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Accepted papers to appear in an upcoming issue

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

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

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

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

Femtosecond laser self-assembly for silver vanadium oxide flower structures

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

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

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

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

Jingtao Dong and Rong-sheng Lu

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

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

Gradual ghost imaging of moving objects by tracking based on crosscorrelation

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Ultrasound modulated laser feedback tomography in reflective mode

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

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

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

Squeezed vacuum phase control at 2 μm

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

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

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

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

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

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

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

Ultrasound beam steering using fiber optic ultrasound phased array

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

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

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

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

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

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

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

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

Xinying Zhao, Xiaoyan Pang, and Guobin Wan

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Jérôme Le Perchec

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

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

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

Ping Xu and Yongxing Wang

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

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

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

Young-Sik Ghim and Hyug-Gyo Rhee

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

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

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

Evan Jelly, Zachary Steelman, and Adam Wax

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

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

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

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

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

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

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

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

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

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

Ultrafine intravascular photoacoustic endoscope with a 0.7 mm diameter probe

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

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

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

General framework for the analysis of imperfections in nonlinear systems

Matteo Santandrea, Michael Stefszky, and Christine Silberhorn

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

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

Depth-resolved volumetric two-photon microscopy based on dual Airy beam scanning

Hongsen HE, Cihang Kong, Xiaojie Tan, KA YAN CHAN, Yu-Xuan Ren, Kevin Tsia, and Kenneth Kin-Yip Wong

Doc ID: 377231 Received 09 Sep 2019; Accepted 03 Oct 2019; Posted 04 Oct 2019  View: PDF

Abstract: We demonstrate a dual-Airy-beam-scanning based volumetric two-photon microscopy (TPM) with depth-resolving capability. A pair of Airy beams with opposite acceleration are used as the exciting lights to sequentially illuminate the sample, and depth information can be resolved based on the deflection of the Airy beam. The depth-resolving range of the volumetric TPM is beyond 32 um. The advantages of the depth-resolved volumetric TPM are the depth-resolving capability over Bessel beam based TPM and less scanning times over traditional Gaussian beam based TPM. The depth-resolved volumetric TPM provides a promising fast imaging tool to study the dynamics in neural biology.

Polariton surface solitons under resonant pump

Yaroslav Kartashov and Victor Vysloukh

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

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

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

Korato Hiramatsu, Jørgen Peterson, and Keisuke Goda

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

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

Intense Stimulated Raman Scattering in CO2-filled Hollow Core Fiber

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

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

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

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

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

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

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

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

Teemu Kääriäinen and Guillaume Genoud

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

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

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

Ravi Pant, VARUN K, and Akhileshwar Mishra

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Angular Control of Anisotropy-Induced Bound States in the Continuum

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

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

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

Amplified noise nonstationarity in a mode-locked laser based on nonlinear polarization rotation

Philippe Guay, Carlos Perilla, Jean-Daniel Deschênes, and Jérôme Genest

Doc ID: 376145 Received 27 Aug 2019; Accepted 01 Oct 2019; Posted 01 Oct 2019  View: PDF

Abstract: Beat note measurements between a mode-locked and a continuous-wave laser as well as between two mode-locked sources were used to demonstrate that the sub-threshold, cavity filtered, amplified spontaneous emission is not stationary even when a fast mode-locking mechanism, such as nonlinear polarization rotation, is used to generate short pulses. A few percents gain modulation created by high intensity pulses is relatively small, but can produce a near 100% modulation of the amplified noise once synchronously accumulated over several cavity round-trips, even if the repetition rate is faster than the gain dynamics

Experimental characterization of recurrences and separatrix crossing in modulational instability

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

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

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

Lithium Niobate-Based Transparent Ultrasound Transducers for Photoacoustic Imaging

Ajay Dangi, Sumit Agrawal, and Sri-Rajasekhar Kothapalli

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

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

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

Iam-Choon Khoo and Chun-Wei Chen

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

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

Mueller matrix of the particle-free atmosphericenhanced backscatter

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

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

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

High-speed polarization modulation with intrinsic stability for secure quantum key distribution

Shengkai Liao, Yang Li, Yuhuai Li, Hong-Bo Xie, Zheng-Ping Li, Xiao Jiang, Wen-Qi Cai, Ji-Gang Ren, Juan Yin, and Cheng-Zhi Peng

Doc ID: 374485 Received 06 Aug 2019; Accepted 30 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: High-performance polarization modulation plays a key role in polarization-encoding quantum key distribution (QKD). Here we report a new polarization modulation scheme based on an inherently stable Sagnac interferometer. Compared with previous implementations, the presented scheme is free of polarization mode dispersion and calibration as well as insensitive to environmental influences. Successful experiments at a repetition frequency of 1.25 GHz have been conducted to demonstrate the feasibility and stability of the scheme. The measured average quantum bit error rate of the four polarization states is as low as 0.27% for 80 consecutive minutes without any adjustment. This high-speed intrinsically stable polarization modulation can be widely applied to many polarization-encoding QKD systems, such as BB84, MDI, etc.

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

Mohammad Hossein Daemi and Saifollah Rasouli

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

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

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

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

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

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

Direct scattering transform of large wave packets

A Gelash and Rustam Mullyadzhanov

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

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

Compact linear polarization spectrometer based on radiation mode shaped in-fiber diffraction grating

Huabao Qin, Qinyun He, Yarien Moreno, Zhikun Xing, Xi Guo, Zhijun Yan, Qizhen Sun, Kaiming Zhou, Deming Liu, and Lin Zhang

Doc ID: 376282 Received 26 Aug 2019; Accepted 30 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We proposed a compact linear polarization spectrometer based on the in-fiber polarization dependent diffraction grating. The beam profile of radiation light of the grating has been shaped to a Gaussian profile to improve the performance of the spectrometer, where the size of the focused light spot has been reduced from 44um to 33um with the shaped radiation mode of the grating. Based on the experimental results, the proposed spectrometer could achieve 0.05nm resolution and 115 nm wavelength responding range from 1495nm to 1610nm. To verify the performance of the proposed fiber spectrometer, we have measured the transmission spectra of an excessively tilted fiber grating (Ex-TFG), which has a pair of orthogonal polarization transmission spectra. Compared with the traditional measuring method, the proposed fiber spectrometer has integrated the polarizing and spectral analyzing functions in the measuring system and achieved the polarization sensitive spectral analysis, which showed good wavelength consistency and perfect polarization characteristics.

A highly accurate, absolute optical-encoder using a hybrid positioning-method

Shi ping, Kai Ni, li xinghui, ZHOU QIAN, and Xiaohao Wang

Doc ID: 377517 Received 09 Sep 2019; Accepted 29 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: An absolute optical encoder with nanometric positioning accuracy is introduced and investigated. The encoder consists of an improved scale-grating and a compact two-probe reading head. The scale grating contains multiple unevenly spaced distance-marks that are superimposed onto grating grooves. The two probes, which are located in the sensor head, read the marks and the grating grooves to determine position and displacement simultaneously. For one of the two probes, a mask with the same code-design, with the marks on the scale-grating, generates a pulse signal to locate the position of the marks approximately - with an accuracy of less than about half a grating period (0.5 m). For the other probe, light beams are configured for grating interferometry to measure displacement with nm-scale resolution. In this paper, high-quality sinusoidal signals of grating interferometry are used to accurately locate the marks on the scale grating, with stable 100-subdivision phase-information. Tests of this prototype show that the positioning accuracy can reach 10 nm for a motion range of several tens of millimeters.

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

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

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

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

Mitigation for turbulence effects in a 40-Gbit/s orbital-angular-momentum-multiplexed free-space optical link between a ground station and a retro-reflecting UAV using MIMO equalization

Long Li, Runzhou Zhang, Peicheng Liao, Yinwen Cao, Haoqian Song, Yifan Zhao, Jing Du, Zhe Zhao, Cong Liu, Kai Pang, Hao Song, Ahmed Almaiman, DMITRY STARODUBOV, Brittany Lynn, Robert Bock, Moshe Tur, Andreas Molisch, and Alan Willner

Doc ID: 371058 Received 10 Jul 2019; Accepted 29 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We experimentally demonstrate turbulence effect mitigation in a 100-m round-trip orbital-angular-momentum (OAM)-multiplexed free-space optical (FSO) communication link between a ground transmitter and a ground receiver via a retro-reflecting hovering unmanned-aerial-vehicle (UAV) using multiple-input-multiple-output (MIMO) equalization. In our demonstration, two OAM beams at 1550 nm are transmitted to the UAV through emulated atmospheric turbulence, each carrying a 20-Gbit/s signal. 2×2 MIMO equalization is used to mitigate turbulence-induced crosstalk between the two OAM channels. Bit error rates (BERs) below the 7% overhead forward error correction (FEC) limit of 3.8×10-3 are achieved for both channels.

Optical machine learning with incoherent light and a single-pixel detector

Shuming Jiao, Jun Feng, Yang Gao, Ting Lei, Zhenwei Xie, and Xiaocong Yuan

Doc ID: 377825 Received 12 Sep 2019; Accepted 28 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: An optical diffractive neural network (DNN) can be implemented with a cascaded phase mask architecture. Like an optical computer, the system can perform machine learning tasks such as number digit recognition in an all-optical manner. However, the system can only work under coherent light illumination and the precision requirement in practical experiments is quite high. This paper proposes an optical machine learning framework based on single-pixel imaging (MLSPI). The MLSPI system can perform the same linear pattern recognition task as DNN. Furthermore, it can work under incoherent lighting conditions, has lower experimental complexity and can be easily programmable.

Scale factor improvement for angular velocity measurement based on an optoelectronic oscillator

Muguang Wang, jing zhang, yu tang, Qi Ding, and Nai Zhang

Doc ID: 376384 Received 28 Aug 2019; Accepted 28 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: A novel scheme of angular velocity measurement with improved scale factor is proposed and experimentally demonstrated based on a joint operation of a Sagnac loop and optoelectronic oscillator (OEO). In this scheme, the Sagnac-induced phase difference is mapped into the oscillating frequency shift of the OEO with a large scale factor by making one of the two counter-propagating signals in the Sagnac loop carrier-suppressed modulated and the other just travel through the modulator. The cascaded Sagnac loop and OEO structure can further improve the scale factor by setting a long Sagnac loop and a short OEO loop independently. A sensitivity scale factor as high as 742 kHz/(rad/s) is obtained in our experiment.

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

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

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

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

Orbital angular momentum and informational entropy in perturbed vortex beams

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

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

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

Silica optical fibre drawn from 3D printed preforms

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

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

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

Power scaling of the self-frequency doubled quasi-two-level Yb:YCOB laser with 30% optical conversion efficiency

Dazhi Lu, Qiannan Fang, Xiangsheng Yu, Xuekun Han, jiyang wang, Haohai Yu, and Huaijin Zhang

Doc ID: 378064 Received 16 Sep 2019; Accepted 27 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: The lab-on-chip integration of photonic devices is attracting increasing attention recently and multifunctional materials provide natural platforms to realize the desirable performance by coupling of different functionalities. The insufficient coupling efficiency of the laser and nonlinear processes in self-frequency-doubled (SFD) lasers is the limiting factor for the output power and further practical applications. Here, we demonstrate a SFD Yb3+ doped calcium yttrium oxoborate (Yb:YCOB) crystal laser with unprecedented optical conversion efficiency of 30% and output power of 6.2 W at 513 nm. The successful realization of this laser operating in a quasi-two-level configuration is based on enhanced coupling of the laser and frequency-doubling processes using a microchip configuration, benefiting from an ultimately small laser quantum defect, the anisotropic gain cross-sections, and the high effective nonlinearity of the monoclinic YCOB for beam propagation outside the principal planes. Solid-state lasers in the spectral range around 510 nm are scarce and the present results present not only a significant advancement in the field of SFD lasers but are also expected to pave the way for future applications of such green lasers especially in medical treatment, daily life, scientific investigations, etc..

Interrogation of a large-capacity densely-spaced FBG array using chaos-based I-OFDR

JiaQi Wang, Zhengying Li, Qian Yang, Xuelei Fu, Xin Gui, Changjia Wang, and Honghai Wang

Doc ID: 375933 Received 30 Aug 2019; Accepted 27 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: An interrogation technique for large-capacity densely-spaced fiber Bragg grating (FBG) arrays is demonstrated using incoherent optical frequency domain reflectometry. A distributed-feedback laser diode under chaotic oscillation, modulated by a frequency-swept microwave, is adopted as the optical source. The reflected sensing signals are converted into electrical signals and subsequently mixed with the original microwave. Fast Fourier transform is applied to the generated beat signal to obtain the position of individual FBGs, while thermal tuning of the lasing wavelength leads to the demodulation of wavelength. By using the chaotic source, interference among the reflected sensing signals is reduced, leading to a significantly improved spatial resolution of 10 cm, with a multiplexing capacity of 3640 and wavelength demodulation accuracy of 15 pm.

Second Harmonic Generation exaltation in Cavity Resonator Integrated Grating Filters

François Renaud, Antoine Monmayrant, Stephane Calvez, Olivier Gauthier-Lafaye, Anne-Laure Fehrembach, and Evgeny Popov

Doc ID: 374370 Received 31 Jul 2019; Accepted 27 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: Second harmonic generation (SHG) in compact grating devices is measured experimentally and modeled numerically for several different systems including thin plane layer of LiNbO3 without and with grating coupler to excite a waveguide mode. We demonstrate that when the waveguide mode is put in a cavity resonator integrated grating filter (CRIGF, a planar cavity resonator made of Bragg grating reflectors), designed to work with focused incident beams, the SHG power is increased more than 30 times, compared to the case of a single grating coupler used with an almost collimated pump beam.

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

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

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

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

Super-low-power optical trapping of single nanoparticle

Yu Zhang, Tang Xiaoyun, WENJIE SU, Yaxun Zhang, Zhihai Liu, Xinghua Yang, Jianzhong Zhang, Jun Yang, and Libo Yuan

Doc ID: 373200 Received 19 Jul 2019; Accepted 26 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We propose and demonstrate a simple approach for noncontact, 3-dimensional, and stable trapping of a single nanoparticle with a super low incident laser power (0.7 mW) via the single-fiber optical tweezers. We splice a section of single-mode fiber and a section of multimode fiber to construct a Bessel-like beam, which produces the narrow output laser beams. We integrate a high-refractive-index glass microsphere on the tip of the multimode fiber to focus the narrow output laser beams. The focused beams provide a nanoscale optical trap for a single nanoparticle (polystyrene sphere, the diameter of 200 nm). The proposed nanotweezers based on the optical fiber are completely autonomous and do not require bulky optical components. This optical fiber probe has the advantages of high laser transmission efficiency, high spatial resolution, and minimum joule heating. The proposed approach extends the application potential of fiber-based optical manipulations, such as nanoparticle sorting, single-cell organelle analysis, and bio-sensing.

Controlling directional absorption with chiral exceptional surfaces

QI ZHONG, Seth Nelson, Sahin Ozdemir, and Ramy El-Ganainy

Doc ID: 376931 Received 03 Sep 2019; Accepted 26 Sep 2019; Posted 02 Oct 2019  View: PDF

Abstract: Significant efforts have been dedicated to engineering optical systems with predefined, excitation-dependent light absorption. An important concept along this line is that of exceptional points which allow for engineering directional light absorbing schemes. Current systems, however, do not lend themselves to easy design criterion or robust experimental realization. Here we demonstrate that an optical microring resonator coupled to a waveguide terminated with a mirror supports a chiral exceptional surface that can be used as a platform for tailoring directional light absorption in a straightforward fashion. We further demonstrate that this configuration can be used to implement a unidirectional coherent perfect absorber with controllable differential loss by tuning only a single parameter.

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

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

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

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

Cascaded multiple Fabry–Perot interferometers fabricated in no-core fiber with a waveguide for high-temperature sensing

Dongning Wang, Qiaohan Wang, and Hua Zhang

Doc ID: 376494 Received 27 Aug 2019; Accepted 25 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: An optical fiber high-temperature sensor is proposed and demonstrated by use of cascaded multiple Fabry–Perot interferometers in no-core fiber with a waveguide fabricated by femtosecond laser pulse inscription. The device can sustain the high temperature up to 1100°C, and the temperature sensitivity obtained is 8.9 pm/°C within the temperature range between 100°C and 400°C, and 16.36 pm/°C within the temperature range between 400°C and 1100°C, respectively. Such a no-core fiber based device can be fabricated in a simple way and operated reliably, which make it attractive for extreme environment monitoring.

Flexible degenerate cavity with ellipsoidal mirrors

Ze-di Cheng, Zheng-Hao Liu, qiang li, Zhou Zheng Wei, Jin-Shi Xu, Chuanfeng Li, and Guang-can Guo

Doc ID: 374942 Received 07 Aug 2019; Accepted 25 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: Optical cavities have provided great facilities in modern physics, ranging from laser technology to condensed matter physics. In recent years, photonic synthetic dimensions in degenerate cavities have been explored to investigate many fundamental phenomena. However, experimental progress is limited due to the difficulty in implementing such a flexible degenerate cavity. Here we present a novel design of a travelling-wave optical cavity containing four identical ellipsoidal mirrors arranged in a square. The cavity is proved to support more than 21 Laguerre-Gaussian modes simultaneously. There is a polarization splitting in the cavity, which can be used for polarization filting with a high isolation level. The structure of the cavity is flexible to couple with similar cavities, in which synthetic optical dimensions can be employed to demonstrate gauge field effects and topological photonic phenomena. Our work would find important applications in future large scale optical quantum simulation.

Low short-wavelength loss fibre Bragg gratings inscribed in small-core fibre by femtosecond laser point-by-point technology

Xueya Liu, Yiping Wang, Ziliang Li, Shen Liu, Ying Wang, Cailing Fu, Changrui Liao, Zhiyong Bai, Jun He, Zhengyong Li, and Laipeng Shao

Doc ID: 375437 Received 14 Aug 2019; Accepted 25 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: A femtosecond-laser-induced FBG usually has a high insertion loss at the shorter wavelength than at the reflection wavelength, i.e. so-called short-wavelength loss. High-quality fibre Bragg gratings (FBGs) are inscribed in different types of small-core single mode fibres (SMFs) by use of the femtosecond laser point-by-point (PbP) technology in order to investigate the effect of the fibre core diameter on the grating inscription efficiency and on the short-wavelength loss. A lower laser pulse energy is required to achieve the same grating reflectivity in a smaller-core fibre than in a large-core fibre. The short-wavelength loss of the small-core FBG is lower than that of the large-core FBG with the same reflectivity. Furthermore, a series of FBGs with a low short-wavelength loss are inscribed in a small-core SMF along the fibre axis to achieve so-called series-integrated FBGs (SI-FBGs). Finally, the effect of the input light direction on the reflection peak of the SI-FGBs is investigated to reduce the influence of the grating short-wavelength loss in the sensing and communication applications.

Scanning a focus through scattering media without using the optical memory effect

Bahareh Mastiani, Tzu-Lun Wang, and Ivo Vellekoop

Doc ID: 375860 Received 20 Aug 2019; Accepted 24 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: Wavefront shaping makes it possible to form a focus through opaque scattering materials. In some cases, this focus may be scanned over a small distance using the optical memory effect. However, in many cases of interest, the optical memory effect has a limited range or is even too small to be measured. In such cases, one often resorts to measuring the full transmission matrix (TM) of the sample to completely control the light transmission. However, this process is time-consuming and may not always be possible. We introduce a new method for focusing and scanning the focus at any arbitrary position behind the medium by measuring only a subset of the transmission matrix, called Sparse Field Focusing (SFF). With SFF, the scan range is not limited to the memory effect and there is no need to measure the full transmission matrix. Our experimental results agree well with our theoretical model. We expect this method will find applications in imaging through scattering media, especially when the optical memory effect range is small.

Bi-functional polarization conversion in hybrid graphene-dielectric metasurfaces

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

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

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

All-fiber passively mode locked ultrafast laser based on a femtosecond laser inscribed in-fiber Brewster device

Zinan Huang, Qianqian Huang, Antreas Theodosiou, XI CHENG, zou hang, dai lilong, Kyriacos Kalli, and Chengbo Mou

Doc ID: 371423 Received 01 Jul 2019; Accepted 24 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: We report a new type of in-fiber Brewster device, a 45°-tilted fiber grating (TFG) directly written by plane-by-plane femtosecond laser inscription method. Up to 10 dB polarization dependent loss was achieved, proving effective polarizing functionality. Furthermore, we employ it as an in-line polarizer to successfully mode lock a fiber laser through the nonlinear polarization rotation technique. Stable soliton pulse train has been generated at 1563.64 nm with a pulse width of 624 fs and pulse energy of 0.42 nJ. With proper polarization adjustment, the laser also can operate in a noise-like regime. The parameters of this kind of 45°-TFG can be flexibly customized owing to the high flexibility and controllability of femtosecond laser inscription approach. In particular, such in-fiber polarizing devices inscribed by femtosecond laser inscription without removing the fiber coating is extremely robust for fiber lasers working at a broad wavelength region including the mid-infrared.

Curved space plasmonic optical elements

danveer singh, Ana Libster, Roy Shiloh, and Ady Arie

Doc ID: 372694 Received 15 Jul 2019; Accepted 24 Sep 2019; Posted 01 Oct 2019  View: PDF

Abstract: We have designed and experimentally studied non-planar curved space plasmonic optical elements. Three different smooth curved space plasmonic structures were studied: a dome that acts either as a focusing element, or as a deflector for plasmonic beams, a cone that acts as a plasmonic prism and a tapered book cover that alters the size of a plasmonic guided wave. The functional mechanism of these elements relies purely on the curvature induced effective potential, and does not require any additional dielectric layer for shaping the plasmonic beams. The curved space plasmonic elements open exciting new possibilities for guiding, focusing, deflecting, and controlling the propagation of plasmonic beam in a compact manner.

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

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

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

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

Influence of the Doppler effect of a periodically moving mirror on the carrier-envelope frequency of a pulse train

Gunter Steinmeyer, Tianli Feng, and Pascal Rustige

Doc ID: 369394 Received 12 Jun 2019; Accepted 23 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: We investigate the influence of the optical Doppler-effect on the carrier-envelope frequency (CEF) of a mode-locked pulse train. The laser pulses are Doppler-shifted in frequency during reflection off a periodically moving mirror that is driven by an electro-dynamical exciter (EDE) inside an f-2f interferometer. Depending on the relative movement of the mirror at the instant of reflection, we experimentally demonstrate a CEF shift of the laser pulses up to +/- 69 kHz. This shift is sufficient for carrier-envelope phase control of laser amplifiers with repetition rates of 10 kHz and beyond. Using piezoelectric thick films the scheme also appears adaptable to the MHz repetition rates of typical oscillators. As the phase control is exerted extra-cavity, Doppler-induced CEF modulation is virtually free of any side effects of traditional stabilization schemes that typically act on the pump power.Finally, the Doppler scheme may overcome servo loop bandwidth limitations associated with pump power control.

A highly coherent multi-section semiconductor swept source OCT laser

Svetlana Slepneva, Anton Kovalev, Natalia Rebrova, Konstantin Grigorenko, Evgeny Viktorov, and Guillaume Huyet

Doc ID: 374178 Received 08 Aug 2019; Accepted 23 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: We theoretically investigate the influence of optical feedback onto the dynamics of a semiconductor swept source laser. In particular, we show that optical feed- back can be used to lock the phase of the successive las- ing modes of a multi-section semiconductor laser com- monly used for Optical Coherence Tomography (OCT) applications. We also identify two different regimes called sliding frequency self-mixing and sliding fre- quency mode-locking. The second regime demon- strates sub-nanosecond sliding frequency pulses for non-linear optics applications.

All-Chalcogenide Single-Mode Optical Fiber Couplers

Mohsen Rezaei and Martin Rochette

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

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

Robust contrast-transfer-function phase retrieval via flexible deep learning networks

Chen Bai, Meiling Zhou, Junwei Min, Shipei Dang, Xianghua Yu, Peng Zhang, Tong Peng, and Baoli Yao

Doc ID: 375938 Received 20 Aug 2019; Accepted 22 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: By exploiting the total variation (TV) regularization scheme and the contrast-transfer-function (CTF), a phase map can be retrieved from single-distance coherent diffraction images via the sparsity of the investigated object. However, the CTF-TV phase retrieval algorithm often struggles in presence of strong noise, since it is based on the traditional compressive sensing optimization problem. Here, convolutional neural networks, a powerful tool from machine learning, are used to regularize the CTF-based phase retrieval problems and improve the recovery performance. This proposed method, the CTF-Deep phase retrieval algorithm, was tested both via simulations and experiments. The results show that it is robust to noise and fast enough for high-resolution applications.

Time transfer through the optical supervisory channel in WDM systems

Hanhuang Cheng, Guiling Wu, Faxing Zuo, Liang Hu, and Jianping Chen

Doc ID: 374540 Received 06 Aug 2019; Accepted 22 Sep 2019; Posted 30 Sep 2019  View: PDF

Abstract: We present an optical fiber time transfer scheme through the optical supervisory channel (OSC) in WDM systems. A sub-band of the standard OSC band is used to transmit time signals by only adding sub-OSC filters in commercial WDM systems. The transmission of the existing communication data service is not affected. The wavelengths of bidirectional time transmission in the same sub-band can be very close, or even the same to maximize the bidirectional propagation symmetry and improve the precision of time transfer. Combined time, optical supervisory signal and communication data transmission is experimentally demonstrated along a single 100 km optical fiber in a WDM system in laboratory.

Control of diameter and numerical aperture of microlens by a single ultra-short laser pulse

Hua Fan, Xiao-wen Cao, Lei Wang, Zhen-Ze Li, Qi-Dai Chen, Saulius Juodkazis, and Hong-Bo Sun

Doc ID: 375366 Received 13 Aug 2019; Accepted 21 Sep 2019; Posted 27 Sep 2019  View: PDF

Abstract: We demonstrate a versatile method for a fast and flexible fabrication of single microlenses and arrays. Multi-foci axial intensity distribution is defined by a phase pattern on a spatial light modulator (SLM) and irradiated to silica causing ablation and its internal modification. The following wet etching step defines the radius r while the curvature radius R (hence the focal length f) is maintained the same. As a result, the numerical aperture NA = r/f was changed from 0.2 to 0.4 for the same pulse energy (but different number of the multi-foci) during ablation. An isotropic wet etching of silica becomes highly anisotropic for the initial stages of etching following the irradiated pattern. Subsequent evolution of the shape is governed by an isotropic silica etch and forms a spherical lens. This method can be extended to other materials and geometries of micro-optical elements.

Impact of intra- and inter-unit cell symmetry breaking on the optical response of the arrays of nanotrimers

Ning Wang, Markus Schmidt, Matthias Zeisberger, and Uwe Hübner

Doc ID: 371234 Received 02 Jul 2019; Accepted 21 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Understanding the impact of geometric changes on the properties of otherwise symmetric nanostructures is of essential importance for nanophotonics. Here we show that intra- and inter-unit cell symmetry breaking can substantially modify the optical properties of nanotrimers from both experimental and simulation perspectives. Specifically, shifting the location of one nano-dot within the trimer unit cell leads to the formation of magnetic Fano resonances with loop-like polarization patterns that are not present in the symmetric configuration. We further unlock the impact of lattice modification on the optical response of square arrays of asymmetric trimers with intra-trimer distances as small as 25 nm, showing distinctively different spectral evolutions of the electric and magnetic Fano resonances. The results achieved highlight symmetry breaking as an essential tool to unlock and strengthen predefined resonances, which can have important applications particular in the field of sensing.

Changing the speed of optical coherence in free space

Ayman Abouraddy and Murat Yessenov

Doc ID: 375619 Received 19 Aug 2019; Accepted 20 Sep 2019; Posted 20 Sep 2019  View: PDF

Abstract: It is typically assumed that the fluctuations associated with a stationary broadband incoherent field propagate in free space at the speed of light in vacuum c. Here we introduce the concept of `coherence group velocity', which -- in analogy to the group velocity of coherent pulses -- is the speed of the peak of the coherence function. We confirm experimentally that incorporating a judicious spatio-temporal spectral structure into a field allows tuning its coherence group velocity in free space. Utilizing light from a super-luminescent diode, we interferometrically measure the group delay encountered by the cross-correlation of a structured field synthesized from this source and the unstructured diode field. By tracking the propagation of this cross-correlation function, we measure coherence group velocities in the range from 12c to -6c.

Real time hyper-spectral low-frequency vibrational imaging via impulsive Raman excitation

Dekel Raanan, Xavier Audier, Siddarth Shivkumar, Maor Asher, Matan Menahem, Omer Yaffe, Nicolas Forget, Herve Rigneault, and Dan Oron

Doc ID: 368972 Received 04 Jun 2019; Accepted 20 Sep 2019; Posted 23 Sep 2019  View: PDF

Abstract: Real time vibrational microscopy has been recently demonstrated by various techniques, most of them utilizing the well-known schemes of coherent anti-stokes Raman scattering (CARS) and stimulated Raman scattering (SRS). These techniques readily provide valuable chemical information mostly in the high vibrational frequency regime (>400 cm^-1). Addressing the low vibrational frequency regime (<200 cm^-1) is challenging due to the usage of spectral filters that are required to isolate the signal from the Rayleigh scattered excitation field. In this letter we report on real time high resolution low-frequency (<130 cm^-1) vibrational microscopy using impulsive coherent Raman excitation. By combining impulsive excitation with a fast acousto-optics delay line we detect the Raman-induced optical Kerr lensing and spectral shift effects with a 25us pixel dwell time to produce real time shot-noise limited low frequency hyper-spectral images of various samples.

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

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

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

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

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

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

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

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

High-Frequency Vector Harmonic Mode-Locking Driven by Acoustic Resonances

Hani Kbashi, Sergey Sergeyev, Mohammed Al Arami, Alex Rozhin, Dmitry Korobko, and Andrei Fotiadi

Doc ID: 374487 Received 02 Aug 2019; Accepted 18 Sep 2019; Posted 19 Sep 2019  View: PDF

Abstract: A controllable passive harmonic mode-locking (HML) in Erbium-doped fiber laser with a soliton pulse shaping using a single-wall carbon nanotube (SWCNT) has been experimentally demonstrated. By increasing the pump power and adjusting the in-cavity polarization controller, we reached 51st-order harmonic (902 MHz) having the output power of 37 mW and the pulse width of 990 fs. We attribute the observed high-frequency HML to the electrostriction effect caused by periodic pulses and leading to excitation of the radial and torsional-radial acoustic modes in the transverse section of the laser. The exited acoustic modes play the role of the bandpass filter, which stabilizes the high-frequency HML regime.

Gallium Indium Phosphide Microstructures with Suppressed Photoluminescence for Applications in Nonlinear Optics

Eleonora De Luca, Marcin Swillo, Dennis Visser, and Srinivasan Anand

Doc ID: 370595 Received 21 Jun 2019; Accepted 18 Sep 2019; Posted 19 Sep 2019  View: PDF

Abstract: Gallium indium phosphide (Ga0.51In0.49P), lattice matched to gallium arsenide, shows remarkable second-order nonlinear properties, as well as strong photoluminescence due to its direct band gap. By measuring the second-harmonic generation from the GaInP microwaveguide (0.2 x 11 x 1300 μm) before and after stimulating intrinsic photobleaching, we demonstrate that the photoluminescence could be strongly suppressed (-34dB), leaving the nonlinear properties unchanged, making it suitable for low-noise applications.

Scalable 30 fs laser source with 530 W average power

Peter Russbueldt, Johannes Weitenberg, Jan Schulte, Rudolf Meyer, Christoph Meinhardt, Dieter Hoffmann, and Reinhart Poprawe

Doc ID: 374525 Received 02 Aug 2019; Accepted 17 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: We present a power-scalable laser source with 30 fs pulse duration, 530 W average power at 500 kHz rep-etition rate and almost diffraction-limited beam qual-ity M² < 1.2. The compact and efficient setup consists of ytterbium-based Innoslab amplifiers and subse-quent nonlinear pulse compression by means of an argon-filled Herriott cell.

All-fiber widely tunable ultrafast laser source for multimodal imaging in nonlinear microscopy

Armin Zach, Mojtaba Mohseni, CHRISTOPH POLZER, Jeffrey Nicholson, and Thomas Hellerer

Doc ID: 376182 Received 26 Aug 2019; Accepted 16 Sep 2019; Posted 25 Sep 2019  View: PDF

Abstract: We present an all-fiber, easy to use, wavelength tunable, ultrafast laser based on soliton self-frequency-shifting in an Er-doped polarization-maintaining very large mode area (PM VLMA) fiber. The system is tunable over 370 nm starting at 1620 nm with an average power of up to 1.5 W that emits 120 fs short laser pulses directly out of the fusion-spliced fiber without the use of bulky pulse compression optics. The output is subsequently frequency doubled to a wavelength range covering 810 nm up to almost 1000 nm with more than 500 mW average power and 120 fs pulse width. Having a polarization extinction ratio better than 40 dB and a M² of 1.1, the fully computer controlled laser system presents a robust and compact laser source. These parameters make the laser perfectly suited for multimodal imaging in nonlinear microscopy.

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

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

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

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

Bloch-surface-wave photonic crystal nanobeam cavity

Tommaso Perani, Daniele Aurelio, and Marco Liscidini

Doc ID: 373967 Received 31 Jul 2019; Accepted 16 Sep 2019; Posted 16 Sep 2019  View: PDF

Abstract: We theoretically demonstrate a nanobeam cavity based on a photonic crystal ridge that supports localized Bloch surface waves (BSWs) propagating at the truncation interface of a periodic multilayer. Combining the appealing characteristics of a nanobeam cavity (these including flexible geometry, small footprint size, etching-free fabrication with the leading lithographic technologies) with the versatility of BSWs (whose dispersion relation is finely tunable as compared to other surface waves), this structure may prove to be a customizable visible-to-IR platform, well-suited for a number of applications ranging from optical sensing to the control of single-photon emission from embedded nanoemitters, such as quantum dots or color centers.

Single-shot phase retrieval with complex diversity

Akira Eguchi and Thomas Milster

Doc ID: 372702 Received 25 Jul 2019; Accepted 15 Sep 2019; Posted 19 Sep 2019  View: PDF

Abstract: The concept of complex diversity is introduced that adequately accounts for special considerations in the design of the system and the reconstruction algorithm for single-shot phase retrieval techniques. Complex-number pupil filters containing both amplitude and phase values are extracted by numerical propagation from a computer-generated hologram design, which generates multiple images in a single acquisition. The reconstruction is performed by a Fourier iterative algorithm modified with an area restriction to avoid noise amplification. Numerical simulations show that the complex diversity technique estimates extrinsic Kolmogorov aberration better than conventional single-shot techniques for a distant point object. Experiments show that sensor-less adaptive optics correction is achieved using the complex diversity technique.

An Algorithmic Approach to the Design of Plasmonic Nanotweezers

Neuton Li, Jasper Cadusch, and Kenneth Crozier

Doc ID: 373887 Received 29 Jul 2019; Accepted 12 Sep 2019; Posted 20 Sep 2019  View: PDF

Abstract: We use machine learning (simulated annealing) to design plasmonic nanoapertures that function as optical nanotweezers. The nanoapertures have irregular shapes that are chosen by our algorithm. We present electromagnetic simulations that show that these produce stronger field enhancements and extraction energies than nanoapertures comprising double nanoholes with the same gap geometry. We show that performance is further improved by etching one or more rings into the gold surrounding the nanoaperture. Lastly, we provide a direct comparison between our design and work that is representative of the state of the art in plasmonic nanotweezers at the time of writing.

Linear control of light scattering with multiple coherentwaves excitation

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

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

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

47 W continuous-wave 1726 nm thulium fiber laser core-pumped by an erbium fiber laser

Mark Burns, Peter Shardlow, Pranabesh Barua, Thomas Jefferson-Brain, Jayanta Sahu, and W. Clarkson

Doc ID: 373486 Received 24 Jul 2019; Accepted 09 Sep 2019; Posted 10 Sep 2019  View: PDF

Abstract: High power, short-wavelength operation of a thulium-doped silica fiber laser at 1726 nm has been demonstrated in a core-pumped monolithic (all-fiber) resonator configuration, in-band pumped by a high power erbium-only fiber laser operating at 1580 nm. The thulium fiber laser yielded 47 W in a single-spatial-mode output beam for 60 W absorbed pump power. The corresponding slope efficiency with respect to absorbed pump power of 80% compares favorably with the theoretical maximum (Stokes) efficiency of 91.5%. The prospects for further scaling of single-mode power in this wavelength regime to >100 W are considered, as well as the potential applications for high power lasers operating in this difficult-to-reach wavelength band.

Broadband dispersive Ge/YbF3 mirrors for mid-infrared spectral range

Tatiana Amotchkina, Michael Trubetskov, Syed Ali Hussain, Daniel Hahner, Ioachim Pupeza, Ferenc Krausz, Vladimir Pervak, Daniel Gerz, Hans Schweinberger, and Marinus Huber

Doc ID: 370564 Received 20 Jun 2019; Accepted 08 Sep 2019; Posted 13 Sep 2019  View: PDF

Abstract: Broadband dispersive mirrors operating in the mid-infrared spectral range 6.5-11.5 µm are developed for the first time. The mirrors comprise Ge and YbF3 layers which have not been used before for manufacturing multilayer dispersive optics. The design and production processes are described; expected mechanical stresses of the coatings are calculated; spectral and phase properties of the produced mirrors are measured. The mirrors compensate group delay dispersion of ultrashort laser pulses accumulated by propagation through 4 mm-ZnSe windows and additional residual phase modulation of an ultrashort laser pulse.

Zeeman-tunable Modulation Transfer Spectroscopy

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

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

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

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

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

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

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

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

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

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

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

Nonlinear optical response spatial self-phase modulation in MoTe2: Correlations between χ(3) and mobility or effective mass

Jimin Zhao, Lili Hu, Fei Sun, and Hui Zhao

Doc ID: 376426 Received 27 Aug 2019; Accepted 05 Sep 2019; Posted 11 Sep 2019  View: PDF

Abstract: We report an unambiguous observation of third-order nonlinear optical effect, spatial self-phase modulation (SSPM), in a MoTe2 dispersion. The values of the third order nonlinear optical coefficients effectively for one layer MoTe2, χ(3)one-layer, are obtained through the SSPM method at excitation wavelengths 473, 532, 750 and 801 nm, respectively. The wind-chime model is used to explain the ring formation time. The wavelength dependence of χ(3)one-layer compares well with the photo-absorption spectra. Significantly, we find a correlation between χ(3) and the carrier mobility μ or effective mass m*, which again further supports the laser-induced ac electron coherence in 2D materials.

Iris-assisted Terahertz Field-Induced Second Harmonic Generation in Air

Sharly Fleischer, Amit Beer, and Dror Hershkovitz

Doc ID: 370948 Received 26 Jun 2019; Accepted 27 Aug 2019; Posted 06 Sep 2019  View: PDF

Abstract: Terahertz field-induced second harmonic generation (TFISH) is a technique for optical detection of broad-band THz fields. We show that by placing an iris at the interaction volume of the THz and optical fields, the TFISH signal increases by few ten-fold in atmospheric air. The iris-assisted TFISH amplification is characterized at varying air pressures and probe intensities and provides an elegant platform for studying nonlinear phase-matching in the gas phase.

Steriograthic Geometry of Coherence and Which-path Information

Yusef Maleki

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

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

Optofluidic in-fiber integrated SERS detection based on hollow optical fiber with suspended core

Xinghua Yang, Danheng Gao, pingping teng, Zhihai Liu, Jun Yang, Depeng Kong, Jianzhong Zhang, meng luo, Libo Yuan, Fengjun Tian, and Xinghua Yang

Doc ID: 370649 Received 21 Jun 2019; Accepted 09 Jul 2019; Posted 26 Sep 2019  View: PDF

Abstract: In this paper, we first proposed a novel kind of in-fiber optofluidic Raman SERS sensor based on a microstructured hollow fiber (MHF) with a suspended core. Taking the advantages of its unique internal structure, silver nanoparticles with SERS effect are immobilized in the MHF by chemical bond. The Raman signal of the microfluidic sample is excited by the excitation light in the suspended core through evanescent field. Then, the on-line SERS signal can be coupled back into the core and be detected. To demonstrate the feasibility of the device, we choose rhodamine 6G (R6G) as the analyte and high quarlity SERS spectra were detected with the limit (LOD) of 1 x 10-14 M. Furthermore, we conducted an on-line optofluidic test on ceftriaxone (C18H18N8O7S3) to examine its capabilities in antibiotic sensing. Results show that the LOD of the samples is 10-6 M. Significantly, this work provide an integrated optofluidic in-fiber SERS sensor with a micro-channel which can be integrated with chip devices without spatial optical coupling, which had a broad application in medicine, food safety, as well as various aspects of biological in-fiber sensing.

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