FD-DOS depth sensitivity and dynamic range is typically constrained by photodetector sensitivity. Here we present FD-DOS utilizing a silicon photomultiplier (SiPM) detector that has a higher signal to noise ratio (SNR) compared to an avalanche photodiode (APD), and thus enabling extended source-detector (S/D) separations and increased depth penetration. We find the SiPM to have 10-30dB greater SNR than a comparably sized APD while detecting 1.5-2 orders of magnitude lower light levels, down to ~4pW at 50MHz modulation. The SiPM and APD recover optical property values of tissue simulating phantoms within 13% agreement and are stable with 1% coefficient of variation over one hour. Finally, the SiPM is used to accurately recover optical properties in a reflectance geometry at S/D separations up to 48mm in phantoms mimicking human breast tissue.

Towards X-ray Transient Grating Spectroscopy

Cristian Svetina, Roman Mankowsky, Gregor Knopp, Frieder Koch, Gediminas Seniutinas, Benedikt Rösner, adam kubec, Maxime Lebugle, Iacopo Mochi, Martin Beck, Claudio Cirelli, Juraj Krempasky, Claude Pradervand, Giulia Mancini, Jeremy Rouxel, Serhane Zerdane, Bill Pedrini, Vincent Esposito, Gerhard Ingold, Ulrich Wagner, Uwe Flechsig, Rolf Follath, Majed Chergui, Christopher Milne, Henrik Lemke, Christian David, and Paul Beaud

Doc ID: 350045 Received 07 Nov 2018; Accepted 22 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: The extension of transient grating spectroscopy (TGS) to the x-ray regime will create numerous opportunities ranging from the study of thermal transport in the ballistic regime to charge, spin and energy transfer processes with atomic spatial and femtosecond temporal resolution. Studies involving complicated split-and-delay lines have not yet been successful in achieving this goal. Here, we propose a novel, simple method based on the Talbot effect for converging beams, which can easily be implemented at current X-ray Free Electron Lasers. We validate our proposal by analyzing printed interference patterns on PMMA and Gold samples using ~3 keV X-ray pulses.

Single-pixel imaging with Fourier filtering: application to vision through scattering media

YESSENIA JAUREGUI SANCHEZ, Pere Clemente, Jesus Lancis, and Enrique Tajahuerce

Doc ID: 347638 Received 08 Oct 2018; Accepted 22 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: We present a novel approach for imaging through scattering media that combines the principles of Fourier spatial filtering and single-pixel imaging. We compare the performance of our single-pixel imaging setup with that of a conventional system. Firstly, we show that a single-pixel camera does not reduce the frequency content of the object, even when a small pinhole is used as a low-pass filter. Second, we show that the introduction of Fourier gating improves the contrast of imaging through scattering media in both optical systems. We conclude that single-pixel imaging fits better than conventional imaging on imaging through scattering media by Fourier gating.

Tunable hybrid silicon nitride and thin-film lithium niobate electro-optic micro-resonator

Abu Naim Rakib Ahmed, Shouyuan Shi, Matthew Zablocki, Peng Yao, and Dennis Prather

Doc ID: 352894 Received 27 Nov 2018; Accepted 22 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: This paper presents the first hybrid Si3N4-LiNbO3 based tunable micro-ring resonator where the waveguide is formed by loading a Si3N4 strip on an electro-optic (EO) material of X-cut thin-film LiNbO3. The developed hybrid Si3N4-LiNbO3 micro-ring exhibits high intrinsic quality factor of 1.85 × 105, with a ring propagation loss of 0.32 dB/cm, resulting in a spectral line width of 13 pm, and a resonance extinction ratio of ~27 dB within optical C-band for transverse electric (TE) mode. Using the EO effect of LiNbO3, a 1.78 pm/V resonance tunability near 1550 nm wavelength is demonstrated.

Bragg filter bandwidth engineering in subwavelength grating metamaterial waveguides

Pavel Cheben, Jiri Ctyroky, Jens Schmid, shurui wang, Jean Lapointe, J. Gonzalo Wangüemert-Pérez, I. Molina-Fernández, Alejandro Ortega-Moñux, Robert Halir, Daniele Melati, Dan-Xia Xu, Siegfried Janz, and Milan Dado

Doc ID: 352260 Received 18 Nov 2018; Accepted 22 Dec 2018; Posted 14 Jan 2019  View: PDF

Abstract: Bragg gratings are fundamental building blocks for integrated photonic circuits. In the high-index contrast silicon-on-insulator material platform it is challenging to accurately control the grating strength and achieve narrow spectral bandwidths. Here, we demonstrate a novel Bragg grating geometry utilizing a silicon subwavelength grating (SWG) waveguide with evanescently coupled periodic Bragg loading segments placed outside of the SWG core. We report experimental 3-dB filter bandwidths in a range from 8 nm to 150 pm by adjusting the distance of the Bragg loading segments from the core and the relative phase shift of the segments on the two sides of the waveguide, with a structure that has a minimum feature size of 100 nm.

Tunable multi-wavelength third harmonic generation using exposed-core microstructured optical fiber

Stephen C. Warren-Smith, Kay Schaarschmidt, Mario Chemnitz, Erik Schartner, Henrik Schneidewind, Heike Ebendorff-Heidepriem, and Markus Schmidt

Doc ID: 352973 Received 27 Nov 2018; Accepted 21 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: We demonstrate that exposed-core microstructured optical fibers offer multiple degrees of freedom for tailoring third harmonic generation, through core diameter, input polarization, and nanofilm deposition. Varying these parameters allows control of the phase-matching position between an infrared pump wavelength and the generated visible wavelengths. In this work we show how increasing the core diameter over previous experiments (2.57 µm compared to 1.85 µm) allows the generation of multiple wavelengths, which can be further controlled by rotating the input pump polarization and the deposition of dielectric nanofilms. This can lead to highly tailorable light sources for applications such as spectroscopy or nonlinear microscopy.

Realization of a second-order quantum interference based quantum clock synchronization at the femtosecond-level

Quan Run ai, Ruifang Dong, Yiwei Zhai, Fei Hou, Xiao Xiang, Hui Zhou, chaolin lv, Zhen Wang, Lixing YOU, Tao Liu, and Shou-Gang Zhang

Doc ID: 352454 Received 20 Nov 2018; Accepted 21 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: Quantum clock synchronization schemes utilizing frequency entangled pulses have flourished for their potentially superior precision to the classical protocols. In this paper, a new experimental record based on the second-order quantum interference algorithm is reported. The synchronization accuracy between two parties separated by a 6-km fiber coiling link, which is evaluated by the time offset shift relative to that withthe fibers removed, has been measured to be 13±1 ps. The stability in terms of TDEV of 0.81 ps at averaging time of 100 s has been achieved. The long-term synchronization stability is seen determined by the measurement device, and a minimum stability of 60 fs has been reached at 25600 s. Furthermore, for the first time we quantify the performance of this quantum synchronization scheme and very good agreements with the experimental results have been achieved. According to the quantum simulation, further improvements for both the synchronizing stability and accuracy can be expected.

Controllable Rotating Gaussian Schell-model Beams

Daomu Zhao and Lipeng Wan

Doc ID: 351892 Received 14 Nov 2018; Accepted 21 Dec 2018; Posted 03 Jan 2019  View: PDF

Abstract: A new class of partially coherent beams whose spectral density and degree of coherence tend to rotate during propagation is introduced. Unlike the previously reported twisted Gaussian Schell-model (TGSM) beams, this family of rotating beams are constructed without the framework of rotationally invariant cross-spectral density (CSD) functions. Thus, these beams have different underlying physics and exhibit distinctive twist effects. It is shown that such beams can undergo a twist of more than 90 degrees, providing larger degrees of freedom for flexibly tailoring the beam twist. Additionally, the effect of the orbit angular momentum (OAM) on the beam twist is found to be rather significant. Our results may pave the way toward synthesizing rotating partially coherent beams for applications in optics and, in particular, inspire further studies in the field of twist phase proposed 25 years ago.

Low-cost line-scanning confocal microendoscope for nuclear morphometry imaging in real time

Yubo Tang, Alex Kortum, Imran Vohra, Mohamed Othman, Sadhna Dhingra, Nabil Mansour, Jennifer Carns, Sharmila Anandasabapathy, and Rebecca Richards-Kortum

Doc ID: 351943 Received 15 Nov 2018; Accepted 21 Dec 2018; Posted 03 Jan 2019  View: PDF

Abstract: Fiber-optic endomicroscopy is a minimally invasive method to image cellular morphology in vivo. In this study, we demonstrate a low-cost and compact fluorescence microendoscope capable of line-scanning confocal imaging by synchronizing a digital light projector with a CMOS camera. We present the digital aperture design to enable real-time confocal imaging, and we implement parallel illumination to improve the optical sectioning performance. Furthermore, we show that the confocal microendoscope can enhance visualization of disease-associated features when imaging highly scattering esophageal specimens.

Formation of high-quality photonic nanojets by decorating spider silk

Cheng-Yang Liu, C.B. Lin, and Zih-Huan Huang

Doc ID: 349920 Received 01 Nov 2018; Accepted 21 Dec 2018; Posted 07 Jan 2019  View: PDF

Abstract: Photonic nanojet is a highly concentrated beam with low divergence in the shadow side of dielectric microparticle. In this letter, we first theoretically and experimentally investigate the formation of high-quality photonic nanojets by decorating spider silk. The dragline silks are directly extracted from cellar spider and capable of efficiently collecting ultraviolet cure adhesive. The liquid-collecting capacity of the capture silk is the result of a singular fiber structure with periodic spindle-knots. Using a scanning-optical-microscope system, we show that high-quality photonic nanojets are generated by silk fiber with spindle-knots. With the variation of the spindle-knot dimension, the properties of photonic nanojets such as intensity distribution, focal length and full width at half-maximum are able to tune elastically. By combining the unique biocompatibility, flexibility and tensile strength, the silk filaments with spindle-knots pave the method for original bio-photonic applications.

Truncated-correlation photothermal coherence tomography derivative imaging modality for small animal in-vivo early tumor detection

Andreas Mandelis, PANTEA TAVAKOLIAN, KONESWARAN SIVAGURUNATHAN, Hai Zhang, Wei Shi, and Fei-Fei Liu

Doc ID: 351752 Received 20 Nov 2018; Accepted 20 Dec 2018; Posted 03 Jan 2019  View: PDF

Abstract: Early cancer non-invasive diagnosis is a leading medical topic worldwide, due to the threat to human life and the high death rate of this disease. Light-absorption-based thermophotonic diagnostic imaging is well positioned for this challenge thanks to its speed, safety and high molecular contrast advantages. In this letter, an enhanced truncated-correlation photothermal coherence tomography (TC-PCT) imaging modality is presented for early in-vivo tumor detection and tested using a nude mouse thigh. Compared with conventional TC-PCT, the enhanced imaging modality was found to exhibit higher contrast that contributed to the precise measurement of the size and shape of the detected tumor. The experimental results were validated following histological analysis from hematoxylin and eosin staining. This increased contrast advantage gives rise to possible clinical applications in early tumor detection and treatment and in monitoring the effects of anti-tumor drugs.

Oscillatory trajectory of an optical beam propagating in free space

Octávio Santana and Luis de Araujo

Doc ID: 348844 Received 22 Oct 2018; Accepted 20 Dec 2018; Posted 21 Dec 2018  View: PDF

Abstract: We describe the experimental observation of nonrectilinear trajectories of a nearly-Gaussian light beam propagating in free space, after reflecting from a glass-air interface near critical incidence. The angular-dependent reflection coefficients modulate the incident beam’s angular spectrum, shifting the reflected beam from the rectilinear path predicted by geometrical optics. The beam trajectory shows a strong dependence on the angle of incidence, changing from rectilinear to oscillatory within 0.07o. Our results are in excellent agreement with the predictions of a theoretical model.

Generation of pulse-width controllable dissipative solitons and bound solitons by using all fiber saturable absorber

Wang Zhaokun, liujiang Li, Dongning Wang, Zichun Le, SHUQIN ZHANG, Shiying Cao, and Zhanjun Fang

Doc ID: 349865 Received 01 Nov 2018; Accepted 19 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: A passively mode-locked fiber laser with controllable pulse width is demonstrated by use of an all-fiber saturable absorber based on a hybrid no-core fiber (NCF) - graded index multimode fiber (GIMF) structure incorporated into an Er-doped fiber ring cavity. Such a hybrid NCF-GIMF structure has a tunable intra-cavity filtering effect. As a result, the mode-locking operation is achieved with the controllable pulse-width and spectral bandwidth in normal dispersion regime by only stretching the fiber device. Soliton pulses with the pulse width of 7.7 ps to ps are generated and the bound solitons with variable widths are also experimentally demonstrated. The results obtained reveal the versatility and flexibility of the NCF-GIMF structured device in controlling the pulse dynamics for different experimental requirements.

A diode-pumped solid-state laser platform for compact and long-lasting strontium-based optical clocks

Alberto Sottile, Eugenio Damiano, Alberto Di Lieto, and Mauro Tonelli

Doc ID: 351617 Received 13 Nov 2018; Accepted 18 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: Optical clocks based on strontium atoms and ions are currently used to provide precise standards for measuring time. These devices require several narrow-band visible laser sources at specific wavelengths to operate. We report on the diode-pumped continuous-wave laser operation at 674, 688, 689, 698 and 707 nm of a single crystal of Pr³+:LiGdF₄ (Pr:GLF). To the best of our knowledge, Pr:GLF is the only active medium suitable for solid-state laser operation at all the wavelengths of interest for Sr-based clocks in the deep-red region. We also investigated the spectral tunability of this source, achieving an uninterrupted tuning range of 17 nm, between 697 and 714 nm.

Conical refraction output from a Nd:YVO4 laser with an intracavity conerefringent element

Reza Akbari, Arkady Major, Grigorii Sokolovskii, Edik Rafailov, Ksenia Fedorova, and Chandan Qumar Howlader

Doc ID: 353357 Received 03 Dec 2018; Accepted 17 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: A conical refraction (CR) laser based on an a-cut Nd:YVO4 laser was demonstrated. By using a KGW crystal as a CR element, a typical laser with a Gaussian intensity output profile was transformed into a laser with conically refracted output. The CR laser delivered 220 mW of output power for 500 mW of pump power. The separation of the laser gain medium and the CR element reduced the complexity of the pumping scheme and resulted in the generation of well-behaved CR laser beams with outstanding quality. The presented approach is power-scalable and offers a unique possibility of studying the transformation of a Gaussian laser mode into a conically refracted one in a laser cavity.

Nd:YVO₄ high power master-oscillator power-amplifier laser system for second generation gravitational wave detectors

Fabian Thies, Nina Bode, Patrick Oppermann, Benno Willke, Maik Frede, and Bastian Schulz

Doc ID: 354549 Received 04 Dec 2018; Accepted 17 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: Ultra stable high power laser systems are essential components of the long baseline interferometers that detected the first gravitational waves from merging black holes and neutron stars. One way to further increase the sensitivity of current generation gravitational wave detectors (GWDs) is to increase the laser power injected into the interferometers.In this paper, we describe and characterize a 72W and a 114W linearly polarized, single frequency laser system at a wavelength of1064nm, each based on single pass Nd:YVO₄ power amplifiers. Both systems have low power and frequency noise and very high spatial purity with less than 10.7% respectively 2.9% higher order mode content. We demonstrate the simple integration of these amplifiers into the laser stabilization environment of operating GWDs and show stable operation of one of the amplifier systems in such an environment for more than 45 days.

Combined multiphoton and photoacoustic imaging for stratigraphic analysis of paintings

George Tserevelakis, Vassilis Tsafas, Kristalia Melessanaki, Giannis Zacharakis, and George Filippidis

Doc ID: 351349 Received 07 Nov 2018; Accepted 17 Dec 2018; Posted 11 Jan 2019  View: PDF

Abstract: Herewith, we demonstrate the effective combination of non-linear (multiphoton) and photoacoustic imaging for the high resolution stratigraphic analysis of multilayered art objects with emphasis on paintings. A novel convolution based algorithm is additionally applied for the precise discrimination of non-linear signals, providing valuable information as regards to the thickness and composition of successive varnish and paint layers in mock-up samples. On the other hand, photoacoustic contrast complements the extracted data by revealing well-hidden graphite underdrawings below the paint, at high sensitivity levels. The final composite images are directly compared with cross-sectional brightfield observations, validating the capabilities of the bimodal diagnosis in terms of measurement accuracy and contrast specificity. The presented hybrid diagnostic approach has the potential to optimize delicate interventions in works of art such as the selective removal of aged materials, promoting thus a significantly improved restoration outcome.

Dynamics for encircling an exceptional point in a nonlinear non-Hermitian system

Haiwen Wang, Sid Assawaworrarit, and Shanhui Fan

Doc ID: 351177 Received 12 Nov 2018; Accepted 15 Dec 2018; Posted 17 Dec 2018  View: PDF

Abstract: We study the dynamics near an exceptional point, in a nonlinear non-Hermitian system consisting of a pair of resonators. One of the resonators has a linear loss, and the other resonator has a saturable gain. We show that the system dynamics exhibits a topological and chiral characteristics. And moreover, unique to the nonlinear system, such dynamics allows one to adiabatically switch between bistable states at the same system parameter. Such bistable switching is potentially interesting in optical memory based on coupled laser systems.

Direct characterisation of tuneable few-femtosecond dispersive-wave pulses in the deep UV

Christian Brahms, Dane Austin, Francesco Tani, Allan Johnson, Douglas Garratt, John Travers, John Tisch, Philip Russell, and Jonathan Marangos

Doc ID: 348301 Received 15 Oct 2018; Accepted 13 Dec 2018; Posted 13 Dec 2018  View: PDF

Abstract: Dispersive wave emission (DWE) in gas-filled hollow-core dielectric waveguides is a promising source of tuneable coherent and broadband radiation, but so far the generation of few-femtosecond pulses using this technique has not been demonstrated. Using in-vacuum frequency-resolved optical gating, we directly characterise tuneable 3 fs pulses in the deep ultraviolet generated via DWE. Through numerical simulations, we identify that the use of a pressure gradient in the waveguide is critical for the generation of short pulses.

Two-photon PSF-engineered Image Scanning Microscopy

Omer Tzang, Daniel Feldkhun, Anurag Agrawal, Alexander Jesacher, and Rafael Piestun

Doc ID: 351579 Received 13 Nov 2018; Accepted 11 Dec 2018; Posted 20 Dec 2018  View: PDF

Abstract: We present two-photon fluorescence Image Scanning Microscopy with engineered excitation and detection point-spread-functions enabling 3D imaging in a single 2D scan. This demonstration combines excitation using a holographic multi-spot array of focused femtosecond pulses with a high-efficiency single-helix PSF phase mask detection. Camera detection along with a multi-view reconstruction algorithm allows volumetric imaging of biological samples over a depth of field spanning more than 1500 nm with an axial resolution of better than 400 nm.The nonlinear two-photon process improves sectioning and the inherent longer wavelengths increase the penetration depth in scattering samples.Our method extends the performance of 3D Image Scanning Microscopy towards thicker biological samples.

Thermal Approach to Classifying Sequentially Written Fiber Bragg Gratings

Senta Scholl, Alexander Jantzen, Rex Bannerman, Paul Gow, Devin Smith, James Gates, Lewis Boyd, Peter Smith, and Christopher Holmes

Doc ID: 345891 Received 02 Oct 2018; Accepted 11 Dec 2018; Posted 12 Dec 2018  View: PDF

Abstract: We demonstrate thermal classification of sequentially written fiber Bragg gratings. This Letter presents a process to determine the type of fiber Bragg grating written in SMF28 and GF4A by introducing the gratings to thermal treatment. This technique can be applied to several approaches based on sequential writing, including the small spot direct ultraviolet writing technique. Four different types of gratings have been identified, which are dependent on the fiber type and the fluence used during the writing process.

Photoacoustic communications: delivering audible signals via absorption of light by atmospheric H2O

Ryan Sullenberger, Sumanth Kaushik, and Charles Wynn

Doc ID: 346799 Received 25 Sep 2018; Accepted 11 Dec 2018; Posted 03 Jan 2019  View: PDF

Abstract: We describe a means of communication in which a user with no external receiver hears an audible audio message directed only at them. A laser transmits the message, which is encoded upon a modulated laser beam and sent directly to the receiver’s ear via the photoacoustic effect. A 1.9 µm thulium laser matched to an atmospheric water vapor absorption line is chosen to maximize the sound pressure while maintaining eye-safe optical power densities. We examine the photoacoustic transfer function describing this generation of audible sound and the important operational parameters, such as laser spot size, and their impact on a working system. Additionally, we map the spatial distribution of the photoacoustic energy.

Influence of optics vibration on synchrotron beam coherence

Walan Grizolli, Xianbo Shi, and Lahsen Assoufid

Doc ID: 352829 Received 27 Nov 2018; Accepted 10 Dec 2018; Posted 14 Jan 2019  View: PDF

Abstract: Vibration of optics is one of the major limiting factors of the performance of state-of-the-art beamlines at low-emittance synchrotron facilities. We present a theoretical model with experimental data describing vibration-induced effects on X-ray beam coherence. Owing to the incoherent nature of vibration, the decrease in the beam spatial coherence perturbed by optics vibrations can be characterized by modeling the effective source profile of the vibrating beam. The measurements were carried out by using grating interferometry and a refractive lens with controlled vibration as a test optics. The experimental results confirm the model and reveal the dependency of the measured beam spatial coherence on the acquisition time. The proposed method can be used to identify the eigenfrequency of the optical system as well as to optimize beamline operation and experimental conditions for coherence-related techniques.

A handheld line-scanned dual-axis confocal microscope with pistoned MEMS actuation for flat-field fluorescence imaging

Linpeng Wei, Chengbo Yin, Yoko Fujita, Nader Sanai, and Jonathan Liu

Doc ID: 351274 Received 08 Nov 2018; Accepted 08 Dec 2018; Posted 02 Jan 2019  View: PDF

Abstract: A handheld line-scanned dual-axis confocal (LS-DAC) microscope has been developed for high-speed (16 frames/sec) fluorescence imaging of tissues with sub-nuclear resolution. This is the first miniature fluorescence LS-DAC system that has been fully packaged for handheld clinical use on patients. A novel MEMS-scanning mechanism, with synchronized tilting and pistoning, is used to achieve flat-field en face imaging. We show that this facilitates video mosaicking to generate images that sample an extended lateral field of view.

Investigation of structural mechanisms of laser-written waveguide formation through third harmonic microscopy

Jun Guan, Xiang Liu, and Martin Booth

Doc ID: 351841 Received 13 Nov 2018; Accepted 04 Dec 2018; Posted 05 Dec 2018  View: PDF

Abstract: The mechanisms of laser-induced modification of transparent materials are complex combinations of different processes that depend upon material itself and a range of processing parameters. As such, the mechanisms are still subject to ongoing study. We use a custom-built adaptive third-harmonic-generation (THG) microscope to study those mechanisms. New femtosecond-laser-written phenomena are revealed through this method of imaging. Our study together with previous reports by Miyamoto (Opt. Express 24, 25718) and Fernandez (J. Phys. D: Appl. Phys. 48, 155101) indicate that the spatiotemporal distribution of the generated plasma during writing is responsible for the newly revealed phenomena.

Silicon-on-insulator free-carrier injection modulators for the mid-infrared

Milos Nedeljkovic, Callum Littlejohns, Ali Khokhar, Mehdi Banakar, Wei Cao, Jordi Soler Penades, Denh Tran, Frederic Gardes, David Thomson, Graham Reed, Hong Wang, and Goran Mashanovich

Doc ID: 351242 Received 06 Nov 2018; Accepted 01 Dec 2018; Posted 07 Dec 2018  View: PDF

Abstract: Experimental demonstrations of silicon-on-insulator waveguide based free-carrier effect modulators operating at 3.8 μm are presented. PIN diodes are used to inject carriers into the waveguides, and are configured to a) use free-carrier electroabsorption to create a variable optical attenuator with 34 dB modulation depth, and b) use free-carrier electrorefraction with the PIN diodes acting as phase shifters in a Mach-Zehnder interferometer, achieving a VπLπ of 0.052 V.mm and DC modulation depth of 22 dB. Modulation is demonstrated at data rates of up to 125 Mbit/s.

Improvement of coupling efficiency in free spaceoptical communication with a multi actuator adaptivelens

Seyed Ayoob Moosavi, Martino Quintavalla, Jacopo Mocci, Riccardo Muradore, Hossein Saghafifar, and Stefano Bonora

Doc ID: 351948 Received 18 Nov 2018; Accepted 27 Nov 2018; Posted 12 Dec 2018  View: PDF

Abstract: In Free-Space Optical communication (FSO), the propagation of a laser beam through the atmosphere causes wavefront distortions that decrease the Coupling Efficiency (CE) from free space to Single Mode Fiber (SMF).This tremendously degrades the performance of the communication channel even in case of weak turbulence regime. In this paper we demonstrate that a multi actuator adaptive lens working in closed loop with a wavefront sensor can strongly reduce the effect of the turbulence while reducing the system complexity with respect to correction systems using deformable mirrors or liquid crystal spatial light modulators. We obtain a 3-fold increase in the CE in weak turbulence regime.

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