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Unusual polarizing effect of cylindrical plasmonic holes

Yuri Gorodetski, Matan Revah, and Sergey Nechayev

Doc ID: 334722 Received 11 Jun 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We observe an unusual polarization state conversion in the light that passes through a cylindrical hole in a thick metal film. This phenomenon is related to the helicity locking of the guided mode due to the plasmonic transverse spin - an intrinsic angular momentum of the surface waves. We show how this effect is linked to the generation of the plasmonic vortex inside the hole and can be altered by varying the hole diameter. In addition, the total light transmission through the hole is shown to be partially contributed from the direct transmission which can further modify the resulting light polarization state.

Intensity fluctuation-invariant maximum likelihood estimation of speckle order

Francois Goudail and Jan Dupont

Doc ID: 337992 Received 05 Jul 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We present a speckle order estimation method invariant to mean intensity variations inside the sample. It is based on the acquisition of two statistically independent speckle images. Cramer Rao Lower bound (CRLB) and maximum likelihood (ML) estimator are derived, and shown to have performance very close to classical estimation methods that are not invariant to mean intensity fluctuations. This method is also shown to be robust to Poisson shot noise and additive noise, and is validated on an optical experiment with a standard camera. It is thus useful for estimating speckle order in real-world coherent images.

106 W, picosecond Yb-doped fiber MOPA system with a radially polarized output beam

Di Lin, Shaif-Ul Alam, David Richardson, and Neda Baktash

Doc ID: 340924 Received 31 Jul 2018; Accepted 14 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: We report the generation of high average output power, high peak power and high pulse energy radially polarized picosecond pulses from a compact gain-switched laser-diode-seeded Yb-doped fiber (YDF) master oscillator power amplifier (MOPA) system. A q-plate was employed as a mode converter prior to the final power amplifier to efficiently convert the linearly polarized Gaussian-shaped beam into a donut-shaped radially polarized beam. The desired vector beam was efficiently amplified yielding ~110ps pulses with a maximum output pulse energy of ~30.7µJ and a peak power of ~280kW at a repetition rate of 1.367MHz. The average power was scaled up to 106W by increasing the repetition rate to 5.468MHz

Thulium-doped nonlinear fiber amplifier delivering 50 fs-pulses at 20 W of average power

Tobias Heuermann, Christian Gaida, Martin Gebhardt, and Jens Limpert

Doc ID: 338794 Received 16 Jul 2018; Accepted 13 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: High average power ultrafast laser sources with small footprints are enabling tools for spectroscopic applications in medical and life sciences. In this work, we present an optimized nonlinear amplification scheme in the 2 µm wavelength region. This laser source delivers 50 fs-pulses at 80 MHz repetition rate with exceptional temporal pulse quality and 20 W of average output power. According to predictions from numerical simulations, it is experimentally confirmed that dispersion management is crucial to prevent the growth of side-pulses and an increase of the energy content in a temporal pedestal surrounding the self-compressed pulse. Based on these results, we discuss guidelines to ensure high temporal pulse quality from nonlinear femtosecond fiber amplifiers in the anomalous dispersion regime.

Multi-channel velocity multiplexing of single virus detection on an optofluidic chip

Jennifer Black, Vahid Ganjalizadeh, Joshua Parks, and Holger Schmidt

Doc ID: 336170 Received 11 Jul 2018; Accepted 13 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Liquid-core waveguide-based optofluidic devices have proven to be valuable tools for analysis of biological samples in fluid. They have enabled single bioparticle sensitivity while maintaining in-plane detection via light induced fluorescence. The incorporation of multi-spot excitation with multimode interference (MMI) waveguides has enabled spatially and spectrally multiplexed detection of single viruses on an oxide-based optofluidic platform. Here, we introduce a new way of MMI-based multiplexing on an all polymer platform where multiple analysis channels are placed within a single multi-spot pattern. This stacked channel design enables both velocity and spectral multiplexing of single particles. The principle is demonstrated with differentiated detection of single H3N2 and H1N1 viruses on a PDMS platform.

Ultracompact Polarizing Beam Splitter based on Single-Material Birefringent Photonic Crystal

Ehsan Ordouie, Hossein Alisafaee, and Azad Siahmakoun

Doc ID: 341054 Received 30 Jul 2018; Accepted 13 Aug 2018; Posted 14 Aug 2018  View: PDF

Abstract: An ultracompact polarizing beam splitter (PBS) is designed and fabricated based on a single-material birefringent photonic crystal structure.The fabrication method is based on e-beam physical vapor deposition where an oblique angle deposition technique is also incorporated.The PBS is designed for high tolerances in volume production.The main ingredient of the PBS is an alternating high and low refractive index modulation created from titanium dioxide (TiO2) deposited at angles of 0° and 70°.The measurements exhibited successful separation of two states of polarization with efficiencies of more than 92% over a total devices length of under 6μm.

Electro-optic polarization tuning of microcavities with a single quantum dot

Johnathon Frey, Henk Snijders, Justin Norman, Arthur Gossard, John Bowers, Wolfgang Loffler, and Dirk Bouwmeester

Doc ID: 331146 Received 08 May 2018; Accepted 12 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: We present an oxide aperture microcavity with embedded quantum dots that utilizes a three contact design to independently tune the quantum dot wavelength and birefringence of the cavity modes. A polarization splitting tuning of ~5 GHz is observed. For typical microcavity polarization splittings, the method can be used to achieve perfect polarization degeneracy that is required for many polarization-based implementations of photonic quantum gates. The embedded quantum dot wavelength can be tuned into resonance with the cavity, independent of the polarization tuning.

Dual-view acoustic-resolution photoacoustic microscopy with enhanced resolution isotropy

Junjie Yao, Emelina Vienneau, and Wei Liu

Doc ID: 332215 Received 21 May 2018; Accepted 11 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: Acoustic-resolution photoacoustic microscopy (AR-PAM) can provide penetration depths beyond the optical diffusion limit, but its lateral resolution is typically much worse than its axial resolution, resulting in a low resolution isotropy. We herein present a dual-view AR-PAM (DV-AR-PAM) system that exploits two orthogonally-arranged focused ultrasonic transducers. Taking advantage of their complementary acoustic detecting profiles, DV-AR-PAM allows the fusion of the dual-view signals, resulting in an enhancement in the resolution isotropy from 27% to 95% within one imaging plane, as demonstrated by simulation results on densely packed particles and experimental results on a single carbon fiber. Application of this method in vivo revealed distinct microvasculature structures in the mouse skin that were previously indistinguishable with single-view detection, demonstrating the potential of DV-AR-PAM for vascular and neurological studies.

Sub-100 W TEM₀₀ bulk Nd:GdVO₄ oscillator based on orthogonal thermal compensation

Xiaoyan Liang, Di Sun, Hua Lin, Jie Guo, and Wei Wang

Doc ID: 340772 Received 27 Jul 2018; Accepted 11 Aug 2018; Posted 14 Aug 2018  View: PDF

Abstract: We present a Nd:GdVO₄ bulk crystal oscillator with > 70 W TEM₀₀ laser output based on the orthogonal thermal compensation architecture. The asymmetry of thermo-optical effects in the anisotropic crystal was well compensated, and the overall thermal load was also distributed to lower the crystal temperature and the risk of crystal fracture. At an output coupling of 60%, a 71.2 W, TEM₀₀ laser output was achieved with 44% optical efficiency. Diffraction limited beam quality was measured to be M²x = 1.01 and M²y = 1.04 in the orthogonal directions.

Watt-level green random laser at 532 nm

sergio rota-rodrigo, benoit gouhier, Clément Dixneuf, Laura Antoni-Micollier, Germain Guiraud, Daniel Leandro, Manuel Lopez-Amo, Nicholas Traynor, and GIORGIO SANTARELLI

Doc ID: 331041 Received 08 May 2018; Accepted 10 Aug 2018; Posted 13 Aug 2018  View: PDF

Abstract: We have developed a Watt-level random laser at 532 nm. The laser is based on a 1064 nm random distributed ytterbium-gain assisted fiber laser seed with a 0.35 nm line-width 900mW polarized output power. A study for the optimal length of the random distributed mirror was carried out. An ytterbium-doped fiber master oscillator power amplifier architecture is used to amplify the random seeder laser without additional spectral broadening up to 20 W. By using a PPLN of 10 mm in a single pass configuration we generate in excess of 1 W random laser at 532 nm by second harmonic generation with an efficiency of 9 %. The green random laser exhibits an instability <1 %, optical signal to noise ratio >70 dB, 0.1 nm linewidth and excellent beam quality.

Comparison of Compressive Basis Patterns for Quantitative Single-Pixel Fluorescence Lifetime Imaging

Marien Ochoa Mendoza, Qi Pian, Ruoyang Yao, Nicolas Ducros, and Xavier Intes

Doc ID: 331961 Received 21 May 2018; Accepted 10 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: A novel hyperspectral single pixel system was used to compare different compressive basis patterns for intensity imaging, lifetime imaging, and FRET quantification. Six popular basis patterns were compared experimentally in a phantom containing two fluorescent dyes. The basis patterns that performed best for lifetime quantification were used to measure FRET occurrence in well-plate samples with varying acceptor-donor ratios. The ABS-WP approach using Haar patterns and the compressive sensing approach with Hadamard Ranked patterns displayed the best overall performances at a 50% compression ratio.

High-speed fiber scanning endoscope for volumetric multi-megahertz optical coherence tomography

Hinnerk Schulz-Hildebrandt, Tom Pfeiffer, Tim Eixmann, Sabrina Lohmann, Martin Ahrens, Josua Rehra, Wolfgang Draxinger, Peter König, Robert Huber, and Gereon Huttman

Doc ID: 332604 Received 25 May 2018; Accepted 10 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: We present a forward viewing fiber scanning endoscope for high-speed volumetric optical coherence tomography (OCT). Reduction in size of the probe was achieved by substituting the focusing optics by an all fiber-based imaging system which consists of a combination of scanning single mode fiber, a glass spacer, made from a step-index multi-mode fiber, and a GRIN fiber. A lateral resolution of 11 μm was achieved at a working distance of 1.2 mm. The newly designed piezo-based fiber scanning endoscope has an outer diameter of 1.6 mm and a rigid length of 13.5 mm. By moving the whole imaging optic in spirals for scanning the sample, the beam-quality remains constant over the entire field of view with a diameter of 0.8 mm. The scanning frequency was adjusted to 1.22 kHz for use with a 3.28 MHz Fourier domain mode locked (FDML) OCT system. Densely-sampled volumes have been imaged at a rate of 6 volumes per second.

Sum frequency generation of multi-line slab RF discharge CO laser system with intracavity nonlinear BaGa₂GeSe₆ crystal

Andrey Ionin, Dmitry Badikov, Valeriy Badikov, Igor Kinyaevskiy, Yuriy Klimachev, Andrey Kotkov, Andrey Kozlov, Adilya Sagitova, and Dmitrii Sinitsyn

Doc ID: 338090 Received 12 Jul 2018; Accepted 10 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: A compact repetitively pulsed broadband CO laser system with intracavity frequency conversion, for which a nonlinear crystal was also used as an output coupler, was launched for the first time. The laser system simultaneously operated in two spectral ranges: CO laser fundamental band (4.9-6.0 μm) and its sum frequencies band (2.45-2.95 μm). Different designs of the laser cavity were considered. Peak power of the fundamental and sum frequencies laser pulses was up to 2 kW and 10 W, respectively.

X-ray spectroscopy with variable line spacing based on reflection zone plate optics

Zhong Yin, Heike Löchel, Jens Rehanek, Claudia Goy, Anton Kalinin, Alexander Schottelius, Florian Trinter, Piter Miedema, Avni Jain, Joana Valerio, Philipp Busse, Felix Lehmkuhler, Johannes Moeller, Gerhard Gruebel, Anders Madsen, Jens Viefhaus, Robert Grisenti, Martin Beye, Alexei Erko, and Simone Techert

Doc ID: 339934 Received 23 Jul 2018; Accepted 09 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: X-ray spectroscopy is an ideally suited method to investigate the electronic structure of matter, which has been enabled by the rapid developments in light sources and instruments. The X-ray fluorescence lines of life-relevant elements such as carbon, nitrogen, and oxygen are located in the soft X-ray regime and call for suitable spectrometer devices. In this work, we present a high resolution spectrum of liquid water, recorded with a soft X-ray spectrometer based on a reflection zone plate (RZP) design. The RZP-based spectrometer with meridional variation of line space density from 2953 l/mm to 3757 l/mm offers extremely high detection efficiency and at the same time medium energy resolution. We can reproduce the well-known splitting of liquid water in the lone pair regime with 10 s acquisition time.

Ultrabroadband Mid-Infrared Noncollinear Difference Frequency Generation in a Silver Thiogallate Crystal

Yaroslav Aulin, Eric Borguet, and Aashish Tuladhar

Doc ID: 331419 Received 15 May 2018; Accepted 09 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: We report the generation of ultrabroadband mid-infrared (mid-IR) pulses by noncollinear difference frequency mixing. The signal and the idler output beams of an optical parametric amplifier are combined in a silver thiogallate crystal (AgGaS2) to generate mid-infrared radiation. We show that a noncollinear geometry facilitates broadband phase matching. Spectral bandwidths up to 1750 cm-1 were obtained at an external noncollinear angle of 4.2 degrees, which is more than three times broader than in a collinear geometry. The broadband spectrum is tunable in the range of 1500 - 4500 cm-1. Pulse energies up to 1 µJ were achieved. The broadband pulses were used in sum frequency generation in ZnSe and in vibrational absorption spectroscopy experiments of liquid samples.

Interference Patterns of Vortex Beams Based on Photonic Band Gap Structure

Zhiguo Wang, JIAWEI YANG, Yanyong Sun, and Yanpeng Zhang

Doc ID: 334513 Received 05 Jun 2018; Accepted 09 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: We experimentally observe a vortex six-wave mixing (SWM), namely enhanced four-wave mixing (FWM), signal with its orbital angular momentum transferred from a vortex probe via a photonic band gap (PBG)structure in a hot rubidium vapor cell. By analyzing spatial images and interference patterns, we investigate the characteristics of transmitted signal and reflected band gap signal from the PBG. In detail, we demonstratethe spatial shift and splitting of the images as well as the shift of the phase singularity for the probe transmission signal under the nonlinear phase of different dressing fields. As for the reflected vortex SWM signal, we observe defocusing and shift of its images as well as shift of its singularity by scanning the frequency detuning of related field. Moreover, we findthe interference patterns of the vortex probe can be switched from parallel shape to spiral shape by changing its incident angle. Besides, we further research the spiral interference patterns of the transmitted signal byscanning the probe detuning, observing that the number of forks changes with the detuning. We consider the transmitted signal is a combined beam of the linear probe and nonlinear FWM, which are separated under Kerr effect. It is the separation that causes the fork number to change with probe detuning. Our studies are useful for better understanding and manipulationof optical vortices and have wide applications in quantum communication and information processing.

One-Volt Silicon Photonic Crystal Nanocavity Modulator with Indium Oxide Gate

Erwen Li, Qian Gao, Spencer Liverman, and Alan Wang

Doc ID: 335973 Received 25 Jun 2018; Accepted 09 Aug 2018; Posted 14 Aug 2018  View: PDF

Abstract: The ever-increasing global network traffic requires high level of seamless integration between optical interconnect systems and complementary metal–oxide–semiconductor (CMOS) circuits. Therefore, it brings stringent requirement for future electro-optic (E-O) modulators, which should be ultra-compact, energy efficient, high bandwidth and in the meanwhile, able to be directly driven by the state-of-the-art CMOS circuits. In this manuscript, we report a low-voltage silicon photonic crystal nanocavity modulator using an optimized metal-oxide-semiconductor (MOS) capacitor consisting of In2O3/HfO2/p-Si stacked nanostructure. The strong light-matter interaction from the accumulated free carriers with the nanocavity resonant mode results in holistic improvement in device performance, including a high tuning efficiency of 250pm/V and an average modulation strength of 4dB/V for a moderate Q factor of ~3,700 using an ultra-short electrode length of only 350nm. With one-volt driving voltage over a capacitive loading of only 13fF, the silicon photonic nanocavity modulator can achieve more than 3dB extinction ratio with energy consumption of only 3fJ/bit. Such low-voltage, low capacitance silicon nanocavity modulator provides the feasibility to be directly driven by a CMOS logic gate for single-chip integration.

Graphene-based all-optical multi-parameter regulations for ultrafast fiber laser

Yu Long Cao, Lei Gao, Yujia Li, Jingdong Zhang, Fuhui Li, and Tao Zhu

Doc ID: 332556 Received 29 May 2018; Accepted 08 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: Ultrafast lasers with tunable capabilities of pulse-duration and spectrum have widespread applications in telecommunication, spectroscopy and nonlinear optical bio-imaging. However, traditional mechanical and electrical tuning methods are still challenging for precise and stable controlling. Based on graphene’s photo-thermal effect, we tune the bandwidths and wavelengths of chirped fiber Bragg gratings with flexible graphene-coating approaches. By inserting the fabricated devices into an ultrafast fiber laser cavity, durations and wavelengths of the generated pulses can be all-optically tuned with sensitivities of 470 fs/mW and 2.9 pm/mW, separately. Such an optical-controlled method provides a compact and precise way to regulate various laser properties.

Side lobes controlled photonic nanojet with a horizontal graded-index microparticle

Yihui Wu, Wenchao Zhou, and Huaming Xing

Doc ID: 340030 Received 25 Jul 2018; Accepted 08 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: A photonic nanojet generated by the transparent dielectric microparticle (microsphere or microcylinder) is a sub-wavelength focused beam. The properties of photonic nanojet have been modified by changing the refractive index and structure of micropaticles. In the paper, a super narrow photonic nanojet with the full-width at half maximum (FWHM) waist approximately 116.6nm (λ/4.3, with 500nm excitation wavelength) is obtained by a horizontal graded-index microparticle, which is divided by multilayers parallel to the direction of light propagation. The method for side lobes controlling by the waves superposition from the modified graded refractive index and that of the center layer is proposed and discussed. Besides, a structure assembled with different height plates approaching to the desire circular section is suggested for decreasing the difficulties of fabrication, and generates a similar photonic nanojet.

Twisted tilted fiber Bragg gratings: new structures and polarization properties

Piotr Kisała, Janusz Mroczka, Sławomir Cięszczyk, Krzysztof Skorupski, and Patryk Panas

Doc ID: 338475 Received 13 Jul 2018; Accepted 08 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: In this Letter it has been shown that the twisting of TFBGs (tilted fiber Bragg gratings) decreases its sensitivity to the polarization of the input light. It is proved by a theoretical simulation study that twisting the TFBG by 180 ̊ eliminates the sensitivity of the grating to input light polarization changes. We have experimentally proved that such a structure produced by us has 18 times lower coefficient of variation of transmission for polarization changes than the untwisted TFBG. This paper also presents a new method for manufacturing the TTFBG (twisted tilted fiber Bragg grating). We have demonstrated the possibility of writing the TTFBG structure twisted by 90° on a fiber with a length of 10 mm. The structure has been further twisted in the other direction by 90 degrees, which is consistent with a structure twisted by 180 degrees. The properties of both structures were determined. Due to the fiber's strength, the TTFBG twisted by 180 degree has to be 2 cm long. An advantage of the proposed method of producing TTFBG is that there is a twist of the structure itself after fabrication. This creates new possibilities of using the structure in many applications. This type of grating can be used to reduce sensitivity to polarization in various sensing applications, in particular, to measure the refractive index. In addition, 180 degrees twisted TTFBG has properties of direction discrimination in twist sensing applications.

Integrated Germanium-on-Silicon Franz-Keldysh Vector Modulator Used with Kramers-Kronig Receiver

Yeyu Tong, Qiulin Zhang, Xinru Wu, Chi Wai Chow, Chester C.T. Shu, and Hon Tsang

Doc ID: 341244 Received 02 Aug 2018; Accepted 07 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: We proposed an integrated vector modulator based on two compact and high-speed germanium-on-silicon Franz-Keldysh electro-absorption modulators (Ge-EAMs). The proposed vector modulator is extremely compact with a total footprint of only 1800×200 µm2. We further experimentally demonstrated a 4-quadrature-amplitude-modulation (4-QAM) at 40 Gb/s over a 20-km standard single-mode fiber transmission. The complex signal is successfully re-constructed with a single-ended photodiode (PD) in a recently proposed Kramers-Kronig receiver for the future low-cost, low-power and low-footprint datacenter interconnects applications. The preliminary performance of the vector modulator with a 16-QAM was also investigated.

Realizing high transmission intensity in photonic crystal nanobeams using a side-coupling waveguide

Sami Halimi, Shuren Hu, Francis Afzal, and Sharon Weiss

Doc ID: 339998 Received 18 Jul 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Side-coupled photonic crystal (PhC) nanobeam cavities were investigated to overcome challenges in measuring low-order resonances in traditional in-line PhC nanobeams that arise due to the trade-off between achieving high quality factor and high transmission intensity resonances. On the same PhC nanobeam, we demonstrate that only the side-coupling approach leads to measurable resonances when high mirror strength unit cells severely limit the intensity of transmitted light through the in-line configuration. In addition, by coupling light directly into the cavity center, the design of side-coupled PhC nanobeams can be simplified such that high quality factor PhC nanobeams can be achieved using only two different hole radii and uniform hole spacing.

Multi-octave supercontinuum generation in YAG pumped by mid-infrared, multi-picosecond pulses

Siqi Cheng, Gourab Chatterjee, Friedjof Tellkamp, Axel Ruehl, and R. J. Dwayne Miller

Doc ID: 335292 Received 14 Jun 2018; Accepted 07 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: High-energy, multi-octave supercontinuum (SC) generation in bulk media, pumped with picosecond pulses in the mid-infrared, though pivotal in a myriad of applications, poses severe constraints due to the wavelength-scaling of the critical power criterion and the propensity to induce avalanche-ionization-seeded breakdown mechanisms. Here, we demonstrate a simple experimental geometry, relying on a very low numerical aperture for the pump pulse and a crystal length commensurate with the Rayleigh length of the focusing geometry, generating a multi-octave, stable SC in YAG. The SC ranges from 500 nm to 3.5 $\mu$m (measured at -30 dB with spectral components at wavelengths up to 4.5 $\mu$m), when pumped by a 3-ps pulse centered at 2.05 $\mu$m in the anomalous dispersion regime. We also investigate the dynamics of filament formation in this interaction regime by monitoring the spectral and temporal evolution of the pulse during its propagation through the length of the crystal.

Timing jitter of high-repetition-rate mode-locked fiber lasers

Yan Wang, Haochen Tian, Yuxuan Ma, Youjian Song, and Zhigang Zhang

Doc ID: 332745 Received 30 May 2018; Accepted 07 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: We characterized the timing jitter of the pulse trains from 880 MHz Yb-doped NPE mode-locked fiber lasers based on balanced optical cross-correlation method. Jitter spectral density at different net-cavity dispersion has been characterized and the near-zero dispersion shows the lowest rms timing jitter (10 fs rms, integrated from 30 kHz to 5 MHz). The measurements have been compared with analytical models. Comparison shows that the RIN coupled timing jitter by nonlinearity is the dominated origin of the measured timing jitter below ~100 kHz, while ASE noise makes a major contributions in the high frequency above hundreds of kHz. To the best of our knowledge, it is the first high precision timing jitter characterization for the ~GHz level repetition rate mode-locked fiber lasers. The results will be of great importance for further improving the laser performance for many applications.

High fidelity cavity soliton generation in crystalline AlN micro-ring resonators

Zheng Gong, Alexander Bruch, Mohan Shen, Xiang Guo, Hojoong Jung, Linran Fan, Xianwen Liu, Liang Zhang, junxi wang, jinmin li, jianchang Yan, and Hong Tang

Doc ID: 338423 Received 11 Jul 2018; Accepted 07 Aug 2018; Posted 14 Aug 2018  View: PDF

Abstract: Chip-scale mode-locked dissipative Kerr solitons have been realized on various materials platforms, making it possible to achieve a miniature, highly coherent frequency comb source with high repetition rates. Aluminum nitride (AlN), an appealing nonlinear optical material having both Kerr (𝜒3) and Pockels (𝜒2) effects, has immerse potential for comb self-referencing without the need for external harmonic generators. However, cavity soliton states have not been yet achieved in AlN microresonators. Here, we demonstrate mode-locked Kerr cavity soliton generation in crystalline AlN microring resonator. By utilizing ultrafast tuning of the pump frequency through single-side-band modulation, in combination with optimized wavelength scan and pump power-ramp patterns, we can deterministically elongate a ~400ns short lived soliton to a time span as long as we wish to hold it.

Piston alignment of segmented optical mirrors via Convolutional Neural Networks

Dailos Ramos, Lara Díaz García, Juan José Fernández Valdivia, Juan Trujillo Sevilla, and José Manuel Rodríguez Ramos

Doc ID: 334328 Received 04 Jun 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: Two of the most commonly used methods for the alignment of segmented mirrors nowadays are based on Curvature and Shack-Hartman wavefront sensors. We investigate a different approach that employs Convolutional Neural Networks. The method allows the piston step values between segments to be measured with high accuracy as well as large capture range at visible wavelengths. It does not require special hardware and is fast to be used at any time during the observation.

78-fs pulses from a SWCNT-SA mode-locked Tm:CLNGG disordered garnet crystal laser at 2017 nm

Yicheng Wang, Yongguang Zhao, Zhongben Pan, Ji Eun Bae, Sun Young Choi, Fabian Rotermund, Pavel Loiko, Josep Maria Serres, Xavier Mateos, Haohai Yu, Huaijin Zhang, Mark Mero, Uwe Griebner, and Valentin Petrov

Doc ID: 334404 Received 11 Jun 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: A passively mode-locked Tm:CLNGG laser using single-walled carbon nanotubes as saturable absorber is demonstrated at 2017 nm. Pulses as short as 78 fs are generated at 86 MHz repetition rate with an average output power of 54mW, the shortest pulses for a crystalline host in the 2-μm spectral range to the bestof our knowledge. By increasing the output coupling from 0.5% to 1.5%, a higher average output power of 100 mW is achieved for slightly longer pulses with duration of 105 fs at 1996 nm.

Extreme-ultraviolet high-order harmonic generation from few-cycle annular beams

Thomas Gaumnitz, arohi Jain, and Hans Jakob Woerner

Doc ID: 336549 Received 02 Jul 2018; Accepted 06 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: An annular infrared (IR) laser beam has been used for high-order harmonic generation reaching a cut-off energy of 90 eV for XUV-IR pump-probe experiments in an intrinsically stable attosecond beamline. The generation of harmonics along the laser axis in the missing portion of the laser beam decreases the IR power load on thin metallic foils that are used for removing the residual IR and shaping the extreme ultraviolet pulses from the HHG. This finds applications in high average power few-cycle laser systems, where high average IR power destroys the foils. The spatial separation of IR and XUV will moreover simplify the realization of attosecond time-resolved measurements.

Effect of Tm3+ concentration on the emission wavelength shift in Tm3+-doped silica microsphere lasers

Angzhen Li, Jiquan Zhang, Meng Zhang, Wenhao li, Shunbin Wang, Elfed Lewis, Gilberto Brambilla, and Pengfei Wang

Doc ID: 334574 Received 06 Jun 2018; Accepted 06 Aug 2018; Posted 09 Aug 2018  View: PDF

Abstract: In this work, a Tm3+-doped sol-gel silica microsphere lasing at 2.0 μm is reported. Microspheres with different Tm3+ concentrations are fabricated by overlaying different Tm3+ concentration sol-gel solutions on the surface of a pure silica microsphere resonator and then annealing the sample with a CO2 laser. Based on a traditional fiber taper-microsphere coupling method, single and multimode microsphere lasing in the wavelength range 1.8-2.0 μm is observed if an 808 nm laser diode is used as a pump source. A relatively low threshold pumping power of 1.2 mW is achieved using this arrangement. This sol-gel method allows for an easy varying of the Tm3+ doping concentration. The observed laser output shifts to longer wavelengths when the Tm3+ doping concentration increases. This has been explained by the larger Tm absorption at shorter wavelengths. The ability to fabricate sol-gel co-doped silica glass microlasers represents a new generation of low threshold and compact infrared laser sources for use as miniaturized photonic components for a wide range of applications including gas sensing and medical surgery.

Laser performance of a 966 nm LD side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 μm

Xuyao Zhao, Dunlu Sun, Jianqiao Luo, Huili Zhang, Zhongqing Fang, Cong Quan, Lunzhen Hu, Maojie Cheng, Qing-li Zhang, and Shaotang Yin

Doc ID: 337888 Received 05 Jul 2018; Accepted 06 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: We demonstrate a 966 nm LD side-pumped Er,Pr:GYSGG laser crystal operated at 2.79 μm with high repetition rate. The lifetimes of the upper level 4I11⁄2 and lower level 4I13⁄2 are 0.66 and 0.85 ms, respectively. The laser performance under different repetition rates and pulse widths is experimentally studied with the optimal cavity structure. A maximum output power of 8.86 W is achieved at the 125 Hz and 200 μs pulse width, corresponding to the slope efficiency of 14.8% and electrical-to-optical efficiency of 7.7%. With increasing frequency from 50 to 200 Hz, the slope efficiency varies from 24.7% to 11.7% operated at 125 μs pulse width. Moreover, the Mx2/My2 factors of 7.52/7.59 and Θx/Θy far-field divergences of 16.1/16.5 mrad are also measured. The results indicate that a high performance 2.79 μm laser could be realized on the Er,Pr:GYSGG radiation resistant crystal by deactivation and LD side-pumping.

Laser Resistance Dependence of Interface for High-Reflective Coatings Studied by Capacitance-Voltage and Absorption Measurement

Nuo Xu, Meiping Zhu, Yingjie Chai, Behshad Roshanzadeh, Steve Boyd, Wolfgang Rudolph, Yuanan Zhao, Rong Chen, and Jianda Shao

Doc ID: 338644 Received 13 Jul 2018; Accepted 06 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: HfO2/SiO2 bilayer coatings and multilayer high reflection (HR) coatings without and with modified co-evaporated interface (MCEI) have been prepared. MCEI is designed to be evaporated at an oxygen-deficient environment to achieve higher absorption than the conventional (CON) discrete interface. Capacitance-voltage measurements and absorption measurements demonstrate that MCEI increases the trap density and leads to higher absorption. The laser induced damage threshold (LIDT) and nano-indenter test results indicate that the MCEI multilayer coating exhibits better laser-resistance and mechanical property despite the larger absorption. The experimental results suggest that adhesive force between layers play a more important role in nanosecond laser damage resistance than interface absorption.

0.43 J / 100 ps Nd:YAG laser with adaptive compensation of thermally induced lens

Roman Balmashnov, Aleksey Kornev, Igor Kuchma, Arsen Davtian, and Dmitry Oborotov

Doc ID: 337619 Received 02 Jul 2018; Accepted 06 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: We demonstrate a diode-pumped MOPA Nd:YAG 1064 nm laser with sub-joule-level output energy of 0.43 J, high pulse repetition rate of 200 Hz and short pulse duration of 100 ps. The 5 mJ master oscillator consisted of 100 nJ / 100 ps Nd:YVO₄ microchip-laser and end-pumped Nd:YAG regenerative amplifier. The two-pass output amplifier was based on two Ø10×140 mm Nd:YAG laser rods. We apply an adaptive compensator with an analyzer based on an astigmatic optical system and a quadrant photodiode to compensate for low-order wave-front non-stationary thermal distortions in high-energy laser amplifier. The adaptive compensator demonstrates high sensitivity to curvature changes of λ/100, and it provides output beam divergence near to 1.5×DL in 100 ps 0.43 J×200 Hz of operation mode.

Speckle noise reduction for digital holographic images using multi-scale convolutional neural networks

Wonseok Jeon, Wooyoung Jeong, Kyungchan Son, and Hyun Yang

Doc ID: 337803 Received 04 Jul 2018; Accepted 04 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: In this Letter, we propose a real-time speckle noise reduction method with only a single reconstructed image based on convolutional neural networks. The proposed network has multi-size kernels that can capture the speckle noise component effectively from digital holographic images. For robust noise reduction performance, the network is trained with a large noisy image dataset that has object-dependent noise and a wide range of noise levels. The experimental results show the fast, robust and outstanding speckle noise reduction performance of the proposed approach.

Nearly twice-quantum-efficiency 2 μm CW laser in LD-pumped Tm3+, La3+: CaF2 single crystal

Liangbi Su, Zhen Zhang, xinsheng guo, Jingya Wang, Cheng Zhang, and Jie liu

Doc ID: 338085 Received 11 Jul 2018; Accepted 03 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: A Tm3+, La3+: CaF2 single crystal was grown and its spectral properties and laser performance were investigated. Under diode end-pumping, continuous-wave laser has been demonstrated. The slope efficiency up to 67.8% was first achieved in the co-doping crystal, which is close to twice the theoretical quantum efficiency. A maximum output power of 4.269 W and a broad tunable range of 192 nm was also obtained, indicating this system is a promising candidate for highly efficient ~2 μm lasers.

arization-insensitive beam splitters using all dielectric phase gradient metasurfaces at visible wavelengths

Ahmet Ozer, Nazmi Yilmaz, Hasan Kocer, and Hamza Kurt

Doc ID: 336122 Received 26 Jun 2018; Accepted 03 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: Beam splitters play important roles in several optical applications such as interferometers, spectroscopy, and optical communications. In this study, we propose and numerically examine polarization-insensitive beam splitters utilizing two-step phase gradient all dielectric metasurfaces in the visible spectrum. The metasurface is made of periodically arranged binary unit cells and phase difference between neighboring unit-cells on the surface is 180 degrees. The metasurface has shown to have a special phase gradient whose sign changes periodically. The angle of the split beams to both sides and the corresponding total transmission value at 532 nm wavelength are found to be ± 46.8° and 0.90, respectively.

Power scaling of actively Q-switched orthogonally polarized dual-wavelength Nd:YLF laser at 1047 nm and 1053 nm

Zhi-Yu Zuo, Shi-Bo Dai, Si-Qi Zhu, Hao Yin, Zhen Li, and Zhenqiang Chen

Doc ID: 339900 Received 18 Jul 2018; Accepted 02 Aug 2018; Posted 10 Aug 2018  View: PDF

Abstract: We report a high average power continuous-wave (CW) and actively Q-switched (AQS) orthogonal polarization dual-wavelength Nd:YLF laser at 1047 nm and 1053 nm. A maximum CW output power of 14.2 W was obtained under the incident pump power of 41.7 W, corresponding to an optical-to-optical conversion efficiency of 34.1% and a slope efficiency of 38.3%. Active Q-switching was accomplished by inserting an acousto optic modulator in the cavity. Under the incident pump power of 40 W, this setup delivered a maximum average output power of 10 W at the pulse repetition frequency (PRF) of 30 kHz and a largest pulse energy of 3.4 mJ at the PRF of 1 kHz, respectively. To our knowledge, there are the highest average output powers for both CW and AQS orthogonally polarized dual-wavelength lasers based on laser crystals.

Mode interference induced oscillation in propagation speed of fiber fuse in few-mode fibers

Shoulin Jiang, Lin Ma, Wang Shuai, Xinyu Fan, and Zuyuan He

Doc ID: 340144 Received 20 Jul 2018; Accepted 02 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: We investigated the fiber fuse propagation speed in different kinds of few-mode fibers (FMFs) by combining heterodyne detection and time-frequency analysis. The periodic speed oscillation due to mode interference was observed and we confirm that the characteristic length Lc (defined as optical discharge propagation distance within a period of speed oscillation) is independent of the launched power, which is different from that observed in single-mode fibers. Moreover, we believe that the optical field modulation with enough intensity led to the variation of the optical discharge center position. Lc about half of the beat length in the two-mode fiber was observed accordingly. In addition, we show that pure-silica core FMFs with large effective area are desired for fiber fuse suppression in mode-division multiplexing transmission.

Multi-channel perfect absorber based on one-dimensional topological photonic crystal heterostructure with graphene

xi wang, Yanzhao Liang, Leiming Wu, Jun Guo, Xiaoyu Dai, and Yuanjiang Xiang

Doc ID: 340323 Received 20 Jul 2018; Accepted 02 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: The topological edge mode, which exists at the interface of one-dimensional (1D) topological photonic crystal (PhC) heterostructure, provides the possibility to realize perfect absorption for its strong field local effect. In this letter, it is found that a huge absorption enhancement appears because of the excitation of topological edge mode while the graphene is sandwiched between two 1D PhC. The single peak perfect absorption is realized by means of the intense coupling of incident light and Tamm plasmon polaritons (TPPs) which is excited with Ag-PhC structure. Moreover, based on the effect of topological edge mode, TPPs and critical coupling, we theoretically demonstrate that multi-channel perfect absorption can be achieved with the constructed by two PhC, a monolayer graphene and Ag mirror. The angular selectivity of the proposed absorber is also investigated. Both of the absorption peak are extremely narrow and the absorption can be maintained more than 97% with the incident angle varying from 0° to 50° degree. Hence, our results may have potentially applications in optical switches, thermal emissions, and narrowband selective filters.

Amplified measurement of weak optical activity using spin-phase gradient beam

Nirmal Viswanathan and Rashmi Ranjan Suna

Doc ID: 336071 Received 25 Jun 2018; Accepted 02 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Development of alternate techniques to polarimetry for the measurement of weak optical rotation, with improved sensitivity, is becoming increasingly important as one understands the role of chirality in drug design and synthesis and the fundamentals of chiral light-matter interaction. We demonstrate here an optical amplification scheme using spin-phase gradient beam to measure ultra-small optical rotation angle (4 mdeg), with a sensitivity of 220 deg/m, due to dilute (mg/ml) dextro-rotatory sugar solution. A Soleil-Babinet compensator is used to generate tunable spin-phase gradient beam that enables us to achieve high measurement sensitivities. Theoretical formalism of the technique leads us to the possibility to realize much higher measurement sensitivity of up to 10 deg/m by tuning-in the experimental parameters.

Interpolating light-scattering properties of irregularly shaped, absorbing particles

Evgenij Zubko, Gorden Videen, Jessica Arnold, Benjamin Maccall, ALYCIA WEINBERGER, and Yuriy Shkuratov

Doc ID: 337785 Received 04 Jul 2018; Accepted 02 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: Success in developing remote-sensing methods is largely based on adequate modeling of target-particle shape. In various terrestrial and cosmic applications, submicron- and micron-sized dust particles appear to have a highly irregular morphology. Light scattering by such irregularly shaped particles can be computed only with a numerical technique that, in practice, is a time-consuming approach, demanding significant computational resources. In this Letter we discuss an efficient way to accelerate light-scattering computations through interpolation of the numerical results obtained at different levels of material absorption. We find a non-linear dependence of the light-scattering response on the imaginary part of refractive index Im(m). Over the range of ΔIm(m)=0.05, the dependence can be satisfactorily described with a cubic polynomial function, whose determination requires exact computations at four different values of Im(m). The light-scattering response at other intermediate values of Im(m) can be inferred with great accuracy via interpolation.

Design and performance of terahertz absorber based on patterned graphene

Yan Jiang, Huaide Zhang, Jiao Wang, Chaoning Gao, Jia Wang, and Weiping Cao

Doc ID: 335363 Received 19 Jun 2018; Accepted 02 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: Modern terahertz (THz) technology offers the advantage of enhanced target detection ability with high spatial and temporal resolutions in the THz band, which makes it a formidable threat to stealth targets. Consequently, THz absorbers have outstanding potential as an electromagnetic countermeasure. In this work, we design, fabricate, and characterize a THz absorber based on patterned graphene. We present the transfer, photolithography, and etching processes involved in graphene patterning as well as the experimental measurements of the fabricated absorber. Our simulations show that with increase in the Fermi energy, the performance of the designed absorber gradually improves and finally decreases slightly. Further, the absorption bandwidth firstly broadens and then narrows slightly. The effective bandwidth with absorption greater than 90% ranges from 1.54THz to 2. THz, with the relative bandwidth (RBW) reaching about 36.6%. Although the measured RBW (from ~12% to ~14% and then to ~8%) slightly deviates from the simulated one, the position of the resonant frequency is well matched between theory and experiment. Moreover, we illuminate the absorption mechanism using the theory of destructive interference. Our study can significantly contribute to the design, manufacture, and application of patterned-graphene-based THz absorbers.

Programmable optical transport of particles in knot circuits and networks

Jose Rodrigo, Mercedes Angulo, and Tatiana Alieva

Doc ID: 340078 Received 18 Jul 2018; Accepted 02 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: A freestyle single-beam laser trap allows for multi-particle optical transport along arbitrary open or closed trajectories with independent control of the all-optical confinement and propulsion forces exerted over the particles. Here, exploiting this manipulation tool, we propose and experimentally demonstrate an optical dynamic routing technique to assist multi-particle transport in knot circuits and networks exhibiting multiple crossing paths. This new functionality for optical transport enables the particle circulation in such complex systems handling traffic jams and making possible particle separation/mixing in them. It is important for the development of programmable particle delivery and other automated optical transport operations of interest in colloidal physics, optofluidics, biophysics, etc.

Manipulating polarization for generating plasmon radially vector beam with linearly polarized light

chuanfu Cheng, yuqin zhang, Xiangyu Zeng, Ruirui Zhang, Zijun Zhan, Xing Li, Li Ma, chunxiang liu, and CHANGWEI HE

Doc ID: 334756 Received 08 Jun 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: We show that the polarization state of wave field can be manipulated through the plasmonic metasurface consisting of orthogonal nanoslit pairs, the output polarization angle is independent of the incident linearly polarized light and is highly dependent on the orientations of nanoslit pairs. After exploring the general physical mechanism of unit nanoslit pair for the manipulation of polarization state, we combine the Archimedes spiral with the nanoslit pairs to compensate for the Pancharatnam-Berry phase induced by the orientation of nanoslits, as well as achieved the radially polarized vector beam under the illuminations of different linearly polarized lights for the first time. Furthermore, experiments are performed to successfully realize the radially polarized vector beam and the results are in excellent agreement with the numerical simulations.

Surpassing the limit of slow-light based tunable optical delay via four-wave-mixing Bragg scattering

Ning Zhang, Xuelei Fu, Jie Liu, and Chester C.T. Shu

Doc ID: 336045 Received 26 Jun 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: We demonstrate a tunable optical delay that surpasses the tuning speed limit of the conventional slow-light induced optical delay. A novel nonlinear optical coupler, implemented by four-wave-mixing (FWM) Bragg scattering process, is utilized to perform interference of the slow-light delayed signal pulse and a non-delayed reference pulse. In the destructive interference region, the Brillouin-induced group delay based on frequency-dependent phase-shift of the synthesized pulse is amplified. The group delay amplification factor, determined by the coupling ratio of the nonlinear optical coupler, can be controlled through varying the FWM pump power to provide an ultrafast response. Our experimental result demonstrates that an initial 6.2 ns Brillouin-induced optical delay can be amplified and rapidly tuned within the range of -5.2 to 27.2 ns.

Ultrasensitive optofluidic resonator refractive index sensor

Xianfeng Chen, Zhiyuan Xiao, and Hailang Dai

Doc ID: 337766 Received 04 Jul 2018; Accepted 02 Aug 2018; Posted 02 Aug 2018  View: PDF

Abstract: We report an optofluidic resonator refractive index sensor based on an integrated structure constructed by a free-space coupling architecture. It uses symmetrical metal-cladding hollow-core waveguide and a prism to generate surface plasmon polarization. The sensor achieves very high sensitivity by coupling the core mode to ultrahigh order modes in waveguide layer can obtain refractive index of detailed low order value of 10-6. We demonstrate the device through infiltration of different fluids into the hollow core along an optofluidic resonator. A detection limit of 1.010-6 refractive index units has been derived from measurements. The presented method can be applied to the detection of molecular structure and bio-chemistry.

Dual-wavelength intensity-modulated Fabry-Perot refractive index sensor driven by temperature fluctuation

Ying Wu, Li Xia, and Nian Cai

Doc ID: 334827 Received 11 Jun 2018; Accepted 02 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: A refractive index sensor based on in-line Fabry-Perot (FP) interferometer is proposed and experimentally demonstrated. Two lasers are combined and injected into the sensor head. The power responses of two wavelengths are measured by a dual-channel optical power meter simultaneously. The two reflected power signals distribute along an ellipse. The refractive index of the liquid is calculated from the half length of the longer axes of the fitted ellipse. The refractive index sensing system is demonstrated to measure the refractive index of the salt solutions with different concentrations. The demodulated results matched well with the refractive index measured by the Abbe refractometer. Since the temperature is eliminated during the ellipse fitting, the measuring result is insensitive to the temperature fluctuation. The proposed refractive index sensing sensor has outstanding advantages, such as low demodulation cost, simple fabrication, easy to clean and good mechanical strength, and will be of importance in biological detection, chemical analysis, and water pollution monitoring.

Multi-cell coordination for 60 GHz RoF fronthaul enabled by non-orthogonal multiple access scheme without successive interference cancellation

Yu Tian, Christina Lim, Ampalavanapilla Nirmalathas, and Alan Lee

Doc ID: 336214 Received 28 Jun 2018; Accepted 02 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: We propose and experimentally demonstrate a non-orthogonal multiple access (NOMA) enabled 60 GHz radio-over-fiber (RoF) fronthaul system with coordinated base stations (BSs), improving the data rate and coverage of 60 GHz millimeter-wave (mm-wave) RoF systems. Firstly, coordinated multipoint (CoMP) transmission using space-time block coding (STBC) is adopted in the fronthaul links, achieving 1.3 dB improvement in receiver sensitivity compared to two fronthaul links transmission without STBC. Secondly, fronthaul link performance characterization is carried out to offer thorough references for future 60 GHz CoMP fronthaul link design. Further, multi-cell coordination in RoF fronthaul is presented, where a multi-level code (MLC) based NOMA scheme is employed. A sum rate of 6 Gbps for three users is achieved along 10 km fronthaul transmission and 1.24 m wireless transmission. Experimental results show that the valid power allocation ratio range improves from 3.5≤R≤4.2 in conventional superposition code (SPC) based NOMA fronthaul to 3≤R≤5 in our proposed coordinated MLC-NOMA fronthaul link.

Tunable mid-infrared generation via wide-band four wave mixing in silicon nitride waveguides

Abijith Kowligy, Dan Hickstein, Alexander Lind, David Carlson, Henry Timmers, Nima Nader, Daniel Maser, Daron Westly, Kartik Srinivasan, Scott Papp, and Scott Diddams

Doc ID: 338710 Received 13 Jul 2018; Accepted 02 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: We demonstrate wide-band frequency down-conversion to the mid-infrared (MIR), using four-wave-mixing (FWM) of near-infrared (NIR) femtosecond-duration pulses from an Er:fiber laser, corresponding to 100 THz spectral translation. Photonic-chip-based silicon-nitride waveguides provide the FWM medium. Engineered dispersion in the nanophotonic geometry and the wide transparency range of silicon nitride enable large-detuning FWM phase-matching, and results in tunable MIR from 2.6-3.6 μm on a single chip with 100-pJ-scale pump-pulse energies. Additionally, we observe up to 25 dB broadband parametric gain for NIR pulses when the FWM process is operated in a frequency up-conversion configuration. Our results demonstrate how integrated photonic circuits pumped with fiber lasers could realize multiple nonlinear optical phenomena on the same chip and lead to engineered synthesis of broadband, tunable, and coherent light across the NIR and MIR wavelength bands.

Hilbert transform based single shot plasmon microscopy

Terry Chow, Bei Zhang, and Michael Somekh

Doc ID: 338442 Received 12 Jul 2018; Accepted 02 Aug 2018; Posted 15 Aug 2018  View: PDF

Abstract: The localized properties of surface plasmons and surface waves can be measured with a modified confocal microscope. An interference signal arises from a locally generated reference close to normal incidence and the beam that forms the surface wave. A spatial light modulator can impose different phase shifts on part of the incident light to recover the properties of the surface plasmon. We report a Hilbert transform method to recover the wavenumber with a single shot. The method is faster and potentially less expensive than previous approaches. The signal to noise is equivalent to the phase stepping method. The signal processing necessary to condition the signal is described.

Round-robin-differential-phase-shift quantum key distribution with monitoring signal disturbance

Rong Wang, Yin Zhen Qiang, Shuang Wang, Guang-can Guo, Wei Chen, and Zhengfu Han

Doc ID: 338836 Received 16 Jul 2018; Accepted 01 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: In recent years, Round-robin-differential-phase-shift (RRDPS) quantum key distribution (QKD) has attracted great attention for its unique characteristics, i.e. the information leakage can be bounded without learning bit error rate. Though the RRDPS QKD has made a breakthough, it's still a question that how RRDPS will perform with monitoring signal disturbance, e.g. decoy-state and error rate statistics are both used. Here, we present simulations to study RRDPS protocol with monitoring signal disturbance. To our excitement, when using infinite decoy-states method, RRDPS protocol can outperform the commonly used BB84 protocol in term of channel length under typical experimental parameters. In the case of finite decoy-states, we find that only two decoy-states and one signal state are sufficient to obtain performance very close to infinite decoy-states case. Our simulations prove that RRDPS is a competitive protocol in real-life situations.

Multimode interference dynamic light scattering

Aristide Dogariu and Jose Guzman-Sepulveda

Doc ID: 334812 Received 08 Jun 2018; Accepted 01 Aug 2018; Posted 01 Aug 2018  View: PDF

Abstract: When dealing with dynamic scattering systems, being able to collect strong signals while maintaining a high signal-to-noise ratio (SNR) is critical. It is well known that a spatially coherent measurement provides the largest SNR while a partially coherent one provides better means for proper spatial averaging. In this paper, we present a robust implementation of a fiber-based, single-mode, common-path interferometer assisted by multimode interference (MMI). We show that light can be efficiently collected from larger coherent regions while keeping a high SNR that is comparable to that of a pure single-mode arrangement. Additionally, our implementation allows having both a stable local oscillator encoding information on the fiber-medium interface and a linear dependence on scattering density. These two attributes, in turn, permit accessing the effective optical properties of the dynamic complex system

Simultaneous Two-Photon Resonant Optical Laser Locking (STROLLing) in the hyperfine Paschen--Back regime

Renju Mathew, Francisco Ponciano-ojeda, James Keaveney, Daniel Whiting, and Ifan Hughes

Doc ID: 336476 Received 03 Jul 2018; Accepted 01 Aug 2018; Posted 01 Aug 2018  View: PDF

Abstract: We demonstrate a technique to lock simultaneously two laser frequencies to each step of a two-photon transition in the presence of a magnetic field sufficiently large to gain access to the hyperfine Paschen-Back regime. A ladder configuration with the 5S$_{1/2}$, 5P$_{3/2}$ and 5D$_{5/2}$ terms in a thermal vapour of $^{87}$Rb atoms is used. For the sum of the laser frequencies, which represents the stability of the two-photon lock, we measure a frequency instability of less than the Rb D$_2$ natural linewidth of 6 MHz for nearly all measured time scales.

Resolution gain in Space-Time Digital Holography (STDH) by self-assembling of the object frequencies

Vittorio Bianco, Zhe Wang, Yutong Cui, Melania Paturzo, and Pietro Ferraro

Doc ID: 331832 Received 16 May 2018; Accepted 01 Aug 2018; Posted 03 Aug 2018  View: PDF

Abstract: Space-Time Digital Holography (STDH) exploits the object motion to record the hologram in a hybrid space-time domain. This representation adds new capabilities to conventional DH, e.g. unlimited Field of View (FoV) and variable phase shifting. This is the best candidate for imaging biological samples flowing in microfluidic channels. Here we show that STDH is able to improve the spatial resolution as well. Differently from other super-resolution approaches, stitching between holograms or their spectra is no longer required. Moreover, we introduce a new oblique STDH modality to record and process hybrid space-time representations. This allows improving resolution in 2D with one single object scan, paving the way to the use of STDH for superresolution imaging onboard Lab on a Chip devices.

In-fiber beam splitters for construction of in-line Michelson interferometers

Dongning Wang and Jing Liu

Doc ID: 337750 Received 05 Jul 2018; Accepted 01 Aug 2018; Posted 07 Aug 2018  View: PDF

Abstract: We demonstrate optical fiber in-line Michelson interferometers based on two in-fiber beam splitters crossing the core of single mode fiber, fabricated by femtosecond laser. The in-fiber beam splitter reflects part of the incident light to the air-cladding interface before being reflected back while passing the rest to travel along the fiber core. The two in-fiber beam splitters, air-cladding interfaces and the cutting fiber end face together form a combined three in-line Michelson interferometers. Such a Michelson interferometer device is robust in mechanical strength, easy in fabrication, compact in size and low in cost.

Highly efficient injection microdisk lasers based on quantum well-dots

Eduard Moiseev, Natalia Kryzhanovskaya, Mikhail Maximov, Fedor Zubov, Alexey Nadtochiy, Marina Kulagina, Yirii Zadiranov, Nikolay Kalyuzhnyy, Sergey Mintairov, and Alexey Zhukov

Doc ID: 332921 Received 26 Jun 2018; Accepted 01 Aug 2018; Posted 08 Aug 2018  View: PDF

Abstract: We study injection GaAs-based microdisk lasers capable of operating at room and elevated temperatures. A novel type of active region is used, namely InGaAs quantum well-dots representing a dense array of indium-rich islands formed inside In-depleted residual quantum well by metalorganic vapor phase epitaxy. We demonstrate a high output power of 18 mW, differential efficiency of about 31 % and peak electrical-to-optical power conversion efficiency of 15 % in a 31 µm in diameter microdisk laser. The CW lasing is observed up to 110°C.

A simple approach for aberration-corrected OCT imaging of the human retina

Helge Sudkamp, Dierck Hillmann, Peter Koch, Malte vom Endt, Hendrik Spahr, Michael Münst, Clara Pfäffle, Reginald Birngruber, and Gereon Huttman

Doc ID: 331574 Received 15 May 2018; Accepted 31 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: Aberration-corrected imaging of human photoreceptor cells, whether hardware- or software based, presently requires a complex and expensive setup. Here, we use a simple and inexpensive off-axis full-field time-domain optical coherence tomography approach to acquire volumetric data from an in vivo human retina. Full volumetric data are recorded in 1.3 seconds. After computationally correcting for aberrations, single photoreceptor cells were successfully visualized. In addition, the numerical correction of ametropia is demonstrated. Our implementation of Full-field OCT combines a low technical complexity with the possibility to use the phase of the recorded light for computational image correction.

Origins of clustered frequency combs in Kerr microresonators

Noel Sayson, Hoan Pham, Karen Webb, Vincent Ng, Luke Trainor, Harald Schwefel, Stephane Coen, Miro Erkintalo, and Stuart Murdoch

Doc ID: 332978 Received 29 May 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: Recent experiments have demonstrated the generation of widely-spaced parametric sidebands that can evolve into "clustered" optical frequency combs in Kerr microresonators. Here we describe the physics that underpinsthe formation of such clustered comb states. In particular, we show that the phase-matching required for the initial sideband generation is such that (at least) one of the sidebands experiences anomalous dispersion, enablingthat sideband to drive frequency comb formation via degenerate and non-degenerate four-wave mixing. We validate our proposal through a combination of experimental observations made in a magnesium fluoridemicroresonator and corresponding numerical simulations. We also investigate the coherence properties of the resulting clustered frequency combs. Our findings provide valuable insights on the generation and dynamics of widely-spaced parametric sidebands and clustered frequency combs in Kerr microresonators.

Transverse mode switchable all-fiber Brillouin laser

JiuLin Gan, Xiaobo Heng, Zhishen Zhang, Jiong Li, muqiao li, Hua Zhao, Qi Qian, Shanhui Xu, and Zhongmin Yang

Doc ID: 334705 Received 08 Jun 2018; Accepted 30 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: A transverse mode switchable all-fiber Brillouin laser architecture is proposed. This laser architecture mainly consists of an optical switch, a set of cascaded mode selection couplers (MSCs) and a few mode fiber ring cavity. By switching the output signal of optical switch, specific transverse modes generated by MSCs can be coupled into the ring cavity to excite the corresponding Brillouin scattering light. Based on Brillouin nonlinear effect, the desired mode resonant amplification is guaranteed and transverse mode switchable laser beam is obtained. As a proof-of-principle, we have implemented an all-fiber Brillouin laser with switchable output of fundamental transverse (LP01) mode and second order transverse (LP11) mode at the wavelength of 1550 nm. The slope efficiency and linewidth for LP01 and LP11 mode are 25.1% and 4.9 kHz, 20.9% and 4.96 kHz, respectively. Additionally, the orbital angular momentum laser beam with l = +1, -1 or 0 switchable output is also demonstrated from our all-fiber Brillouin laser system. Owing to the compact all-fiber architecture, this transverse mode switchable Brillouin fiber laser is reliable during long-term operation and thus promising for many practical applications.

Z-Scan Measurements of Water from 1150 nm to 1400 nm

Christopher Marble, Joseph Clary, Gary Noojin, Sean O'Connor, Dawson Nodurft, Andrew Wharmby, Benjamin Rockwell, Marlan Scully, and Vladislav Yakovlev

Doc ID: 338516 Received 11 Jul 2018; Accepted 30 Jul 2018; Posted 02 Aug 2018  View: PDF

Abstract: Understanding the nonlinear properties of water is essential for multiphoton microscopy applications related to deep tissue imaging, as well as understanding supercontinuum generation in water. Unfortunately, the nonlinear properties of water for wavelengths longer than 1064 nm are poorly understood. We extend the application of the Z-scan technique in water to determine its nonlinear refractive index (n2) and nonlinear absorption (β) for wavelengths in the 1150 nm to 1400 nm range, where linear absorption is also significant. We observe the wavelength dependent variation of the nonlinear properties of water around the water absorption band.

Broadband linearly chirped light source with narrow linewidth based on external modulation

ZHAOYU LU, Tianxin Yang, Zhi-Yong Li, Cheng Guo, Zhaoying Wang, Dongfang Jia, and Chunfeng Ge

Doc ID: 327538 Received 02 May 2018; Accepted 30 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: An external modulation method is proposed and experimentally demonstrated for the generation of linearly chirped light over broadband with narrow linewidth. Our chirped light source is a combination of an optical recirculating frequency shifter loop and an optical frequency linear sweeper. A linearly chirped light over a range of 200 GHz at a chirp rate of 3.6×10^16 Hz/s is generated. The instantaneous linewidth of the chirped light is estimated to be less than 50 kHz.

Low-threshold optical bistability in field-enhanced nonlinear GMR grating nanostructure

Zhiqiang Ge, Xuwei Hei, Leiran Wang, Qibing Sun, Jinhai Si, Wei Zhao, Guoxi Wang, and Wenfu Zhang

Doc ID: 335277 Received 02 Jul 2018; Accepted 29 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: We have numerically studied the optical bistability in guided-mode resonance assisted nonlinear grating nanostructure. A low-index slot is introduced to significantly improve the confinement of light in nonlinear material. In this way, the proposed novel configuration possesses low-threshold optical switching intensity (~3 MW/cm2), which is about 58 times lower than that of typical nonlinear grating nanostructure without the low-index slot. This bistability study provides an effective method to reduce the threshold of optical switching intensity and thus can be applied in optical logic, optical computation and all-optical memory.

Tapered fiber enabled high power, high spectral purity random fiber lasing

hanwei zhang, Jun Ye, Pu Zhou, Xiaolin Wang, Jinyong Leng, Xu Jiangming, Jian Wu, and Xiaojun Xu

Doc ID: 336262 Received 27 Jun 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Random distributed feedback Raman fiber laser (RRFL) is a new kind of light source that can be applied to generate high power laser. In this letter, we report on a high power, high spectral purity RRFL based on tapered fiber, in which four-wave mixing (FWM) effect has been sufficiently suppressed. By choosing appropriate tapered fiber length, we achieve a maximum random laser output of 491 W and the spectral purity can reach to as high as 94%. We carefully compare the influence on FWM effect with different tapered fiber length and splicing pattern by cutting back method and lateral-offset splicing. The results show that the transverse modes dispersion is responsible to the appearance of FWM by compensating the phase mismatch. It is believed that kilo-watt-level random laser can be achieved by further optimizing the parameters of tapered fiber.

Mutually-induced soliton explosions in a fiber laser

Ying Yu, Zhi-Chao Luo, Jiqiang Kang, and Kenneth Kin-Yip Wong

Doc ID: 336307 Received 27 Jun 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Soliton explosions are among the most intriguing nonlinear dynamics in dissipative systems, manifesting themselves as a self-recovered localized structure when suffering explosive instabilities. Herein, we report on the investigation of soliton explosions in an ultrafast fiber laser operating in the multi-soliton regime. It is demonstrated that explosion of one soliton could be induced by another one through the soliton interactions mediated by transient gain response of erbium-doped fiber. We denote this phenomenon as “mutually-induced soliton explosion” when referring to the multi-soliton regime. The results provide the first investigation of soliton explosions in the multi-soliton regime, and therefore will enhance a more comprehensive understanding of the soliton exploding phenomenon.

10.8 kW, 2.6 times diffraction limited laser based on a continuous wave Nd:YAG oscillator and an extra-cavity adaptive optics system

Licheng Sun, GUO ding, shao chongfeng, li yang, Yamin Zheng, Chuang Sun, Xiao-Jun Wang, and Lei Huang

Doc ID: 337978 Received 05 Jul 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: In this letter, a 10.8 kW, 2.6 times diffraction limited laser based on a continuous wave (CW) Nd:YAG oscillator using an unstable resonator and an extra-cavity adaptive optics (AO) system was presented. Two Nd:YAG slabs and a disk-laser configuration were used to make the laser compact and power scalable. The output was a rectangular annulus, which was further expanded to a square annulus and was adaptively corrected by an extra-cavity deformable mirror (DM). The DM was designed to be capable of correcting the square annular wavefront aberrations. In the experiment, the vertical beam quality (VBQ) was improved from 51.7 to 2.6 times diffraction limited after correction. To our best knowledge, this is the highest power and brightness based on a CW Nd:YAG oscillator.

Photonics in highly dispersive media: The exact modal expansion

Frederic Zolla, Andre Nicolet, and Guillaume Demesy

Doc ID: 338174 Received 09 Jul 2018; Accepted 28 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: We present exact modal expansions for photonic systems including highly dispersive media. The formulas, based on a simple version of the Keldysh theorem, are very general since both permeability and permittivity can be dispersive, anisotropic, and even possibly non reciprocal. A simple dispersive test case where both plasmonic and geometrical resonances strongly interact exemplifies the numerical efficiency of our approach.

Direct generation of narrow linewidth Laguerre-Gaussian vortex laser in a monolithic nonplanar oscillator

Guoping Lin, Yaqin Cao, Ranran Ji, Cuifang Hou, and Zehuang Lu

Doc ID: 338540 Received 13 Jul 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Vortex laser beams carrying orbital angular momentum have been attracting lots of interest in recent years. Here we demonstrate the direct generation of vortex laser in a monolithic nonplanar ring cavity. Unidirectional and single frequency operation of Laguerre–Gaussian (LG) modes are observed and characterized. Fork interferograms have been obtained using a simple interferometer based on a plano-concave lens, and the topological charge of vortex beam is determined. A spectral linewidth as narrow as 2.3 kHz is measured by beating with a reference laser. We believe that such high coherent vortex laser can be beneficial for numerous applications including precision measurements and optical communications.

Design of a multiple self-mixing interferometer for a fiber ring laser

Liheng Shi, Dongmei Guo, yifeng cui, Hui Hao, Wei Xia, Yiping Wang, Xiaoqi Ni, and Ming Wang

Doc ID: 337668 Received 03 Jul 2018; Accepted 27 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: In this letter, a novel multiple self-mixing interferometer for a fiber ring laser (FRL) is designed by introducing a circular feedback cavity. A system model is established based on an injection-seeded erbium-doped FRL proposed by Dragic. Owing to the reflection of collimating lens, the multiplied fringes have different depths, which shows two Doppler frequencies in the spectrum of the self-mixing signal. A double-peak frequency identification algorithm is proposed to extract the Doppler frequency from the unique signal. This technique has the potential to improve the accuracy of fiber self-mixing measurement systems, particularly in Doppler velocimeters.

Nonsymmetric curved beams within a symmetric caustic skeleton

Pablo Frigerio Parenza, Dafne Amaya, Oscar Martinez Matos, and Pablo Vaveliuk

Doc ID: 331774 Received 17 May 2018; Accepted 27 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: Nonsymmetric curved beams having a symmetric caustic skeleton are presented. They arise from a finite jump in the symmetric spectral phase that breaks the symmetry of the beam intensity without altering its associate caustic curve. These nonsymmetric beams can be represented as a superposition of two caustic beams whose wave fields have well-defined even and odd symmetries with weight coefficients dependent on the phase jump. In this approach, the phase jump acts as a measure of the beam asymmetry degree that can be easily controlled in experiments. This scheme is a promising step towards optical cryptography and quantum optics applications.

Vertical mode transition in hybrid lithium niobate and silicon nitride based PIC structures

Abu Naim Rakib Ahmed, Andrew Mercante, Shouyuan Shi, Dennis Prather, and Peng Yao

Doc ID: 339986 Received 17 Jul 2018; Accepted 27 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: This letter presents an optical mode transition structure for use in Si3N4/LiNbO3 based hybrid photonics. A gradual modal transition from a Si3N4 waveguide to a hybrid Si3N4/LiNbO3 waveguide is achieved by etching of a terrace structure into sub-micrometer thick LiNbO3 film. The etched film is then bonded to predefined LPCVD Si3N4 waveguides. Herein we analyze hybrid optical devices both with and without the aforementioned mode transition terrace structure. Experimental and simulated results indicate that inclusion of the terrace significantly improves mode transition compared to an abrupt transition, i.e., 1.78 dB lower mode transition loss compared to the abrupt transition. The proposed transition structure is also applied to the design of hybrid Si3N4-LiNbO3 micro-ring resonators. A high-quality factor (Q) resonator is demonstrated with the terrace transition which mitigates undesired resonances.

Simultaneous recovery of a full set of optical properties in turbid media using incomplete P5 approximation to CW radiance

Lingling Liu, Wenbo Wan, jiao li, Huijuan Zhao, and Feng Gao

Doc ID: 336212 Received 28 Jun 2018; Accepted 27 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: Traditional methods for determining the optical properties of turbid media are implemented in diffusive regimes, where the scattering coefficient μs and anisotropy factor g are inseparable due to the similarity relation for anisotropy scattering. Determining μs and g in addition to the absorption coefficient, μa, normally requires measurements using thin samples or media of low scattering, which are inappropriate for in vivo applications. In this work, we propose an analytical method to simultaneously recover μa, μs and g based on the incomplete P5 approximation (P5in) to the CW radiative transport equation. The proposed method was verified using both simulated and experimental data with the relative errors less than 6.6%, 11.6% and 8.2%, for μa ranging 0.0071-0.0168 mm-1, μs ranging 2.35-8.47 mm-1 and g ranging 0.61-0.81, respectively. Since the P5in-based radiance method can be easily implemented with several measurements, it’s expected to be used for recovering a full set of the optical properties in vivo.

Narrow-linewidth single-frequency photonic microwave generation in optically injected semiconductor lasers with filtered optical feedback

Chenpeng Xue, Songkun Ji, Anbang Wang, Ning Jiang, Kun Qiu, and Yanhua Hong

Doc ID: 334147 Received 31 May 2018; Accepted 27 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: Narrow-linewidth single-frequency photonic microwave generation scheme by using an optically injected semiconductor laser with a filtered optical feedback has been proposed. The filtered feedback comes from a single feedback loop, which includes a narrow band-pass filter. With the filter feedback, linewidth of the generated microwave can be significantly reduced from 22.4 MHz to 9.0 kHz with the side-peak suppression of 28 dB. The proposed scheme shows superior performance compared with the conventional single feedback configuration in terms of linewidth reduction and side-peak suppression. The proposed scheme also achieves better results compared with the complex dual feedback setting. The mechanism for the better performance of filter optical feedback is that the filter feedback can effectively limit the external cavity modes and stabilize the period one dynamics. In addition, the microwave linewidth decreases with the increase of the filter width until the optimized filter width is reached. Furthermore, the linewidth reduction and the side peaks suppression of photonic microwave using FOF is relatively insensitive to the frequency detuning between the filter center frequency and the free-running frequency of the semiconductor laser.

Flexoelectro-optic liquid crystal analog phase-only modulator with 2π range and 1 kHz switching

Julian Fells, xiuze wang, S. Elston, Christopher Welch, George Mehl, Martin Booth, and Stephen Morris

Doc ID: 336475 Received 02 Jul 2018; Accepted 26 Jul 2018; Posted 01 Aug 2018  View: PDF

Abstract: We present a flexoelectro-optic liquid crystal (LC) analog phase modulator with >2π phase range at a 1 kHz switching frequency. The chiral nematic LC mixture consists of the bimesogen CBC7CB with chiral dopant R5011, aligned in the uniform lying helix mode. The mixture exhibits >π/4 rotation of the optic-axis for a drive voltage of ±21.5 V (E=4.5 V/μm). The rotation of the optic-axis is converted into a phase modulation with the aid of a reflective device configuration incorporating a ~5 μm LC cell, a polarizer, two quarter-wave plates and a mirror. The residual amplitude modulation is found to be < %. This flexoelectro-optic phase modulator combination has the potential to enable analog spatial light modulators with very fast frame rates suitable for a range of applications

Hybrid coupling enhances photoluminescence of monolayer MoS2 on plasmonic nanostructures

Wenbo Shi, Lei Zhang, Di Wang, Rui-Li Zhang, Yingying Zhu, Li-Heng Zhang, Ruwen Peng, Wen-Zhong Bao, Ren-Hao Fan, and Mu Wang

Doc ID: 334991 Received 12 Jun 2018; Accepted 26 Jul 2018; Posted 30 Jul 2018  View: PDF

Abstract: The efficiency of photoluminescence (PL) of transition-metal dichalcogenides (TMDCs) significantly influences their practical applications in optoelectronic devices. In this work, we study multiple coupling among excitons, surface plasmons and optical modes, and their effects on PL of monolayer MoS2 atop on plasmonic nanohole arrays. Under the illumination of visible light, strong intensity enhancement of PL from monolayer MoS2 are observed in the system. We further demonstrate that there exists the excitons induced from MoS2, localized and propagating surface plasmons excited from nanoholes, and optical modes related to the incident laser. And hybrid coupling of those modes significantly improve the PL signals and also lighten the PL images of monolayer MoS2. This work provides a unique way to improve the emission of monolayer TMDCs. The atomically thin TMDCs coupled to plasmonic metamaterials is also promising for advanced applications such as ultrathin integrated light-emission diodes, photo-detection and nanolasers.

Photonic Crystal Based Compact Hybrid WDM/MDM (De)multiplexer for SOI Platforms

Omnia Nawwar, Hossam Shalaby, and Ramesh Pokharel

Doc ID: 335811 Received 21 Jun 2018; Accepted 26 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: A compact hybrid wavelength- and mode-division (de)multiplexer is proposed and its performance is evaluated. The design of the device is based on 2D photonic crystals with square lattice and Si rods. The device canmultiplex two eigen modes, TM0 and TM1, and two wavelengths, 1550 nm and 1300 nm. Two identical multimode interference couplers (MMIs) and an asymmetric directional coupler are used in implementing both the wavelength- and mode-division multiplexing functions, respectively. To avoid back reflections, tapers are used at waveguide junctions. The structure is compact with dimensions of 29 μm × 12 μm , which is suitable for on-chip integration. Simulation results reveal that the insertion losses and crosstalks are less than-1.0927 dB and -11.9024 dB, respectively, for all four channels.

Ultra-slow light in one-dimensional Cantor photonic crystals

Y. C. Lin, C. H. Tsou, and Wen-Jeng Hsueh

Doc ID: 336534 Received 05 Jul 2018; Accepted 26 Jul 2018; Posted 27 Jul 2018  View: PDF

Abstract: Ultra-slow light and complete transmission properties in one-dimensional Cantor photonic crystals are presented. In contrast to traditional dielectric photonic crystals, the proposed structure have large group delay, slower group velocity and high quality factor in the same layers and materials. The study shows that the larger than 1 μs group delay and slower than 1 m/s group velocity are achieved in Cantor photonic crystal fifth order with 52.75 μm length. This ultra-slow light structure is a very promising application in advanced slow light devices. The high quality factor of 109 and multiband filters with complete transmission also can be obtained by this approach.

On-chip multi-stage optical delay based on cascaded Brillouin light storage

Birgit Stiller, Moritz Merklein, Christian Wolff, Khu Vu, Pan Ma, Chris Poulton, Stephen Madden, and Benjamin Eggleton

Doc ID: 330147 Received 24 Apr 2018; Accepted 26 Jul 2018; Posted 08 Aug 2018  View: PDF

Abstract: Storing and delaying optical signals plays a crucial role in data centers, phased array antennas, communication and future computing architectures. Here, we show a delay scheme based on cascaded Brillouin light storage, that achieves multi-stage delay at arbitrary positions within a photonic integrated circuit. Importantly these multiple resonant transfers between the optical and acoustic domain are controlled solely via external optical control pulses, allowing cascading of the delay without the need of aligning multiple structural resonances along the optical circuit.

Bending losses and modal properties of nano-bore optical fibers

Kay Schaarschmidt, Stefan Weidlich, Daniel Reul, and Markus Schmidt

Doc ID: 332929 Received 31 May 2018; Accepted 24 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: The nano-bore optical fiber geometry represents a new waveguide platform that uniquely allows studying the interaction of low-index fluids and light inside the core of an optical fiber while maintaining total internal reflection as light guidance mechanism. Here we have analyzed several application-relevant properties of this novel geometry experimentally and from the simulation perspective, including the analysis of the power fraction inside the bore, the determination of radius-dependent cut-offs and the identification of single mode operation domains. The obtained results will pave the way for new application of fiber optics in fields such as optofluidics, nonlinear light generation and bioanalytics.

Tm,Ho:LiYF4 planar waveguide laser at 2.05 μm

Patrice Camy, Rémi Soulard, Gurvan BRASSE, Jean-Louis DOUALAN, Alain BRAUD, Aleksey Tyazhev, Ammar Hideur, and Pavel Loiko

Doc ID: 335401 Received 15 Jun 2018; Accepted 23 Jul 2018; Posted 31 Jul 2018  View: PDF

Abstract: The first Holmium fluoride waveguide laser is reported using a 25-μm-thick Gd3+-ion-modified 4.5 at.% Tm3+, 0.5 at.% Ho3+-codoped LiYF4 active layer grown by liquid phase epitaxy on (001)-oriented LiYF4 substrate. Pumped by a Ti:Sapphire laser at 797.2 nm, the planar waveguide laser generates 81 mW of CW output at ~2051 nm with a slope efficiency of 24%. Power scaling up to 186 mW at 2051&2065 nm in quasi-CW regime is demonstrated. The parameters of the Tm3+ ↔ Ho3+ energy transfer are determined. Tm,Ho:LiYF4/LiYF4 epitaxies are promising for waveguide lasers and amplifiers at above 2 μm. © 2018 Optical Society of America

172 fs, 24.3 kW peak power pulse generation from a Ho-doped fiber laser system

Mengmeng Wang, Hui Zhang, Rongling Wei, Zexiu Zhu, Shuangchen Ruan, Peiguang Yan, Jinzhang Wang, Tawfique Hasan, and Zhipei Sun

Doc ID: 337596 Received 03 Jul 2018; Accepted 21 Jul 2018; Posted 23 Jul 2018  View: PDF

Abstract: We demonstrate a high peak power femtosecond fiber laser system based on single-mode holmium (Ho) doped fibers. 833 fs, 27.7 MHz pulses at 2083.4 nm generated in a passively mode-locked Ho fiber laser are amplified and compressed to near transform-limited 172 fs, 7.2 nJ pulses with 24.3 kW peak power. We achieve this performance level by using soliton effect and high-order soliton compression. This is the first demonstration of sub-200 fs pulses, with peak power exceeding 10 kW from a Ho-doped single-mode fiber laser system without using bulk optics compressors.

Optimized ultra-narrow atomic bandpass filters via magneto-optic rotation in an unconstrained geometry

James Keaveney, Steven Wrathmall, Charles Adams, and Ifan Hughes

Doc ID: 335953 Received 26 Jun 2018; Accepted 16 Jul 2018; Posted 17 Jul 2018  View: PDF

Abstract: Atomic bandpass filters are widely used in a variety of applications, owing to their high peak transmission and narrow bandwidth. Much of the previous literature has used the Faraday effect to realize such filters, where an axial magnetic field is applied across the atomic medium. Here we show that by using a non-axial magnetic field, the performance of these filters can be improved in comparison to the Faraday geometry. We optimize the performance of these filters using a numerical model and verify their performance by direct quantitative comparison with experimental data. We find excellent agreement between experiment and theory. These optimized filters could find use in many of the areas where Faraday filters are currently used, with little modification to the optical setup, allowing for improved performance with relatively little change.

Low-noise 750-MHz spaced Yb:fiber frequency combs

Yuxuan Ma, Bo Xu, Hirotaka Ishii, Fei Meng, Yoshiaki Nakajima, Isao Matsushima, Thomas Schibli, Zhigang Zhang, and Kaoru Minoshima

Doc ID: 334691 Received 08 Jun 2018; Accepted 13 Jul 2018; Posted 16 Jul 2018  View: PDF

Abstract: We demonstrate two low-noise 750-MHz ytterbium (Yb) fiber frequency combs that are independently stabilized to a continuous wave (CW) laser. A bulk electro-optic modulator (EOM) and a single-stack piezo-electric transducer (PZT) are employed as fast actuators for stabilizing the respected cavity length to heterodyne beat notes (fbeat). Both combs exhibit in-loop fractional frequency instabilities of ~10^−18 at 1 s. This is the first demonstration of tightly phase-locked (<1 rad RMS phase) fiber frequency combs with 750 MHz fundamental repetition rate.

Validation of the Angular Quasi-Phase-Matching theory for the biaxial optical class using PPRKTP

lu dazhi, Alexandra Pena, Patricia Segonds, Jérôme Debray, Simon Joly, Andrius Zukauskas, Fredrik Laurell, Valdas Pasiskevicius, Haohai Yu, Huaijin Zhang, Jiyang Wang, Carlota Canalias, and Benoit Boulanger

Doc ID: 331307 Received 09 May 2018; Accepted 06 Jul 2018; Posted 12 Jul 2018  View: PDF

Abstract: We report the first experimental validation of angular quasi-phase-matching (AQPM) theory in a biaxial crystal by performing second-harmonic generation (SHG) in the periodically-poled Rb-doped KTiOPO4 (PPRKTP) crystal cut as a sphere. Both AQPM and birefringence phase-matching (BPM) angles were measured thanks to a Kappa circle.

Tunable SNAP Microresonators via Internal Ohmic Heating

Dashiell Vitullo, Sajid Zaki, Gabriella Gardosi, Brian Mangan, Robert Windeler, Michael Brodsky, and Misha Sumetsky

Doc ID: 331025 Received 16 May 2018; Accepted 01 Jul 2018; Posted 03 Jul 2018  View: PDF

Abstract: We demonstrate a thermally tunable Surface Nanoscale Axial Photonics (SNAP) platform. Stable tuning is achieved by heating a SNAP structure fabricated on the surface of a silica capillary with a metal wire positioned inside. Heating a SNAP microresonator with a uniform wire introduces uniform variation of its effective radius which results in constant shift of its resonance wavelengths. Heating with a nonuniform wire allows local nanoscale variation of the capillary effective radius, which enables differential tuning of the spectrum of SNAP structures as well as creation of temporary SNAP microresonators that exist only when current is applied. As an example, we fabricate two bottle microresonators coupled to each other and demonstrate differential tuning of their resonance wavelengths into and out of degeneracy with precision better than 0.2 pm. The developed approach is beneficial for ultraprecise fabrication of tunable ultralow loss parity-time symmetric, optomechanical, and cavity QED devices.

Non-destructive characterization of rare-earth-doped optical fiber preforms

Marilena Vivona, Jae Sun Kim, and Michalis Zervas

Doc ID: 334155 Received 05 Jun 2018; Accepted 26 Jun 2018; Posted 27 Jun 2018  View: PDF

Abstract: We present a non-destructive optical technique for rare-earth-doped optical fiber preform inspection, which combines luminescence spectroscopy measurements, analyzed through an optical tomography technique, and ray-deflection measurements for calculating the refractive index profile of the sample. We demonstrate the technique on an optical fiber preform sample with an Yb3+-doped aluminosilicate core. The spatial distribution of the photoluminescence signals originating from Yb3+-single ions and from Yb3+-Yb3+ cluster sites were obtained inside the core. By modifying the characterization system, we were able to concurrently evaluate the refractive index profile of the core, and thus establishing with good accuracy the dopant distribution within the core region. This technique will be useful for quality evaluation and optimization of optical fiber preforms.

Comments to: "Quadrature detection for self-mixing interferometry" by Junfeng Wu and Fengfeng Shu

Silvano Donati

Doc ID: 331097 Received 10 May 2018; Accepted 22 Jun 2018; Posted 07 Aug 2018  View: PDF

Abstract: I make comment to paper : "Quadrature detection for self-mixing interferometry"

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