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Accepted papers to appear in an upcoming issue

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Design of Asymmetrical Directional Couplers on Ridge and Strip SOI technology with high dimensional variation tolerance

David Rodriguez, Juan L Corral, and Roberto Llorente

Doc ID: 325164 Received 12 Mar 2018; Accepted 23 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: The supermode analysis of asymmetrical directional couplers (ADC) based on SOI technology for strip and ridge structures at 1550nm is herein reported targeting to reduce ADC device fabrication requirements. The reported analysis based on supermodes permits to analyze the sensitivity of the ADC coupling efficiency by calculating the index difference between even and odd supermodes. Optimum designs have been found for 100 nm and 400 nm gaps, respectively, capable of converting and (de) multiplexing both TE0 and TE1 modes taking into account the width, gap, height and slab thickness variations produced with respect to the nominal design.

Dense Relativistic Electron Mirrors from a Laguerre-Gaussian Laser-Irradiated Micro-Droplet

Li-Xiang Hu, Tong-Pu Yu, Hanzhen Li, Yan Yin, Paul McKenna, and F Q Shao

Doc ID: 325415 Received 06 Mar 2018; Accepted 23 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly-polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser transverse ponderomotive force and are steadily accelerated to about 100 MeV by the inherent longitudinal electric field. Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge, narrow energy spread and large angular-momentum, which can be utilized for bright compact X/γ-ray pulse generation and photon vortex formation.

Fs-laser writing of photonic devices in borate glasses compositionally designed to be laser writable

Antonio Ponte, Francisco Munoz, Asier Alvarez, Pedro Moreno, Julia Atienzar, Ana Urbierta, Paloma Fernandez, Marina Pardo, Rosalia Serna, and Javier Solis

Doc ID: 326082 Received 15 Mar 2018; Accepted 23 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: The design and performance of borate glass samples compositionally pre-designed to be fs-laser writable via laser-induced ion-migration is reported in this letter. It is demonstrated that borate glasses modified on purpose with La₂O₃ and Na₂O can be straightforwardly used to produce high index contrast waveguides by fs-laser assisted ion-migration. The positive index contrast (Δn) of the waveguides is caused by the local enrichment of La₂O₃ in the guiding region. Spectroscopic ellipsometry analysis of several, non-processed, glass samples with different La₂O₃ contents reveals a linear dependence of the refractive index on the La₂O₃ content with a slope of 8·10-³/mol%. The refractive index contrast (Δn) of the waveguides, estimated from numerical aperture (NA) measurements, is consistent with this slope value and with the local enrichment of La₂O₃ in the guiding region of the waveguides measured by EDX. Additionally, it has been observed that the maximum achievable index contrast of the structures can be controlled through the initial La₂O₃ content of the glass, with maximum Δn values above 10-² for samples with just 5.5 mol% of La₂O₃.

Very sharp adiabatic bends based on inverse design

Yingjie Liu, Wenzhao Sun, Hucheng Xie, Nan Zhang, Ke Xu, Yong Yao, Shumin Xiao, and Qinghai Song

Doc ID: 327246 Received 29 Mar 2018; Accepted 23 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: Very sharp 90°micro-bends for adiabatic optical wave propagation in multimode waveguides are demonstrated by inverse design method and the devices are fabricated on silicon-on-insulator platform. The compact bending structures are based on digital waveguide metastructures with footprints as small as 2.6×2.6 μm². For waveguides width of 2μm and bending radius of only 1 μm, the TE00 mode is able to turn around the sharp corner with 1dB loss and >20 dB suppression ratio to higher order modes. The transmission spectra of the devices are measured with ~1 dB loss over 40 nm bandwidth which are consistent with the numerical simulations.

Transmission of dual-chirp microwave waveform over fiber with compensation of dispersion-induced power fading

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

Doc ID: 327244 Received 30 Mar 2018; Accepted 23 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: We propose a microwave photonic link to transmit dual-chirp microwave waveform over fiber with compensation of dispersion-induced power fading. In a center office (CO), we use a polarization-dependent dual-parallel Mach-Zehnder modulator (DPMZM) which is driven by a radio frequency (RF) carrier and a baseband single-chirped waveform to realize carrier-suppressed dual-sideband (CS-DSB) modulation at two orthogonal polarization states. When the CS-DSB optical signal is detected by a photodetector (PD) at a base station (BS), the dual-chirp signal is generated. However, along with the transmission to different BSs before emission, the chromatic dispersion of fiber will cause power fading. In our link, we can simply adjust the polarization controller (PC) in each base station to compensate the dispersion-induced power fading for different transmission distances and RF carrier frequencies. Besides, the link can realize one-to-multi transmission with shared dual-chirp microwave source in CO for radars. The system can ensure a broad operation bandwidth and wide tunability since it is optical and electrical filter free. The proposed scheme is theoretically analyzed and experimentally verified.

High-Speed Demodulation of Weak FBGs Based on Microwave Photonics and Chromatic Dispersion

Lei Zhou, Zhengying Li, Na Xiang, and Xiaoyi Bao

Doc ID: 324903 Received 27 Feb 2018; Accepted 22 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: A high speed demodulation technique based on microwave photonics and chromatic dispersion is proposed for distributed weak fiber Bragg grating (FBG) sensing. A broadband light modulated with a frequency-swept microwave is reflected by FBGs, and the reflected signal mixes with the original microwave to produce a beat frequency. A dispersion compensation fiber (DCF) changes the beat frequency within the FBG wavelength range. With crossing microwave sweep, all wavelengths of cascade FBGs can be fast decoded by measuring the change of the beat frequency. Chirp-Z and Hanning window algorithm helps to analyze the beat frequency in a single cycle. By adopting the single-peak filter as a reference, the thermal drift of DCF can be also eliminated. Therefore, the wavelength detection accuracy is greatly improved and high speed demodulation can be realized at 40 kHz sampling rate. We have demonstrated 105 FBGs of 0.1% reflectivity and 1 m spatial interval with the achieved wavelength accuracy to be 8 pm.

Stretchable Fiber Bragg Grating Based Sensor

Li Xu, Ning Liu, Jia Ge, Xianqiao Wang, and Mable Fok

Doc ID: 321154 Received 02 Feb 2018; Accepted 21 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: Fiber Bragg grating (FBG) based sensor is a very popular fiber optic sensor due to its simplicity, mature fabrication technology, and sensitivity to a number of physical stimuli. However, due to the stiff nature of optical fiber, it is impossible to heavily stretch a FBG sensor. Stretchable sensor is highly desired in soft robotics, human motion detection, and biomedical applications, which could involve motions like tension, bending, and twisting. In this letter, we demonstrate a stretchable FBG-based fiber-optic sensor by embedding a FBG-written optic fiber sinusoidally in a soft silicone film at an off-center position. This unique structure enables 30% of elongation in length that facilitates tension, bending, and twisting measurement.

Superresolution second-harmonic photoacoustic microscopy based on nonlinear thermal diffusion

Zhenhui Zhang, Yujiao Shi, Sihua Yang, and Da Xing

Doc ID: 318605 Received 27 Dec 2017; Accepted 21 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: We have developed a second-harmonic photoacoustic microscopy (SH-PAM) for super-resolution imaging based on the nonlinear thermal diffusion. When a sine-modulated Gaussian temperature field is introduced by a laser beam, the temperature dependence of the thermal diffusivity induces nonlinear photoacoustic (PA) effect and thus results in the production of second-harmonic PA signals. We demonstrate through both simulation and experiment that, the second-harmonic PA images can be reconstructed with a lateral resolution exceeding that of conventional optical-resolution PA microscopy. The feasibility of the SH-PAM was verified on phantom samples. Amphioxus zygotes and germinated pollens have been studied by the SH-PAM to demonstrate its biomedical imaging capability. This method expands the scope of conventional PA imaging and opens up new possibilities for superresolution imaging, prefiguring great potential for biological imaging and material inspection.

All-optical photoacoustic Doppler transverse blood flow imaging

Da Xing, WEI QIAO, Zhongjiang Chen, and Wangting Zhou

Doc ID: 320086 Received 18 Jan 2018; Accepted 21 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: The method of measuring blood flow in photoacoustic microscopy usually relies on ultrasonic transducers in contact fashion, which is not favored in many applications, such as wound area, burns and anabrosis. Here, we present a noncontact photoacoustic velocity measurement method to quantitatively map transverse blood flow based on photoacoustic Doppler (PAD) bandwidth broadening method with all-optical photoacoustic microscopy (AOPAM) system. It is validated that the PAD bandwidth broadening is proportional to the transverse flow within a certain range. The transverse flow speed ranging from 0 to 5.5 mm/s as well as sectional flow images was obtained in the blood-mimicking flow phantoms. Furthermore, the blood flow image of the mouse ear demonstrates that the all-optical photoacoustic Doppler (AOPAD) method can acquire the information of blood flow in vivo, which could significantly broaden the scope of applications for obtaining the blood flow velocity of the microvasculature in biomedicine.

Terabit optical OFDM superchannel transmission via coherent carriers of a hybrid chip-scale soliton frequency comb

Yong Geng, Xiatao Huang, Wenwen Cui, Yun Ling, Bo Xu, Jing Zhang, Xingwen Yi, Bao-Jian Wu, Shu-Wei Huang, Kun Qiu, Chee Wei Wong, and Heng Zhou

Doc ID: 325130 Received 06 Mar 2018; Accepted 21 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: We demonstrate seamless channel multiplexing and high bitrate superchannel transmission of coherent optical orthogonal-frequency-division-multiplexing (CO-OFDM) data signals utilizing a dissipative Kerr soliton (DKS) frequency comb generated in an on-chip microcavity. Aided by comb line multiplication through Nyquist pulse modulation, the high stability and mutual coherence among mode-locked Kerr comb lines are exploited for the first time to eliminate the guard intervals between communication channels and achieve full spectral density bandwidth utilization. Spectral efficiency as high as 2.625 bit/Hz is obtained for 180 CO-OFDM bands encoded with 12.75 Gbaud 8-QAM data, adding up to total bitrate of 6.885 Tb/s within 2.295 THz frequency comb bandwidth. Our study confirms that high coherence is the key superiority of Kerr soliton frequency combs over independent laser diodes, as a multi-spectral coherent laser source for high-bandwidth high-spectral-density transmission networks.

Enhanced luminescence efficiency of CsPbBr₃ perovskite nanocrystals on stretchable templates with Au/SiO₂ plasmonic nanoparticles

Jin-Hyeon Yun, Alexander Polyakov, Kyu-Cheol Kim, Yeon-Tae Yu, Donghyun Lee, and In-Hwan Lee

Doc ID: 326145 Received 19 Mar 2018; Accepted 20 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: We propose stretchable plasmonic templates of Au and Au/SiO₂ nanoparticles (NPs) to improve the luminescence efficiency of CsPbBr₃ perovskite nanocrystals (PNCs). These templates are highly flexible and consist of polymer-metal NP composites that facilitate the luminescence enhancement by localized surface plasmons (LSPs) due to coupling with metal NP. This template also prevents the disturbance of the carrier injection for perovskite light-emitting diodes (PeLEDs) by embedding metal NPs in polymer. The luminescence efficiency of PNC film on the template with Au NPs decreases by 21% compared to PNC films on the reference (polymer film without metal NPs), while it increases by 54% for the templates with Au/SiO₂ NPs. The observed effects are explained by the luminescence enhancement due to coupling to LSPs formed by the Au/SiO₂ NPs and by the prevalence of electron tunneling and dumping for Au NPs.

Stabilization of Broad Area Semiconductor Laser sources by simultaneous index and pump modulations

Waqas Ahmed, Shubham Kumar, Judith Medina, Muriel Botey, Ramon Herrero, and Kestutis Staliunas

Doc ID: 323399 Received 22 Feb 2018; Accepted 20 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: We show that the emission of broad area semiconductor amplifiers and lasers can be efficiently stabilized by introducing, two-dimensional periodic modulations simultaneously on both the refractive index and the pump (gain-loss) profiles, in the transverse and longitudinal directions. The interplay between such index and gain-loss modulations efficiently suppresses the pattern forming instabilities, leading to highly stable and bright narrow output beams from such sources. We also determine the stabilization performance of the device as a function of pump current and linewidth enhancement factor.

Signal intensity influences on the atomic Faraday filter

Longfei Yin, Bin Luo, Junyu Xiong, Jingbiao Chen, and Hong Guo

Doc ID: 326748 Received 23 Mar 2018; Accepted 20 Apr 2018; Posted 20 Apr 2018  View: PDF

Abstract: Previous studies of the Faraday anomalous dispersion optical filter (FADOF) mainly focus on the weak signal light filtering, without regard for the influences of the signal light intensity on the filter itself. However, in some applications the signal light is strong enough to change the filter's performance. In this work, the influences of the signal light intensity on the transmittance spectrum is experimentally investigated in a 780 nm ⁸⁵Rb FADOF in both the line-center and wings operation modes. The results show that the transmittance spectrum varies significantly with the signal light intensity. As the signal light increases, some existing transmittance peaks decline, some new transmittance peaks appear, and the maximum transmittance peak frequency may change. The spectrum in strong signal lights can be quite different from those calculated by programs in the condition of weak signal lights. These results are important for applications of the FADOF in the condition of strong signal lights.

Efficient continuous-wave and passive Q-switched mode-locked Er3+:CaF2–SrF2 lasers in the mid-infrared region

Jing Liu, Xiaoyue Feng, Fan Xiu-Wei, Zhen Zhang, Bo Zhang, Jie Liu, and Liangbi Su

Doc ID: 327062 Received 27 Mar 2018; Accepted 20 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: An efficient Er3+-doped CaF2–SrF2 mixed crystal was grown using the temperature gradient technique, and its laser characteristics were studied. In a compact linear cavity, a continuous-wave output power of 712 mW was obtained with the highest slope efficiency of 41.4%. Using a semiconductor saturable absorber mirror, a passive Q-switched mode-locked Er3+:CaF2–SrF2 laser emitting at 2729.5 nm was demonstrated for the first time. The maximum average output power of 125 mW was obtained at an absorbed pump power of 1.81 W, and the repetition rate of the Q-switched envelope was 4.17 kHz. The mode-locked pulses in the Q-switched pulse envelope had a repetition rate of 136.3 MHz, and its duration was estimated to be approximately 1.78 ns. These results indicate that the Er3+-doped CaF2–SrF2 mixed crystal is promising for the development of an ultrafast laser in the mid-infrared regime.

Dependence of soliton Kerr frequency comb lines on EDFA-induced pump noise for 64-QAM transmission

Peicheng Liao, Changjing Bao, Arne Kordts, Maxim Karpov, Martin Pfeiffer, Lin Zhang, Yinwen Cao, Ahmed Almaiman, Amirhossein Mohajerin Ariaei, fatemeh alishahi, Ahmad Fallahpour, Kaiheng Zou, Moshe Tur, Tobias Kippenberg, and Alan Willner

Doc ID: 325835 Received 12 Mar 2018; Accepted 20 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: We experimentally investigate the dependence of soliton Kerr frequency comb lines on EDFA-induced pump noise for 64-quadrature amplitude modulation (QAM) transmission. We find that the optical carrier-to-noise ratios (OCNRs) of the comb lines across C-band almost linearly depend on the pump OCNR and are similar for a constant input pump power and noise. For a specific three-soliton state, despite higher comb line power, there is no noticeable OCNR improvement compared to the single-soliton comb. When the ASE noise on the pump is varied by 10 dB in the stable single-soliton state, the comb linewidths remain relatively unchanged and similar to the pump linewidth. Furthermore, four lines of the single-soliton Kerr comb produced by a pump light at an OCNR larger than 52 dB are used as coherent light sources to transmit 20-Gbaud 64-QAM signals over a 25-km fiber with bit error rate (BER) below forward-error correction threshold.

Retrieving nonlinear refractive index of nanocomposites using finite-difference time-domain simulations

Andrey Panov

Doc ID: 328207 Received 12 Apr 2018; Accepted 19 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: In this Letter, it is proposed a method which utilizes three-dimensional finite-difference time-domain (FDTD) simulations of light propagation for restoring the effective Kerr nonlinearity of nanocomposite media. In this approach, a dependence of the phase shift of the transmitted light on the input irradiance is exploited. The reconstructed values of the real parts of the nonlinear refractive index of a structure of randomly arranged spheres are in good agreement with the predictions of the effective medium approximations.

Centimeter-scale Yb-free heavily Er-doped silica fiber laser

Fan Wang, Zhiquan Lin, Chongyun Shao, Qinling Zhou, Lei Zhang, Meng Wang, Danping Chen, Guojun Gao, Shikai Wang, Chunlei Yu, and Lili Hu

Doc ID: 327196 Received 29 Mar 2018; Accepted 19 Apr 2018; Posted 20 Apr 2018  View: PDF

Abstract: The laser behavior of a centimeter-scale Er3+/Al3+ codoped silica fiber with core numerical aperture (NA) and core diameter of 0.15 and 8 μm, respectively, is reported. The core-glass was prepared by sol-gel method combined with high temperature sintering; it contained Er3+ ion concentration as high as 132  1024 ions/m3 and Al/Er mole ratio of 10. The high doping homogeneity of Er3+ ion in fiber core was confirmed by the Electron probe microanalyzer (EPMA) element scanning, long Er3+:4I13/2 emission lifetime of 11.4 ms, and low refractive index fluctuation of fiber (± 1 × 10-4). The small signal gain of fibers with 4.6 cm, 10 cm, and 16 cm lengths was tested in the 1500–1620 nm range. The high net gain per unit length of 0.6 dB/cm at 1560 nm was achieved for the 4.6 cm-long fiber. Aimed for CO2 sensor application, the laser behavior of Er/Al codoped fiber was tested at 1572 nm. The output power of 18 mW was achieved in a 16 cm-long fiber with a pump power of 240 mW. A slope efficiency of 9.8 % was achieved. The newly developed silica fiber is promising for use in high-repetition-rate laser.

Spin-Hall effect in the scattering of structured light from plasmonic nanowire

Deepak Sharma, Vijay Kumar, Adarsh Vasista, Shailendra Chaubey, and G.V. Pavan Kumar

Doc ID: 325873 Received 12 Mar 2018; Accepted 19 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: Spin-orbit interactions are subwavelength phenomena which can potentially lead to numerous device related applications in nanophotonics. Here, we report Spin-Hall effect in the forward scattering of Hermite-Gaussian and Gaussian beams from a plasmonic nanowire. Asymmetric scattered radiation distribution was observed for circularly polarized beams. Asymmetry in the scattered radiation distribution changes the sign when the polarization handedness inverts. We found a significant enhancement in the Spin-Hall effect for Hermite-Gaussian beam as compared to Gaussian beam for constant input power. The difference between scattered powers perpendicular to the long axis of the plasmonic nanowire was used to quantify the enhancement. In addition to it, nodal line of HG beam acts as the marker for the Spin-Hall shift. Numerical calculations corroborate experimental observations and suggest that the Spin flow component of Poynting vector associated with the circular polarization is responsible for the Spin-Hall effect and its enhancement.

Quantum resonances vs Landau damping in electromagnetic response of metallic nanoslabs

Felipe Pérez-Rodríguez, Nykolay Makarov, and Shunashi Guadalupe Castillo-López

Doc ID: 326664 Received 23 Mar 2018; Accepted 19 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: The resonant quantization of Landau damping in far-infrared absorption spectrum of metal nano-thin films is predicted within the Kubo formalism. Specifically, it is found that the discretization of the electromagnetic and electron wave numbers inside a metal nanoslab produce quantum nonlocal resonances well-developed at slab thicknesses smaller than the electromagnetic skin depth. Landau damping manifests itself preciselyas such resonances, tracing the spectral curve obtained within the semiclassical Boltzmann approach. For slab thicknesses much greater than the skin depth, the classical regime emerges. Here the results of the quantum model and the Boltzmann approach coincide. Our analyticalstudy are in perfect agreement with corresponding numerical simulations.

Demonstration of a highly stable 10 GHz optical frequency comb with low timing jitter from a SCOWA-based harmonically mode-locked nested cavity laser

Kristina Bagnell, Anthony Klee, Peter Delfyett, Paul Juodawlkis, and Jason Plant

Doc ID: 303011 Received 05 Mar 2018; Accepted 19 Apr 2018; Posted 20 Apr 2018  View: PDF

Abstract: An optical frequency comb with mode spacing of 10 GHz operating in the c-band is produced from a harmonically mode-locked laser using a SCOWA device with a fiber-coupled external cavity. An intracavity Fabry-Perot etalon serves as a high finesse optical filter for supermode suppression and as the reference for cavity length stabilization using a multicombline Pound Drever Hall setup. The Allan deviation of a single optical combline near 193.4 THz is measured via a heterodyne beat with a cavity stabilized cw laser and reaches a minimum fractional frequency deviation of 3E-13 at τ = 30 ms. In addition, the phase noise of the photodetected pulsed output of the laser shows a timing jitter of < fs integrated from 1 Hz to the Nyquist frequency.

Orbital Angular Momentum symmetry in a driven Optical Parametric Oscillator

Rafael Rodrigues, Junior Gonzales, Braian Silva, Jose Augusto Huguenin, Marcelo Martinelli, Renné Medeiros de Araújo, Carlos Eduardo Souza, and Antonio Khoury

Doc ID: 325798 Received 13 Mar 2018; Accepted 19 Apr 2018; Posted 20 Apr 2018  View: PDF

Abstract: We investigate the dynamics of a driven optical parametric oscillator under injection of orbital angular momentum. The injected mode is adiabatically driven through arbitrary transformations on the Poincar\'e sphere of first order paraxial beams. As a result, the down converted beam conjugated to the seed is shown to follow a path imposed by a nontrivial symmetry on the Poincar\'e sphere.This symmetry allows controllable distinguishability between the spatial modes of the down converted beams.

Unexpected large nanoparticle size of single dimer hotspot systems for broadband SERS enhancement

Yu Huang, Yun Chen, Xiaotian Xue, Yanni Zhai, Lingling Wang, and Zhengjun Zhang

Doc ID: 323202 Received 13 Feb 2018; Accepted 19 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: We have numerically demonstrated the feasibility and possibility to achieve broadband surface enhanced Raman scattering (SERS) enhancement in the visible and near-infrared wavelength range using single nanoparticle (NP) dimer hotspot systems. Instead of the conventionally reported sub-100 nm, we find that the optimal NP size is as large as 200 nm in diameter for both Ag and Au. The key lies in the continuous arising of the bonding dipole plasmon (BDP) mode and higher-order resonances at shorter wavelengths. Further, it is revealed that the near- and far-field optical responses of these hotspot systems correlate well with each other, despite of the intrinsic enormous near- to far-field redshift for individual large NPs. The physical principles demonstrated here benefit significantly the fundamental understanding and engineering optimization of broadband SERS substrates.

Intensity-modulated directional torsion sensor based on in-line optical fiber Mach-Zehnder interferometer

Qinjiang Fu, Jingdong Zhang, Chuancan Liang, IROEGBU PAUL Ikechukwu, Guolu Yin, Lei Lu, Yifan Shao, Liu Liu, Dongxiao Liu, and Tao Zhu

Doc ID: 325918 Received 16 Mar 2018; Accepted 19 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: In this paper, we demonstrated an intensity-modulated directional torsion sensor based on in-line Mach-Zehnder interferometer in single mode fiber. A non-circular symmetric perturbation is created to excite non-circular symmetric cladding mode and then interference with the core mode at the second perturbation. An initial rotation angle is designed between two perturbations for the purpose of discriminating the torsion direction. Both experimental and theoretical results enforce that the spectral peak/dip turns to be the dip/peak when the fiber is twisted from the clockwise to the counter-clockwise direction. Benefiting from the reversal between peak and dip, an intensity-modulated direction torsion sensor is realized in the range from -50 to 50 rad/m with a liner sensitivity of 45.3%/(rad/cm).

Fluoride-fiber-based Side-pump Coupler for High-power Fiber Lasers at 2.8 μm

Christian Schäfer, Hiyori Uehara, Daisuke Konishi, Satoshi Hattori, Hiraku Matsukuma, Masanao Murakami, Seiji Shimizu, and Shigeki Tokita

Doc ID: 324956 Received 01 Mar 2018; Accepted 18 Apr 2018; Posted 23 Apr 2018  View: PDF

Abstract: A side-pump coupler made of fluoride fibers was fabricated and tested. The tested device had a coupling efficiency of 83% and was driven with an incident pump power of up to 83.5 W, demonstrating high-power operation. Stable laser output of 15 W at a wavelength of around 2.8 μm was achieved over 1 h when using an erbium-doped double-clad fiber as the active medium. To the best of our knowledge, this is the first time a fluoride–glass-fiber-based side-pump coupler has been developed. A test with two devices demonstrated further power scalability.

Singly-resonant pulsed optical parametric oscillator based on orientation-patterned gallium phosphide

Chaitanya Kumar Suddapalli, Hanyu Ye, Wei Junxiong, Peter Schunemann, and Majid Ebrahim-Zadeh

Doc ID: 325847 Received 12 Mar 2018; Accepted 18 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: We report a pulsed singly-resonant optical parametric oscillator (OPO) based on the new nonlinear crystal, orientation-patterned gallium phosphide (OP-GaP). Pumped by a Q-switched Nd:YAG laser at 1064 nm, and using a 40-mm-long OP-GaP crystal with a single grating period of =16m, the OPO generates signal and idler output across 1.6-1.7 μm and 2.8-3.1 μm, respectively, under temperature tuning. For an average pump power of 4.8 W at 50 kHz pulse repetition rate, mid-infrared idler powers of up to ~20 mW have been obtained at 2966 nm with high output stability. For pump pulses of ~13 ns duration, the OPO generates ~6 ns output signal pulses. From temperature-dependent wavelength tuning measurements at two different pump powers of 4.2 W and 1.2 W, a discrepancy of 11-17 ºC in the internal crystal temperature is estimated, implying that the OP-GaP sample suffers from increasing thermal effects at higher pump powers due to absorption.

Spectral density of vortex beams propagating in atmospheric turbulence with new simulation method

Daomu Zhao and Zhenglin Liu

Doc ID: 326405 Received 22 Mar 2018; Accepted 18 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: We study the spectral density of vortex beams propagating in atmospheric turbulence by numerical simulation and experiment with spatial light modulator (SLM). It is found that the figures produced by experiment with SLM are quite different from those by traditional numerical simulation. In view of this, we put forward an improved simulation method that refers to the theory of beam wander, leading to a consistency between numerical simulation and experimental results eventually. The new simulation method could improve the accuracy of beam simulation greatly in optical study.

Coaxial excitation longitudinal shear wave measurement for quantitative elasticity assessment using phase-resolved optical coherence elastography

Jiang Zhu, Junxiao Yu, Yueqiao Qu, Youmin He, Yan Li, Qiang Yang, Tiancheng Huo, xingdao he, and Zhongping Chen

Doc ID: 325342 Received 05 Mar 2018; Accepted 17 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: Optical coherence elastography (OCE) is an emerging imaging modality for assessment of mechanical properties in soft tissues. Transverse shear wave measurements using OCE can quantify the elastic moduli perpendicular to the force direction, however, missed the elastic information along the force direction. In this study, we developed coaxial excitation longitudinal shear wave measurements for quantification of elastic moduli along the force direction using M-scans. Incorporating Rayleigh wave measurements using non-coaxial lateral scan into longitudinal shear wave measurements using coaxial excitation, directionally dependent elastic properties can be quantified along the force direction and perpendicular to the force direction. Therefore, the reported system has the capability to image elasticity of anisotropic biological tissues.

Flexible binary phase photon sieves on polyimide substrates by laser ablation

Mool Gupta, Matthew Julian, and David Macdonnell

Doc ID: 326554 Received 21 Mar 2018; Accepted 17 Apr 2018; Posted 18 Apr 2018  View: PDF

Abstract: Binary phase diffractive optical element photon sieve is fabricated by direct laser ablation of a thin, flexible polyimide substrate with a nanosecond-pulsed ultraviolet (UV) laser. The binary phase photon sieve operates at 633 nm and was designed with 19 rings and a focal length of 400 mm. The total time to fabricate the photon sieves were tens of seconds. Surface properties of the laser-processed areas are examined, and optical performance of the photon sieve is characterized and compared to FDTD simulations. By optimizing the laser fluence and travel distance between laser pulses, features with sub-wavelength surface roughness were achieved. The photon sieve showed good focusing ability with suppressed side-lobes. When the fractional area of photon sieve pinholes was made to approach 50%, the binary sieve diffraction efficiency approached 11%; matching the highest value reported in the literature for a photon sieve. Thus, this work demonstrates both high efficiency, lightweight diffractive optics suitable for space satellite and other applications, with capabilities for low cost and high throughput fabrication.

656 W Er-doped Yb-free large-core fiber laser

Huaiqin Lin, Yujun Feng, Yutong Feng, Pranabesh Barua, Jayanta Sahu, and Johan Nilsson

Doc ID: 324633 Received 21 Feb 2018; Accepted 16 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: A continuous-wave erbium-doped ytterbium-free fiber laser generates a record-breaking pump-power-limited output power of 656 W at ~1601 nm when cladding pumped by 0.98-μm diode lasers. The slope efficiency was 35.6% with respect to launched pump power and the beam quality factor (M²) was ~10.5. This M²–value excludes a fraction ~25% of the power which emerged from the cladding, which we attribute in part to mode-coupling between the 146-μm core and 700-μm inner cladding. Whereas these parameters are adequate for in-band tandem-pumping of Tm-doped fiber lasers, we predict that an output power of over 1 kW is possible by pumping with state-of-the-art 0.98-μm diode lasers, even with a smaller core that allows for improved beam quality.

Controllable coherent backscattering of light in disordered media filled with liquid crystal

Jose Trull, Marc Cuevas, Josep Salud, Crina Cojocaru, and David López

Doc ID: 326070 Received 14 Mar 2018; Accepted 16 Apr 2018; Posted 17 Apr 2018  View: PDF

Abstract: We have investigated multiple scattering of light in a disordered system based on liquid crystals for a temperature-controllable random laser. Coherent backscattering measurements at several temperatures have been well fitted by the theoretical model deduced for a random collection of spherical point scatters based on a diffusion approximation. The transport mean free path exclusively depends upon the diffusivity of the liquid crystalline phase of the hybrid scattering system. It is shown how the laser threshold excitation intensity is strongly correlated with the transport mean free path.

Thermo-optic soliton routing in nematic liquid crystals

Armando Piccardi, Ula Laudyn, Michal Kwasny, Miroslaw Karpierz, and Gaetano Assanto

Doc ID: 322957 Received 13 Feb 2018; Accepted 16 Apr 2018; Posted 17 Apr 2018  View: PDF

Abstract: We demonstrate thermo-optic control on the propagationof optical spatial solitons in nematic liquid crystals.By varying the sample temperature, both linearand nonlinear optical properties of the reorientationalmaterial are modulated by acting on the refractive indices,the birefringence and the elastic response. Asa result, both trajectory and transverse confinement ofspatial solitons can be adjusted, demonstrating an effectivemeans to tune and readdress self-induced opticalwaveguides.

Optical comb for generation of continuously tuneable coherent THz signal from 122.5 GHz to 2.7 THz

Lalitha Ponnampalam, Martyn Fice, Haymen Shams, Cyril Renaud, and Alwyn Seeds

Doc ID: 322635 Received 08 Feb 2018; Accepted 16 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: We present a continuously tuneable optical frequency comb generator (OFCG), with comb lines spanning over 3.8 THz, the widest span yet reported for a single phase modulator OFCG system. The line spacing, exactly determined by a microwave reference, can be continuously tuned, and by heterodyning two lines enables the generation of a continuously tuneable electrical signal from 122.5 GHz to >2.7 THz. The composite noise of the heterodyne between two lines has been measured up to a record frequency of 300 GHz, and is -75 dBc/Hz at 10 kHz offset at 300 GHz, limited by the multiplied phase noise of the reference synthesizer.

Resonance-domain diffractive lens for the terahertz region

Christian Nadell, Kebin Fan, and Willie Padilla

Doc ID: 325272 Received 02 Mar 2018; Accepted 15 Apr 2018; Posted 16 Apr 2018  View: PDF

Abstract: Diffractive optics have long served as the basis of spectroscopicmeasurements of materials. Operation inthe resonance domain further allows these elements toachieve high efficiency and polarization control. Effectivemedium theory is a practical tool for modelingsuch optics, and here we extend use of this theory tothe terahertz (THz) region, experimentally demonstratingan all-dielectric binary off-axis diffractive lens. Weachieve a high efficiency, polarization independent opticwhich both focuses and disperses THz light, suggestingpotential applications in pharmaceutical, security,and semiconductor imaging

Spectroscopic properties and continuous wave deep-red laser operation of Eu3+-doped LiYF4

Maxim Demesh, Anatol Yasukevich, Viktor Kisel, Alexei Kornienko, Elena Dunina, Valentin Orlovich, Vladimir Dashkevich, Elena Castellano-Hernández, Christian Kraenkel, and Nikolai Kuleshov

Doc ID: 326022 Received 14 Mar 2018; Accepted 13 Apr 2018; Posted 17 Apr 2018  View: PDF

Abstract: Eu3+-doped LiYF4 is reexamined as a laser material for the visible spectral region. Polarized absorption and emission cross sections as well as the fluorescence lifetime are determined. Branching ratios and radiative lifetime are calculated within the theory of 4f-4f transition intensities which takes into account the influence of an excited configuration of the opposite parity 4fN-15d. CW laser operation at 702 nm is demonstrated with a maximum output power of 15 mW and a slope efficiency of 4.6% under pumping with a frequency doubled Ti:sapphire laser at 393.5 nm.

Out-of-plane band structure of a two-dimensional dispersive photonic crystal

Jesús Valenzuela-Sau and Raul Garcia-Llamas

Doc ID: 325983 Received 13 Mar 2018; Accepted 13 Apr 2018; Posted 16 Apr 2018  View: PDF

Abstract: We calculated the out-of-plane band structure of a two-dimensional photonic crystal (PC). To achieve this goal, the Plane Wave Expansion Method (PWEM) was implemented in conjunction with a novel numerical algorithm; the Dispersive Photonic Crystal Iterative Method (DPCIM). The PC is a circular cross section dispersive MgO Lorentz single-pole rods in square lattice. The frequency bands are calculated starting at Γ as function of the oblique component of the wave vector; γ. For the lowest frequencies, it was found that the modes bend drastically to the horizon as the dielectric constant, ɛ(ω), is increased to a very positive value. For frequencies above the longitudinal optical phonon circular frequency, where ɛ(ω) has very low positive values, the modes show a low dispersive behavior, the expected degeneration occurs in the transparency window, ɛ (ω) ~1, and a line of modes behave close to the line of light.

Inverse prism based on temporal discontinuity andspatial dispersion

Alireza Akbarzadeh, Nima Chamanara, and Christophe Caloz

Doc ID: 321063 Received 31 Jan 2018; Accepted 13 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: We introduce the concept of the inverse prism asthe dual of the conventional prism and deducefrom this duality an implementation of it based ontemporal discontinuity and spatial dispersion providedby anisotropy. Moreover, we show that thisinverse prism exhibits the following three uniqueproperties: chromatic refraction birefringence,ordinary-monochromatic and extraordinary polychromatictemporal refraction, and linear to-Lissajous polarization transformation.

Experimental demonstration of beacon-less beam displacement tracking for an orbital-angular-momentum-multiplexed free-space optical link

Long Li, Runzhou Zhang, Guodong Xie, Yongxiong Ren, Zhe Zhao, Zhe Wang, Cong Liu, haoqian song, Kai Pang, Robert Bock, Moshe Tur, and Alan Willner

Doc ID: 325093 Received 05 Mar 2018; Accepted 12 Apr 2018; Posted 18 Apr 2018  View: PDF

Abstract: In this letter, we experimentally demonstrate beacon-less beam displacement tracking for a free-space optical communication link multiplexing multiple orbital-angular-momentum (OAM) beams, where the data-carrying OAM beams themselves are used for position detection. In our demonstration, 400-Gbit/s data transmission is achieved under emulated lateral displacement of up to ±10 mm with power penalties of less than 3 dB for all channels. Channel crosstalk is reduced by the beam tracking system to below -18 dB. Moreover, we investigate using a Gaussian-beacon for beam displacement tracking, and achieve similar channel crosstalk and power penalties compared with using the beacon-less beam tracking.

Intrinsic bias in Fisher Information calculations formulti-mode image registration

David Tyler

Doc ID: 324849 Received 28 Feb 2018; Accepted 12 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: To address the need for quantitative analysis of imageprocessing and optical requirements in multi-modeimaging systems, such as multi-spectral and polarimetricimagers, I have developed a Fisher Information matrixto quantify errors in estimating the shift betweentwo images with non-transformational feature differences.If images of same field have differences not attributableto a geometric transformation, uncertainty inestimating the parameters of the transformation willbe increased by intrinsic bias; or bias inherent in thedata itself, as opposed to bias originating in the estimationalgorithm. The approach to shift-estimation erroranalysis described in this Letter accounts for intrinsicbias, has intuitively-expected properties, and givenplanned system sensitivity and operating conditions,can be used with simulated imagery to bound imageregistration error and develop realistic requirements.

Record Fifth-Harmonic–Generation Efficiency Producing 211-nm, Joule-Level Pulses Using Cesium Lithium Borate

Ildar Begishev, Jake Bromage, Steven Yang, Philip Datte, Siddharth Patankar, and Jonathan Zuegel

Doc ID: 328182 Received 12 Apr 2018; Accepted 12 Apr 2018; Posted 25 Apr 2018  View: PDF

Abstract: The fifth harmonic of a pulsed Nd:YLF laser has been realized in a cascade of nonlinear crystals with a record efficiency of 30%. Cesium lithium borate is used in a Type-I configuration for sum-frequency mixing of 1053 nm and 266 nm, producing 211-nm pulses. Flattopped beam profiles and pulse shapes optimize efficiency. Energies of the fifth harmonic up to 335 mJ in 2.4 ns pulses were demonstrated.

Raman Scattering Enhancement of a Single ZnO Nanorod Decorated with Ag Nanoparticles: Synergies of Defects and Plasmons

Ruibin Lin, Liang Hu, Jinzhang Wang, Wenjing Zhang, Shuangchen Ruan, and Yujia Zeng

Doc ID: 326030 Received 14 Mar 2018; Accepted 11 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Surface enhanced Raman scattering (SERS) of a single ZnO nanorod (NR) is demonstrated by coating with Ag nanoparticles (NPs). An enhancement factor of 4.4×102 and 3.9×101 has been obtained for E2 (high) mode (437cm-1) and A1 (TO) mode (378 cm-1), respectively. Electron paramagnetic resonance (EPR) measurements reveal an unintentional donor state in ZnO NRs. The enhancement of deep-level emission and micro-absorption mapping of a single ZnO NR further confirm the presence of the donor state. The SERS is believed to result from the charge transfer (CT) between ZnO NRs and Ag NPs, which can be enhanced by the empty donor state in ZnO. Finally, single ZnO NRs coated with Ag can be used as good SERS substrates for R6G molecules. This study highlights the interaction between point defects and SERS effect down to a single semiconductor NR.

Transition of Fabry-Perot and antiresonant mechanisms via a SMF-Capillary-SMF structure

Xiaobei Zhang, Haiyang Pan, Huawen Bai, Ming Yan, Jiawei Wang, Deng Chuanlu, and Tingyun Wang

Doc ID: 325885 Received 12 Mar 2018; Accepted 10 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: In this paper, we investigate the transition of the well-known Fabry-Perot (FP) and antiresonant (AR) mechanisms via a single mode fiber (SMF)-capillary-SMF structure. The critical length for this transition is analytically found as a linear relation with the capillary inner diameter based on the ray optic method, which shows the agreement with both numerical simulations and experiments. Evolutions of the transmission and reflection spectra verify that FP and AR mechanisms are close related to the critical length. Observed AR envelope modulated by the FP mechanism in the reflection strengthens gradually with the increase of the capillary length, which is expected to be a novel method for potential applications in multi-parameters sensing because of its combined mechanisms. The transition and critical length can be also found and explained using the same method in other types of AR fibers or waveguides with a hollow core.

Wideband tunable optoelectronic oscillator based on microwave photonic filter with ultra-narrow passband

Haitao Tang, Yuan Yu, Ziwei Wang, Xu Lu, and Xinliang Zhang

Doc ID: 326254 Received 20 Mar 2018; Accepted 10 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: A novel wideband tunable optoelectronic oscillator based on microwave photonic filter (MPF) with ultra-narrow passband is proposed and experimentally demonstrated. The single passband MPF is realized by cascading a MPF based on the stimulated Brillouin scattering and an infinite impulse response (IIR) MPF based on active fiber recirculating delay loop. The measured full width at half maximum bandwidth of the cascaded MPFs is 150 kHz. To the best of my knowledge, this is the first time to realize such a narrow passband in single passband MPF. The oscillation frequency of the OEO can be tuned from 0 to 40 GHz owing to the wideband tunability of the MPF. Thanks to the ultra-high mode selectivity of the IIR filter, the mode hopping is successfully suppressed. A stable microwave signal at 8.18 GHz is obtained with phase noise of -113 dBc/Hz at 10 kHz and the side mode noise is below -95 dBc/Hz. The signal-to-noise ratio exceeds 50 dB during the tuning process

Universal holonomic single quantum gates over a geometric spin with phase-modulated polarized light

Naoki Ishida, Takaaki Nakamura, Touta Tanaka, Shota Mishima, Hiroki Kano, Ryota Kuroiwa, Yuhei Sekiguchi, and Hideo Kosaka

Doc ID: 325683 Received 16 Mar 2018; Accepted 10 Apr 2018; Posted 16 Apr 2018  View: PDF

Abstract: We demonstrate universal non-adiabatic non-abelian holonomic single quantum gates over a geometric electron spin with phase-modulated polarized light and 93% average fidelity. This allows purely geometric rotation about an arbitrary axis by any angle defined by light polarization and phase using a degenerate three-level Λ-type system in a negatively-charged nitrogen-vacancy center in diamond. Since the control light is completely resonant to the ancillary excited state, the demonstrated holonomic gate is not only fast with low power, but also precise without the dynamical phase being subject to control error and environmental noise. It thus allows pulse shaping for further fidelity.

Photon statistics as an interference phenomenon

Thomas Mehringer, Simon Mährlein, Joachim von Zanthier, and Girish Agarwal

Doc ID: 320069 Received 31 Jan 2018; Accepted 10 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Interference of light fields, first postulated by Young in 1801, is one of the fundamental pillars of physics. Dirac extended this observation later to the realm of the quantum world by stating that each photon interferes only with itself. A precondition for interference to occur is that no welcher-weg information labels the paths the photon takes, otherwise the interference vanishes. This remains true even if two-photon interference is considered as, e.g., in the Hong-Ou-Mandel-experiment. Here, the two photons interfere only if they are indistinguishable in frequency, momentum, polarization and time.Less known is the fact that two-photon interference and photon indistinguishability also determines the photon statistics in the overlapping light fields of two independent sources.As a consequence, measuring the photon statistics in the far field reveals the degree of indistinguishability of photons emitted by independent sources. In this letter, we first prove this statement theoretically using a quantum mechanical treatment. We then demonstrate the result with a simple experimental setup consisting of two statistically independent thermal light sources with adjustable polarizations. We find that the photon statistics varies indeed as a function of the polarization settings, the latter determining the degree of welcher-weg information of the photons emanating from the two sources.

Dielectric-mirror-less femtosecond optical parametric oscillator with ultrabroad-band tunability

Jintao Fan, CHENGLIN Gu, Jun Zhao, Ruoyu Liao, Yuxi Chu, Lu Chai, Qingyue Wang, and Ming-lie Hu

Doc ID: 320777 Received 01 Feb 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: We demonstrate a high average power, widely tunable, dielectric-mirror-less optical parametric oscillator (OPO) based on MgO:PPLN, which is synchronously pumped by a 1040 nm femtosecond fiber laser. The OPO does not require any dielectric coating mirrors. By exploiting the four-prism-sequence-system combined with the gold mirrors, the oscillating laser pulses could span the spectral regions both in the signal and idler, the outputpulses of OPO can be tuned across 1367—1914 nm in the signal, and 2152—4480 nm in the idler as well. This device can deliver as much as 1.2 W of average power at 1482 nm in the signal and up to 411 mW at 3487 nm inthe idler, respectively. The ultrabroad-band spectra tunability, along with the high average output property makes the dielectric-mirror-less OPO an attractive alternative to the conventional OPOs.

Microwave photonics instantaneous frequency measurement receiver based on Sagnac Loop

Hossein Emami, Mohammadreza Hajihashemi, Sayyed Alavi, and abu sahmah m supa'at

Doc ID: 323487 Received 19 Feb 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: A microwave photonics instantaneous frequency measurementreceiver was conceived and practicallydemonstrated. The systems is based on phase modulationinside a Sagnac loop and therefore needs nobias voltage resulting in no DC bias drifts. The systemprovides a DC output whose amplitude is a function of input RF signal and thus no high-frequency photo-detector is required. Furthermore, the system exhibits a very good sensitivity without the aid of any sort of electrical noise cancellation techniques such as lock-in amplification. This makes the system response faster which would be another benefit for electronic warfare applications. Less than 6% measurement error was achieved over a 0.01-40 GHz frequency range for -30 dBm RF level. Also, a -51 dBm sensitivity was obtained accepting a 10% error.

Dispersion Tuning in Sub-Micron Tapers for Third Harmonic and Photon Triplet Generation

Jonas Hammer, Andrea Cavanna, Riccardo Pennetta, Maria Chekhova, Philip Russell, and Nicolas Joly

Doc ID: 325649 Received 08 Mar 2018; Accepted 09 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: Precise control of the dispersion landscape is of crucial importance if optical fibers are to be successfully used for generation of three-photon states of light – the inverse of third harmonic generation. Here we report gas-tuning of intermodal phase-matched third-harmonic generation in sub-micron-diameter tapered optical fiber. By adjusting the pressure of the surrounding argon gas up to 50 bar, intermodally phase-matched third harmonic light can be generated for pump wavelengths within a 15 nm range around 1.38 µm. We also measure the infrared fluorescence generated in the fiber when pumped in the visible and estimate that the accidental coincidence rate in this signal is lower than the predicted detection rate of photon triplets.

A 45 fs Diode-Pumped Yb:CALGO Laser Oscillator With 1.7 MW of Peak Power

Arkady Major and Sujith Manjooran

Doc ID: 326251 Received 16 Mar 2018; Accepted 09 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: A high power sub-50 fs diode-pumped Yb:CALGO laser oscillator was demonstrated. The peak power achieved for 45 fs pulses directly from the oscillator was 1.7 MW. We believe that this is the highest peak power in the sub-50 fs pulse regime that was ever produced directly from any diode-pumped Yb-ion-doped laser oscillators to date. The shortest generated pulses were 38 fs long with 187 kW of peak power.

Compact, circular, and optically stable multipass cell for mobile laser absorption spectroscopy

Manuel Graf, Bela Tuzson, and Lukas Emmenegger

Doc ID: 326235 Received 16 Mar 2018; Accepted 09 Apr 2018; Posted 18 Apr 2018  View: PDF

Abstract: Compact and lightweight laser absorption spectrometers for accurate trace gas measurements are of great scientific and commercial importance. In these instruments, the multipass cell (MPC) represents a critical element in terms of achievable size and sensitivity. Herein, we introduce a versatile MPC-concept that unifies compactness, mechanical rigidity, and optical stability. Relying on fundamental cavity design principles and modern diamond turning techniques, we have developed a segmented circular MPC allowing efficient and interference-free beam folding. A protoype cell is presented that features up to 10 m optical path length at a total mass of less than 200 g. Incorporated in a highly compact setup without any beam pre-shaping optics, we demonstrate a normalized noise level of low 10-⁴ (2σ) at 1 Hz.

Fabrication and optical properties of Pr3+ doped Ba (Sn, Zr, Mg, Ta) O3 transparent ceramic phosphor

Zicheng Wen, Chaoyang Ma, chong zhao, Fei Tang, Zhijun Cao, Zhiquan Cao, xuanyi yuan, and yongge cao

Doc ID: 326511 Received 30 Mar 2018; Accepted 09 Apr 2018; Posted 18 Apr 2018  View: PDF

Abstract: A novel transparent ceramic phosphor of Pr3+ doped Ba (Sn, Zr, Mg, Ta) O3 (Pr3+: BMT) were successfully fabricated via high temperature solid-state reaction method. The in-line transmittance of 59% at 650 nm was measured. The Pr3+: BMT ceramic phosphor can emit 650nm red light excited by 447nm blue light. The ceramic phosphor can still work at 383K. The activation energy was calculated to be 0.17 eV. The efficiency of the ceramic phosphor is twice as much as that of its powder phosphor. The Pr3+: BMT ceramic phosphor showed good thermal stability and enhanced the chromaticity of its white LEDs, which make it a promising red phosphor for lighting.

Polymer/silica hybrid integration add-drop filter based on grating-assisted contradirectional coupler

Liang Tian, Fei Wang, Yuanda Wu, Yi Yunji, Xiaoqiang Sun, and Da-Ming Zhang

Doc ID: 325104 Received 15 Mar 2018; Accepted 09 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: A polymer/silica hybrid integration add-drop filter based on grating-assisted contradirectional coupler fabricated through simple and low-cost contact lithography is proposed. First, the structure pattern of the add-drop filter was formed in the silica cladding layer by contact lithography and inductively coupled plasma (ICP) etching. Then, a SU-8 film was fabricated on top of it by spin-coating method, and an inverted-rib waveguide was formed. Next, the slab layer of the inverted-rib waveguide was removed by ICP etching. We observe a rejection band with an extinction ratio of 13 dB and a 3-dB bandwidth of 0.6 nm at a wavelength of 1509.4 nm from the through port, and a pass band with a side-mode suppression ratio of 12 dB and a 3-dB bandwidth of 0.5 nm at a wavelength of 1509.4 nm from the drop port. The shift of the pass band with temperature over the range 25–55 °C is approximately 4.8 nm. This temperature dependence exhibits an average slope of -0.16 nm/°C.

Exact calculation of the nonlinear characteristics of 2D isotropic and anisotropic nonlinear slot waveguides

Mahmoud Elsawy and Gilles Renversez

Doc ID: 325569 Received 08 Mar 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: We use our vector Maxwell’s nonlinear eigenmodesolver to study the stationary solutions in 2D cross-section plasmonic slot waveguides with isotropic andanisotropic Kerr nonlinear cores. First, for the isotropiccase, we demonstrate that, even in the low powerregime, 1D studies may not provide accurate and meaningful results compared to 2D ones. Second, we studyincluding at high powers the link between the nonlinear parameter γ nl and the change of the nonlinear propagation constant ∆β. Third, we demonstrate that our approach is also valid for anisotropic waveguides, and we show how to improve by a factor two the figure of meritof nonlinear plasmonic slot waveguides using realisticmaterials.

High-power, continuous-wave, tunable mid-IR, higher-order vortex beam optical parametric oscillator

A. Aadhi, Varun Sharma, and Goutam K. Samanta

Doc ID: 325665 Received 08 Mar 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: We report on a novel experimental scheme to generate continuous-wave (cw), high power, and higher-order optical vortices tunable across mid-IR wavelength range. Using cw, two-crystal, singly resonant optical parametric oscillator (T-SRO) and pumping one of the crystals with Gaussian beam and the other crystal with optical vortices of orders, lp = 1 to 6, we have directly transferred the vortices at near-IR to the mid-IR wavelength range. The idler vortices of orders, li = 1 to 6, are tunable across 2276–3576 nm with a maximum output power of 6.8 W at order of, li = 1, for the pump power of 25 W corresponding to a near-IR vortex to mid-IR vortex conversion efficiency as high as 27.2%. Unlike the SROs generating optical vortices restricted to lower orders (≤2) due to the elevated operation threshold of SRO with higher order pump vortices, here, the coherent energy coupling between the resonant signals of two crystals of T-SRO facilitates the transfer of pump vortex of any order to the idler wavelength without stringent operation threshold condition. The generic experimental scheme can be used in any wavelength range across the electromagnetic spectrum and in all time scales from cw to ultrafast regime.

Surface plasmon resonance sensing in gaseous media with optical fiber gratings

Alvaro Gonzalez-Vila, Andreas Ioannou, Médéric Loyez, Marc Debliquy, Driss Lahem, and Christophe Caucheteur

Doc ID: 324990 Received 01 Mar 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Surface plasmon resonance excitation with optical fiber gratings has been typically studied in aqueous solutions. This work describes the procedure to excite a plasmon wave in gaseous media and perform refractive index measurements in these environments. Grating photo-inscription with 193 nm excimer laser radiation allows to obtain slightly tilted fiber Bragg gratings exhibiting a cladding mode resonance comb along several hundreds of nm. Their refractive index sensitive range extends from gases to liquids, so operation in both media is compared. We demonstrate that the thickness of the metal coating required for surface plasmon excitation in gases is roughly one third of the one usually used for liquids. The developed platforms exhibit a temperature insensitive response of 78 nm/RIU when tested with different gases.

Photonic analog-to-digital conversion using red frequency chirp in a quantum-dot semiconductor optical amplifier

Motoharu Matsuura, Takuya Okada, and Hiroki Hoshino

Doc ID: 325203 Received 01 Mar 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: A photonic analog-to-digital conversion (PADC) based on intensity-to-frequency conversion using frequency chirp in a quantum-dot semiconductor optical amplifier (QD-SOA) is proposed. The presented PADC has a simple scheme whereby optical quantization is achieved using a single QD-SOA, with multiple rectangular bandpass filters placed in parallel. In this work, we successfully achieve 10-GSamples/s, 8-level optical quantization using a QD-SOA. The PADC also has much lower input signal pulse power requirements for optical quantization, compared with conventional PADCs.

Lineshape-asymmetry elimination in weak atomic transitions driven by an intense standing wave field

Dionysis Antypas, Anne Fabricant, and Dmitry Budker

Doc ID: 325248 Received 15 Mar 2018; Accepted 09 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Owing to the ac-Stark effect, the lineshape of a weak optical transition in an atomic beam can become significantly distorted, when driven by an intense standing wave field. We use an Yb atomic beam to study the lineshape of the 6s2 1S0 → 5d6s 3D1 transition, which is excited with light circulating in a Fabry-Perot resonator. We demonstrate two methods to avoid the distortion of the transition profile. Of these, one relies on the operation of the resonator in multiple longitudinal modes, and the other in multiple transverse modes.

Refractive index sensing by Brillouin scattering in side-polished optical fibers

Romeo Bernini, Gianluca Persichetti, Ester Catalano, Luigi Zeni, and Aldo Minardo

Doc ID: 320437 Received 24 Jan 2018; Accepted 09 Apr 2018; Posted 12 Apr 2018  View: PDF

Abstract: In this paper, we demonstrate the possibility to measure the refractive index of a liquid, using the stimulating Brillouin scattering in a 3cm-long side-polished optical fiber. In addition, we show that, depositing a high-refractive index layer on the polished surface, the sensitivity of the Brillouin frequency shift (BFS) can be increased thanks to a higher penetration of the evanescent field in the outer medium. Experiments show a maximum BFS change of about 11 MHz when varying the refractive index of the external medium from 1 (air) to 1.402, and a BFS sensitivity to refractive index of about 293 MHz/RIU around 1.40.

1.8mJ, 3.5kW single frequency optical pulses at 1572nm generated from an all-fiber MOPA system

Wangkuen Lee, Jihong Geng, Shibin Jiang, and Anthony Yu

Doc ID: 321046 Received 31 Jan 2018; Accepted 09 Apr 2018; Posted 12 Apr 2018  View: PDF

Abstract: High energy single frequency optical pulses at 1572nm were generated from an all-fiber MOPA system for atmospheric CO2 LIDAR system application. We report experimental demonstration of 1.8mJ, peak power of 3.5kW at the pulse repetition of 2.5 kHz, as well as 1.3mJ, peak power of 2.5kW at the pulse repetition of 7.5 kHz single frequency optical pulses at 1572nm using single-mode large core polarization maintaining Er-Yb co-doped silicate glass fiber amplifiers pumped at 976nm. To our best knowledge, this is the highest pulse energy of single frequency at 1572nm from an all-fiber amplifier system.

Photoluminescence enhancement in metallodielectric-capped non-polar ZnO films

YONGHUI ZHOU, Shanshan Chen, Xinhua Pan, and Zhizhen Ye

Doc ID: 322570 Received 06 Feb 2018; Accepted 09 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: Non-polar ZnO thin films were grown on m-plane sapphire substrates by plasma-assisted molecular beam epitaxy. Emission enhancement from non-polar ZnO thin films coated with Al/AlOx has been studied by photoluminescence spectroscopy. AlOx has been used to mediate the surface plasmons (SPs) energy of Al nanoparticles. Taking advantage of the resonant coupling between UV emission of non-polar ZnO film and Al nanoparticle SPs, a 84-fold enhancement of the UV emission and a 8.3-fold enhancement of internal quantum efficiency (ηint) have been achieved under the optimized sputtering time and energy of SPs.

Controlling the Degree of Polarization of Partially Coherent Electromagnetic Beams with Lenses

Taco Visser, Govind Agrawal, and Xinying Zhao

Doc ID: 324583 Received 20 Feb 2018; Accepted 08 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: We show theoretically that the degree of polarization of a partially coherent electromagnetic beam changes dramatically as the beam is being focused. A low numerical aperture lens can considerably enhance the degree of polarization at its geometrical focus. When two identical lenes are employed in a 4f configuration, the degree of polarization of a beam can be tailored by using amplitude masks in the Fourier plane located in the middle of the two lenses. Our findings open up the possibility to control this fundamental property of random beams in a simple manner.

Charge compensation effects of Yb3+ on the Bi+: near-infrared emission in PbF2 crystal

Peixiong Zhang, Nan Chen, Rui Wang, Xingbin Huang, Siqi Zhu, Zhen Li, Hao Yin, and Zhenqiang Chen

Doc ID: 326283 Received 19 Mar 2018; Accepted 08 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: The used of Yb3+ codoping for enhancing the near infrared (NIR) emission in Bi, Yb codoped PbF2 crystal was investigated for the first time, to the best of our knowledge. The NIR and visible fluorescence emission properties of the as-grown crystals were investigated in details. It is found that the Yb3+ ion can act as an effective charge compensated ion to bring about the conversion from Bi2+ to Bi+, enhancing the NIR fluorescence emission in Bi:PbF2 crystal. Moreover, the NIR fluorescence emission peaking at around 1090 and 1485 nm were demonstrated to be two different Bi+ related centers, Bi(I) and Bi(II), respectively. These results suggest that Bi, Yb codoped PbF2 crystal may become an attractive gain material for developing NIR broadband lasers under the pump of different wavelengths.

Partially coherent sources with radial coherence

Gemma Piquero, Massimo Santarsiero, Rosario Martinez-Herrero, Juan Carlos de Sande, Massimo Alonzo, and Franco Gori

Doc ID: 325575 Received 07 Mar 2018; Accepted 08 Apr 2018; Posted 13 Apr 2018  View: PDF

Abstract: Partially coherent sources with radial coherence are proposed. They present a circularly symmetric intensity profile and a degree of coherence whose absolute value only depends on the angular difference between the two considered points. In particular, the source is completely coherent at pairs of points belonging to the same radius. The modal structure of such sources is determined in the general case, and conditions are derived under which the field propagated in paraxial approximation remains radially coherent at any transverseplane.In such cases, the angular dependence of the correlation function is preserved upon propagation, although the intensity profile generally changes.An example of this kind of sources has been experimentally synthesizedby means of a simple set up and its coherence characteristics have been tested by means of a Young interferometer.

In Vivo Time Gated Diffuse Correlation Spectroscopy at Null Source-Detector Separation

Marco Pagliazzi, Sanathana Konugolu Venkata Sekar, Laura Di Sieno, lorenzo colombo, Turgut Durduran, Davide Contini, Alessandro Torricelli, Antonio Pifferi, and Alberto Dalla Mora

Doc ID: 321030 Received 12 Feb 2018; Accepted 07 Apr 2018; Posted 18 Apr 2018  View: PDF

Abstract: We demonstrate time domain diffuse correlation spectroscopy at null source-detector separation by using a fast time-gated single-photon avalanche diode (SPAD) without the need of a time-tagging electronics. This approach allows for increased photon collection, simplified real time instrumentation and reduced probe dimensions. Depth discriminating, null-distance measurement of blood flow in a human subject is presented. We envision the miniaturization and integration of matrices of optical sensors of increased spatial resolution and the enhancement of the contrast of local blood flow changes.

Two-pole microring weight banks

Alexander Tait, Allie Wu, Thomas Ferreira de Lima, Mitchell Nahmias, Bhavin Shastri, and Paul Prucnal

Doc ID: 319497 Received 29 Jan 2018; Accepted 07 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Weighted addition is an elemental multi-input to single-output operation that can be implemented with high-performance photonic devices. Microring weight banks bring programmable weighted addition to silicon photonics. Prior work showed that their channel limits are affected by coherent inter-channel effects that occur uniquely in weight banks. We fabricate two-pole designs that exploit this inter-channel interference in a way that is robust to dynamic tuning and fabrication variation. Scaling analysis predicts a channel count improvement of 3.4-fold, substantially greater than predicted by incoherent analysis used in conventional microring devices. Advances in weight bank design expand the potentials of reconfigurable analog photonic networks and multi-channel microwave photonics.

Sparsity-Based Reconstruction for Super-Resolved Limited-View Photoacoustic Computed Tomography Deep in a Scattering Medium

David Egolf, Ryan Chee, and Roger Zemp

Doc ID: 324989 Received 08 Mar 2018; Accepted 07 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: Delay-and-sum beamforming (DSB) of photoacoustic data does not incorporate a priori spatial sparsity of the imaging target. By incorporating this information into beamforming for limited-view photoacoustic computed tomography, we experimentally obtained enhanced resolution images of wires at a depth of 8.5 mm in a tissue mimicking scattering medium. Using a 21 MHz transducer, we improved resolution from the 200-250 μm achieved by DSB to 75 μm. After applying smoothing, the full width at half maximum (FWHM) of the sparsity-based technique was roughly 25 μm and 10 μm in the lateral and axial directions, much smaller than the 180 μm and 120 μm lateral and axial FWHM's of DSB.

Parallel sorting of orbital and spin angular momenta of light in record large number of channels

Gary Walsh, Luciano De Sio, David Roberts, Nelson Tabiryan, Francisco Aranda, and Brian Kimball

Doc ID: 326151 Received 15 Mar 2018; Accepted 06 Apr 2018; Posted 06 Apr 2018  View: PDF

Abstract: Parallel sorting of orbital and spin angular momentum components of structured optical beams is demonstrated. Both spin channels are multiplexed within the novel orbital angular momentum sorter reducing size, weight, and number of elements. Sorted states are linearly spaced over 70 topological charge values. We experimentally and theoretically evaluate operational range and crosstalk between neighboring channels and find 30 orbital angular momentum states are available per spin channel for quantum communication or cryptography. This is achieved using an angular momentum sorter we developed based on geometric phase optical elements. We present two devices consisting of liquid crystal polymer films photoaligned with complex two-dimensional patterns. The components show 96% diffraction efficiency.

A new auto-focus and reconstruction method based on connected domain

Haiyan Ou, Wu Yong, Edmund Lam, and Wang Bing-Zhong

Doc ID: 318868 Received 05 Jan 2018; Accepted 06 Apr 2018; Posted 06 Apr 2018  View: PDF

Abstract: In this letter, we propose a new method for autofocusing and reconstruction without defocus noise in optical scanning holography. By using connected domain (CD) to calculate the area of different domains, which are labeled by connected component (CC), the focus distance can be found via certain criteria. Meanwhile, the sectional images without defocus noise can also be reconstructed based on the labeled domains. The effectiveness of this method has been verified with simulation and experiments.

Chemical elemental analysis of single acoustic-levitated water droplets by laser-induced breakdown spectroscopy

Victor Contreras Loera, Ricardo Valencia, Jairo Peralta, Hugo Sobral, Marco Antonio Meneses-Nava, and Horacio Martinez

Doc ID: 324870 Received 27 Feb 2018; Accepted 05 Apr 2018; Posted 06 Apr 2018  View: PDF

Abstract: Laser Induced Breakdown Spectroscopy is presented for trace element detection of liquid samples by analyzing a single droplet levitated by ultrasonic waves. A single liquid droplet is placed in the node of a standing acoustic wave produced by a uniaxial levitator for further chemical analysis. The acoustic levitator consists on a commercial Langevin type transducer, attached to a concave mechanical amplifier, and a concave reflector. A micro-syringe was used to manually place individual liquid droplet samples in the acoustic levitation system. For chemical analysis, a laser-induced plasma is produced by focusing a single laser pulse on the levitated water-droplet after it partially dries. The performance of the acoustic levitator on micron-size droplets is discussed and the detection of Ba, Cd, Hg and Pb at ppm (mg/L) and sub-ppm levels is reported. The process, starting from placing the sample in the acoustic levitator and ending on the chemical identification of the traces, takes few minutes. The approach is particularly interesting in applications demanding limited volumes of liquid samples and relative simple and inexpensive techniques.

Focusing Short-Wavelength Surface Plasmons by a Plasmonic Mirror

Erdem Ogut, Cenk Yanik, Ismet Kaya, Cleva Ow-Yang, and Ibrahim Sendur

Doc ID: 325714 Received 09 Mar 2018; Accepted 05 Apr 2018; Posted 06 Apr 2018  View: PDF

Abstract: Emerging applications in nanotechnology, such as super-resolution imaging, ultra-sensitive biomedical detection, and heat-assisted magnetic recording require plasmonic devices that can generate intense optical spots beyond the diffraction limit. One of the important drawbacks of surface plasmon focusing structures is their complex design, which is significant for ease of integration with other nanostructures and fabrication at low-cost. In this study, a planar plasmonic mirror is investigated that can focus surface plasmons to produce intense optical spots having lateral and vertical dimensions of λ/9.7 and λ/80, respectively. Intense optical spots beyond the diffraction limit were produced from the plasmonic parabolic mirror by exciting short-wavelength surface plasmons. The refractive index and numerical aperture of the plasmonic parabolic mirror were varied to excite short-wavelength surface plasmons. Finite-element method simulations of the plasmonic mirror, and scanning near-field optical microscopy experiments have shown very good agreement.

Strong confinment of optical fields using localized surface phonon polaritons in cubic boron nitride

Ioannis Chatzakis, ATHITH KRISHNA, JAMES CULBERSTON, NICHOLAS SHARAC, ALEXANDER GILES3, MICHAEL SPENCER, and Joshua Caldwell

Doc ID: 322634 Received 14 Feb 2018; Accepted 05 Apr 2018; Posted 05 Apr 2018  View: PDF

Abstract: Phonon polaritons (PhPs) are long-lived electromagnetic modes that originate from the coupling of infrared photons with the bound ionic lattice of a polar crystal. Cubic-Boron nitride (cBN) is such a polar, semiconductor material, which due to the light atomic masses can support high frequency optical phonons. Here, we report on random arrays of cBN nanostructures fabricated via an unpatterned reactive ion etching process. FTIR reflection spectra suggest the presence of localized surface PhPs within the Reststrahlen band, with quality factors in excess of 38 observed. These can provide the basis of next generation infrared optical components like antennas for communication, improved chemical spectroscopies, and enhanced emitters, sources and detectors.

Nonlinear pulse compression based on a gas-filled multipass cell

Loïc Lavenu, Michele natile, Florent Guichard, Yoann Zaouter, Xavier Delen, Marc Hanna, Eric Mottay, and Patrick Georges

Doc ID: 324809 Received 23 Feb 2018; Accepted 05 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: We demonstrate nonlinear temporal compression of a high energy Yb-doped fiber laser source in a multipass cell filled with argon. The 160 µJ 275 fs input pulses are compressed down to 135 µJ 33 fs at the output, corresponding to an overall transmission of 85%. We also analyze the output beam, revealing essentially no space-time couplings. We believe this technique can be scalable to higher pulse energies and shorter pulse durations, enabling access to a wider parameter range for a large variety of ultrafast laser sources.

Phase-Dependent Laser Acceleration of Electrons with Symmetrically Driven Silicon Dual Pillar Gratings

Kenneth Leedle, Dylan Black, Yu Miao, Karel Urbanek, Andrew Ceballos, Huiyang Deng, James Harris, Olav Solgaard, and Robert Byer

Doc ID: 320534 Received 25 Jan 2018; Accepted 05 Apr 2018; Posted 05 Apr 2018  View: PDF

Abstract: We present the demonstration of phase-dependent laser acceleration and deflection of electrons using a symmetrically driven silicon dual pillar grating structure. We show that exciting an evanescent inverse Smith-Purcell mode on each side of a dual pillar grating can produce hyperbolic cosine acceleration and hyperbolic sine deflection modes, depending on the relative excitation phase of each side. Our devices accelerate sub-relativistic 99.0 keV kinetic energy electrons by 3.0 keV over a 15 μm distance for accelerating gradients of 200 MeV/m with 40 nJ, 300 fs, 1940 nm pulses from an optical parametric amplifier. These results represent a significant step towards making practical dielectric laser accelerators for ultrafast, medical, and high energy applications.

Measurement of differential modal group delay of a few-mode fiber using a Fourier domain mode-locked laser

Deepa Venkitesh, Varun Kelkar, and Smaranika Swain

Doc ID: 323324 Received 16 Feb 2018; Accepted 03 Apr 2018; Posted 03 Apr 2018  View: PDF

Abstract: We propose and experimentally demonstrate a methodfor measuring the differential modal group delay(DMGD) of a few mode fiber using a Fourier domainmode-locked laser (FDML). We use the fast frequency-swept,wavelength-tunable output of the FDML in orderto perform time domain measurements of interferenceof the modes, which is further post processed toextract the DMGD. We demonstrate the measurementof DMGD for a commercial two-mode fiber over the C-band.This method is not limited by the magnitude ofDMGD and the number of modes and is minimally affectedby time-dependent polarization and mode fluctuations,environmental noise and spectral resolution ofinstruments.

Quadrature detection for self‐mixing interferometry

Junfeng Wu and Fengfeng Shu

Doc ID: 324878 Received 01 Mar 2018; Accepted 03 Apr 2018; Posted 03 Apr 2018  View: PDF

Abstract: We establish a new quadrature detection system for self‐mixing interferometry using two photodiodes and a 22.5 degrees rotated beam splitter. The method is based on a rotating beam splitter placed between the laser diode and measured object, and two quadrature self-mixing signals can be obtained. Then an arctangent phase algorithm can be used to demodulate the quadrature signal to acquire the object vibration information. This method simplifies the self-mixing signal demodulation process and allows demodulate the vibrating displacement more easily. Experimental results demonstrate the feasibility of quadrature detection for self-mixing optical measurement. This Letter provides guidance for the design of self‐mixing interferometers.

Integrated all-optical programmable logic array based on semiconductor optical amplifiers

Dong wenchan, Zhuyang Huang, Jie Hou, Rui Santos, and Xinliang Zhang

Doc ID: 325021 Received 05 Mar 2018; Accepted 03 Apr 2018; Posted 03 Apr 2018  View: PDF

Abstract: All-optical programmable logic array (PLA) is one of the most important optical complex logic devices, which can implement combinational logic functions. In this Letter, we propose and experimentally demonstrate an integrated all-optical PLA at the operation speed of 40 Gb/s. The PLA mainly consists of a delay interferometer (DI) and semiconductor optical amplifiers (SOAs) of different lengths. The DI is used to pre-code the input signals and improve the reconfigurability of the scheme. The longer SOAs are nonlinear mediums for generating canonical logic units (CLUs) using four-wave mixing (FWM). The shorter SOAs are used to select out the appropriate CLUs by changing the working states, then reconfigurable logic functions can be output directly. Results show that all the CLUs are realized successfully and the optical signal-to-noise ratios are above 22 dB. The exclusive NOR gate and exclusive OR gate are experimentally demonstrated based on output CLUs.

Observation of an Optical Spring With a Beamsplitter

Jonathan Cripe, Baylee Danz, Benjamin Lane, Mary Lorio, Julia Falcone, Garrett Cole, and Thomas Corbitt

Doc ID: 314774 Received 09 Jan 2018; Accepted 03 Apr 2018; Posted 05 Apr 2018  View: PDF

Abstract: We present the experimental observation of an optical spring without the use of an optical cavity. The optical spring is produced by interference at a beamsplitter and, in principle, does not have the damping force associated with optical springs created in detuned cavities. The experiment consists of a Michelson-Sagnac interferometer (with no recycling cavities) with a partially reflective GaAs microresonator as the beamsplitter that produces the optical spring. Our experimental measurements at input powers of up to 360 mW show the shift of the optical spring frequency as a function of power and are in excellent agreement with theoretical predictions. In addition, we show that the optical spring is able to keep the interferometer stable and locked without the use of external feedback.

A fast and robust standard-deviation based method for bulk-motion compensation in phase-based functional OCT

Xiang Wei, Acner Benech, Shaohua Pi, William Cepurna, David Huang, John Morrison, and Yali Jia

Doc ID: 320185 Received 22 Jan 2018; Accepted 03 Apr 2018; Posted 05 Apr 2018  View: PDF

Abstract: Phase-based optical coherence tomography (OCT), such as OCT angiography (OCTA) and Doppler OCT, is sensitive to the confounding phase shift introduced by subject bulk motion. Traditional bulk motion compensation methods are limited by their accuracy and computing cost-effectiveness. In this paper, we present a novel bulk motion compensation method for phase-based functional OCT. Bulk-motion associated phase shift can be directly derived by solving its equation using standard deviation of phase-based OCTA and Doppler OCT flow signals. This method was evaluated on rodent retinal images acquired by a prototype visible-light OCT and human retinal images acquired by a commercial system. The image quality and computational speed were significantly improved, compared to two conventional phase compensation methods.

Coherence Distance in Indoor Optical Wireless Communication Channels

Dima Bykhovsky

Doc ID: 325894 Received 15 Mar 2018; Accepted 02 Apr 2018; Posted 11 Apr 2018  View: PDF

Abstract: The coherence distance (CD) is the spatial distance over which the channel does not change appreciably. It is a common and important wireless communication channel parameter. While adoption of this parameter in the realm of radio-frequency (RF) is well established, it is a less familiar concept in the realm of optical wireless communication (OWC), where it can be beneficial as a measure for spatial optical channel changes. In this letter, the average coherence distance is proposed as a metric to characterize indoor OWC channels and a method for its evaluation is outlined.

Wide dynamic range high-speed three-dimensional quantitative OCT angiography with hybrid-beam scan

Taejin Park, Sun-Joo Jang, Myounghee Han, Sukyoung Ryu, and Wang-Yuhl Oh

Doc ID: 324790 Received 23 Feb 2018; Accepted 01 Apr 2018; Posted 05 Apr 2018  View: PDF

Abstract: We demonstrate a novel hybrid-beam-scanning-based quantitative optical coherence tomography angiography (OCTA) that provides high-speed wide dynamic range blood flow speed imaging. The hybrid-beam scanning scheme enables multiple OCTA image acquisitions with a wide range of multiple time intervals simultaneously, providing wide dynamic range blood flow speed imaging independent of the blood vessel orientation, which was quantified over a speed range of 0.6 mm/s ~ 104 mm/s through the blood flow phantom experiments. A fully automated high-speed hybrid-beam-scanning-based quantitative OCTA system demonstrates visualization of blood flow speeds in various vessels from main arteries to capillaries in 4 mm x 4 mm area (1024 A-lines x 512 B- scans) in vivo in 20 seconds, showing its potential as a useful imaging tool for various biomedical applications.

Phase imaging and synthetic aperture super-resolutionvia total internal reflection microscopy

Guillaume Maire, Hugues Giovannini, Anne Talneau, Patrick Chaumet, Kamal Belkebir, and Anne Sentenac

Doc ID: 321235 Received 06 Feb 2018; Accepted 31 Mar 2018; Posted 05 Apr 2018  View: PDF

Abstract: Total internal reflection microscopy is mainly used inits fluorescence mode, and is the reference technique toimage fluorescent proteins in the vicinity of cell membranes.Here, we show that this technique can easilybecome a phase microscope by simply detecting the coherentsignal resulting from the interference betweenthe field scattered by the probed sample and the totalinternal reflection. Moreover, combining several illuminationangles permits to generate synthetic aperturereconstructions with improved resolutions compared tostandard label-free microscopy techniques.

Angular momentum switching and orthogonal fieldconstruction of C-points

B.S.Bhargava Ram, Ruchi ., and Paramasivam Senthilkumaran

Doc ID: 322953 Received 09 Feb 2018; Accepted 31 Mar 2018; Posted 03 Apr 2018  View: PDF

Abstract: In this Letter, we take on the non-trivial problem oftransforming a C-point singularity into its orthogonalstate by switching its angular momentum components.For homogeneous distribution, orthogonal transformationis a trivial operation of using a single half-wave plate (HWP). For C-point singularity, this entailschange in the handedness without disturbing the index,followed by rotation of state of polarizations in thedistribution. Swapping the spin angular momentum(SAM) components of C-point singularities leads to indexand handedness inversion. Switching of orbital angularmomentum (OAM) components of C-point can bemade to result only in handedness inversion. We showhere, by changing the SAM and OAM components insequence a C-point can be transformed into its orthogonalstate. While experimentally demonstrating this, wealso show that a spiral phase plate, which is a phaseelement can also perform polarization transformationoperation.

Single-beam spectrally encoded color imaging

Mitsuhiro Ikuta, DongKyun Kang, Dukho Do, Adel Zeidan, and Guillermo Tearney

Doc ID: 325340 Received 05 Mar 2018; Accepted 31 Mar 2018; Posted 11 Apr 2018  View: PDF

Abstract: We have developed a new method of conducting spectrally-encoded color imaging using a single light beam. In the new method, a single broadband light beam was incident on a diffraction grating, where the overlapped 3rd order of the red, 4th order of the green, and 5th order of the blue spectral bands were focused on a line illuminating tissue. This configuration enabled each point on the line to be illuminated by three distinctive wavelengths, corresponding to red, green, and blue. A custom grating was designed and fabricated to achieve high diffraction efficiencies for the wavelengths and diffraction orders used for color spectrally-encoded imaging. A bench system was built to test the new spectrally-encoded color imaging method. For a beam diameter of 174 µm, the bench system achieved 89,000 effective pixels over a 70º circular field. Spectrally-encoded color images of excised swine tissue revealed blood vessels with a similar color appearance to those obtained via a conventional color camera. Results suggest that this single-beam spectrally-encoded color method is feasible and can potentially simplify color spectrally-encoded endoscopy probe designs.

Higher-order cladding mode excitation of femtosecond-laser-inscribed tilted FBGs

Andreas Ioannou, Antreas Theodosiou, Kyriacos Kalli, and Christophe Caucheteur

Doc ID: 325968 Received 13 Mar 2018; Accepted 30 Mar 2018; Posted 05 Apr 2018  View: PDF

Abstract: We study the modal behaviour of plane-by-plane femtosecond laser fabricated tilted fibre Bragg gratings (TFBGs). The focus is made on the differential strain and temperature sensitivities between the cladding mode resonances of a nth grating order and those of the (n-i)th orders (with i=1–n), which are collocated in the same wavelength range. Whereas the Bragg mode exhibits an axial strain sensitivity of 1.2 pm/με, we experimentally show that the strain sensitivity of ultra-high order cladding modes is negative and at -1.99 pm/με in the same spectral window. Using a finite element mode solver, the modal refractive index value is computed to be well below 1, thus confirming that these modes are in reality leaky modes.

Multimilliwatt, tunable, continuous-wave, mid-infrared generation across 4.6-4.7 μm based on orientation-patterned GaP

Kavita Devi, Anuja Padhye, Peter Schunemann, and Majid Ebrahim-Zadeh

Doc ID: 319865 Received 16 Jan 2018; Accepted 30 Mar 2018; Posted 11 Apr 2018  View: PDF

Abstract: We report the generation of tunable continuous-wave (cw) mid-infrared (mid-IR) radiation across 4608-4694 nm using the new nonlinear material, orientation-patterned gallium phosphide (OP-GaP). By exploiting difference-frequency-mixing between a cw Tm-fiber laser and a home-built cw optical parametric oscillator in a 40-mm-long crystal, we have generated up to 43 mW of cw output power, with >30 mW across >95% of the mid-IR tuning range. The output at 4608 nm exhibits high beam quality, with a passive power stability of 2.5% rms over 1.5 mins. The temperature acceptance bandwidth of the OP-GaP crystal has been measured and compared with theory. The performance of the mid-IR source at high pump powers and polarization-dependent transmission in OP-GaP has been investigated.

Dual-channel operation in a synchronously-pumped optical parametric oscillator for generation of broadband mid-infrared coherent light sources

Zhaowei Zhang, Pei Liu, Puyuan He, and Sicong Wang

Doc ID: 326730 Received 23 Mar 2018; Accepted 29 Mar 2018; Posted 05 Apr 2018  View: PDF

Abstract: We report a novel approach for generating broadband mid-infrared (mid-IR) light by implementing a dual-channel scheme in a synchronously-pumped OPO (SPOPO). Two-channel operation was achieved by inserting a prism-pair and two reflection-mirrors inside an OPO cavity. Pumped by a Yb: fiber laser, the OPO generated an idler wave at ~3150 nm with a -10-dB bandwidth of ~13.2 THz, which was twice as much as that of the pump source. This scheme represents a promising technical route to transform conventional SPOPOs into a device capable of generating mid-IR light with very broad instantaneous bandwidth.

Orbital angular momentum transition of light using a cylindrical vector beam

Ya Han, Lei Chen, Yange Liu, Zhi Wang, Hong Zhang, Kang Yang, and Keng Chou

Doc ID: 323421 Received 16 Feb 2018; Accepted 29 Mar 2018; Posted 30 Mar 2018  View: PDF

Abstract: We demonstrate that using a single cylindrical vector (CV) beam in the two-mode fibers, the orbital angular momentum (OAM) of light can be switched among -1, 0, and 1. The input CV beam can be a conventional radial and azimuthal polarization distribution or a generalized CV beam, and we firstly use and verify that a rocking-long period fiber grating generates the tunable generalized CV beam. Because of using a single CV beam as the light source, this approach not only provides an increased stability compared to the conventional superposed eigenmodes method, but also builds a bridge between polarization singularities beam and phase singularities beam.

Optical-resonance-enhanced nonlinearities in aMoS₂-coated single-mode fiber

Haojie Zhang, Noel Healy, Antoine Runge, Chung Che Huang, Daniel William Hewak, and Anna Peacock

Doc ID: 321040 Received 01 Feb 2018; Accepted 27 Mar 2018; Posted 30 Mar 2018  View: PDF

Abstract: Few-layer molybdenum disulfide (MoS₂) has an electronicband structure that is dependent on the numberof layers and is, therefore, a very promising material foran array of optoelectronic, photonic and lasing applications.In this work, we make use of a side-polished opticalfiber platform to gain access to the nonlinear opticalproperties of the MoS₂ material. We show that the nonlinearresponse can be significantly enhanced via resonantcoupling to the thin film material, allowing for theobservation of optical modulation and spectral broadeningin the telecoms band. This route to access thenonlinear properties of 2D materials promises to yieldnew insights into their photonic properties.

Coherent injection of light into absorbing scattering medium with a microscopic pore

Alexey Yamilov, Raktim Sarma, Vladislav Yakovlev, and Hui Cao

Doc ID: 320959 Received 31 Jan 2018; Accepted 27 Mar 2018; Posted 05 Apr 2018  View: PDF

Abstract: We demonstrate that an interplay between absorption and scattering in a dielectric medium with a microscopic pore gives rise to eigenchannels concentrated in the pore. Such circumvention of attenuation leads to high transmission. By exciting such eigenchannels in a disordered nano-photonic system with wave-front shaping technique, we experimentally confirm enhanced injection at depths exceeding the limiting length scales set by scattering, absorption and diffraction.

2.6mJ/100Hz CEP stable near-single-cycle 4μm laser based on OPCPA and hollow-core-fiber compression

Pengfei Wang, Yanyan Li, Wenkai Li, hongpeng su, Beijie Shao, Shuai Li, Cheng Wang, Ding Wang, ruirui zhao, Yujie Peng, Yuxin Leng, Ruxin Li, and Zhizhan Xu

Doc ID: 320896 Received 30 Jan 2018; Accepted 26 Mar 2018; Posted 05 Apr 2018  View: PDF

Abstract: A carrier envelope phase stable near-single-cycle mid-infrared laser based on optical parametric chirped pulse amplification and hollow-core-fiber compression is demonstrated. 4 μm laser pulse with 11.8 mJ energy is delivered from a KTA based OPCPA with 100 Hz repetition rate, and compressed to 105 fs by a two-grating compressor with efficiency over 50%. Subsequently, the pulse spectrum is broadened by employing a krypton gas-filled hollow-core-fiber. Then, the pulse duration is further compressed to 21.5 fs through a CaF2 bulk material with energy of 2.6 mJ and stability of 0.9% RMS, which is about 1.6 cycle for 4 μm laser pulse. The carrier envelope phase of the near-single-cycle 4 μm laser pulse is passively stabilized with 370 mrad.

Perceptually uniform color space for visualizing trivariate linear polarization imaging data

Andrew Kruse, Andrey Alenin, Israel Vaughn, and J. Scott Tyo

Doc ID: 322557 Received 05 Feb 2018; Accepted 26 Mar 2018; Posted 06 Apr 2018  View: PDF

Abstract: The visualization of polarimetric data is often done bycolormapping the linear parameters using the three channelsin the HSV color space. Because this color spaceis not an accurate model of human color perception, theresulting visualization mixes the perceptual channels andcontains non-uniformity. We present a new mapping strategythat reliably and accurately depicts reality by placingthe polarization parameters directly into the perceptuallyuniform channels of CAM02-UCS. This mapping also ensuresthat regions of high polarization will be more visible,even when the measured irradiance is low.

Fabrication of controllably variable sub-100 nm gaps in silver nanowires by photothermal-induced stress

Pintu Ghosh, JINSHENG LU, Hao Luo, Ziquan Xu, XIAOYUAN YAN, yewu wang, Jun Lu, Min Qiu, and Qiang Li

Doc ID: 323465 Received 19 Feb 2018; Accepted 24 Mar 2018; Posted 28 Mar 2018  View: PDF

Abstract: A technique to fabricate nanogaps with controllably variable gap width in silver (Ag) nanowires (NWs) by photothermal-induced stress utilizing a focused continuous wave laser (532 nm) is presented. For the case of an Ag NW on gold thin film, a gap width starting from ~ 20 nm is achieved with a critical minimum power (CMP) of about 160 mW. Whereas in case of an Ag NW placed on top of a zinc oxide NW, the attained gap width is as small as a few nm (< 10 nm) with a CMP of only ~ 100 mW. In both cases, the CMP is much lower as compared to the required CMP (~ 280 mW) for an Ag NW placed on a bare silica substrate. The photothermal-induced stress combined with melting/sublimation of silver aids in breaking the Ag NW. In particular, the former one plays a key role in attaining extremely narrow gap. This technique to fabricate sub-100 nm nanogaps in metal NWs can be extensively implemented in fabrication and maintenance of nanomechanical, nanoplasmonic, and nanoelectronic devices.

Efficient point-by-point Bragg gratings fabricated in embedded laser-written silica waveguides using ultrafast Bessel beams

Guodong Zhang, Cheng Guanghua, Manoj Bhuyan, ciro d'amico, and Razvan Stoian

Doc ID: 321129 Received 31 Jan 2018; Accepted 21 Mar 2018; Posted 03 Apr 2018  View: PDF

Abstract: We demonstrate highly efficient Bragg gratings written point-by-point by sequential single-pulse ultrashort Bessel laser beams in laser photoinscribed single mode waveguides in bulk fused silica. The use of chirped non-diffractive Bessel beams determines a strong Bragg resonance in a weak-to-strong transitional regime, augmenting to a record value of 40\,dB/cm at 1550\,nm in the third order. The Bessel-induced refractive index modulation is negative and localized to sub-micron (200\,nm) transverse scales. The strong light confinement in Bessel beams ensuring uniform one-dimensional void conditions allows thus for enhanced precision in the Bragg grating waveguide design. We demonstrate flexible fabrication of multiplexed waveguide gratings for multiple and tunable spectral resonances.

Towards femtosecond-level intrinsic Laser Synchronization at 4th Generation Lightsources

Min Chen, Sergey Kovalev, Nilesh Awari, Zhe Wang, Semyon Germanskiy, Bert Green, Jan Deinert, and Michael Gensch

Doc ID: 324753 Received 09 Mar 2018; Accepted 20 Mar 2018; Posted 26 Mar 2018  View: PDF

Abstract: In this letter, the proof of principle for a scheme providing intrinsic femtosecond-level synchronization between an external laser system and 4th generation light sources is presented. The scheme is applicable at any accelerator-based light source that is based on the generation of coherent radiation from ultra-short electron bunches such as superradiant terahertz (THz) facilities or X-FEL’s. It makes use of a superradiant THz pulse generated by the accelerator as an intrinsically synchronized gate signal for electro-optical slicing. We demonstrate that the scheme enables a reduction of the timing instability by more than two orders of magnitude. This demonstration experiment thereby proves that intrinsically synchronized time-resolved experiments utilizing laser and accelerator-based radiation pulses on few tens of femtosecond (fs) to few fs timescales are feasible.

Gas spectroscopy with integrated frequency monitoring through self-mixing in a terahertz quantum-cascade laser

Rabi Chhantyal-Pun, Alex Valavanis, James Keeley, Pierluigi Rubino, Iman Kundu, Yingjun Han, Paul Dean, Lian He Li, Giles Davies, and Edmund Linfield

Doc ID: 323151 Received 15 Feb 2018; Accepted 12 Mar 2018; Posted 15 Mar 2018  View: PDF

Abstract: We demonstrate a gas spectroscopy technique, using self-mixing in a 3.4-THz quantum-cascade laser (QCL). All previous QCL spectroscopy techniques have required additional THz instrumentation (detectors, mixers or spectrometers) for system pre-calibration or spectral analysis. By contrast, our system self-calibrates the laser frequency (i.e., with no external instrumentation) to a precision of 630 MHz (0.02%) by analyzing QCL voltage perturbations in response to optical feedback within a 0-800-mm round-trip delay-line. We demonstrate methanol spectroscopy by introducing a gas cell into the feedback path, and show that a limiting absorption coefficient of ~1e-4 / cm is resolvable.

Filamentation of mid-IR pulses in ambient air in the vicinity of molecular resonances

Valentina Shumakova, Skirmantas Alisauskas, Pavel Malevich, Claudia Gollner, Andrius Baltuska, Daniil Kartashov, Aleksei Zheltikov, Alexander Mitrofanov, Aleksandr Voronin, Dmitry Sidorov-Biryukov, and Audrius Pugzlys

Doc ID: 322812 Received 08 Feb 2018; Accepted 26 Feb 2018; Posted 05 Mar 2018  View: PDF

Abstract: Properties of filaments ignited by multi-millijoule, 90 fs mid-IR pulses centered at 3.9 µm are examined experimentally by monitoring plasma density and losses as well as spectral dynamics and beam profile evolution at different focusing strengths. By softening the focusing from strong (f=0.25 m) to loose (f=7 m) we observe a shift from plasma assisted filamentation to filaments with low plasma density. In the latter case, filamentation manifests itself by beam self-symmetrization and spatial self-channeling. Spectral dynamics in the case of loose focusing is dominated by the non-linear Raman frequency downshift, which leads to the overlap with the CO2 resonance in the vicinity of 4.2 µm. The dynamic CO2 absorption in the case of 3.9 µm filaments with their low plasma content is the main mechanism of energy losses and either alone or together with other nonlinear processes contributes to the arrest of intensity.

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