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Accepted papers to appear in an upcoming issue

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Carrier-envelope phase stabilization of an Er:Yb:glass laser via feed-forward technique

Randy Lemons, Wei Liu, Irene Fernandez De Fuentes, Stefan Droste, Gunter Steinmeyer, Charles Durfee, and Sergio Carbajo

Doc ID: 374786 Received 15 Aug 2019; Accepted 22 Oct 2019; Posted 22 Oct 2019  View: PDF

Abstract: Few-cycle pulsed laser technology highlights the need for control and stabilization of the carrier-envelope phase (CEP) for applications requiring shot-to-shot timing and phase consistency. This general requirement has been achieved successfully in a number of free space and fiber lasers via feedback and feed-forward methods. Expanding upon existing results, we demonstrate CEP stabilization through the feed-forward method applied to a SESAM mode-locked Er:Yb:glass laser at 1.55 µm with a measured ultralow timing jitter of 2.9 as (1 Hz – 3 MHz) and long-term stabilization over a duration of eight hours. Single-digit attosecond stabilization at telecom wavelengths opens a new direction in applications requiring ultra-stable frequency and time precision such as high-resolution spectroscopy and fiber timing networks.

Unidirectional invisibility and enhanced reflection ofshort pulses in quasi-PT-symmetric layered media

Boris Mantsyzov, Vladimir Bushuev, Vladimir Konotop, and Dmitri M. Tsvetkov

Doc ID: 378663 Received 24 Sep 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We consider interaction of a short optical pulse withlayer with periodically modulated permittivity and periodic gain-and-loss landscape. It is found that if themedium is quasi-PT-symmetric, in the vicinity ofthe exceptional point, the propagation manifests strongunidirectional reflection and invisibility. Due to strongfrequency selectivity, quasi-PT-symmetric periodiclayers manifest efficient filtering of back radiation.

Enhanced electro-optic beam deflection of relaxor ferroelectric KTN crystals by electric field induced high permittivity

Chang-Jiang Chen, Ju-Hung Chao, Yun-Goo Lee, Annan Shang, RUIJIA LIU, Shizhuo Yin, Robert Hoffman, and Mark Dubinskii

Doc ID: 373834 Received 31 Jul 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Most of applications of ferroelectrics based electro-optic beam deflector have been limited by the high applied voltage. In this paper, we report a dramatically increased electro-optic beam deflection in relaxor ferroelectric potassium tantalate niobate (KTN) crystals by using the electric field enhanced permittivity. Due to the existence of electric field induced phase transition in relaxor ferroelectric materials, the dielectric permittivity could be substantially increased by the applied electric field at a certain temperature. Both the theoretical study and the experimental verifications on the enhanced beam deflection and EO effect in the case with the electric field induced high permittivity were conducted. The experimental results shown that there was a 3-fold increase in the deflection angle, which represented a dramatic increase in deflection angle. Such a largely enhanced beam deflection is a great beneficial for the KTN deflector by offering a wider deflection range and a lower driving voltage.

Ionization-induced adiabatic soliton compression in gas-filled hollow-core photonic crystal fibers

Zhi Yuan Huang, Yifei Chen, Fei Yu, Dakun Wu, Yu Zhao, Ding Wang, and Yuxin Leng

Doc ID: 374552 Received 02 Aug 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We observe in the experiments ionization-induced adiabatic soliton compression phenomena in a He-filled single-ring photonic crystal fiber. We demonstrate that in a certain pulse-energy region, the plasma-driven blueshifting soliton shows little residual light near the pump wavelength, leading to a high-efficiency frequency up-conversion. In contrast, at higher pulse-energy levels, excessive pulse energy can result in intense residual light generation deviating from pump wavelength, decreasing the frequency-conversion efficiency. Even though the intense pulses lose some energy due to gas-ionization effects, the remaining energy after ionization is still intense. The pulses with soliton order of >1 need to release excess energy into the linear modes, simultaneously adjusting their peak power and pulse duration to maintain a fundamental soliton, resulting in the residual light generation. Our experimental results, well-supported by numerical simulations, offer some insightful understanding on ionization-induced adiabatic soliton compression in gas-filled optical fibers. The ultrafast pulses generated using our set-up, with >300 nm tunable range, will find many applications in pump-probe spectroscopy.

Polarization-insensitive wavefront shaping using the Pancharatnam-Berry phase

Alessandro Alberucci, Jisha Pannian, and Stefan Nolte

Doc ID: 376209 Received 23 Aug 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We discuss a method to achieve a polarization-independent modulation of the electromagnetic wavefront based upon the Pancharatnam-Berry phase. When the length of the twisted anisotropic material is equal to the birefringence length (i.e., full wave plate length), a phase delay proportional to the squared transverse derivative of the twisting angle appears. Physically, the phase delay is associated with the Kapitza effect applied to the Pancharatnam-Berry phase. Our theoretical results are confirmed by FDTD-based numerical simulations.

Detection of atomic oxygen in a plasma-assisted flame via backward lasing technique

Pengji Ding, Maria Ruchkina, Davide Cont-Bernard, Andreas Ehn, Deanna Lacoste, and Joakim Bood

Doc ID: 377872 Received 16 Sep 2019; Accepted 21 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: In this work, we have investigated 845-nm lasing generation in atomic oxygen, present in a lean methane-air flame, using 2-photon pumping with femtosecond 226-nm laser pulses, particularly focusing on the impact of nanosecond repetitively pulsed glow discharges forcing on the backward lasing signal. Characterizations of the backward lasing pulse, in terms of its spectrum, beam profile, pump pulse energy dependence and divergence, were conducted to establish the presence of lasing. With plasma forcing of the flame, the backward lasing signal was observed to be enhanced significantly, ~50%. The vertical concentration profile of atomic oxygen was revealed by measuring the backward lasing signal strength as a function of heights in the flame. The results are qualitatively consistent with results obtained with 2-dimensional femtosecond two-photon-absorption laser-induced fluorescence (fs-TPLIF), suggesting that the backward lasing technique can be a useful tool for studies of plasma-assisted combustion processes, particularly in geometries requiring single-ended standoff detection.

High power traveling wave photodetector based on an aperiodically loaded open-circuit electrode

Zhilei Fu, hui Yu, qiang zhang, Xiaofei Wang, Penghui Xia, and Jianyi Yang

Doc ID: 378235 Received 23 Sep 2019; Accepted 20 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We demonstrate a 4-stage silicon distributed traveling-wave photodetector (TWPD) whose input terminal is open-circuit so as to enhance the RF output power. In order to mitigate the bandwidth drop caused by the RF reflection at the open input terminal, PD units are aperiodically loaded on the TW electrode. With the aid of an equivalent circuit model, we optimize spacings between PD units, and then improve the 3 dB bandwidth from 7 GHz to 10 GHz. A good agreement between measurement and modeling is obtained. Thanks to the cancellation of the input termination impedance, maximum RF output powers of the device are 10.2 dBm and 6.5 dBm at 5 GHz and 10 GHz, respectively. Corresponding power conversion efficiencies are 7.0 % and 3.2 %.

How perfect are Perfect Vortex beams?

Jonathan Pinnell, Valeria Rodriguez-Fajardo, and Andrew Forbes

Doc ID: 378457 Received 26 Sep 2019; Accepted 20 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Perfect (optical) vortex (PV) beams are fields whose radial profile is mooted to be independent of orbital angular momentum (OAM). To date, the best experimental approximation of these modes is obtained from passing Bessel-Gaussian beams through a Fourier lens. However, the OAM-dependent width of these quasi-PVs is not precisely known and is often understated. We address this here by deriving and experimentally confirming an explicit analytic expression for the second moment width of quasi-PVs. We show that the width scales in proportion to $\sqrt{\ell}$ in the best case, the same as most ``regular" vortex modes albeit with a much smaller proportionality constant. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping, tweezing and communications.

1.2-15.2 μm supercontinuum generation in a low-loss chalcohalide fiber pumped at deep anomalous-dispersion region

Kai Jiao, Jinmei Yao, Xiange Wang, Xunsi Wang, zheming Zhao, Bin Zhang, Nian Si, jia liu, Xiang Shen, Peiqing Zhang, Shixun Dai, Qiuhua Nie, and Rongping Wang

Doc ID: 379100 Received 27 Sep 2019; Accepted 20 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: A novel low-loss selenium-based chalcohalide fiber, with a low zero dispersion wavelength, was prepared by an innovative preparation process. The composition optimized fiber has a wide transmission range up to 11.5 μm, a lowest fundamental mode zero dispersion wavelength of 4.03 μm and a minimum optical loss of 1.12 dB/m at 6.4 μm, which provides a possibility to replace As₂S₃ and As₂Se₃ in a cascade of ZBALN-As₂S₃-As₂Se₃ fiber in the practical all-fiberized SC source. Meanwhile, the broadest supercontinuum spectrum, ~1.3 to 15 µm, was achieved by pumping a 12 cm-long fiber with a femtosecond laser at deep anomalous-dispersion region. Furthermore, simulations are adopted to interpret the results as well as to demonstrate spectral evolution along the fiber. To the best of our knowledge, this is the broadest SC spectrum reported in any selenium-based chalcogenide fiber.

Bragg labeled wavelength calibrates interferometric sensors in hollow core fiber

Yiyang Luo, Wenjun Ni, Ran Xia, Ping Shum, Yu Zheng, and Zhenggang Lian

Doc ID: 379101 Received 27 Sep 2019; Accepted 19 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Bragg labeled wavelength (BLW) employed to the sensitivity calibration in interference pattern has been proposed and experimentally demonstrated. According to the critical condition of Fabry-Perot (FP) interference and anti-resonant (AR) effect, the length of hollow core fiber (HCF) is artificially controlled to form a FP microcavity by collapsed fusion splicing. Dual-spectral features of the BLW and inline multimode interference (IMMI) dominate the transmission spectrum of the collapsed Bragg HCF (BHCF). The location of the BLW remains unchanged once the air-core diameter is selected. Sensing performance is investigated to validate the calibration function of the proposed BHCF. In particular, the temperature sensitivity of the BLW and multimode interference are 12.8 pm/℃ and 87.1 pm/℃, respectively corresponding to the reference sensitivity induced by the Bragg structure and the measurement sensitivity of the IMMI. All these findings highlight the calibration of HCF based interferometric sensors in practical applications.

Electric Field Vector Measurements Via Nanosecond Electric Field Induced Second Harmonic Generation

Tat Loon Chng, Maya Naphade, Benjamin Goldberg, Igor Adamovich, and Svetlana Starikovskaya

Doc ID: 374833 Received 15 Aug 2019; Accepted 19 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Electric field induced second harmonic generation, or E-FISH, has received renewed interest as a non-intrusive tool for probing electric fields in gas discharges and plasmas using ultrashort laser pulses. An important contribution of this work lies in establishing that the E-FISH method works effectively in the nanosecond regime, yielding field sensitivities of about a kV/cm at atmospheric pressure from a 16 ns pulse. This is expected to broaden its applicability within the plasma community, given the wider access to conventional nanosecond laser sources. A Pockels-cell-based pulse-slicing scheme, which may be readily integrated with such nanosecond laser systems, is shown to be a complementary and cost-effective option for improving the time resolution of the electric field measurement. Using this scheme, a time resolution of ~3 ns is achieved, without any detriment to the signal sensitivity. This could prove invaluable for non-equilibrium plasma applications, where time resolution of a few nanoseconds or less is often critical. Finally, we take advantage of the field vector sensitivity of the E-FISH signal to demonstrate simultaneous measurements of both the horizontal and vertical components of the electric field.

Parallel real-time quantum random number generator

Yanqiang Guo, Xiaomin Guo, chen cheng, Mingchuan Wu, Qinzhong Gao, and Pu Li

Doc ID: 372421 Received 11 Jul 2019; Accepted 18 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: Quantum random number generation exploits inherent randomness of quantum mechanical processes and measurements. Real-time generation rate of quantum random numbers is usually limited by electronic bandwidth and data processing rates. Here we use a multiplexing scheme to create a fast real-time quantum random number generator based on continuous variable vacuum fluctuations. Multiple sideband frequency modes of quantum vacuum state within a homodyne detection bandwidth are concurrently extracted as randomness source. Parallel post-processing of raw data from three sub-entropy sources is realized in one FPGA based on Toeplitz-hashing extractors. Cumulative generation rate of 8.25 Gbps in real-time is achieved. The system relies on optoelectronic components and circuits that could be integrated in a compact, economical package.

Green-pumped optical parametric oscillator based on fan-out grating periodically-poled MgO-doped congruent LiTaO3

Sukeert ., Chaitanya Kumar Suddapalli, and Majid Ebrahim-Zadeh

Doc ID: 378029 Received 18 Sep 2019; Accepted 18 Oct 2019; Posted 21 Oct 2019  View: PDF

Abstract: We report a green-pumped optical parametric oscillator (OPO) based on periodically-poled MgO-doped congruent lithium tantalate (MgO:cPPLT). Pumped at 532 nm by a frequency-doubled Q-switched Nd:YAG laser, and using a fanned grating structure, the singly-resonant OPO provides continuous tuning across 689-1025 nm in the signal and 1106- 36 nm in the idler at room temperature by simple mechanical translation of the crystal. The tuning range can be further extended to 677 nm and 2479 nm in the signal and idler, respectively, by temperature tuning the crystal to 200 °C. With 29-mm-long crystal, the OPO generates 131 mW of average idler power at 1476.5 nm for an input pump power of 1.8 W at 25 kHz repetition rate, with a slope efficiency of 11.3%. Bulk damage in the MgO:cPPLT crystal has been observed for pump powers above ~1.8 W, and at pump powers beyond ~1.4 W under long-term operation. The passive power stability of the generated idler at 1357 nm is 3.9% over 30 minutes, with output in Gaussian spatial profile.

Study on the temperature dependent characteristics of O-band bismuth-doped fiber amplifier

Yu Wang, Naresh Kumar Thipparapu, Siyi Wang, Pranabesh Barua, David Richardson, and Jayanta Sahu

Doc ID: 375387 Received 20 Aug 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: We report the temperature dependent performance of an O-band bismuth (Bi)-doped fiber amplifier (BDFA) in both single and double pass configurations in the temperature range from -60 to +80 ºC. At room temperature, maximum gains of 27 and 40 dB with NFs of 4.3 and 4.8 dB are measured for - dBm signal power in the single and double pass BDFA, respectively. An increment in gain and reduction in NF is observed as the ambient temperature of the BDFA is reduced. In the double pass BDFA, the temperature-dependent-gain coefficient from -60 to +80 ºC is found to be around -0.02 and -0.03 dB/ ºC across the wavelength band of 1300-1360 nm for -10 and - dBm signal powers, respectively. We also study the gain and NF characteristics with pump power and signal power at different temperatures, and a maximum gain of 45 dB is obtained at -60 ºC for -30 dBm signal power. Moreover, we compare the temperature dependent gain and NF of different BDFAs, and correlate this with the Bi-doped fiber unsaturable loss and OH concentration.

Fast pulse train control using filled-aperture coherent beam combining for high-average-power laser systems

Koji Tsubakimoto, Hayaki Higuchi, Kou Fukuishi, Hidetsugu Yoshida, and Noriaki Miyanaga

Doc ID: 378401 Received 20 Sep 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: This study demonstrates fast pulse train switching using a coherent polarization beam combiner with a phase difference speculation (PDS) algorithm. Based on the highly stable feedback control obtained with the PDS algorithm, stable burst-mode extraction with an arbitrary duty cycle was achieved with a contrast ratio of 800:1 for a 5-MHz pulsed fiber laser. The proposed method can be effectively used for high-speed switching in high-average-power pulsed laser systems.

Reflection suppression via elastomeric films

David Miller, Marvin Alim, and Robert McLeod

Doc ID: 368888 Received 31 May 2019; Accepted 18 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: Transparent substrates introduce challenges in optical metrology, recording, and microscopy. Backside reflections reduce signal to noise, are recorded as artifacts, or introduce spurious signals. These reflections often need to be suppressed, but large angular and spectral bandwidths preclude the use of anti-reflection coatings. Using elastomeric materials doped with optical absorbers, we detail a method and a materials set for temporary suppression of Fresnel reflections for multiple substrates spanning wide spectral and angular bandwidth. Tuning the refractive index of the elastomer to match a substrate minimizes reflection, and the addition of different absorptive dopants allows for either broadband or wavelength-selective reflection suppression. As performance is limited only by index mismatch, both spectral and angular performance significantly exceed that of anti-reflection coatings. We demonstrate reflection suppression in excess of 30 dB spanning over 500 nm bandwidth. After use, these light traps may be removed and reused without damaging the substrate.

Impact of laser-ionized liquid nonlinear characteristics on the efficiency of terahertz waves generation

Eugenia Ponomareva, Sviatoslav Shtumpf, Anton Tsypkin, and Sergey Kozlov

Doc ID: 378522 Received 20 Sep 2019; Accepted 17 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: Free electrons dynamics in plasma is considered as the dominant mechanism for generating THz radiation during the ionization of liquid by sub-picosecond laser pulses. Dependences of the THz emission generation efficiency on the contribution of plasma nonlinearity with a fixed third-order nonlinearity value revealed the existence of weak and strong ionization modes. It is shown the transition between these modes is determined by the ratio of plasma to Kerr nonlinearity coefficients and the pump energy. In the strong ionization mode and with the fixed contribution of plasma nonlinearity, the optical-to-terahertz conversion efficiency decreases with increasing Kerr nonlinearity due to the redistribution of the pump energy for the third-order effects. These results contribute to estimating the potential of liquid media as highly-efficient THz sources.

Second harmonic generation in gold crescent- and comma-like nanostructures

Irina Kolmychek, Evgeniy Mamonov, Vladimir Bochenkov, and Tatyana Murzina

Doc ID: 376527 Received 28 Aug 2019; Accepted 17 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: Anisotropic metal nanostructures reveal unique optical properties providing new optical effects. Here we study experimentally the nonlinear-optical response of planar arrays of gold comma-like and crescent-like nanostructures made by colloidal lithography. We show that anisotropy of the nonlinear-optical response is defined not only by the shape of the particles, but also by the relative phase of second-order susceptibility components, which are found to be spectrally sensitive. High values of circular dichroism in the second harmonic generation response up to 70% are observed in comma-like nanostructures.

A silicon dual-series Mach-Zehnder modulator with high linearity

qiang zhang, hui Yu, Linghua Wang, Penghui Xia, Qiman Cheng, Zhilei Fu, Xiaofei Wang, and Jianyi Yang

Doc ID: 376569 Received 29 Aug 2019; Accepted 17 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: In this paper, we demonstrate a highly linear silicon modulator based on the dual-series Mach-Zehnder modulator (MZM) architecture. The two sub-MZMs are biased at quadrature points of opposite polarities. A proper power splitting ratio of the driving RF signal on the two sub-MZMs enables the suppression of the 3rd order intermodulation distortion (IMD3). The spurious-free dynamic ranges (SFDR) for IMD3 are 109.5/100.5 dB·Hz2/3 at 1/10 GHz. In contrast, the reference single MZM on the same chip exhibits SFDRs of 95.2/86.8 dB·Hz2/3 at 1/10 GHz at its optimal reverse bias voltage.

A high relative-phase precision beam duplicator for mid-IR femtosecond pulses

Antoine Camper, Hyunwook Park, Stephen Hageman, Greg Smith, T. Auguste, Pierre Agostini, and Louis DiMauro

Doc ID: 376727 Received 29 Aug 2019; Accepted 17 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: We use a 0-$\pi$ square-wave phase grating to shape \SI{1350}{nm} and \SI{1450}{nm} femtosecond pulses and create two intense lobes at the focus of a lens. We show that the relative phase between these two lobes (the 1$^{st}$ and -1$^{st}$ orders of diffraction of the grating) is controlled very simply and precisely by shifting the position of the grating in its plane. We generate high harmonic orders from the two bright lobes and record the beating between the two emissions for each harmonic orders up to the 53$^{rd}$ order.

Ultra-low-noise carrier-envelope phase stabilization of a KLM YbCYA laser frequency comb

Ziyue Zhang, Hainian Han, Huibo Wang, Xiaodong Shao, SHAOBO FANG, and Zhiyi Wei

Doc ID: 376456 Received 27 Aug 2019; Accepted 16 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: We demonstrate ultra-low-noise carrier-envelop phase (CEP) stabilization of a Kerr lens mode locked (KLM) Yb: CYA laser frequency comb, which is the first time, to the best of our knowledge, that feed forward method has been applied to 1 um all solid state lasers. We obtain signal to noise ratio (SNR) of more than 38 dB for carrier-envelope phase offset (CEO) beat signals in both the standard f-to-2f interferometers. The linewidth of stabilized out-of-loop CEO is narrowed to 1.1 mHz. The residual integrated phase noise amounts to 79.3 mrad from 1 Hz to 1 MHz, corresponding to 44 as timing jitter. We also investigated long term performances of the CEP stabilization in feed forward scheme, phase-locked feedback systems and the combing locking techniques in terms of sub-hertz frequency resolved phase noise and Allan deviation in 1000s. The results indicate that although the feed-forward CEP stabilization method dominates in the range of 1Hz to 1MHz Fourier frequency, feedback methods with time integration effect is superior in sub-hertz Fourier frequency phase noise suppression.

Slow light enabled high-modulation-depth graphene modulator with plasmonic metasurfaces

Lin Chen and Ren Tangxuan

Doc ID: 377216 Received 06 Sep 2019; Accepted 16 Oct 2019; Posted 17 Oct 2019  View: PDF

Abstract: Graphene has attracted the interest of researchers seeking to develop compact optical modulators with the flexible tunability of graphene conductivity by tuning the Fermi level. Plasmonic structures have provided a robust way to enhance the modulation depth (MD) of graphene optical modulators, but the available schemes suffer from low MD, fabrication complexities, or both. Here, an ultra-thin plasmonic metasurface structure capable of guiding slow surface plasmons (SPs) is proposed to construct graphene-based optical modulators. The designs take advantage of the strong field enhancement of slow SP mode as well as the orientation match between the electric field and the graphene plane. A typical 0.96 μm long metasurface-based graphene modulator presents a significantly improved MD of 4.66 dB/μm and an acceptable insertion loss of 1.4 dB/μm, while still having ease of fabrication.

Highly Efficient Deep UV Generation by Four-Wave Mixing in Gas-Filled Hollow Core Photonic Crystal Fiber

Federico Belli, Amir Abdolvand, John Travers, and Philip Russell

Doc ID: 373084 Received 29 Jul 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: We report on a highly-efficient experimental scheme for the generation of deep-ultraviolet ultrashort light pulses using four-wave mixing in gas-filled kagomé-style photonic crystal fiber. By pumping with ultrashort, few µJ, pulses centered at 400 nm, we generate an idler pulse at 266 nm, and amplify a seeded signal at 800 nm. We achieve remarkably high pump-to-idler energy conversion efficiencies of up to 38%. Although the pump and seed pulse durations are ~100 fs, the generated ultraviolet spectral bandwidths support sub-15 fs pulses. These can be further extended to support few-cycle pulses. Four-wave mixing in gas-filled hollow-core fibres can be scaled to high average powers and different spectral regions such as the vacuum ultraviolet (100-200 nm)

Dissipative surface solitons in a nonlinear fractional Schr\"{o}dinger equation

Changming Huang and Liangwei Dong

Doc ID: 378877 Received 26 Sep 2019; Accepted 16 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: We study the existence and stability of dissipative surface solitons supported by the nonlinear fractional Schr\"{o}dinger equation (NLFSE) with an interface between a semi-infinite chirped lattice and a uniform Kerr medium.In such a system, the existence domain of dissipative surface solitons depends on an upper cutoff value of the linear gain coefficient at a fixed nonlinear loss. The results of linear stability analysis are in good agreement with those of propagation simulation in fractional dimension. Stable dissipative surface solitons generally feature low energy and small propagation constants, and adapt to a wide range of two-photon absorption.The instability of solitons can be suppressed by increasing the chirp rate of the lattice. Robust nonlinear dissipative surface states can be easily excited by a Gaussian input beam. Similar characteristics of the two-dimensional dissipative surface solitons are also addressed.

Surface-enhanced Raman scattering of monolayer transition metal dichalcogenides on Ag nanorod arrays

Liqin Su, layne bradley, Yiling Yu, Yifei Yu, Linyou Cao, Yiping Zhao, and Zhang yong

Doc ID: 373880 Received 29 Jul 2019; Accepted 15 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: In this work, we studied surface-enhanced Raman scattering (SERS) of MS₂ (M = Mo, W) monolayers that were transferred onto Ag nanorod arrays. Compared to the suspended monolayers, the Raman intensity of monolayers on an Ag nanorod substrate was strongly enhanced for both in-plane and out-of-plane vibration modes: up to 8 (5) for E₂g and 20 ( ) for A₁g in MoS₂ (WS₂). This finding reveals a promising SERS substrate for achieving uniform and strong enhancement for two-dimensional materials in the applications of optical detecting and sensing.

Nanoimprinting and Tapering of Chalcogenide Photonic Crystal Fibers for Cascaded Supercontinuum Generation

Christian Petersen, Mikkel Lotz, Getinet Woyessa, AMAR GHOSH, Thibaut Sylvestre, Laurent Brilland, Johann Troles, Mogens Jakobsen, Rafael Taboryski, and Ole Bang

Doc ID: 376382 Received 26 Aug 2019; Accepted 15 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: Improved long–wavelength transmission and supercontinuum (SC) generation is demonstrated by antireflective (AR) nanoimprinting and tapering of chalcogenide photonic crystal fibers (PCF). Using a SC source input spanning from 1–4.2 μm, the total transmission of a 15 μm core diameter PCF was improved from ~53 % to ~74 % by nanoimprinting of AR structures on both input– and output facets of the fiber. Through a combined effect of reduced reflection and red–shifting of the spectrum to 5 μm, the relative transmission of light >3.5 μm in the same fiber was increased 60.2 %. Further extension of the spectrum to 8 μm was achieved using tapered fibers. The spectral broadening dynamics and output power was investigated using different taper parameters and pulse repetition rates.

Surface modifications of optical fiber ferrule for diffusive optical-thermal transport

Steven Peng, mike obrien, Thomas Hasenberg, and Hyun Wook Kang

Doc ID: 374027 Received 15 Aug 2019; Accepted 14 Oct 2019; Posted 17 Oct 2019  View: PDF

Abstract: The current study aimed to develop surface modifications of a capillary ferrule to avoid misalignment-related thermal damage in the fiber connector and the eventual fiber failure during high power laser lithotripsy. Numerical analysis showed that the modified surface diffused leaking rays (high order modes) from the misalignment. The light diffusion subsequently confined absorption-induced heat accumulation to the stainless steel connector tip (used as heat sink). Light-offset experiments validated minimal transient and steady-state heating of the modified connector surface with no thermal damage in the connector due to diffusive optical-thermal transport. The ferrule surface modifications may prevent fiber failure during the lithotripsy.

Direct detection of pilot-assisted PAM-4 signals with large phase noise tolerance

xiang li, Ming Luo, Cai Li, chao yang, Li Haibo, and Shaohua Yu

Doc ID: 376941 Received 05 Sep 2019; Accepted 14 Oct 2019; Posted 16 Oct 2019  View: PDF

Abstract: A pilot-assisted direct detection scheme is experimentally demonstrated when distributed feedback (DFB) lasers are used as transmitter carrier and pilot carrier sources. In this scheme, the electrical field can be constructed digitally after photodetection, which is not suffered from power fading problem due to chromatic dispersion (CD). In order to combat with large laser phase noise due to large linewidth of DFB laser, phase pre-compensation is realized by extracting the carrier phase information digitally. After phase pre-compensation, finite impulse response (FIR) filtering based linear or nonlinear channel equalization can be applied to deal with the inter-symbol interference (ISI) induced by CD and channel nonlinear distortions. 56-Gb/s 4-level pulse amplitude modulated (PAM-4) optical signal over 320-km standard single mode fiber (SSMF) transmission is experimentally demonstrated without inline CD compensation. The experimental results show that the proposed phase pre-compensation scheme can successfully recover the signal suffering from strong laser phase noise. It is also shown that complex Volterra series based channel equalization can improve the system performance after 720-km SSMF transmission.

Dissipative soliton resonance in a mode-locked Nd-fiber laser operating at 927 nm

Rezki Becheker, mincheng tang, Mohamed Touil, Thierry Robin, benoit cadier, Mathieu Laroche, Thomas Godin, and Ammar Hideur

Doc ID: 377380 Received 09 Sep 2019; Accepted 14 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: We demonstrate for the first time an all-polarization-maintaining double-clad neodymium fiber laser operating in the dissipative soliton resonance (DSR) regime where stable mode-locking is achieved using a nonlinear amplifying loop mirror (NALM) with large normal dispersion in a figure-8 cavity design. The laser thereby generates square-shaped nanosecond pulses whose duration linearly scales with pump power from 0.5 ns up to 6 ns, with a maximum energy of 20 nJ. In addition, output pulses feature a remarkably narrow bandwidth of 60 pm along with a signal-to-noise ratio higher than 80 dB. This study then paves the way towards using such DSR-based sources for efficient frequency doubling in the blue spectral range.

Ultrasensitive ultrasound detection using an intra-cavity phase-shifted fiber Bragg grating in self-injection-locked diode laser

Yupeng Zhu, Lingling Hu, Zigeng Liu, and Ming Han

Doc ID: 375059 Received 08 Aug 2019; Accepted 14 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: We report a high-sensitivity fiber-optic ultrasonic sensor system using a self-injection-locked distributed feedback (DFB) diode laser where a π-phase-shifted fiber Bragg grating (πFBG) serves as both the locking resonator and the sensing element in a fiber ring feedback loop. By controlling the delay time of the feedback light through a fiber stretcher, the laser wavelength is locked to an external cavity mode on the spectral slope of the πFBG and the ultrasound-induced wavelength shifts of the πFBG is converted to laser intensity variation. The ultrasonic sensing scheme simplifies the feedback control because the self-injection locking automatically pulls the laser wavelength to the πFBG resonant wavelength. In addition, it improves the detection sensitivity because of the frequency noise of the DFB laser is drastically reduced. We show that the sensor system achieves a strain sensitivity of 78 fε/Hz½ at around 200 kHz.

Transferring freeform lens design into phase retrieval through intermediate irradiance transport

ZeXin Feng, Dewen Cheng, and Yongtian Wang

Doc ID: 376052 Received 21 Aug 2019; Accepted 14 Oct 2019; Posted 15 Oct 2019  View: PDF

Abstract: Freeform lens design for the prescribed irradiance without thin element and paraxial approximations is very complicated. We propose to transport the source irradiance before the required freeform lens into an intermediate irradiance behind the lens. In this way, the complicated freeform lens design problem could be transferred into a simpler problem of retrieving the phase from the intermediate and target irradiances. The transport from the source irradiance to the intermediate irradiance is simply realized by applying a collinear relationship among the coordinates on the intermediate plane, exit freeform surface and target plane to energy conservation. The phase retrieval solution can help construct an approximate lens, which is subsequently used to update the intermediate irradiance. Several iterations could bring a good performance, as demonstrated by three designs.

Femtosecond laser self-assembly for silver vanadium oxide flower structures

Yi-Ke Sun, Wei-Wei Xu, Toshihiro Okamoto, Masanobu Haraguchi, and Lei Wang

Doc ID: 377681 Received 16 Sep 2019; Accepted 13 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Flower-liked silver vanadium oxide (SVO) micropatterns were realized by femtosecond laser in-situ writing from its precursor. Self-assembled petals irradiated by femtosecond laser were observed growing vertically to the substrate along with the scanned routine assisted by the formation of silver seeds and plasmonic-mediated effects. By controlling the concentration of ammonium monovanadate and the laser exposure time, different thickness of petals was manipulated from ~ 100 nm to microns. The SVO products were confirmed Ag4V2O7, AgVO3 and part of Ag3VO4 by X-ray diffraction (XRD) measurement. Photodynamic self-assembly for in-situ fabrication of microstructures presents to be an effective and facile technique for SVO and other functional compounds.

High speed data transmission using directly modulated microdisk lasers based on InGaAs/GaAs quantum well-dots

Fedor Zubov, Mikhail Maximov, Natalia Kryzhanovskaya, Eduard Moiseev, Maria Muretova, Alexey Mozharov, Nikolay Kalyuzhnyy, Sergey Mintairov, Marina Kulagina, Nikolay Ledentsov Jr., Łukasz Chorchos, Nikolay Ledentsov, and Alexey Zhukov

Doc ID: 377651 Received 11 Sep 2019; Accepted 13 Oct 2019; Posted 17 Oct 2019  View: PDF

Abstract: We report on direct large signal modulation and the reliability studies of microdisk lasers based on InGaAs/GaAs quantum well-dots. A µm in diameter microlaser exhibits an open eye diagram up to 12.5 Gbit/s and is capable of error-free 10 Gbit/s data transmission at 30ºC without temperature stabilization. The ageing tests of a 31 µm in diameter microdisk laser were conducted at room and elevated temperatures during more than 1200 hr. The average rate of the output power degradation was about 25 and 29 nW/hr at 40 and 60ºC, respectively.

Ultra-compact low-loss 1×4 optical power splitter with splitting ratio of 1:2:4:8 based on two-stage cascaded MMI couplers

zezheng Li, Yang Liu, huan guan, Weihua Han, and Zhi-Yong Li

Doc ID: 376771 Received 03 Sep 2019; Accepted 13 Oct 2019; Posted 18 Oct 2019  View: PDF

Abstract: An ultra-compact low-loss 1×4 optical power splitter with splitting ratio of 1:2:4:8 is proposed and demonstrated on a 220-nm-thick silicon-on-insulator (SOI) platform at C band. The splitter is based on two stages of cascaded 1×3 multimode interference (MMI) coupler and 4×4 MMI coupler and the size of main structure is 124.0 μm×6.4 μm, which is more compact than the traditional scheme of four-stage cascaded 1×2 MMI coupler. Phase shifters based on taper waveguides are incorporated in the device as the connection of two MMI couplers. The fabricated device exhibits a 3-dB power difference with a deviation less than 0.88 dB from 1530 nm to 1570 nm. The average power difference is 3.14 dB at the center of C band with an insertion loss of 1.84 dB.

2 mJ room temperature Fe:CdTe laser tunable from 5.1 to 6.3 µm

Vladimir Kozlovsky, M. Frolov, Yuriy Korostelin, and Yan Skasyrsky

Doc ID: 377175 Received 05 Sep 2019; Accepted 11 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: We report a room temperature (RT) operation of a Fe:CdTe laser pumped by a Q-switched 2.94-µm Er:YAG laser. The Fe:CdTe laser produced 2 mJ of output energy at λ = 5.55 µm with slope efficiency of 16% with respect to absorbed pump energy. With the use of an intracavity prism, the spectral tuning was demonstrated in the 5.1-6.3 µm range, being the longest wavelength tuning achieved for Fe2+:II-VI lasers. The lifetime of the upper laser level was measured to be 530 ns at RT. © 2019 Optical Society of America

Graphene-based metasufaces for switching polarization states of anomalous reflection and focusing

Hua Zhu, Shuqi Chen, jing wen, Jian Wang, and Lin Chen

Doc ID: 375839 Received 20 Aug 2019; Accepted 11 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: Metasurfaces have shown great potential to manipulate electromagnetic waves, and hence have found numerous applications in photonics. However, the functionalities of most of the reported metasurfaces are polarization-unfriendly after the fabrication process and can not be reconfigured dynamically with switchable polarization. Here, graphene-based metasurfaces are proposed to exhibit polarization-switchable electromagnetic response before and after switch of the chemical potential of graphene. The phase shifts covering 0-to-2π range can be switched from x polarization to y polarization by tuning the chemical potential of graphene from one value to another one. High-performance polarization-switchable anomalous reflection and focusing have been demonstrated with the designed metasurfaces. The presented design strategy can be applied to make other polarization-switchable meta-devices in different frequency domains, and impact numerous photonic applications.

A dual-loop Sagnac interferometer with a geometric phase shifter for quadrature phase bias locking

Jingtao Dong and Rong-sheng Lu

Doc ID: 377138 Received 05 Sep 2019; Accepted 11 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: A stable quadrature phase bias is highly demanded in the balanced Sagnac interferometer to achieve sufficient detection sensitivity and unambiguity. We demonstrate a straightforward and effective quadrature phase locking technique in a free-space balanced Sagnac interferometer by using a dual-loop, one for sensing and the other for bias feedback. The sensing loop and the feedback loop operate on linearly polarized beams at two separate wavelengths and overlap for the most of area. A geometric phase shifter showing wavelength independence placed on the common-path of the two loops introduces two almost identical nonreciprocal phase shifts between the counter-propagating beams for the two separate wavelengths, so that a real-time compensation of the phase bias for the sensing loop can be implemented by the error signal of the feedback loop. Proof-of-concept experimental results demonstrated successful locking of the quadrature phase bias in the presence of the signal fading due to the birefringence disturbance. The correction of the residual chromatism of the interferometer is discussed before the conclusion is made.

Gradual ghost imaging of moving objects by tracking based on crosscorrelation

Shuai Sun, Jun-Hao Gu, Huizu Lin, Liang Jiang, and WeiTao Liu

Doc ID: 375563 Received 16 Aug 2019; Accepted 11 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: The requirement on large number of samplings limits the performance of ghost imaging for moving objects. Conventionally, tracking and imaging of the moving objects are done independently, thus sequential clear images of the moving target during its evolution are required. In this paper, we propose to obtain the displacement of the object via crosscorrelation between sequential unclear rough images. Then high quality image of the moving object can be reconstructed gradually during its evolution. In this way, tracking and imaging of the objects are done along with each other. The experiment results show that the trajectory of translation and rotation motion can be obtained, and high-quality images of the moving objects can be gradually achieved.

Bloch oscillations in photonic spectral lattices through phase-mismatched four-wave mixing

Wenwan Li, Chengzhi Qin, Han Tianwen, Hao Chen, Bing Wang, and Peixiang Lu

Doc ID: 377086 Received 11 Sep 2019; Accepted 11 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Here we investigate the Bloch oscillations (BOs) in a photonic spectral lattice created with four-wave mixing Bragg scattering (FWM-BS). By injecting a signal and two pumps with different frequencies into a silicon nitride waveguide, a spectral lattice can be created for the generated idlers through successive FWM-BS. The phase mismatch during FWM-BS acts as an effective force that induces BOs in the spectral lattice. Both the oscillation period and amplitude are determined by the magnitude of the effective force. With cascaded FWM-BS processes, the spectrum of idlers experiences a directional shift as the phase differences of pumps are modulated. Additionally, introducing long-range couplings in the spectral lattice will change the trajectory of BOs within each period. The pattern of BOs for a single frequency input can also be tailored. The study provides a new platform to realize BOs in the frequency dimension and paves a promising way for broadband frequency control with all-optical schemes.

Ultrasound modulated laser feedback tomography in reflective mode

Kaiyi Zhu, Borui Zhou, Yueyue Lu, Puxiang Lai, Shulian Zhang, and Yidong Tan

Doc ID: 378351 Received 20 Sep 2019; Accepted 10 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: A novel method for ultrasound modulated optical tomography (UOT) detection based on the laser feedback technology is proposed. The system has advantages such as simple structure, high sensitivity and reflective configuration. Effective penetration depths of up to 9 cm and 5 cm in phantom and biological tissues, respectively, have been demonstrated in experiment. The detection capability is comparable with the state of the art in transmission mode, but with much lower photon consumption. Although a lot need to be improved, the proposed method is promising for further development towards practical applications.

Squeezed vacuum phase control at 2 μm

Terry McRae, Min Jet Yap, Daniel Gould, paul altin, Nutsinee Kijbunchoo, Georgia Mansell, Robert Ward, Daniel Shaddock, Bram Slagmolen, and David McClelland

Doc ID: 378399 Received 20 Sep 2019; Accepted 10 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: We demonstrate phase control for vacuum squeezed light at a 2 μm wavelength which is a necessary technology for proposed future gravitational-wave observatories. The control scheme allowed examination of noise behavior at frequencies below 1 kHz, and indicated that squeezing below this frequency was limited by dark noise and scattered light. We directly measure 3.9 ± 0.2 dB of squeezing from 2 kHz to 80 kHz and 14.2 ± 0.3 dB of anti-squeezing relative to the shot noise level. The observed maximum level of squeezing is currently limited by photodetector quantum efficiency and laser instabilities at this new wavelength for squeezed light. Accounting for all losses we conclude the generation of 11.3 dB of squeezing at the optical parametric oscillator.

An interferometry-free noncontact photoacoustic detection method based on speckle correlation change

Huanhao Li, Fei CAO, Yingying Zhou, Zhipeng Yu, Lidai Wang, and Puxiang Lai

Doc ID: 377132 Received 10 Sep 2019; Accepted 09 Oct 2019; Posted 14 Oct 2019  View: PDF

Abstract: Optical speckle patterns occur when coherent optical wavefront is randomized but such stochastic yet deterministic information about the medium can be decoded. A simple setup is inspired to monitor the decorrelation of speckle patterns within the memory effect range when the medium is photoacoustically perturbated. Experimentally, a linear relationship is confirmed between the speckle correlation change and the peak-to-peak amplitude of the ultrasonic transducer-detected photoacoustic waves, and the detection sensitivity is comparable. Such a plain specklegram-based method may find special interests when no direct contact is allowed between the sample and the photoacoustic detector.

Generalized wave-packet formulation with ray-wave connections for geometric modes in degenerate astigmatic laser resonators

Yung-Fu Chen, Jung-Chen Tung, M. X. Hsieh, Y. H. Hsieh, Hsing-Chih Liang, and K. F. Huang

Doc ID: 378842 Received 24 Sep 2019; Accepted 09 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: The parametric equations for periodic rays in degenerate astigmatic laser resonators are derived in a generalized way. The derived parametric equations clearly reveal the formation of Lissajous geometric modes with phase variation along the propagation. Using the representation of quantum coherent state, a generalized wave-packet formula is derived to connect with the periodic rays of geometric modes. The derived wave-packet formula is not only validated through comparing with various experimental patterns but also directly exploited to manifest the spatial asymmetries of Lissajous lasing modes due to a highly transmissive output coupler.

Ultrasound beam steering using fiber optic ultrasound phased array

Jingcheng Zhou, xu guo, Cong Du, and Xingwei Wang

Doc ID: 379173 Received 27 Sep 2019; Accepted 09 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: In this letter, a novel fiber optic ultrasound phased array technology is proposed to solve the ultrasound beam steering problems for fiber optic ultrasound biomedical imaging. The ultrasound beam steering feasibility is explored and verified by our unique time delay approach. Theoretical analysis is performed to predict the beam steering angle. Experiments have been performed to verify that the ultrasound beam is steered by using our approach. Four fiber optic ultrasound generators were fabricated and used to build the phased array emitter. The successful accomplishment of this project established a foundation of the prototype of the fiber optic ultrasound imaging transducer.

Sub-cycle mid-infrared coherent transients at 4 MHz repetition rate applicable to lightwave-driven scanning tunneling microscopy

Katsumasa Yoshioka, IPPO IGARASHI, SHOJI YOSHIDA, YUSUKE ARASHIDA, Ikufumi Katayama, Jun Takeda, and Hidemi Shigekawa

Doc ID: 375431 Received 14 Aug 2019; Accepted 09 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: We produce sub-cycle MIR pulses at a 4 MHz repetition rate via the optical rectification (OR) of sub-10 fs near-infrared pulses delivered by an optical parametric chirp pulse amplifier. The coherent MIR pulses generated in a GaSe crystal under an ultrabroadband phase-matching condition contain only 0.85 oscillation cycles within the full width at half-maximum of the intensity envelope. The use of OR enables excellent phase stability of 56 mrad over 5.6 h, which is confirmed by field-resolved detection using electro-optic sampling. An electromagnetic simulation using a finite integration technique reveals that the peak field strength can easily exceed 10 V/nm owing to the field enhancement resulting from focusing MIR pulses onto a tunnel junction.

Tunable degree of polarization of an unpolarized, partially coherent beam with circular coherence in a high numerical aperture system

Xinying Zhao, Xiaoyan Pang, and Guobin Wan

Doc ID: 376135 Received 23 Aug 2019; Accepted 09 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: The polarization properties of a strongly focused, unpolarized partially coherent beam with circular coherence are studied in this letter. It is found that the degree of polarization (DoP) in the focal plane can be adjusted not only by the initial coherence and the semi-aperture angle but also through an annular pupil due to the unusual coherence of the source. Our results show that for an unpolarized, partially coherent incident beam, the field in the focal plane can go from almost unpolarized state to almost fully polarized state along a radial distance, even the initial coherence length is very short. Through adjusting the width of the annular pupil, the DoP on average can be reduced or enhanced significantly. Especially, for the very narrow annulus, the approximation expression of the DoP is derived, from which the accurate positions of the peak values of the DoP can be calculated easily. Our findings provide an alternative way to tailor the DoP in three dimensional optical fields.

Quadrature phase stabilized three-wavelength interrogation of fiber-optic Fabry–Perot acoustic sensor

Qiang Liu, Zhenguo Jing, Yueying Liu, Ang Li, Yang Zhang, Zhiyuan Huang, Ming Han, and Wei Peng

Doc ID: 378115 Received 18 Sep 2019; Accepted 08 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: In this letter, we propose a quadrature phase stabilized three-wavelength demodulation technique for the interrogation of fiber-optic Fabry–Perot acoustic sensors. It is based on accurate and fast tuning of a monolithic modulated grating Y-branch (MG-Y) laser. Three quadrature wavelengths are chosen to perform high-speed cavity length demodulation by wavelength switching, so that avoiding imbalances and disturbances between the three optical paths in the conventional three-wavelength quadrature phase demodulation systems. A feedback stabilization scheme for maintaining the quadrature phase condition has been proposed and demonstrated for the first time, making it potential for long-term monitoring in harsh environments.

Buffered polarization diverse detection for single camera polarization-sensitive optical coherence tomography

Tae Joong Eom, Kwan Seob Park, and Jun Geun Shin

Doc ID: 375436 Received 21 Aug 2019; Accepted 08 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: Herein we propose a method to mitigate a position mismatch problem for a spectral-domain polarization-sensitive optical coherence tomography (SD-PS-OCT) system that uses a single line-scan detection scheme. A single detector-based PS-OCT detects two orthogonal polarization components as two adjacent A-scan signals in turns. Thus two adjacent A-scan signals are not scattered at a fix point in time (position mismatch problem), resulting in uncorrelated signals between them. To achieve sequential detection of simultaneously scattered light, a buffering single mode fiber was connected to one of the two ports coming out of the optical switch, provided a proper time delay. A single-mode optical fiber of 2.69 km in length was used to buffer and its length was determined by a frame rate of the spectrometer used as a detector. With the proposed SD-PS-OCT scheme, the PS-OCT system with a simple configuration and the minimized position mismatch problem between two polarization components can be set.

All-fiber high-order orbital angular momentum (l=±2) generator based on a single-helix helical fiber grating

hua zhao, Peng Wang, Takusai Yamakawa, and Hongpu Li

Doc ID: 375726 Received 19 Aug 2019; Accepted 07 Oct 2019; Posted 09 Oct 2019  View: PDF

Abstract: An all-fiber orbital angular momentum (OAM) generator enabling to directly turn the fundamental mode (HE11) to the second OAM modes (l=±2) with a efficiency of ~90% has been proposed and experimentally demonstrated, which is realized based on utilization of a second-order helical fiber grating written in a few-mode fiber. This is the first time, to the best of our knowledge, that all-fiber high-order OAM (l=±2) have been achieved with using only one component, i.e., the HLPG. The proposed method opens a new way to efficiently generate all-fiber higher order OAM using a conventional multimode fiber.

A compact polarization-entangled photon-pair source based on a dual-periodically-poled Ti:LiNbO₃ waveguide

Changwei Sun, Suheng Wu, Jiachen Duan, Jianwei Zhou, Junlei Xia, Ping Xu, Zhenda Xie, Yanxiao Gong, and Shining Zhu

Doc ID: 372838 Received 18 Jul 2019; Accepted 07 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: We present an experimental realization of a compact and reliable way to build a non-degenerate polarization-entangled photon-pair source basedon a dual-periodically-poled Ti:LiNbO₃ waveguide, which is in the telecommunication window and compatible with the fiber quantum networks. The dual-periodic structure allows two inherently concurrent quasi-phase-matching spontaneous parametric down-conversion processespumped by a single laser beam, hence enabling our source to be compact and stable. We show that our source has a high brightness of B = 1.22×10⁷pairs/(s×mW×nm). With quantum state tomography, we estimate an entanglement fidelity of 0.945±0.003. A violation of Clauser-Horne-Shimony-Holt inequality with S = 2.75±0.03 is also demonstrated.

High-efficiency subwavelength bridge-shape photo-absorbers based on transverse cavity modes

Jérôme Le Perchec

Doc ID: 372959 Received 17 Jul 2019; Accepted 07 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: We study a frequency-selective photon absorber able to efficiently confine light within very thin semi-conducting layers. The active material is appropriately embedded in a cavity resonator where lateral resonances occur, based on non-plasmonic modes, thus minimizing undesired losses in the metallic parts. Typical examples and configurations in the infrared and visible ranges are illustrated. Theoretical quantum efficiencies around 90% may be reached, with a broad angular tolerance. Also, multi-spectral photon sorters may be designed by combining resonators of different size. These results especially find direct applications for elementary ultra-compact detectors and imaging focal plane arrays.

Light confining effect in zero-index waveguide with unenclosed sidewalls and a design scheme of reflectionless polarization converter

Ping Xu and Yongxing Wang

Doc ID: 376604 Received 29 Aug 2019; Accepted 07 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: In our work, we have demonstrated a novel and interesting effect, the light confining effect in a mu-epsilon-near zero (MENZ) waveguide with unenclosed sidewalls. The MENZ waveguide can have perfect transmittance even though the side walls are unenclosed. All the light propagating in the MENZ waveguide is confined to the MENZ when the connection of each sidewall is not broken. We also demonstrate that even most of the surfaces of MENZ is exposed to air rather than covered by perfect electric conductor or perfect magnetic conductor side walls, it is still possible for the MENZ waveguide to exhibit the light confining effect, which is quite different from conventional waveguide. The light confining effect of MENZ waveguide has rarely been discussed in the previous works. Based on the light confining effect, we propose a new design scheme of a reflectionless polarization converter without using optical active medium or structures. Our proposal provides the possibility of the application of zero-index metamaterials in the field of the optical isolate and the modulation of optical polarization.

Instantaneous thickness measurement of multilayer films by single-shot angle-resolved spectral reflectometry

Young-Sik Ghim and Hyug-Gyo Rhee

Doc ID: 378626 Received 25 Sep 2019; Accepted 06 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: In this letter, we describe a new concept of angle-resolved spectral reflectometry with a pixelated polarizing camera for determination of the thickness of each film layer in multilayer films. We can measure the changes in the phase and amplitude of p- and s- polarized lights over a broad spectral range and a wide incident angle at a time. The proposed method is verified by measuring a sample of multilayer films and comparing our measurement results with an ellipsometer. Comparison results show that our proposed technique enables real-time inspection of multilayer films with high precision.

Ultrafine intravascular photoacoustic endoscope with a 0.7 mm diameter probe

Sihua Yang, Peng Lei, Xue Wen, Lei Wang, and Pengfei Zhang

Doc ID: 377640 Received 13 Sep 2019; Accepted 05 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: Intravascular photoacoustic (IVPA), benefiting from high optical contrast, large imaging depth and absorption specificity, is of great potential for lipid-rich plaque detection. However, the diameter of reported IVPA endoscopes are too big to intervene into the coronary artery branches. Here, by designing an ultracompact house embedded with a side-fire fiber and a miniature single-element ultrasound transducer, we developed the ultrafine IVPA endoscope with a diameter of 0.7 mm aiming at coronary artery branches atherosclerotic plaque detection. A stent with an inner diameter of 1.6 mm was imaged to illustrate the reliability and feasibility of the ultrafine IVPA endoscope. Further, the photoacoustic (PA) and ultrasound (US) imaging of a mouse thoracic aorta with diameter of 1.15 mm was conducted to verify the clinical potentiality of the endoscope, and the PA images have well consistency with histological staining results. To our knowledge, this is the first time we achieved the IVPA imaging in fine vessel by the ultrafine endoscope, which paves a way for the translation of IVPA endoscope to clinical application.

Ultra-thin Near Infrared camera enabled by a flat multi-level diffractive lens

Rajesh Menon, Sourangsu Banerji, Monjurul Meem, Apratim Majumder, Fernando Vasquez Guevara, and Berardi Sensale-Rodriguez

Doc ID: 376772 Received 30 Aug 2019; Accepted 05 Oct 2019; Posted 11 Oct 2019  View: PDF

Abstract: We experimentally demonstrate a ~1 mm-thick near infrared (NIR) camera comprised of a multi-level diffractive lens coupled with a conventional monochrome image sensor. We performed careful measurements of the point-spread function, the modulation transfer function, focusing efficiency, aberrations and the field of view the camera.

Optical coherence tomography through a rigid borescope applied to quantification of articular cartilage thickness in a porcine knee model

Evan Jelly, Zachary Steelman, and Adam Wax

Doc ID: 376746 Received 04 Sep 2019; Accepted 05 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: There exists an unmet need for an OCT delivery scheme which is simple, robust, and applicable to general surgical applications. To deliver the beam in a narrow form factor, optical borescopes present an attractive potential solution. We present a method for enabling endoscopic delivery of optical coherence tomography (OCT) using a hand-held rigid borescope adapted to a low-cost OCT engine. The system reduces the distal profile of the scanner, enabling application of the system in otherwise hard-to-access regions. The clinical potential of this design is demonstrated through real-time quantification of articular cartilage thickness, a primary biomarker of joint health during osteoarthritis. This platform has the potential to enable use of OCT for real-time feedback during arthroscopic surgery.

Autocalibration precision of full-Stokes division-of-focal-plane imaging polarimeters

Francois Goudail, Li Xiaobo, Matthieu Boffety, stephane roussel, Tiegen Liu, and Haofeng Hu

Doc ID: 377553 Received 10 Sep 2019; Accepted 05 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: We investigate the validity domain and the precision of autocalibration of full Stokes imaging polarimeters based on a linear division-of-focal-plane polarization camera and a retarder. We demonstrate that the level of precision of auto-calibration in these systems gets worse as the degree of linear polarization of input Stokes vector approaches zero. Autocalibration is impossible when the input is purely circular or totally unpolarized. In all other cases, reaching a given level of precision requires higher signal to noise ratio as input gets closer to circular or unpolarized.

General framework for the analysis of imperfections in nonlinear systems

Matteo Santandrea, Michael Stefszky, and Christine Silberhorn

Doc ID: 370932 Received 25 Jun 2019; Accepted 04 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: In this paper, we derive a framework to understand the effect of imperfections on the phasematching spectrum of a wide class of nonlinear systems. We show that this framework is applicable to many physical systems, such as waveguides or fibres. Furthermore, this treatment reveals that the product of the system length and the magnitude of the imperfections completely determines the phasematching properties of these systems, thus offering a general rule for system design. Additionally, our framework provides a simple method to compare the performance of a wide range of nonlinear systems.

Polariton surface solitons under resonant pump

Yaroslav Kartashov and Victor Vysloukh

Doc ID: 375708 Received 19 Aug 2019; Accepted 03 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: We address formation of stable dissipative surface solitons in the exciton-polariton condensate in one-dimensional array of microcavity pillars under the action of localized resonant pump acting in the edge resonator. We show that localization degree and peak amplitudes of surface solitons can be effectively controlled by the pump frequency and that the allowed energy gap of periodic structure determines the energy range, where surface solitons can form. One observes bistability at sufficiently large pump amplitudes and nonlinearity-induced shift of the position of resonance peak from the allowed energy band of the periodic array into its forbidden energy gap. Growth of the spatial period of the array reduces coupling between pillars and currents from surface pillar into bulk pillars that leads to the increase of the surface soliton amplitude. Strong expansion into the depth of array occurs for pump frequencies corresponding to the middle of the allowed energy band. Surface solitons can be excited from the broadband Gaussian noise. Above certain threshold noise level solitons from stable upper branch of the bistability curve are excited, while below threshold solitons from the lower branch form.

Sagnac-enhanced impulsive stimulated Raman scattering for highly sensitive low-frequency Raman spectroscopy

Korato Hiramatsu, Jørgen Peterson, and Keisuke Goda

Doc ID: 372455 Received 15 Jul 2019; Accepted 03 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: The “fingerprint” (500-1800 cm−1) and “high frequency” (2400-4000 cm−1) regions in Raman spectroscopy are commonly used for label-free chemical analysis, while the “low frequency” region (<200 cm−1) is often overlooked despite containing rich information. This is largely due to the challenge of measuring weak Raman signals that are obscured by strong Rayleigh scattering. Here we propose and experimentally demonstrate Sagnac-enhanced impulsive stimulated Raman scattering (SE-ISRS), a filter-free method for time-domain Raman spectroscopy that overcomes the challenge and provides low-frequency Raman spectra at all probe frequencies. Using SE-ISRS for simultaneous low-frequency and fingerprint region measurements, we demonstrate a >5x enhancement of the signal-to-noise ratio compared to conventional ISRS spectroscopy.

Intense Stimulated Raman Scattering in CO2-filled Hollow Core Fiber

Katarzyna Krupa, Kilian Baudin, Alexandre Parriaux, Gil FANJOUX, and Guy Millot

Doc ID: 372813 Received 16 Jul 2019; Accepted 03 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: We demonstrate experimentally the generation of an intense broadband comb-like spectrum spontaneously builded up through stimulated Raman scattering in low-pressure CO2-filled hollow-core photonic crystal fiber pumped by a single infrared pump.

Asymmetric transmission of light in hybrid waveguide-integrated plasmonic crystals on silicon-on-insulator platform

Guanghui Ren, Xu Han, Thach Nguyen, Iryna Khodasevych, Joachim Hamm, Ortwin Hess, Yonghui Tian, and Arnan Mitchell

Doc ID: 375355 Received 22 Aug 2019; Accepted 02 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: We demonstrate asymmetric transmission of light in a hybrid waveguide-integrated plasmonic crystals where triangular silver islands create a regular array of nanogaps which couples to an underlying silicon-on-insulator (SOI) optical waveguide. Up to 60% difference is observed between light transmission in the forwards and backwards directions. This asymmetric transmission of light is not caused by external magnetic field or nonlinearity but a consequence solely of the structure geometry.

Optical Interruption of a Quantum Cascade Laser for Cavity Ring-Down Spectroscopy

Teemu Kääriäinen and Guillaume Genoud

Doc ID: 375952 Received 28 Aug 2019; Accepted 02 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: We demonstrate optical unlocking of a cavity resonance in a mid-infrared (MIR) quantum cascade laser (QCL) cavity ring-down spectrometer (CRDS) using a low-power multimode near-infrared (NIR) laser diode. A NIR laser with a center wavelength of 1310 nm is injected into a QCL, whose amplitude and frequency is modulated as a result. The shift in frequency leads to a rapid interruption of the cavity resonance. The optical method is compared to cavity interruption with a current step by measuring ring-down times in a high-finesse optical cavity, coupled with a QCL with a center wavelength of 4.5 μm. Results indicate comparable performance of the all-optical method with the more conventional current modulation, but with significantly reduced bandwidth requirements for the QCL driver, opening the way to other potential applications in mid-infrared laser spectroscopy.

Evolution of femtosecond laser damage in a hafnia-silica multi-layer dielectric coating

Velpula Praveen Kumar, Michal Durak, Daniel Kramer, Alexander Ross Meadows, Monika Vilemova, and Bedrich Rus

Doc ID: 374693 Received 06 Aug 2019; Accepted 02 Oct 2019; Posted 07 Oct 2019  View: PDF

Abstract: In order to optimize optical coating materials, designs and technologies for high damage resistance; understanding the growth of laser damage is of paramount importance. In this article, we show the evolution of femtosecond laser damage in a HfO2/SiO2 multilayer dielectric mirror coating. Depending on various spatial features of the damaged sites, we identified several regimes of laser-material interaction with varying laser fluence and incident number of pulses. A change in surface roughness has been observed only for a small number of pulses, and interestingly, a threshold number of pulses is found for nanocrack formation. We report the polarization-dependent orientation of nanocracks and their growth with an increasing number of pulses. The presented results demonstrate that the laser damage is originated from the nano bumps and surface roughening which then lead to the formation of nanocracks. The presented experimental results acknowledge the existing theoretical models in bulk dielectrics to explain the formation of nanostructures by interference of the incident laser with the scattering radiation from laser-induced inhomogeneities and growth of the field enhancement due to nanoplasma.

Slow-Light Based Tunable Delay and Narrowband Comb Filtering at 2 μm

Ravi Pant, VARUN K, and Akhileshwar Mishra

Doc ID: 376434 Received 28 Aug 2019; Accepted 02 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: Development of coherent sources, wideband thulium-doped fiber amplifiers, and fiber components has opened up the wavelength region around 2000 nm for optical communications, sensing and medical surgery. However, several key functionalities that are critical to enable these applications are not yet well developed and, therefore, need attention. Here, we present demonstration of two critical signal processing tasks viz; (i) tunable delay and (ii) tunable narrowband filter, which are important for enabling optical communications using wavelengths around 2000 nm. We exploit stimulated Brillouin scattering (SBS) in a 100 m long SM1950 fiber to report the first demonstration of slow-light based tunable delay around 2000 nm. For a 35 ns input pulse, we tune the delay up to a maximum of 18.8 ns, which corresponds to a relative delay of ∼ 0.5, by varying the pump power to achieve a maximum gain of 12.6 dB. For the 1550 nm wavelength regime, it has been shown that the Brillouin slow-light typically results in a delay of 1 ns/dB, which is less than the 1.67 ns/dB obtained at 2000 nm. For the same gain, the large delay at 2 μm compared to 1.55 μm results from the narrow gain bandwidth (∼ 22 MHz) of the SBS process in this wavelength regime. Using the narrow gain bandwidth of SBS, we present a proof-of-concept experiment to demonstrate filtering of individual comb lines in a comb with frequency spacing < 50 MHz. Demonstration of tunable narrowband filter and delay enables optical signal processing and line-by-line control of comb lines at 2 μm.

Visible blue-to-red 10 GHz frequency comb via on-chiptriple-sum frequency generation

Tobias Herr, Ewelina Obrzud, Victor Brasch, Thibault Voumard, Anton Stroganov, Michael Geiselmann, Francois Wildi, Francesco Pepe, and Steve Lecomte

Doc ID: 377158 Received 05 Sep 2019; Accepted 02 Oct 2019; Posted 03 Oct 2019  View: PDF

Abstract: A broadband visible blue-to-red, 10 GHz repetition rate frequency comb is generated by combined spectral broadening and triple-sum frequency generation in an on-chip silicon nitride waveguide. Ultra-short pulses of 150 pJ pulse energy, generated via electrooptic modulation of a 1560 nm continuous-wave laser, are coupled to a silicon nitride waveguide giving riseto a broadband near-infrared supercontinuum. Modal phase matching inside the waveguide allows direct triple-sum frequency transfer of the near-infrared supercontinuum into the visible wavelength range coveringmore than 250 THz from below 400 nm to above 600 nm wavelength. This scheme directly links the mature optical telecommunication band technology to the visible wavelength band and can find application in astronomical spectrograph calibration as well as referencing of continuous-wave lasers.

Simulation on the nanosecond-pulse laser damage of KDP surface by smoothed particle hydrodynamics (SPH) method

Shengfei Wang, Jian Wang, Xiangyang Lei, Zhichao Liu, Jianfeng Zhang, and Qiao Xu

Doc ID: 373328 Received 23 Jul 2019; Accepted 02 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: We present a simulation method to reproduce the crater formation and particle ejection phenomena observed in the laser-induced surface damage process of KDP crystals. Based on SPH method which is commonly used for solving shock and blast problems, equivalent explosion simulation models of the laser-induced damage process have been established. Moreover, laser damage experiments combined with time resolved techniques are performed on KDP surfaces to investigate the impact of laser fluences on the shockwave propagation and particle ejection speed. We find that the simulation models can predict the laser-induced damage behaviors of KDP crystal, which verifies the validity of the proposed method.

Optomechanical response with nanometer resolution in the self-mixing signal of a terahertz quantum cascade laser

Andrea Ottomaniello, James Keeley, Pierluigi Rubino, Lian He Li, Marco Cecchini, Giles Davies, Edmund Linfield, Paul Dean, Alessandro Pitanti, and Alessandro Tredicucci

Doc ID: 374949 Received 13 Aug 2019; Accepted 02 Oct 2019; Posted 08 Oct 2019  View: PDF

Abstract: Owing to their intrinsic stability against optical feedback, quantum cascade lasers (QCLs) represent a uniquely versatile source to further improve self-mixing interferometry at mid-infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision the deeply subwalength (< λ/6000) mechanical vibrations of a suspended silicon-nitride membrane used as external element of a THz QCL feedback interferometer. Besides representing an extension of the applicability of vibrometric characterization to THz frequencies, our system can be exploited for the realization of optomechanical applications, such as dynamical switching between different optical feedback regimes and a still-lacking THz master-slave configuration.

Experimental characterization of recurrences and separatrix crossing in modulational instability

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

Doc ID: 367826 Received 28 May 2019; Accepted 01 Oct 2019; Posted 02 Oct 2019  View: PDF

Abstract: We experimentally investigate two cycles of Fermi-Pasta-Ulam-Tsingou recurrence in optical fibers. Using three waves input we characterize the distance of maximum compression points against sideband amplitude and relative phase, outlining the qualitative changes of the dynamics due to separatrix crossing. Experimental results are in good agreement with numerical simulations and analytical predictions.

Lithium Niobate-Based Transparent Ultrasound Transducers for Photoacoustic Imaging

Ajay Dangi, Sumit Agrawal, and Sri-Rajasekhar Kothapalli

Doc ID: 373497 Received 23 Jul 2019; Accepted 01 Oct 2019; Posted 02 Oct 2019  View: PDF

Abstract: This work demonstrates lithium niobate (LiNbO3) based transparent ultrasound transducers (TUT) for photoacoustic imaging applications. The TUTs were fabricated by coating the top and bottom surfaces of a 0.25 mm thick LiNbO3 wafer with transparent indium-tin-oxide (ITO) for electrodes. The resulting transducers showed ~80% optical transparency in the wavelength range of 690 – 970 nm. The TUTs had a resonant frequency of 14.5 MHz and ~70% photoacoustic bandwidth. The versatility of TUT approach is demonstrated by introducing two different transparent photoacoustic imaging geometries: in one method that suits endoscopy applications, an optical fiber of a laser diode is directly fixed on the backside of a 2.5 mm diameter TUT and the fiber-TUT device is raster scanned to form 3D photoacoustic images. In the second method, that suits high-throughput applications, a free space optical-only raster scanning of the laser fiber across a 1 cm x 1 cm planar TUT yielded photoacoustic images. The proposed TUT approach is low-cost, easy to manufacture, compatible with conventional clinical ultrasound electronics, and scalable for different configurations including 2D TUT arrays to achieve real-time 3D high-throughput photoacoustic imaging.

Extraordinary polarization rotation of vector beams with ultrahigh-period-number chiral photonic crystals

Iam-Choon Khoo and Chun-Wei Chen

Doc ID: 375404 Received 15 Aug 2019; Accepted 01 Oct 2019; Posted 02 Oct 2019  View: PDF

Abstract: We demonstrate by theory and experiments that well-aligned cholesteric liquid crystals that function as 1D chiral photonic crystals (CPC) having extraordinarily large period number N (N = d/Λ; d: thickness, Λ: grating period) exceeding 1000 possess many optical properties impossible with conventional thin CPCs. Even far away from the circular Bragg resonance, these CPCs are capable of, simultaneously, high transmission and large broad-band polarization rotation of vector beams; the polarization rotation is independent of relative orientation of the input beam polarization vector and a good degree of linear polarization of the output beam can be maintained.

Angular Control of Anisotropy-Induced Bound States in the Continuum

Samyobrata Mukherjee, Jordi Gomis-Bresco, Pilar Pujol-Closa, David Artigas, and Lluis Torner

Doc ID: 373586 Received 24 Jul 2019; Accepted 01 Oct 2019; Posted 01 Oct 2019  View: PDF

Abstract: Radiation of leaky modes existing in anisotropic waveguides can be cancelled by destructive interference at special propagation directions relative to the optical axis orientation, resulting in fully bound states surrounded by radiative modes. Here we study the variation of the loci of such special directions in terms of the waveguide constitutive parameters. We show that theangular loci of the bound states is sensitive to several design parameters, allowing bound states to exist for a broad range of angular directions and wavelengths and suggesting applications in filtering and sensing.

Mueller matrix of the particle-free atmosphericenhanced backscatter

Olga Korotkova, Seyed Rafsanjani, Daniel Montano, and Jasmine Rodriguez

Doc ID: 376523 Received 29 Aug 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: The spatially resolved Mueller matrix of a mono-static opticalsystem with the corner-cube retro-reflector operating inthe presence of clear-air atmospheric turbulence is measuredfor the first time. The changes in the polarization propertiesof the beam are caused by the combination of deterministicpolarimetric modulation by the retro-reflector and randomscalar modulation of the return beam by atmospheric turbulence.In particular, the spatial structure of the Mueller matrixwithin the enhanced backscatter area is revealed.

Direct scattering transform of large wave packets

A Gelash and Rustam Mullyadzhanov

Doc ID: 375691 Received 19 Aug 2019; Accepted 30 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We apply the Magnus expansion to the Zakharov-Shabat system providing a basis for a systematic construction of high-order numerical schemes to solve the direct scattering problem of the integrable one-dimensional nonlinear Schrödinger equation. The presented numerical simulations of previously unreachable wave fields with up to 128 solitons employing second-, fourth- and sixth-order schemes stress the need for delicate numerics to identify the eigenvalues and especially phase coefficients. This approach opens broad perspectives to study large optical wave packets providing fundamental information about its scattering data content and origin of various nonlinear effects.

Distributed detection of hydrogen and deuterium diffusion into a single-mode optical fiber with Chirped-Pulse φOTDR

Andres Garcia-Ruiz, Adriana Morana, Luis Costa, Hugo Martins, Sonia Martin-Lopez, Miguel Gonzalez-Herraez, Aziz Boukenter, Youcef Ouerdane, and Sylvain Girard

Doc ID: 374388 Received 08 Aug 2019; Accepted 30 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: For some infrastructures such as oil and gas extraction boreholes or radioactive waste repositories, where distributed optical fibre sensors are employed to grant the safety of the facilities, the presence of gas species such as hydrogen or deuterium is one of the most relevant parameters to monitor. The possibility of employing the same kind of sensors for this purpose is of special interest, reducing the cost by employing a single interrogator, able to measure multiple parameters by simply employing adequate sensing fibres. To meet this goal, we present here a chemical sensor based on Chirped-Pulse Phase-sensitive Optical Time Domain Reflectometry, which is able to detect these species while they diffuse into the silica fibre. The ability of Chirped-Pulse φOTDR to measure change of refractive index with a sensitivity around 10^{-8} has allowed determining hydrogen concentration with precision in the order of 10^{-3} mol/m^3 and spatial resolution ~6 m. Another experiment provided an indirect measurement of the solubility of deuterium in a standard telecom-grade optical fibre, that is found to be around 1.47×1024 m^3/bar.

Direction-resolved homodyne laser-Doppler vibrometry by analyzing space-time fringes created by the successive 1D intensity profiles of the interference fringes

Mohammad Hossein Daemi and Saifollah Rasouli

Doc ID: 375558 Received 29 Aug 2019; Accepted 30 Sep 2019; Posted 04 Oct 2019  View: PDF

Abstract: In this Letter, we introduce a simple direction-resolved homodyne Laser-Doppler Vibrometry method, by sewing successive one-dimensional images of the interference pattern recorded by a linear array detector, and creating a two-dimensional space-time fringes pattern. A space-time fringes pattern visualizes the vibration form and it can be used for characterizing vibration of the object. We measure the vibration of a harmonically driven loudspeaker as a known source to demonstrate the capability of the method. We also employ the method to characterize the vibrational properties of the resonator elements of a thin-disk laser. The method reveals the environmental and instrumental sources of the vibration. The use of an array detector in the detection system simplifies the fringe chasing procedure and optical setup, and by the aid of space-time image, the vibration waveform is directly determined with no requirement to a time consuming SPS algorithm.

Generation of Flat Wideband Chaos Based on Mutual Injection of Semiconductor Lasers

Lijun Qiao, Tianshuang Lv, Yong Xu, Mingjiang Zhang, Jianzhong Zhang, Tao Wang, Rikai Zhou, Qin Wang, and Henry Xu

Doc ID: 371102 Received 05 Jul 2019; Accepted 29 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: We propose and demonstrate a method to improve the bandwidth and flatness of chaotic signals using a mutual injection structure with two distributed feedback lasers. The frequency detuning and coupling strength are investigated to produce a wideband flat chaos. A chaotic signal that spectrum covers more than 50 GHz which is approximately 6.42 times compared with that generated by optical feedback, with a flatness of ±2.8 dB is achieved when the coupling strength is 1.635 and the frequency detuning is -33.5 GHz.

Long period grating in a multimode CYTOP polymer fibre inscribed using a femtosecond laser

Antreas Theodosiou, Rui Min, Arnaldo Leal Junior, Andreas Ioannou, Anselmo Frizera-Neto, Maria Pontes, Carlos Marques, and Kyriacos Kalli

Doc ID: 375964 Received 20 Aug 2019; Accepted 28 Sep 2019; Posted 03 Oct 2019  View: PDF

Abstract: In this letter, we report on the first inscription of long period gratings (LPGs) in a multimode cyclic transparent optical polymer (CYTOP) fibre using a femtosecond laser inscription method. The LPG was inscribed directly in the centre of the fibre core, tailored for operation at 1560 nm using the plane-by-plane inscription method. The CYTOP-LPG was characterised in transmission and its response for relative humidity and temperature were measured. The humidity measurements are the first for a POF-LPG, whereas the temperature sensitivity is significantly higher than reported in other works. In addition, dynamic mechanical measurements were performed comparing the mechanical characteristics of the laser exposed sections of the polymer fibre, where the LPG was inscribed, with the unexposed regions.

Orbital angular momentum and informational entropy in perturbed vortex beams

Alexander Volyar, Mikhail Bretsko, Akimova Yana, and Egorov Yuriy

Doc ID: 371437 Received 01 Jul 2019; Accepted 27 Sep 2019; Posted 04 Oct 2019  View: PDF

Abstract: We theoretically and experimentally investigated transformations of vortex beams subjected to sector perturbations in the form of hard-edged aperture. The transformations of the vortex spectra, the orbital angular momentum, and the informational entropy of the perturbed beam were measured. We found that relatively small angular sector perturbations have almost no effect on the OAM, although the informational entropy is rapidly increasing due to the birth of new optical vortices caused by diffraction at the diaphragm edges. At large perturbation angles, the uncertainty principle between the angle and OAM involves vortices, with both positive and negative topological charges, so that the OAM decreases to almost zero, and the entropy increases sharply.

Silica optical fibre drawn from 3D printed preforms

Yushi Chu, Xinghu Fu, Yanhua Luo, John Canning, Yuan Tian, Kevin Cook, Jianzhong Zhang, and GangDing Peng

Doc ID: 377005 Received 05 Sep 2019; Accepted 27 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: Step-index silica optical fibre was drawn from a three-dimensional (3D) printed preform. The measured waveguide attenuation is α ~ 5.5 dB/m at λ = 1530 nm. The results demonstrate additive manufacturing of glass optical fibres with its potential to disrupt traditional optical fibre fabrication. It opens up fibre designs for novel applications hitherto not possible.

Characterization of a CEO-stabilized blue- and green-diode-pumped Ti:sapphire frequency comb

Pablo Castro-Marin, Toby Mitchell, Jinghua Sun, and Derryck Reid

Doc ID: 376612 Received 30 Aug 2019; Accepted 26 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: Diode-pumping of Ti:sapphire provides a low-cost route to high quality frequency-comb sources, exploiting the potential of direct diode modulation for wideband control of the carrier-envelope-offset frequency. We present here an fREP- and fCEO-locked, directly diode-pumped Ti:sapphire frequency comb, producing 66-fs pulses at 800 nm and employing f-to-2f interferometry and current-modulation of a 462-nm blue laser diode to achieve a stabilization bandwidth extending to ~70kHz. Characterizations of the fREP and fCEO phase noise are compared with relative intensity noise spectra of the pump diodes to provide insights into how the diode design and performance transfer into the comb stability.

A chip-scale humidity sensor based on a silicon nanobeam cavity

Minmin You, Zude Lin, Yiwei Bai, Fangfang Wang, Xiuyan Li, Yikai Su, and Jing Liu

Doc ID: 375381 Received 15 Aug 2019; Accepted 25 Sep 2019; Posted 02 Oct 2019  View: PDF

Abstract: In this paper, a novel humidity sensor based on a chip-scale silicon nanobeam cavity with PMMA cladding is demonstrated. This sensor is easy to fabricate and compatible with CMOS technology. It shows a humidity sensing with a linear wavelength dependence of 22.9 pm/%RH in a wide range of RH from 10% to 85%, an ultra-fast response time of 540 ms, and high stability. After annealing, the sensor exhibits high reversibility, repeatability and temperature insensitive at the range of 25 ℃~ 40 ℃. To the best of our knowledge, this is the first application of integrated photonics in high performance humidity detection. It provides a new way for the chip-scale sensor integrating with photonic devices and optical systems.

High-Sensitivity Imaging and Quantification of Intratumoral Distributions of Gold Nanoparticles Using a Benchtop X-ray Fluorescence Imaging System

Nivedh Manohar, Francisco Reynoso, SANDUN JAYARATHNA, HEM MOKTAN, Md Ahmed, PARMESWARAN DIAGARADJANE, Sunil Krishnan, and Sang Cho

Doc ID: 375319 Received 14 Aug 2019; Accepted 24 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: A high-sensitivity benchtop x-ray fluorescence (XRF) imaging system, based on a high-power x-ray source and silicon drift detector, has been developed. This system allows gold L-shell XRF-based quantitative imaging of gold nanoparticles (GNPs) at concentrations as low as 0.007 mg/cm3 (7 ppm) in biological tissues/water. Its capability for biomedical applications was demonstrated by imaging the GNP distribution within a small (~12×11×2 mm3) ex vivo sample (extracted from a murine tumor after intravenous GNP administration). The results suggest direct translatability for routine preclinical ex vivo imaging tasks involving GNPs, as well as possibility for in vivo imaging of small/superficial animal tumors.

Bi-functional polarization conversion in hybrid graphene-dielectric metasurfaces

Shengnan Guan, Jie -Rong Cheng, Tiehong Chen, and Shengjiang Chang

Doc ID: 373792 Received 29 Jul 2019; Accepted 24 Sep 2019; Posted 24 Sep 2019  View: PDF

Abstract: In this paper, we propose a hybrid graphene-dielectric metasurface as a bi-functional polarization converter. It can switch between a reflective half-wave plate and a quarter-wave plate around 1 THz by merely applying external biasing voltage, without reoptimizing the dielectric structure. Switching of the two wave plates originates from distinct dispersion of the orthogonal eigenmodes with the chemical potential, which is further explained by the overlapping of graphene and the dielectric resonance modes. Compared with graphene-metallic metasurfaces, combination of graphene with dielectric microstructures offers an alternative solution for active terahertz devices with high efficiency and large flexibility.

All-Chalcogenide Single-Mode Optical Fiber Couplers

Mohsen Rezaei and Martin Rochette

Doc ID: 375403 Received 14 Aug 2019; Accepted 23 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: We demonstrate the fabrication of all chalcogenide single-mode optical fiber couplers including broadband couplers, wavelength division multiplexers, and polarization beamsplitters. The functionnality of each coupler is engineered with a careful design of geometry. As a result, broadband couplers can be set to any arbitrary coupling ratio. Wavelength division multiplexers provide a coupling extinction ratio up to 35 dB, and polarization beamsplitters provide a polarization extinction ratio up to 18 dB.

Phase critical angle scattering for measurement of transient nanoscale growth rate of micron-sized bubble

Yingchun Wu, Lin Shi, Xuecheng Wu, Jianqi Shen, Linghong Chen, and Kefa Cen

Doc ID: 374413 Received 02 Aug 2019; Accepted 20 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We developed phase critical angle scattering (PCAS) to simultaneously measure the spherical and transparent bubble size at the micron scale and transient bubble growth at the nanoscale. The theoretical derivation of PCAS reveals that the phase of the fine structure of critical angle scattering caused by reflection and first-order refraction is highly sensitive to and linearly shifts with bubble diameter growth. Experiments on a single growing bubble are implemented with a Fourier imaging system. The results show that the PCAS technique can measure the tiny bubble growth down to tens of nanometers, providing a promising tool for accurate characterization of bubble dynamics.

Oxychloride glass with low phonon energy as a new choice for infrared laser materials

Feifei Huang, Benle Dou, youjie hua, Yin Li, Ying Tian, and Shiqing Xu

Doc ID: 376698 Received 29 Aug 2019; Accepted 19 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Recently, rare earth doped infrared luminescent glasses have drawn massive attention due to its potential applications in military, medical and communications fields. A system of oxychloride glasses of Si-Ge-O-Cl suitable for rare earth doping has been developed as a new choice for IR luminescent materials in this letter. Raman spectra show a looser glass network because of the decreased phonon energy and density compared to those kinds of heavy metal oxide glasses. The enhanced luminescence from visible to infrared region has been obtained with a beneficial fluorescence decay time. The spectroscopy results indicate that the system of Si-Ge-O-Cl glasses may be a promising candidate for application in infrared laser materials with enhanced luminescence.

Long-pulse 4.4 – 4.6 μm laser oscillations of Fe2+ ions in a Zn1-xMnxSe (x = 0.3) crystal pumped by a 1940 nm Tm fiber laser through Cr2+ -> Fe2+ energy transfer

Maxim Doroshenko, Michal Jelinek, Adam Riha, Jan Sulc, Helena Jelinkova, Vaclav Kubecek, Nazar Kovalenko, and Andrey Gerashimenko

Doc ID: 372413 Received 11 Jul 2019; Accepted 16 Sep 2019; Posted 16 Sep 2019  View: PDF

Abstract: Millisecond-pulse laser operation of Fe2+ ions at 78 K is demonstrated in the Zn1-xMnxSe:Fe2+,Cr2+ (x = 0.3) crystal under Tm fiber 1940 nm laser pumping through Cr2+ -> Fe2+ energy transfer process for the first time to our best knowledge. The laser slope efficiency was 1 % with respect to absorbed pumping energy at 1940 nm. The laser central wavelength shift from 4450 nm at 78 K up to 4510 nm at 110 K was observed. Tunability from 4350 nm up to 4670 nm at 78 K was achieved using an intracavity tuning element.

Linear control of light scattering with multiple coherentwaves excitation

Jeng Yi Lee, YUEH-HENG CHUNG, Andrey Miroshnichenko, and Ray-Kuang Lee

Doc ID: 375081 Received 09 Aug 2019; Accepted 10 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: With the wave interferometric approach, we study howextrinsically coherent waves excitation can dramatically alter the overall scattering properties, resultingin tailoring the energy assignment among radiationand dissipation, as well as filtering multipolar resonances. As an illustration, we consider cylindrical passive systems encountered by arbitrary configurationsof incident waves with various illuminating directions,phases, and intensities. With the formulas for dissipation and radiation powers, we demonstrate that a coherent superposition of incident waves extrinsically interferes the target channels in a desirable way. Moreover,the interferometric results can be irrespective to the inherent system properties such as sizes, materials, andstructures. Our approach paves a non-invasive solutionto manipulate waves-obstacles interaction at will.

mJ kW-class fiber CPA system using electro-optically controlled divided-pulse amplification

Henning Stark, Joachim Buldt, Michael Müller, Arno Klenke, Andreas Tünnermann, and Jens Limpert

Doc ID: 374122 Received 30 Jul 2019; Accepted 07 Sep 2019; Posted 09 Sep 2019  View: PDF

Abstract: The pulse-energy scaling technique electro-optically controlled divided-pulse amplification is implemented in a high-power ultrafast fiber laser system based on coherent beam combination. A fiber-integrated front end and a multi-pass cell based back end allow for a small footprint and a simple implementation. Bursts of 8 pulses are amplified parallel in up to 12 ytterbium-doped large-pitch fiber amplifiers. Subsequent spatio-temporal coherent combination of the 96 total amplified pulse replicas to a single pulse results in a pulse energy of mJ at an average power of 674 W, compressible to a pulse duration of 5 fs. To the best of our knowledge, this is the highest pulse energy ever accomplished with a fiber CPA system.

Zeeman-tunable Modulation Transfer Spectroscopy

Chloe So, Nicholas Spong, Charles Möhl, YUECHUN JIAO, Charles Adams, and T Ilieva

Doc ID: 374412 Received 01 Aug 2019; Accepted 07 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: Active frequency stabilization of a laser to an atomic or molecular resonance underpins many modern-day AMO physics experiments. With a flat background and high signal-to-noise ratio, modulation transfer spectroscopy (MTS) offers an accurate and stable method for laser locking. Despite its benefits, however, the four-wave mixing process that is inherent to the MTS technique entails that the strongest modulation transfer signals are only observed for closed transitions, excluding MTS from numerous applications. Here, we report for the first time the observation of a magnetically tunable MTS error signal. Using a simple two-magnet arrangement, we show that the error signal for the 87Rb F = 2 → F' = 3 cooling transition can be Zeeman-shifted over a range of >15 GHz to any arbitrary point on the rubidium D2 spectrum. Modulation transfer signals for locking to the 87Rb F = 1 → F' = 2 repumping transition as well as 1 GHz red-detuned to the cooling transition are presented to demonstrate the versatility of this technique, which can readily be extended to the locking of Raman and lattice lasers.

Optimizing energy transfer for highly efficient single-emissive-layer white thermally activated delayer fluorescence organic light-emitting diodes

Hui Xu, Feifei Gao, Ruiming Du, and Ying Wei

Doc ID: 370151 Received 24 Jul 2019; Accepted 06 Sep 2019; Posted 09 Sep 2019  View: PDF

Abstract: Thermally activated delayed fluorescence (TADF) white light-emitting diodes (WOLED) with simplified structures have great potential for daily lighting applications. However, the complicated energy and charge transfer processes between TADF emitters limit the development of single-layer white TADF systems. Here, we demonstrate high-efficiency WOLEDs with single emissive layers composed of blue and yellow TADF emitters with approporiate steric hindrances and energy gaps, which optimize the energy transfer from blue to yellow dopants for rational exicton allocation. As consequence, the single-emissive-layer WOLEDs achieve the maximum external quantum efficiency beyond 20% and small roll-offs.

Steriograthic Geometry of Coherence and Which-path Information

Yusef Maleki

Doc ID: 367082 Received 08 May 2019; Accepted 29 Jul 2019; Posted 30 Jul 2019  View: PDF

Abstract: Recently, it was shown that quantum entanglement is an indispensable part of the duality behavior of the light. Here, we report a surprisingly intimate connection between the stereographic projection and the duality--entanglement nature of a single photon. We show that, the recently introduced duality--entanglement relation (Optica \textbf{5}, 942 (2018)), naturally emerges from the stereographic projection geometry. We demonstrate that this geometry is complementarity sensitive; in the sense that, it is sensitive to the particle nature, wave nature, and entanglement nature of a single photon.

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