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Accepted papers to appear in an upcoming issue

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Inverse-designed low-loss and wideband polarization-insensitive waveguide crossing

Zejie Yu, Aosong Feng, Xiang Xi, and Xiankai Sun

Doc ID: 347492 Received 04 Oct 2018; Accepted 15 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: Waveguide crossings are an essential component for constructing complex and functional on-chip photonic networks. Polarization-insensitive waveguide crossings are desired because photonic networks usually involve light with different polarizations. Here, we propose a polarization-insensitive waveguide crossing by using an inverse-design method. In simulation, the designed waveguide crossing can maintain insertion loss below 0.18 (0.25) dB in the wavelength range of 1440‒1640 nm for the TE0 (TM0) mode and achieve the minimal insertion loss as small as 0.08 (0.07) dB at the wavelength of 1550 nm. The crosstalk maintains below −32 dB and −35 dB for the TE0 and TM0 modes, respectively. Experimentally, the fabricated waveguide crossing achieves measured insertion loss less than 0.20 (0.25) dB for the TE0 (TM0) mode with the minimal insertion loss as small as 0.1 dB. The measured crosstalk is below −28 dB and −31 dB for the TE0 and TM0 modes, respectively. Therefore, our proposed waveguide crossing can be widely applied in photonic integrated circuits to construct complex photonic systems with the capabilities of polarization control and mode (de)multiplexing.

2D Optical-controlled Radio Frequency Orbital Angular Momentum Beam Steering System based on Dual-parallel Mach-Zehnder Modulator

Xinlu Gao, Mingyang Zhao, Mutong Xie, Mingzheng Lei, xiyao song, ke bi, Zhennan Zheng, and Shanguo Huang

Doc ID: 348598 Received 17 Oct 2018; Accepted 14 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: An optical controlled system for generating and continuously steering radio frequency (RF) signals with double orbital angular momentum (OAM) modes is proposed and experimentally demonstrated. The optical carrier’s utilization efficiency can be doubled through the distinct electro-optical modulation, which is based on two single-sideband modulation operations on a single optical carrier through a customized dual-parallel Mach-Zehnder modulator. A constructive antenna phase feeding method of a circular antenna array for collectively forming and steering OAM radio beam is proposed and illustrated. A proof-of-concept experiment is conducted to generate and steer a dual-mode RF-OAM beam to the two different directions with two-dimension (2D), independently and simultaneously. One 17GHz OAM beam with mode L=1 is continuously steered to 2D directions (:, 0°, 0°), (:, 0°, 1.70°), (:, 0°, 3.87°), (:, 0°, 6.17°) and(:, 0°, 7.80°), with vortex properties, where “:” means “any value of ”. Meanwhile, the 19GHz OAM beam with mode L=-1 carried is steered from (:, 0°, 0°) to (:, 0°, -6.72°), and the constellations are obtained successfully.

Optomechanical quadrature squeezing in the non-Markovian regime

Biao Xiong, Xun Li, Shi-Lei Chao, and Ling Zhou

Doc ID: 351329 Received 07 Nov 2018; Accepted 14 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: Squeezing of quantum fluctuation plays an important role in fundamental quantum physics and has marked influence on ultrasensitive detection. We propose a scheme to generate and enhance the squeezing of mechanical mode by exposing the optomechanical system to a non-Markovian environment. It is shown that the effective parametric resonance term of mechanical mode can be induced due to the interaction with the cavity and non-Markovian reservoir, thus resulting in quadrature squeezing of the mechanical resonator. And jointing the two kinds of interactions can enhance the squeezing effect. Comparing with the usual Markovian regime, we can obtain stronger squeezing, and significantly the squeezing can approach a low asymptotic stable value.

A single photon detection system for visible and infrared spectrum range

Alexander Divochiy, Marta Misiaszek, Yury VAKHTOMIN, Pavel Morozov, Konstantin Smirnov, Philipp Zolotov, and Piotr Kolenderski

Doc ID: 341001 Received 04 Sep 2018; Accepted 14 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We demonstrate niobium nitride based superconducting single-photon detectors sensitive in the spectral range 452 nm - 00 nm. The system performance was tested in a real-life experiment with correlated photons generated by means of spontaneous parametric down conversion, where one of photon was in the visible range and the other was in the infrared range. We measured a signal to noise ratio as high as 4 x10⁴ in our detection setting. A photon detection efficiency as high as 64% at 1550 nm and 15% at 00 nm was observed.

3.5 kW coherently-combined ultrafast fiber laser

Michael Müller, Arno Klenke, Albrecht Steinkopff, Henning Stark, Andreas Tünnermann, and Jens Limpert

Doc ID: 347857 Received 18 Oct 2018; Accepted 14 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: An ultrafast laser based on coherent beam combination of four ytterbium-doped step-index fiber amplifiers is presented. The system delivers an average power of 3.5 kW and a pulse duration of 430 fs at 80 MHz repetition rate. The beam quality is excellent (M2<1.24∙1.10) and the relative intensity noise is as low as 1% in the frequency span from 1 Hz to 1 MHz. The system is turn-key operable as it features an automated spatial and temporal alignment of the interferometric amplification channels.

Enhancement of surface plasmon polariton excitation via feedback-based wavefront shaping

Xiaona Ye, Haigang Liu, Yanqi Qiao, and Xianfeng Chen

Doc ID: 347879 Received 10 Oct 2018; Accepted 14 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: Surface plasmon polariton (SPP) is an electromagnetic excitation with efficient spatial confinement and high local field intensity at metal/dielectric interface, which has been widely applied in many fields such as nanophotonics, imaging, biosensing, nonlinear optics, and so on. However, the destructive interference, which arises from wavevector mismatching between the spatial components of incident light and SPP, limits the effective excitation of SPP. Here, we experimentally demonstrate the enhancement of SPP excitation via feedback-based wavefront shaping method in Kreschmann configuration. After optimizing phase profile of the incident laser beam, the intensity is enhanced by a factor of 1.58 times even at the resonance angle of fundamental mode Gaussian beam. Besides, the influences of different conditions for the enhancement of SPP excitation are also analyzed. This work provides a flexible and convenient method to further enhance the SPP excitation, and it may have the application of further enhancement of the interaction between SPP and other physical processes.

Diagonal Slice Four-Wave Mixing: Natural Separation of Coherent Broadening Mechanisms

Geoffrey Diederich, Travis Autry, and Mark Siemens

Doc ID: 348630 Received 18 Oct 2018; Accepted 14 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We present an ultrafast coherent spectroscopy data acquisition scheme that samples slices of the time domain used in multidimensional coherent spectroscopy to achieve faster data collection than full spectra. We derive analytical expressions for resonance lineshapes using this technique that completely separate homogeneous and inhomogeneous broadening contributions into separate projected lineshapes for arbitrary inhomogeneous broadening. These lineshape expressions are also valid for slices taken from full multidimensional spectra and allow direct measurement of the parameters contributing to the lineshapes in those spectra as well as our own.

Inscribing diffraction gratings in bulk silicon with nanosecond laser pulses

Maxime Chambonneau, Daniel Richter, Stefan Nolte, and David Grojo

Doc ID: 348711 Received 19 Oct 2018; Accepted 14 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: Diffraction gratings are transversally inscribed in the bulk of monolithic crystalline silicon with infrared nanosecond laser pulses. Nanoscale material analyses of the modifications composing the gratings show that they rely on laser-induced stress associated with a positive refractive index change as confirmed with phase-shift interferometry. Characterizations of the optical properties of the gratings including the diffraction angles as well as efficiency of the different orders are carried out. The refractive index change obtained from these measurements is in good agreement with the phase-shift measurements. Finally, we show that the grating diffraction efficiency depends strongly on the laser writing speed.

Squeezing-enhanced heterodyne detection of 10 Hz atto-Watt optical signals

Sheng Feng and Boya Xie

Doc ID: 349407 Received 29 Oct 2018; Accepted 13 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: A phase-sensitive (PS) heterodyne detector is intrinsically resistant to classical noises and useful in measurement of low-frequency signals below the shot noise. Despite of the existence of image band vacuum, we show that the quantum-noise power level of this heterodyne detector sensing a coherent signal is exactly one light quantum per measurement time, i.e., twice the vacuum fluctuation power, which can be further reduced by use of squeezed light. We then report on an experiment on a PS heterodyne detector with a 10 Hz $1.0\times10^{-18}$ W optical signal (1064 nm wavelength) at its input. The noise floor of the unmodulated coherent light is $2.2(\pm0.1)\times 10^{-19}$ W/Hz from 2 Hz to 20 Hz, and the signal-to-noise ratio is about 6.6 dB for the measured signal when the resolution bandwidth is 1 Hz. The quantum noise floor is reduced by 1.6($\pm$0.3) dB when squeezed light is used, and the sub-shot-noise power spectral density is $1.6(\pm0.1)\times 10^{-19}$ W/Hz between 2 Hz and 20 Hz. This work should be an important advance towards squeezing-improved precision measurements of low-frequency signals with heterodyne detectors, including audio-band gravitational-wave detection.

Isotropic-resolution photoacoustic microscopy with multi-angle illumination

Tianxiong Wang, Naidi Sun, Ruimin Chen, Qifa Zhou, and Song Hu

Doc ID: 341400 Received 03 Aug 2018; Accepted 13 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: We have developed photoacoustic microscopy (PAM) with micron-level spatial resolution in all three dimensions (3D). With multi-angle illumination, PAM images from different view angles can be simultaneously acquired for multi-view deconvolution, without the rotation of imaging target. Side-by-side comparison of this multi-angle-illumination PAM (MAI-PAM) and conventional PAM, which shared the same ultrasonic detector, was performed in both phantoms and live rodents. The phantom study showed that MAI-PAM achieved a high axial resolution of 3.7 µm, which was 10-fold higher than that of conventional PAM and approached the lateral resolution of 2.7 µm. Further, the in vivo study demonstrated that MAI-PAM was able to image the microvasculature in 3D with isotropic resolution.

Multi-band bonding/anti-boding interaction and selectively electrical field confinement in the complementary metamaterial

Liyong Jiang, Jianli Jiang, Lei Zhu, Liang Dong, Shuang Liang, Jing Yuan, Wei Zhang, Jisong Qian, Jing Shu, and Xiangyin Li

Doc ID: 348654 Received 23 Oct 2018; Accepted 13 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We report the experimental and theoretical study on the complementary planar metamaterial with asymmetrical air nanorods. Three high-quality samples are fabricated by the focused ion beam technique. Multi-band Fano-like resonances and selectively electrical field confinement in the visible-near infrared range are presented and well explained by the bonding/anti-boding and Mie theories of plasmonic resonators.

Broadband quarter-wave birefringent meta-mirrors for generating sub-diffraction vector fields

Gang Chen, Yuyan Li, Luyao Cao, Zhongquan Wen, Chunyan Qin, Junbo Yang, Zhihai Zhang, Gaofeng Liang, Zhengguo Shang, Kun Zhang, Shuo Zhang, and Luru Dai

Doc ID: 347357 Received 02 Oct 2018; Accepted 13 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: Independent manipulation of phase and polarization of optical fields is of great interest in various applications, including vector-field generation, optical tweezers, and nanolithography. The integration of phase and polarization manipulation on a single optical device might great simplify optical systems and eases optical alignment. In this paper, a family of reflective cross-shaped quarter-wave birefringent metasurfaces was proposed to achieve full control of polarization and phase of reflected waves. Based on the proposed metasurfaces, two meta-mirrors are designed with a high numerical aperture of 0.96 for a wavelength of λ=1550 nm. Both meta-mirrors integrate the functions of polarization conversion and wave focusing. The meta-mirrors can convert the circular polarization into cylindrical polarization, including radial and azimuthal polarization, and focus the wave into a longitudinal polarized solid spot with sub-diffraction size and an azimuthally polarized hollow spot with super-oscillation size, respectively. Numerical investigations also reveal the achromatic focusing performance of the proposed small meta-mirrors with a bandwidth of 100 nm and 210 nm for longitudinally polarized spot and azimuthally polarized spot, respectively. The proposed broadband quarter-wave birefringent meta-mirrors provide a potential way to realize sub-diffraction vector waves. In addition, the proposed metasurfaces with independent manipulation of polarization and phase provide flexible building blocks for constructing complicated vector optical fields.

Terahertz wave near-field compressive imaging with spatial resolution of over λ/100

Li-Guo Zhu, Sichao Chen, Liang-Hui Du, Kun Meng, jiang li, Zhao-Hui Zhai, qiwu shi, and Ze-Ren Li

Doc ID: 347906 Received 10 Oct 2018; Accepted 13 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We demonstrate terahertz (THz) wave near-field imaging with spatial resolution of ~4.5 μm (λ0/133 at 0.5 THz) using single-pixel compressive sensing enabled by femtosecond-laser (fs-laser) driven vanadium dioxide (VO2)-based spatial light modulator. By fs-laser patterning a 180-nm-thick VO2 nanofilm with a digital micromirror device, we spatially encode the near-field THz evanescent waves. With single-pixel Hadamard detection of the evanescent waves, we reconstructed the THz wave near-field image of an object from a serial of encoded sequential measurements, yielding improved signal-to-noise ratio by one-order magnitude over raster-scanning technique. Further, we demonstrate the acquisition time was compressed by a factor of over four with 90% fidelity using total variation minimization algorithm. The proposed terahertz wave near-field imaging technique inspires new and challenging applications, such as cellular imaging.

Complex degree of coherence modeling with famousplanar curves

Olga Korotkova and Xi Chen

Doc ID: 346566 Received 21 Sep 2018; Accepted 13 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: Several planar curves well-known from mechanics, astronomy,acoustics, etc. and also used in other branchesof optics, such as caustics and light robotics are employedfor modeling of the recently introduced coherencecurves [O. Korotkova and X. Chen, Opt. Lett. 43,4727 (2018)]. These planar curves have intrinsic relationshipsbetween their magnitudes and phases, and hencelead to not previously encountered coherence states.

A high-efficiency, linear-polarization-multiplexing metalens for long-wavelength infrared light

Qing Fan, yilin wang, MIngze Liu, and Ting Xu

Doc ID: 345606 Received 12 Sep 2018; Accepted 13 Nov 2018; Posted 13 Nov 2018  View: PDF

Abstract: Variable-focus lenses are essential elements of optical systems with extensive applications in microscopy, photography, and optical detection. However, the conventional varifocal optical systems obtain a limited tunable capability at the expense of bulk size and slow speed. Metasurfaces are two-dimensional flat structures composed of subwavelength scatterers that exhibit the strong potential for developing ultrathin optics. Here, we propose and experimentally demonstrate an all-dielectric polarization-multiplexing metalens with the capability to selectively focus polarized light. The focal length can be controlled by altering the linear polarization state of the incident light. The metalens has the focusing efficiencies higher than 72% and exhibits nearly diffraction-limited focusing at long-wavelength infrared (LWIR) frequency. In addition, it’s easy to realize high-throughput with low manufacture cost due to the use of CMOS-compatible processes. We envision this type of polarization-dependent device may pave the way towards the development of compact, multifunctional and tunable optics.

A polarization-insensitive silicon waveguide crossing based on multimode interference couplers

Yaocheng Shi and Jingye Chen

Doc ID: 347696 Received 08 Oct 2018; Accepted 12 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: A polarization-insensitive waveguide crossing based on multimode interference (MMI) couplers is proposed and demonstrated on silicon-on-insulator (SOI) platform. By utilizing two orthogonal MMIs, the footprint of the device is about μm× μm. The proposed device, easily fabricated with only one fully-etched step, is characterized with low insertion losses (< 1.5 dB) and low crosstalks (< -25 dB) for both TE- and TM- polarizations from 1520 nm to 1610 nm band.

Quantitative assessment and suppression of defect-induced scattering in low-loss mirrors

Lei Zhang, Zeyong Wei, Jinlong Zhang, Huasong Liu, yiqin ji, Sven Schröder, Marcus Trost, Zhanshan Wang, and Xinbin Cheng

Doc ID: 348221 Received 18 Oct 2018; Accepted 12 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: In this work, defect-induced scattering in 1064 nm high-reflection coatings and its suppression were investigated by artificial nodules, finite-difference time-domain simulations, angular resolved scattering measurements and planarization technology. After establishing the geometric model of the nodules grown from  1 μm SiO2 microspheres, the far-field scattering of the multiple nodules was determined by intensity superposition. For a nodule density of 100 mm-2, there is good agreement between the simulated and measured angular resolved scattering. The total scattering is ~500 ppm for the multilayer coating with artificial nodules, which is more than 10 times that for the coating without nodules. Next, an iterative deposition-etching process was used to planarize the defects, which reduced scattering by almost one order of magnitude. Moreover, detail characterization of the planarized seeds reveals that the planarization technology is a complex process and it still does not produce a perfect flat surface. The results showed that there is a pit over each planarized seed in the coating surface, which leads to additional scattering. The possible reasons for the presence of these pit are briefly discussed and the directions for further research are provided at the end of this paper.

Spatially encoded polarization dependent nonlinear optics

James Ulcickas, Changqin Ding, Fengyuan Deng, and Garth Simpson

Doc ID: 349029 Received 25 Oct 2018; Accepted 12 Nov 2018; Posted 13 Nov 2018  View: PDF

Abstract: A single fixed optic is combined with the sample translation capabilities inherent to most microscopes to achieve precise polarization-dependent SHG microscopy measurements of thin tissue sections. Although polarization measurements have enabled detailed structural analysis of collagen, challenges in integrating rotation stages or fast electro-optic / photoelastic modulation have complicated the retrofitting of existing systems for precise polarization analysis. Placing a static microretarder array (μRA) in the rear conjugate plane resulted in spatially encoded polarization modulation across the field of view. A complete set of polarization rotation measurements was acquired at each pixel by sample translation, recovering local-frame tensors relating to structure within collagenous tissue.

Soliton content in the standard optical OFDM signal

Egor Sedov, Alexey Redyuk, Mikhail Fedoruk, A Gelash, Leonid Frumin, and Sergei Turitsyn

Doc ID: 347646 Received 09 Oct 2018; Accepted 11 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Nonlinear Schrödinger equation (NLSE) is often used as a master path-average model for fiber-optic transmission lines. In general, NLSE describes the co-existence of dispersive waves and soliton pulses. Propagation of signal in such a nonlinear channel is conceptually different from linear systems. We demonstrate here that the conventional orthogonal frequency-division multiplexing (OFDM) input optical signal at powers typical for modern communication systems might have soliton components statistically created by the random process corresponding to the information content. Applying Zakharov-Shabat spectral problem to a single OFDM symbol with multiple sub-carriers we quantify the effect of statistical soliton occurrence in such an information-bearing optical signal. Moreover, we observe that at signal powers optimal for transmission OFDM symbol incorporates multiple solitons with high probability. The considered optical communication example is relevant to a more general physical problem of generation of coherent structures from noise.

Quadratic Soliton Combs in Doubly-Resonant Second-Harmonic Generation

Tobias Hansson, Pedro Parra-Rivas, Martino Bernard, François Leo, Lendert Gelens, and Stefan Wabnitz

Doc ID: 347379 Received 03 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We report a theoretical investigation of quadratic frequency combs in a dispersive second-harmonic generation cavity system. We identify different dynamical regimes and demonstrate that the same system can exhibit both bright and dark localized cavity solitons in the absence of a temporal walk-off.

Pulsating soliton with chaotic behavior in a fiber laser

Zhi-Wei Wei, Meng Liu, Shu-Xian Ming, Aiping Luo, Wen-Cheng Xu, and Zhi-Chao Luo

Doc ID: 342661 Received 17 Aug 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: The pulsating behavior of solitons is one of the interesting dynamics in dissipative nonlinear systems. It was theoretically predicted that the chaotic soliton could exist in the soliton pulsation process. Herein, we reported on the experimental evidence of the pulsating soliton with chaotic behavior in an ultrafast fiber laser. By virtue of dispersive Fourier transformation (DFT) method, the chaotic behavior of soliton pulsation is visualized by the fact that the mode-locked spectrum collapses abruptly in an unpredictable way during the pulsating process. The obtained results provide the first experimental demonstration of the chaotic behavior in the pulsating soliton, which would also give some new insights into the soliton pulsation dynamics in dissipative systems.

High-contrast and low-power all-optical switch using Fano resonance based on a silicon nanobeam cavity

Xinliang Zhang, Gaoneng Dong, and Yilun Wang

Doc ID: 348868 Received 22 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We experimentally demonstrate an ultra-compact all-optical switch involving Fano resonance based on a side-coupled Fabry-Perot (F-P) resonator and a silicon photonic crystal (PhC) nanobeam cavity, with an area of only 11 μm2. By optimizing the structure of the nanobeam cavity to increase its intrinsic quality factor (Q), we achieve a sharp asymmetric transmission spectrum, with an extinction ratio (ER) as high as 40 dB and a peak loss as low as 0.6 dB. As far as we know, this is the highest measured ER in PhC-based Fano resonance. These excellent properties enable us to realize an all-optical switch with shorter switching recovery time, lower power consumption and higher contrast, comparing to that involving Lorentzian resonance. For example, under signal trains of 2.5 Gb/s, switching energy with a contrast of 3 dB for Fano case is 113 fJ, which is 8-dB smaller than that for Lorentzian case. Furthermore, by performing blue-detuned filtering on the 15-Gb/s output signal light, the switching contrast of the all-optical switch based on Fano resonance is significantly improved from 0.67 dB to 9.53 dB.

Nonlinear frequency conversion and manipulation of vector beams

Haigang Liu, Hui Li, Yuanlin Zheng, and Xianfeng Chen

Doc ID: 349213 Received 25 Oct 2018; Accepted 10 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Vector beams have been extensively investigated in recent years because of its fascinating vector character across the beam transverse section, which is demonstrated to be useful for optical micro-manipulation, optical micro-fabrication, optical communication, single molecule imaging, and so on. To date, it is still a challenge to realize nonlinear frequency conversion and manipulation of such vector beams because of the polarization sensitivity in most of nonlinear processes. Here, in our experiment, second-harmonic vector beams are generated by using three-wave mixing processes, which occur in two orthogonal placed nonlinear crystals, and the vector property is recognized by using a Glan-Taylor polarizer. This nonlinear frequency conversion process enables vector beams to be obtained at new wavelengths, and opens up new possibilities for all-optical switching and manipulation of vector beams.

Novel silicon nanoparticles based broadband optical modulators for solid-state lasers

Xinyang Liu, Kejian Yang, Shengzhi Zhao, Tao Li, Wenchao Qiao, Yaling Wang, Lei Guo, Yiran Wang, hongkun nie, Baitao Zhang, and Jingliang He

Doc ID: 346959 Received 28 Sep 2018; Accepted 09 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: Motivated by the tremendous success of carbon nanomaterials in acting as optical nonlinear modulator, in this paper, the optical nonlinearity of its counterpart, silicon nanoparticles (SiNPs), is investigated. For the first time, the nonlinear optical property of SiNPs in 1μm and 2μm wavelength bands is observed. Its practical modulation performance was investigated by employing SiNPs as saturable absorber (SA) in pulsed lasers and the fabrication process, surface morphology, linear and nonlinear optical response property of the prepared SiNPs-SA were presented. Based on the SiNPs-SA, the formed Q-switched Nd:LuAG laser could generate laser pulses with shortest duration of 490 ns at ~1 μm and ~2 μm laser pulses with shortest duration of 453 ns were delivered from a Q-switched Tm:YAP laser, which shows that the SiNPs could be employed as a promising broadband SA for near- and mid-infrared spectral region.

Aperiodic Vogel spirals for broadband optical wave focusing

Taotao Zhao, Yanwen Hu, Shenhe Fu, Xiaonan Li, Yi-Kun Liu, Hao Yin, Zhen Li, Juntao Li, and Zhenqiang Chen

Doc ID: 347335 Received 02 Oct 2018; Accepted 09 Nov 2018; Posted 12 Nov 2018  View: PDF

Abstract: We demonstrate both experimentally and numerically a new type of hole array structures which exhibit optically diffractive focusing phenomenon. The hole arrays are designed based on the aperiodic Vogel spirals. In contrast to periodic and quasi-periodic hole arrays that contain discrete Bragg peaks in reciprocal space, the Vogel spiral hole arrays have particularly continuous Fourier components with circular symmetry, which enables optical wave focusing into a diffraction-limited hotspot for a wide range of incident wavelengths. We further demonstrate that the diffracted fields contain local orbital angular momentum leading to rotations of the diffractive circular rings around the center, although the total orbital angular momentum is zero.

Fiber optic refractive index sensors through spectral detection of Rayleigh backscattering in a chemically etched MgO-based nanoparticle-doped fiber

Marzhan Sypabekova, Sanzhar Korganbayev, Wilfried Blanc, Takhmina Ayupova, Aliya Bekmurzayeva, Madina Shaimerdenova, Kanat Dukenbayev, Carlo Molardi, and Daniele Tosi

Doc ID: 348705 Received 18 Oct 2018; Accepted 09 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We demonstrate and experimentally validate a fiber-optic refractive index (RI) sensor obtained by simply etching a high-scattering MgO-based nanoparticle-doped single-mode fiber in hydrofluoric acid (HF). The fiber has 32.3 dB stronger Rayleigh scattering than a standard fiber, allowing a detection of scattering spectral signatures with an optical backscatter reflectometer (OBR) even when the core is exposed to the outer refractive index. The obtained sensitivity is 1.53 nm/RIU (RI units), measured by correlating the scattering spectra. We prove the possibility of implementing a distributed RI detection (7 locations spaced by 1 mm). The fabrication method for this RI sensor is simplified as it simply requires etching in a HF bath, without the need of inscribing reflective elements or fabricating microstructures on the fiber.

1 W dual-end-pumped Ho:YAG MOPA system and its application to a mid-infrared ZGP2 OPO

Benrui Zhao, baoquan yao, Chuanpeng Qian, gaoyou liu, Yi Chen, Ruixue Wang, Tongyu Dai, and Xiaoming Duan

Doc ID: 349325 Received 26 Oct 2018; Accepted 09 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: A high efficiency and brightness Ho:YAG master-oscillator power-amplifier (MOPA) system dual-end-pumped by Tm:YLF lasers was demonstrated. The maximum output power of 1 W at wavelength of 2090.7 nm was achieved with pulse repetition frequency (PRF) of 10 kHz and pulse width of 22.9 ns, corresponding to pulse energy of .1 mJ and peak power of ~1 MW. The extraction efficiency of the amplifier system was more than 60%. The beam quality factor M2 was measured to be ~1.05. Using the Ho:YAG MOPA system as pump source, the ZGP2 (ZGP) optical parametric oscillator (OPO) delivered an output power of 110 W, corresponding to slope efficiency of 62%.

Compact highly efficient 2.1-W continuous-wave mid-IR Fe:ZnSe coherent source pumped by Er:ZBLAN fiber laser

Andrey Pushkin, Ekaterina Migal, Hiyori Uehara, Kenji Goya, Shigeki Tokita, M. Frolov, Yuriy Korostelin, Vladimir Kozlovsky, Yan Skasyrsky, and Fedor Potemkin

Doc ID: 351238 Received 07 Nov 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We report the compact and robust coherent source operating in mid-IR based on Fe:ZnSe chalcogenide gain medium optically pumped by Er:ZBLAN fiber laser. The output power of 2.1 W with 59% slope efficiency with respect to absorbed pump power at liquid nitrogen cooling is achieved. We show that strong re-absorption at high pump power and iron ion doping concentrations leads to the continuous tuning of central wavelength from 4012 to 4198 nm. Robustness of high power Er:ZBLAN fiber laser combined with prominent spectroscopic properties of Fe:ZnSe media pave the way for the development of reliable tunable CW mid-IR sources for scientific and industrial purposes.

Generation of telecom-band correlated photon pairs in different spatial modes using few-mode fibers

Cheng Guo, Jie Su, Zhenzhen Zhang, Liang Cui, and Xiaoying Li

Doc ID: 346327 Received 19 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We experimentally demonstrate the production of photon pairs at 1555 nm in LP01 mode and at 1566.8 nm in LP11 mode, respectively, via the spontaneous intermodal four-wave mixing in a 100-m-long few-mode fiber. We achieve a coincidence to accidental-coincidence ratio of 28, which clearly indicates the existence of quantum correlation. We also discuss the contribution of spontaneous Raman scattering to the background noise of photon pairs. Our source of photon pairs, compatible with the low-loss multiplexing and de-multiplexing components for space division multiplexing optical fiber communication, can be used for generating higher-dimensional entanglement.

Measurement of high pressure and high temperature using a dual-cavity Fabry-Pérot interferometer created in cascade hollow-core fibers

Zhang Zhe, Jun He, Bin Du, Fengchan Zhang, Kuikui Guo, and Yiping Wang

Doc ID: 346526 Received 21 Sep 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: A compact dual-cavity Fabry-Perot interferometer (DC-FPI) sensor is proposed and demonstrated based on a hollow-core photonic bandgap fiber (HC-PBF) spliced with a hollow-core fiber (HCF). The HC-PBF, which has low transmission loss, was used as the first FPI cavity and also acted as a bridge between the lead-in single-mode fiber (SMF) and the HCF. The HCF was used as the second FPI cavity and also acted as a micro gas inlet into the first FPI cavity. A DC-FPI sensor with different cavity lengths of 226 and 634 μm in the first FPI and the second FPI was created. Both gas pressures ranging from 0–10 MPa and temperatures ranging from 100–800 °C were measured using the DC-FPI sensors together with a fast Fourier transform (FFT) and phase demodulation algorithm. Experimental results showed that the first FPI cavity was gas-pressure sensitive but temperature insensitive, while the second FPI cavity was temperature sensitive but gas-pressure insensitive. A high gas-pressure sensitivity of 1.336 μm/MPa and a temperature sensitivity of 17 nm/°C were achieved in the DC-FPI sensor. Moreover, the cross sensitivity between the gas pressure and temperature was calculated to be ~−15 Pa/°C and ~0.3 °C/MPa. The proposed DC-FPI sensors provide a promising candidate for the simultaneous measurement of high pressures and high temperatures at some precise locations.

Generation of broadband near-field optical spots using thin film silicon waveguide with gradually changing thickness

Kaifeng Zhang, Shin-ichi Taniguchi, and Takehiro Tachizaki

Doc ID: 347462 Received 17 Oct 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We developed a thin film silicon waveguide with gradually changing thickness for generating a near-field optical spot. Theoretical studies show that the surface plasmons that are resonantly excited on the waveguide generate a hot spot with a wide spectral range. We experimentally confirmed generation of the near-field hot spot using continuous waves at 850 nm and 660 nm wavelengths. This waveguide which can generate the enhanced electric field by normal incident of the excitation beam under situations of the practical use is promising for broadband near-field optical technologies.

Non-diffracting linear-shift point-spread function by focus-multiplexed computer-generated hologram

Tomoya Nakamura, Shunsuke Igarashi, Yuichi Kozawa, and Masahiro Yamaguchi

Doc ID: 341864 Received 21 Aug 2018; Accepted 08 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: An Airy beam can be used to implement a non-diffracting self-bending point-spread function~(PSF), which can be utilized for computational 3D imaging. However, the parabolic depth-dependent spot trajectory limits the range and resolution in rangefinding. In this Letter, we propose a novel pupil-phase-modulation method to realize a non-diffracting linear-shift PSF. For the modulation, we use a focus-multiplexed computer-generated hologram, which is calculated by multiplexing multiple lens-function holograms with 2D sweeping of the foci. With this method, the depth-dependent trajectory of the non-diffracting spot is straightened, which improves the range and resolution in rangefinding. The proposed method was verified by numerical simulations and optical experiments. The method can be applied to laser-based microscopy, time-of-flight rangefinding, and so on.

Plasmonic Parametric Absorbers

Shima Fardad and Alessandro Salandrino

Doc ID: 347179 Received 01 Oct 2018; Accepted 08 Nov 2018; Posted 13 Nov 2018  View: PDF

Abstract: Exploiting the dynamics of Plasmonic Parametric Resonance (PPR), we introduce the theory of Plasmonic Parametric Absorbers (PPA). The key insight informing the PPA idea is that in the PPR process a pump field experiences an extinction rate that strongly depends on the intensity of the pump itself, creating two distinct regimes: one of weak absorption under low intensity illumination, and one of strong absorption when the threshold of parametric resonance is met or exceeded. Due to this reverse saturable absorption behavior, PPAs are promising candidates for optical limiting applications.

Femtosecond fiber Bragg grating fabrication with adaptiveoptics aberration compensation

Julian Fells, Patrick Salter, Matthew Woolley, Stephen Morris, and Martin Booth

Doc ID: 342972 Received 22 Aug 2018; Accepted 07 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We present fiber Bragg gratings (FBGs) fabricated using adaptive optics aberration compensation for the first time. The FBGs are fabricated with a femtosecond laser by the point-by-point method using an air-based objective lens, removing the requirement for immersion oil or ferrules. We demonstrate a general phase correction strategy that can be used for accurate fabrication at any point in the fiber cross-section. We also demonstrate a beam shaping approach that nullifies the aberration when focused inside a central fiber core. Both strategies give results which are in excellent agreement with coupled-mode theory. An extremely low wavelength polarization sensitivity of 4 pm is reported.

mJ-level, kHz-rate, CPA-free linear amplifier for 2 µm ultrashort laser pulses

Moritz Hinkelmann, Bastian Schulz, Dieter Wandt, Uwe Morgner, Maik Frede, Joerg Neumann, and Dietmar Kracht

Doc ID: 346692 Received 02 Oct 2018; Accepted 07 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: The generation of mJ-level ultrashort laser pulses at a wavelength of 2.05 μm in a compact CPA-free linear amplifier based on Holmium-doped YLF gain medium is presented. More than 100 MW of pulse peak power has been achieved. We show capabilities of this laser amplifier from 1 kHz up to 100 kHz repetition rate. A detailed numerical description supports the experimental work and verifies the achieved results.

Controlling Dipole Transparency with Magnetic Fields

Stephen Hughes and Girish Agarwal

Doc ID: 346315 Received 21 Sep 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: We describe how magnetic fields can be exploited to control dipole-induced transparency in quantum dot cavity systems. Coupling a linearly-polarized microcavity mode to two spin charged exciton states of a single quantum dot, we demonstrate how cavity-mediated interference and magnetic-field resonance shifts can be utilized to control the transmission of light and on-chip photons, in both magnitude and phase. In particular, we show a triple resonance feature, which also survives with weakly coupled cavities, as long as one operates in the good cooperativity regime. The central peak, which is mediated by the applied magnetic field, is shown to exhibit spectral squeezing. We also demonstrate how the magnetic field allows five regions in which the phase changes by $2\pi$ over a small frequency window, where a possible phase gate could be implemented.

Exceptional points for photon pairs bound by nonlinear dissipation in cavity arrays

Mark Lyubarov and Alexander Poddubny

Doc ID: 347417 Received 08 Oct 2018; Accepted 07 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: We study theoretically the dissipative Bose-Hubbard model describing array of tunneling-coupled cavities with non-conservative photon-photon interaction. Our calculation of the complex energy spectrum for the photon pairs reveals exceptional points where the two-photon states bound by nonlinear dissipation are formed. This improves fundamental understanding of the interplay of non-Hermiticity and interactions in the quantum structures and can be potentially used for on-demand nonlinear light generation in photonic lattices.

Realization of 101 W single-frequency continuous wave all-solid-state 1064 nm laser by means of mode self-reproduction

Yongrui Guo, Minzhi Xu, Weina Peng, Jing Su, Huadong Lu, and Kunchi Peng

Doc ID: 347576 Received 05 Oct 2018; Accepted 07 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We realized an 101 W single-frequency continuous wave (CW) all-solid-state 1064 nm laser by means of mode self-reproduction in this Letter. Two pieces of laser crystals were simultaneously inserted into an identical resonator to relax the thermal lens of the laser crystals and an imaging system was employed to realize cavity mode self-reproduction at the places of the laser crystals. Single-frequency operation of the resonator was realized by employing a new kind of high extinction ratio optical diode (OD) based on the terbium scandium aluminum garnet (TSAG) crystal to realize a stable unidirectional operation of the laser together with introducing large enough nonlinear loss to the resonator to effectively suppress the multi-mode oscillation and mode hoping of the laser. As a result, a 101 W single-frequency 1064 nm laser in a single ring resonator was achieved with 42.3% optical efficiency. The measured power stability for 8 hour and the beam quality were better than ±0.73% and 1.2, respectively.

Photonic Reservoir Computing with quantum cascade lasers under optical delayed feedback

Romain Nguimdo and Thomas Erneux

Doc ID: 345583 Received 28 Sep 2018; Accepted 06 Nov 2018; Posted 16 Nov 2018  View: PDF

Abstract: In previous works, it has been shown that reservoir computing (RC) systems using a laser subject to a delayed optical feedback and stabilized by an injected signal may be highly sensitive to the feedback phase. In this Letter, we show that a RC system using a single Quantum Cascade Laser (QCL) subject to a delayed optical feedback but without injection is robust to the feedback phase for a large range of values of the parameters.

Beam shifting technique for speckle reduction and flow rate measurement in optical coherence tomography

Chen Chaoliang, weisong shi, Ryan Deorajh, NHU NGUYEN, Joel Ramjist, Andrew Marques, and Victor Yang

Doc ID: 346428 Received 20 Sep 2018; Accepted 06 Nov 2018; Posted 08 Nov 2018  View: PDF

Abstract: In this letter, we proposed a beam shifting optical coherence tomography (BSOCT) scheme for speckle reduction and flow rate calculation of blood flow, where variations of speckle pattern and Doppler angle were generated by parallel shifting of the sample beam incident on objective lens. The resultant OCT images could then be averaged for speckle noise reduction and simultaneously analyzed for flow rate measurement. The performance of the proposed technique was verified by both phantom and in vivo experiments.

Strong magnetochiral dichroism in chiral/magnetic layered heterostructures

Aristi Christofi

Doc ID: 348518 Received 17 Oct 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: In the present work we propose a nonreciprocal heterostructure which combines magnetism and chirality in a simple, easy to fabricate design and exhibits at least two orders of magnitude larger magnetochiral dichroism, compared to other proposed metamaterials. This effect stems from the simultaneous lack of time-reversal and space inversion symmetries and is enhanced by collective slow-photon modes originating from the strong bending of the photonic bands at the Brillouin zone boundaries. We investigate the optical properties of this bianisotropic multilayer heterostructure, consisting of consecutive bilayers of chiral and magnetic materials, embedded in air, and discuss associated photonic band structure and transmission/absorption spectra obtained by means of full electrodynamic calculations.

Dynamic mode-switchable optical vortex beams using acousto-optic mode converter

JIAFENG LU, Linghao Meng, Fan Shi, Xiaomin Liu, Zhengqian Luo, Peiguang Yan, Liangjin Huang, Fufei Pang, Tingyun Wang, Xianglong Zeng, and Pu Zhou

Doc ID: 345314 Received 10 Sep 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We propose a dynamic scheme to realize mode-switchable generation of LP11a/b modes and ±1-order orbital angular momentum (OAM) modes simultaneously, which are induced by an acoustically-induced fiber grating driven by a radio frequency modulation. LP11a/b mode degeneration in a few-mode fiber is induced by the geometric irregularity of optical fibers. A dual-wavelength resonance of mode coupling from LP01 to LP11a/b modes is found based on the combined effects of optical and acoustic birefringence. Within the configuration of CW intra-cavity laser output, we experimentally demonstrate a fast-switchable generation of LP11a/b modes and optical vortex beams with ±1-order OAM at a switching speed up to 4.3 kHz. This approach has potential applications in mode division multiplexing, particle manipulation, stimulated emission depletion microscopy and quantum information science.

Ultrafast thulium fiber laser system emitting more than 1kW of average power

Christian Gaida, Martin Gebhardt, Tobias Heuermann, Fabian Stutzki, Cesar Jauregui, and Jens Limpert

Doc ID: 346379 Received 20 Sep 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: In this letter we report on the generation of 1060 W average power and a compressed pulse energy of 13.2 µJ from an ultrafast thulium-doped fiber chirped-pulse-amplification system. The compressed pulse duration of 265 fs at 80 MHz pulse repetition rate results in a peak power of 50 MW spectrally centered at 1960 nm. Even though the average heat-load in the fiber core is as high as 98 W/m, we confirm diffraction-limited beam quality of the compressed output. Furthermore, the evolution of the RIN-noise with increasing average output power has been measured to verify the absence of transversal mode instabilities. This system represents a new average power record for thulium-doped fiber lasers (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality in general, even considering single-channel ytterbium-doped fiber amplifiers.

Liquid crystal based polarization volume grating applied for full-color waveguide displays

Yishi Weng, Yuning Zhang, Jingyi Cui, Ao Liu, Zhongwen Shen, Xiaohua Li, and bao wang

Doc ID: 346571 Received 24 Sep 2018; Accepted 06 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: In this letter, we demonstrated the polarization volume grating (PVG) based couplers for a double-layer waveguide display to realize a full-color near-eye display. The polarized interference exposure with photo-alignment methods was employed to generate a birefringent spiral configuration with two-dimensional periodicity in a chiral-dopant reactive mesogen material. Such a structure presents a unique high efficient single-order Bragg diffraction with polarized selectivity. The prepared PVG-couplers exhibit over 80% diffraction efficiency with large diffraction angles at spectra of blue (457 nm), green (532 nm) and red (630 nm). The demonstrated waveguide prototype showed a full-color display with a diagonal FOV of around 35°. The overall optical efficiency was measured as high as 91.4 cd/m2 per lumen with a transparency of 72% for ambient light.

Polarization-driven spin precession of mesospheric sodium atoms

Felipe Pedreros, Domenico Bonaccini Calia, Dmitry Budker, Mauro Centrone, Joschua Hellemeier, Paul Hickson, Ronald Holzloehner, and Simon Rochester

Doc ID: 342138 Received 13 Aug 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We report experimental results on the first on-sky observation of atomic spin precession of mesospheric sodium driven by polarization modulation of a continuous-wave laser. The magnetic resonance was remotely detected from the ground by observing the enhancement of induced fluorescence when the driving frequency approached the precession frequency of sodium in the mesosphere, between 85 km and 100 km altitude. The experiment was performed at La Palma, and the uncertainty in the measured Larmor frequency (~260 kHz) corresponded to an error in the geomagnetic field of 0.4 mG. The results are consistent with geomagnetic field models and with the theory of light-atom interaction in the mesosphere.

Precise control of evanescent scattering by self-assembled ferromagnetic particles for optical sensing with tunable sensitivity

Hau Ping Chan, Binghui Li, and Kazi Rony

Doc ID: 343101 Received 24 Aug 2018; Accepted 06 Nov 2018; Posted 07 Nov 2018  View: PDF

Abstract: We propose an optical sensing platform that uses evanescent scattering through precise manipulation of self-assembled ferromagnetic particle columns. The movement of column tips can be dynamically controlled down to a submicron range by an external actuation, namely, magnetic field, for interacting with evanescent wave propagation along an optical waveguide that causes a change in its output intensity for optical sensing. To demonstrate the idea, an AC current sensor with only a 5 mm interaction length is proposed and realized. Furthermore, its sensitivity is tunable within 9–20 dB/A by varying a DC-biased signal. The platform shows favorable signal reversibility, stability, broadband operation, and real-time response.

Micro-lensed optical fiber probe for surface-enhanced Raman scattering measurements​

Karolina Milenko, Silje Fuglerud, Snorre Kjeldby, Reinold Ellingsen, Astrid Aksnes, and Dag Hjelme

Doc ID: 345650 Received 12 Sep 2018; Accepted 06 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We present the fabrication and characterization of a novel sensing configuration based on surface-enhanced Raman scattering (SERS) and two micro-lensed optical fibers. The first micro-lensed fiber is used to excite surface plasmon resonance in a gold film deposited over a mono-layer of nano-sphere surface (AuFON) and the second lensed fiber is used to collect the SERS signal. The sensing capabilities of the fabricated device is demonstrated by measuring different concentrations of rhodamine 6G in water solution.

Bright and efficient quantum dot light emitting diodes with double light emitting layers

Qin Zhang, Chun Chang, Weifeng Zhao, Qingcheng Li, Feng Li, Xiao Jin, Feng Zhao, Zhongping Chen, and Qinghua Li

Doc ID: 342754 Received 23 Aug 2018; Accepted 06 Nov 2018; Posted 09 Nov 2018  View: PDF

Abstract: We demonstrate high bright and efficient light emitting diodes (QLEDs) with 60 nm-thick double quantum dot light emitting layers (D-EMLs) based on the poly(p-phenylene benzobisoxazole) precursors (pre-PBO). This structure distributes the charge balance by blocking electrons. The D-EMLs QLEDs exhibit significantly improvement in brightness, efficiency and stability. The external quantum efficiency (EQE) and luminance of D-EMLs QLEDs show 170 % and 48 % enhancement compared with single light emitting layer (S-EML), respectively. The efficiency roll-off of D-EMLs QLEDs is only 16 % of that of S-EML up to 10 V.

Open-loop Fiber-optic gyroscope with a double sensitivity employing a polarization splitter and Faraday rotator mirror

Weiran Wu, Ke Zhou, Chengjie Lu, and Tuohua Xian

Doc ID: 346866 Received 27 Sep 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: In this letter, a novel open-loop fiber-optic gyroscope configuration is proposed to increase the gyro’s sensitivity. In the proposed configuration light waves propagate twice along the same fiber coil in two Orthonormal polarization direction by employing a polarization-maintaining Faraday rotator mirror (PM-FRM) and a polarization beam splitter/combiner (PSC). The reciprocity of the configuration has been verified in theory. The Allan variance analysis of the gyro prototype exhibits 0.03⁰/h bias stability over 5.5h in the laboratory environment

Signal-to-noise ratio improvement of photonic time-stretch coherent radar enabling high-sensitivity ultrabroad W-band operation

Na Qian, Weiwen Zou, Siteng Zhang, and Jianping Chen

Doc ID: 348456 Received 16 Oct 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: The signal-to-noise ratio (SNR) of the photonic time-stretching receiver in the photonic time-stretch coherent radar (PTS-CR) system is theoretically analyzed. According to the analysis based on the Erbium-doped fiber amplifier (EDFA) characteristic, it is found that the SNR is dominantly determined by the input optical power of EDFA. With the improvement of the SNR of the photonic time-stretching receiver, the radar detection sensitivity is consequently enhanced. Furthermore, a PTS-CR system operating at W band with the ultrabroad bandwidth of 12 GHz is experimentally enabled, leading to the range resolution of ~1.48 cm.

Overcoming quantum limit 3 μm Er: YGG crystal lasers by balancing energy transfer and thermal effects

Li You, Dazhi Lu, Zhongben Pan, Haohai Yu, Huaijin Zhang, and jiyang wang

Doc ID: 348589 Received 18 Oct 2018; Accepted 05 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: By balancing the energy transfer and thermal effects, we demonstrate efficient erbium-doped yttrium gallium garnet (Er:YGG) crystal lasers at the wavelength of 2.8-2.9 μm for the first time to the best of our knowledge. Associated with the influence of doping concentration on the energy transfer and thermal effects, the Er3+ doping concentration was optimized to be 10 at.%, and with the optimized crystal, the maximum continuous-wave (CW) output power was 1.38W, corresponding to the slope efficiency of 35.4% overcoming the quantum limits. The thermal effects during the laser process were discussed. We believe that this work should be helpful for optimizing the erbium-doped gain for the 3 μm laser and the development of 3 μm lasers.

Richardson-Lucy deconvolution of time histograms forhigh-resolution Non-Line-of-Sight imaging based onback-projection method

chenfei jin, Jiaheng Xie, Siqi Zhang, Zijing Zhang, and Yuan Zhao

Doc ID: 342020 Received 10 Aug 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: Non-Line-of-Sight (NLoS) imaging is a new developing technique with wide applications in recent years. At present it is difficult for NLoS imaging to acquire a high resolution reconstruction with back projection. We present a novel back projection based on Richardson-Lucy deconvolution of time histograms for high resolution NLoS imaging. In our method, the backscattering photons from LoS scene are used as the essential for the deconvolution of time histogram but not removed as the interference, and then all deconvoluted time histograms are back projected into the space to form a high resolution NLoS reconstruction. The simulated and experimental results demonstrate the reconstructions of NLoS objects with high resolution for our method. Our method also indicates a good ability to restore NLoS objects under high noise level.

70 micron diameter optical probe for Common Path Optical Coherence Tomography in air and liquids

Marica Marrese, Hidde Offerhaus, Erik Paardekam, and Davide Iannuzzi

Doc ID: 344359 Received 27 Aug 2018; Accepted 05 Nov 2018; Posted 06 Nov 2018  View: PDF

Abstract: We investigate and validate a novel method to fabricate ultrathin optical probes for Common-Path OCT. The probes are obtained using a 65 μm barium titanate microsphere inserted into an inward concave cone chemically etched at the end of a single mode fiber. We demonstrate that the high refractive index (n =1.95) of the barium titanate microspheres allows one to maintain high sensitivity even while imaging in liquids, reaching a sensitivity of 87 dB. Thanks to its low cost, flexibility, and ease of use, the probe holds promise for the development of a new generation of ultrathin needle-based OCT systems.

Optical detection of ultrasound by lateral shearing interference of a transparent PDMS thin film

Supannee Learkthanakhachon, Suejit Pechprasarn, and Michael Somekh

Doc ID: 340903 Received 06 Aug 2018; Accepted 04 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A lateral shearing interferometric technique combined with a \SI{11.6}{\micro\meter} Polydimethylsiloxane (PDMS) transparent thin film is proposed and demonstrated for optical detection of ultrasound. We experimentally report the device change of reflectivity with pressure of \SI{5.1e-7}{\per\Pa}, 9.5 times more sensitive than the critical angle based sensor, 31 times more sensitive than the surface plasmon based sensor and comparable to the Fabry-Perot sensor. The objective lens based angle scanning characterization setup inspired from a laser scanning system allows direct comparison between the PDMS sensor and critical angle based sensor by adjusting the incident angle with a scanning mirror, thereby eliminating optical and electronics system dependence. The sensing element is easily fabricated through spin coating and the detection element incorporated into an existing optical system with minimum modification.

Step-index High Absorption Yb-doped Large-mode-area Fiber with Ge-doped Raised Cladding

Raghuraman Sidharthan, Junhua Ji, Kang Jie Lim, Huiting Serene Lim, Huizi Li, Jian Wei Lua, Yanyan Zhou, Chun Ho Tse, Daryl Ho, Yue Seng, Song-Liang Chua, and Seongwoo Yoo

Doc ID: 345845 Received 13 Sep 2018; Accepted 04 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: We report an all-solid large mode area (LMA) step-index fiber offering high absorption and low core numerical aperture (NA) by introducing highly Ytterbium-doped P:Al core and Germanium-doped cladding. The fiber provides core absorption of ~1200 dB/m at 976 nm with a low 0.07 core NA thanks to the raised Ge cladding. Furthermore, matched profiles of P and Al across core is successfully obtained with high concentration of Yb2O3 above 0.4 mol%. The fiber characteristics are routinely achievable by the conventional modified chemical vapor deposition with a solution doping technique. Highly efficient laser with >100 W output power, 86% slope efficiency with respect to launched pump power and a mean M2 of 1.34 has been demonstrated using the fabricated LMA step-index fiber. We also report 80% laser slope efficiency with 58 W output power (pump power limited) within only 0.5 m of the fiber when pumped by a wavelength-stabilized laser diode.

Ultrafast tunable modulation of light polarization at THzfrequencies

Vincent Juve, Gwenaelle Vaudel, Zoltán Ollmann, Janos Hebling, Vasily Temnov, Vitalyi Gusev, and Thomas Pezeril

Doc ID: 346267 Received 27 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Controlling light polarization is one of the most essen-tial routines in modern optical technology. Since thedemonstration of optical pulse shaping by spatial lightmodulators and its potential in controlling quantum re-action path, it paved the way to many applications ascoherent control of photoionization process or as po-larization shaping of Terahertz (THz) pulses. Here weevidenced efficient non-resonant and noncollinear χ( 2 )-type light-matter interaction in femtoseconds polar-ization sensitive time-resolved optical measurements.Such nonlinear optical interaction of visible light andultra-short THz pulses leads to THz modulation of vis-ible light polarization in bulk LiNbO 3 crystal. Theoret-ical simulations based on the wave propagation equa-tion capture the physical processes underlying this non-linear effect. Apart from the observed tunable polar-ization modulation at ultra-high frequencies of visiblepulses, this physical phenomenon can be envisaged inTHz depth-profiling of materials.

Universal quantum gate with hybrid qubits in circuit QED

Chui-Ping Yang, Zhen-Fei Zheng, and Yu Zhang

Doc ID: 346890 Received 26 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Hybrid qubits have recently drawn intensive attention in quantum computing. We here propose a method to implement a universal controlled-phase gate of two hybrid qubits via two three-dimensional (3D) microwave cavities coupled to a superconducting flux qutrit. For the gate considered here, the control qubit is a microwave photonic qubit (particle-like qubit), whose two logic states are encoded by the vacuum state and the single-photon state of a cavity, while the target qubit is a cat-state qubit (wave-like qubit), whose two logic states are encoded by the two orthogonal cat states of the other cavity. During the gate operation, the qutrit remains in the ground state; therefore decoherence from the qutrit is greatly suppressed. The gate realization is quite simple, because only a single basic operation is employed and neither classical pulse nor measurement is used. Our numerical simulations demonstrate that with current circuit QED technology, this gate can be realized with a high fidelity. The generality of this proposal allows to implement the proposed gate in a wide range of physical systems, such as two 1D or 3D microwave or optical cavities coupled to a natural or artificial three-level atom. Finally, this proposal can be applied to create a novel entangled state between a particle-like photonic qubit and a wave-like cat-state qubit.

Multipass nonlinear pulse compression from 1.3 ps to 41 fs at 18 mJ energy

Martin Kaumanns, Vladimir Pervak, Dmitrii Kormin, Vyacheslav Leshchenko, Alexander Kessel, Moritz Ueffing, Yu Chen, and Thomas Nubbemeyer

Doc ID: 347510 Received 05 Oct 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Nonlinear compression of laser pulses with tens of millijoule energy in a gas-filled multipass cell is a promising approach to realize the next generation femtosecond sources. For the first time we demonstrate nonlinear compression of pulses with over 18 mJ of energy at 5 kHz repetition rate from 1.3 ps to 41 fs in an argon filled Herriott cell. In addition to the large compression factor, the output beam has an outstanding quality and excellent spectral homogeneity. Furthermore we discuss prospects to scale the energy to the 100 mJ level in the near future.

Broadband blue emission from ZnO amorphous nanodomains in zinc phosphate oxynitride glass

Muzhi Cai, weim mao, Laurent Calvez, Jean Rocherulle, Hong-li Ma, Ronan Lebullenger, Xiang-Hua Zhang, Shiqing Xu, and Junjie Zhang

Doc ID: 345573 Received 11 Sep 2018; Accepted 03 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: Zn-O amorphous nanostructure in a glass matrix shows unique optical properties. However, although Zn-O amorphous nanostructure can be formed in some settled multi-component silicate glasses, the intensity of its emission is extremely weak. Here, we report a novel and simple zinc phosphate oxynitride glass which can display strong broadband blue emission with a short decay time due to the Zn-O amorphous nanostructure in the glass matrix. The result implies that the glass topological constraints are the key to forming Zn-O amorphous nanostructure. The findings contribute to a deeper understanding of the formation of Zn-O amorphous nanostructure in zinc containing glass.

Bandwidth-tunable, FSR-free, microring-based, SOI filter with integrated contra-directional couplers

Ajay Mistry, Mustafa Hammood, Hossam Shoman, Lukas Chrostowski, and Nicolas Jaeger

Doc ID: 345710 Received 14 Sep 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A silicon-on-insulator, bandwidth (BW)-tunable, free spectral-range (FSR) free, microring resonator (MRR)-based filter is experimentally demonstrated. The device achieves an FSR-free response at its through and drop ports by using a grating-assisted coupler in one coupling region of the MRR and achieves a nonadjacent channel isolation, (nAi), for 400 GHz WDM, greater than 26.7 dB. A thermally tunable Mach Zehnder Interferometer-based coupling scheme is also utilized to compensate for fabrication variations and enable the BW tunability of the filter. The BW of the filter can be continuously tuned from 25 GHz to 60 GHz while maintaining an nAi greater than 26.7 dB. We also show that the phase response at the minor notches in the through port of the filter are suppressed.

Coherent perfect absorber and laser for nonlinear waves in optical waveguide arrays

Vladimir Konotop, Dmitry Zezyulin, and Herwig Ott

Doc ID: 340368 Received 24 Jul 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: A localized non-Hermitian potential can operate as a coherent perfect absorber or as a laser for nonlinear waves. The effect is illustrated for an array of optical waveguides, with the central waveguide being either active or absorbing. The arrays situated to the left and to the right from the center can have different coupling constants and different Kerr nonlinearities. The result can be further generalized to a setup with the central waveguide carrying an additional nonlinear dissipation or gain and to the two-dimensional waveguide arrays with embedded one-dimensional absorbing or lasing sub-arrays.

Stokes mode Raman random lasing in a fully biocompatible medium

Venkata Siva Gummaluri, Sivarama Krishnan, and Vijayan C

Doc ID: 348317 Received 16 Oct 2018; Accepted 02 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: We demonstrate for the first time, Raman random lasing in a continuous-wave (CW) excited, completely biocompatible and biodegradable carrot medium naturally composed of fibrous cellulose scattering medium and rich carotene Raman gain medium. CW laser induced photoluminescence(PL) threshold and linewidth analysis at the Stokes modes of carotene show a characteristic lasing action with threshold of 130 W/cm2 and linewidth-narrowing with mode Q factor up to 1300. Polarization study of output modes reveals that lasing mode mostly retains the source polarization state. A neat and interesting linear temperature dependence of emission intensity is also discussed. Easy availability, bio-compatibility, excitation dependent emission wavelength selectivity and temperature sensitivity are hallmarks of this elegant Raman laser medium with a strong potential as an optical source for applications in bio-sensing, imaging and spectroscopy.

Super smooth surface demonstration and the physical mechanism of CO2 laser polishing of fused silica

Ting He, Chaoyang Wei, Zhigang Jiang, Yuanan Zhao, and Jianda Shao

Doc ID: 340010 Received 22 Aug 2018; Accepted 02 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: This paper reports on the results of experiments aimed at obtaining high-quality super-smooth surfaces, by investigating the laser polishing of fused silica. A maximum reduction in root mean square (RMS) roughness to 0.156 nm was achieved, and laser-polished surfaces exhibited virtually no micro defects or damage. Subsequent analysis using a multi-physics numerical model revealed the underlying physical mechanism of laser polishing of fused silica. The model simulated the surface smoothing process of laser polishing and demonstrated the effects of surface tension, Marangoni effect, light pressure, and gravity in the process. It was found that the surface tension dominates the surface smoothing process and it is a critical factor for achieving sub-nanometer micro roughness of laser polishing of fused silica. Additionally, the model was successfully applied to predict the residual surface roughness of laser polishing, which is in good agreement with the experimental results.

Enhancing the dynamic range of phase-sensitive optical coherence elastography by overcoming speckle decorrelation

Bing Pan, Bo Dong, and Yun Zhang

Doc ID: 346038 Received 17 Sep 2018; Accepted 02 Nov 2018; Posted 02 Nov 2018  View: PDF

Abstract: Phase-sensitive optical coherence elastography (PhS-OCE) is a high-sensitivity optical method for measuring internal displacement fields of semi-transparent materials. Although the displacement measurement sensitivity of PhS-OCE reaches sub-nanometer level, the dynamic range of the measured displacements is limited to micrometers due to displacement-induced speckle decorrelation. In this letter, a displacement tracking method is developed to overcome this limitation. The method uses subset-based match approach and takes the noise number of phase difference map as the match quality, which can effectively track both axial and lateral displacements. For validation, phase changes inside polymer samples due to the displacements produced by the temperature/mechanical load changing were measured. The results show that many previously undetectable mechanical behaviors can be quantitatively detected after enhancing the dynamic range by applying the proposed method.

Add-drop filter with complex waveguide Bragg gratings and multimode interferometers operating on arbitrarily spaced channels

Jiahao Zhan, Yi-Wen Hu, Yang Zhang, Sylvain Veilleux, Joss Bland-Hawthorn, Mario Dagenais, and Shengjie Xie

Doc ID: 346720 Received 26 Sep 2018; Accepted 02 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: We present a silicon nitride/silicon dioxide add-drop filter operating on arbitrarily spaced channels using multimode interferometers (MMI’s) and complex waveguide Bragg gratings (CWBG’s). The add-drop filter shows a rejection ratio of > 40 dB on all five channels, with a line width of 1.2 nm and an on-chip loss of < 1 dB. By designing the CWBG with the Layer Peeling/Layer Adding algorithm, this MMI-CWBG add-drop filter platform has the capability for ultra-broadband add-drop operation on arbitrarily spaced channels.

Polarimetric nonregularity of evanescent waves

Andreas Norrman, Jose Gil, Ari Tapio Friberg, and Tero Setala

Doc ID: 345684 Received 12 Sep 2018; Accepted 01 Nov 2018; Posted 15 Nov 2018  View: PDF

Abstract: Three-dimensional polarization states of random light can be classified into regular and nonregular according to the structure of the related 3x3 polarization matrix. Here we show that any purely evanescent wave excited in total internal reflection of a partially polarized plane-wave field is always in a nonregular polarization state. The degree of nonregularity of such evanescent waves is also studied in terms of a recently advanced measure. Nonregular evanescent waves uncover new aspects of the polarimetric structure and dimensional character of electromagnetic near fields, with potential applications in nanoscale surface optics.

A multifocal multiphoton volumetric imaging technique for high speed time-resolved FRET imaging in vivo

Simon Poland, Grace Chan, James Levitt, Nikola Krstajic, Ahmet Erdogan, Robert Henderson, Maddy Parsons, and Simon Ameer-Beg

Doc ID: 345100 Received 06 Sep 2018; Accepted 01 Nov 2018; Posted 05 Nov 2018  View: PDF

Abstract: In this paper we will discuss the development of a multifocal multiphoton fluorescent lifetime imaging system where 4 individual fluorescent intensity and lifetime planes are acquired simultaneously, allowing us to obtain volumetric data without the need for sequential scanning at different axial depths. Using a phase-only SLM with an appropriate algorithm to generate a holographic pattern, we project a beamlet array within a sample volume of a size, which can be pre-programmed by the user. We demonstrate the capabilities of the system to image live-cell interactions. Whilst only 4 planes are shown, this technique can be rescaled to a large number of focal planes enabling full 3D acquisition and reconstruction.

Three-dimensional direct laser written achromatic multi-component micro lenses

Michael Schmid, Simon Thiele, Alois Herkommer, and Harald Giessen

Doc ID: 345260 Received 24 Sep 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Femtosecond 3D printing is an important technology for manufacturing of nano- and microscopic optical devices and elements. However, most structures in the past have been created using only one photoresist at a time, thus limiting potential applications. In this paper we successfully demonstrate the combination of two different photoresists, namely IP-S and IP-Dip, to realize multi-component three-dimensional direct laser written optics. We use the combination of IP-S and IP-Dip to correct chromatic aberrations and to realize an achromatic axicon. In a second step we demonstrate the first three-dimensional direct laser written Fraunhofer doublet. We characterize their optical properties and measure the substantial reduction of chromatic aberrations. We outline the possibilities and benefits of creating three-dimensional direct laser written multi-component structures for micro-optics.

Degeneracy in the Diffraction of Orbital Angular Momentum Carrying Beams

Surendra Singh, Emily Walla, Chitra Shaji, and Reeta Vyas

Doc ID: 344600 Received 30 Aug 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Symmetry constraints on the far field diffraction of Laguerre-Gauss vortex beams by planar aperture arrays with N-fold rotational symmetry are considered. The experiments reveal a simple structure for the diffraction pattern and high degree of degeneracy in its dependence on the orbital angular momentum index of the incident beam in agreement with analytical and numerical results.

Photoluminescence Enhancement and Ultrafast Relaxation Dynamics in A Novel Low-dimensional Heterostructure: Effect of Plasmon-Exciton Coupling

runlin miao, Yiwen Zhang, Yuxiang Tang, Jie You, Yanbin Zhang, Lei Shi, and Tian Jiang

Doc ID: 346251 Received 18 Sep 2018; Accepted 31 Oct 2018; Posted 02 Nov 2018  View: PDF

Abstract: In this work, we present an in-depth study on the low-dimensional heterostructure comprising the monolayer (ML) WS2 and 1D plasmonic photonic crystal (PPC). The stable-state photoluminescence (PL) experiments are employed to study the optical and electrical properties of WS2 films with and without PPC. In addition, the angle-resolved reflectance and PL microscopy measurements are used to identify the coupling effect between the ML WS2 and 1D PPC. Furthermore, by means of the femtosecond pump-probe experiments, the relaxation time of this newly-proposed heterostructure is extracted to be 0.69ps, 18.84ps, 885.62ps. Importantly, the relaxation process of the weak plasmon-exciton effect is also revealed in the hybrid structure for the first time.

Polarization mediated coherent and incoherent Bessel-moiré generation

Jayeta Banerjee and Mina Ray

Doc ID: 330449 Received 27 Apr 2018; Accepted 31 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: We demonstrate an efficient approach for investigation of polarization states of Bessel beam along the propagation direction. Furthermore, we propose a method to generate Bessel-moiré using Birefringent Lens and Wollaston prism. The analysis showed that experimentally generated incoherent moiré pattern is analogous to theoretically simulated pattern. Moreover, we verified that inhomogeneous polarization states of Bessel beam is still present in Bessel-moiré along its propagation direction. Our observation of Bessel-moiré due to mechanical vibration depicts the fact that incoherent moiré is stable, whereas coherent moiré is sensitive to external vibration only along its propagation direction.

Directional invisibility by genetic optimization

Emre Bor, Ceren Babayigit, Hamza Kurt, Kestutis Staliunas, and Mirbek Turduev

Doc ID: 342235 Received 13 Aug 2018; Accepted 31 Oct 2018; Posted 01 Nov 2018  View: PDF

Abstract: In this study, the novel design of a directional optical cloaking by genetic algorithm is proposed and realized experimentally. Three-dimensional finite-difference time-domain method is combined with the genetic optimization approach to generate the cloaking structure for directional cloaking of a cylindrical object made of perfectly electrical conductor (PEC) by suppressing the undesired scattered fields around the PEC object. The optimization algorithm designs the permittivity distribution of the dielectric polylactide material to achieve an optical cloaking effect. Experimental verification of the designed cloaking structure is performed at microwave frequencies where the proposed structure is fabricated by 3D printing technique. The imperfect conformal mapping due to large scale permittivity distribution and the compensation of the remaining scattering due to small scale permittivity distribution are the basic physical mechanisms of the proposed optical cloaking.

Sculpting complex polarization singularity networks

Eileen Otte and Cornelia Denz

Doc ID: 340659 Received 25 Jul 2018; Accepted 31 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Polarization singularities in vectorial light fields have become an important tool for different cutting-edge applications as in information processing with integer information units. However, even though vectorial singularities naturally form configurations of multiple singular points, up to now only rather simple, mostly cylindrical vector beams including single central singularities have been considered. Here, we demonstrate the customization of extended singularity networks embedded in a class of complexly polarization structured fields based on general Ince-Gaussian modes, namely Ince-Gaussian vector modes. Contributing to fundamental singular optics, our investigations evince the conservation of tailored singularity arrangements upon propagation, whereby respective modes enlarge the range of stable vectorial fields, paving the way to information technologies with a significantly enhanced number of degrees of freedom.

Correlation gating quantifies optical properties of dynamic media in transmission mode

Dawid Borycki, Oybek Kholiqov, and Vivek Srinivasan

Doc ID: 341134 Received 13 Aug 2018; Accepted 31 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Quantifying light transport in turbid media is a long-standing challenge. This challenge arises from the difficulty in experimentally separating unscattered, ballistic light from forward scattered light. Correlation gating is a new approach that numerically separates light paths based on statistical dynamics of the optical field. Here we apply correlation gating with interferometric near-infrared spectroscopy (iNIRS) to separate and independently quantify ballistic and scattered light transmitted through thick samples. First, we present evidence that correlation gating improves isolation of ballistic light in an intrinsically dynamic medium with Brownian motion. Then, from a single set of iNIRS transmission measurements, we determine the ballistic attenuation coefficient and group refractive index from the time-of-flight resolved static intensity, and we determine the reduced scattering and absorption coefficients from the diffusive part of the time-of-flight resolved dynamic intensity. Finally, we show that correlation gating can isolate ballistic light in intrinsically static media in which motion is induced externally. Thus, for the first time, key optical properties of a turbid medium can be derived from a single set of transmission measurements.

Suspended low-loss germanium waveguides for the longwave-infrared.

Ahmed Osman, Milos Nedeljkovic, J. Soler Penades, Yangbo Wu, Zhibo Qu, Ali Khokhar, Kapil Debnath, and Goran Mashanovich

Doc ID: 345563 Received 11 Sep 2018; Accepted 30 Oct 2018; Posted 05 Nov 2018  View: PDF

Abstract: Germanium is a material of high interest for midinfrared (MIR) integrated photonics due to its CMOS compatibility and its wide transparency window covering the 2–15 mm spectral region exceeding the 4 and 8 μm limit of the Silicon-on-Insulator (SOI) platform and Si material respectively. In this Letter, we report suspended germanium waveguides operating at a wavelengthof 7.67 μm with a propagation loss of 2.6 ± 0.3 dB/cm. To our knowledge, this is the first demonstration of low-loss suspended germanium waveguides at such a long wavelength. Suspension of the waveguide is achieved by defining holes alongside the core providing access to the buried oxide layer and the underlying Si layer so that they can be wet etched using HF and TMAH respectively. Our MIR waveguides create a new path towards long wavelength sensing in the fingerprint region.

Optical injection locking at sub nano-Watt powers

Ravikiran Kakarla, Jochen Schroeder, and Peter Andrekson

Doc ID: 346875 Received 28 Sep 2018; Accepted 29 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: We demonstrate optical injection locking (OIL) at record low injection power of -65dBm using EDFA based pre-amplification and an electrical phase locked loop (PLL). Investigating the phase noise characteristics of OIL we find that at low injection powers the slave laser linewidth and injection ratio strongly influence the phase noise of the locked slave output. By introducing an EDFA pre-amplifier, the minimum locking power for OIL is reduced. Moreover using this pre-amplifier we find that there exists an optimum injection power into the slave where the output phase noise is minimized and is below the noise without EDFA. We evaluate an OIL based pump recovery in a phase sensitive amplifier (PSA) receiver system aimed at free space communications.

Frequency comb up- and down-conversion in a synchronously-driven χ² optical microresonator

Simon Herr, Victor Brasch, Jan Szabados, Ewelina Obrzud, Yuechen Jia, Steve Lecomte, Karsten Buse, Ingo Breunig, and Tobias Herr

Doc ID: 344979 Received 04 Sep 2018; Accepted 29 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: Optical frequency combs are key to optical precision measurements. While most frequency combs operate in the near-infrared regime, many applications require combs at mid-infrared, visible or even ultra-violet wavelengths. Frequency combs can be transferred to other wavelengths via nonlinear optical processes, however, this becomes exceedingly challenging for high-repetition rate frequency combs. Here, it is demonstrated that a synchronously driven high-Q microresonator with a second-order optical nonlinearity can efficiently convert high-repetition rate near-infrared frequency combs to visible, ultra-violet and mid-infrared wavelengths providing new opportunities for microresonator and electro-optic combs in applications including molecular sensing, astronomy, and quantum optics.

Off-site and on-site vortex solitons in space-fractional photonic lattices

Xueming Liu and Xiankun Yao

Doc ID: 345022 Received 06 Sep 2018; Accepted 29 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: We address the existence and stability of off-site and on-site vertex solitons with unit topological charge in space-fractional Kerr lattices. In contrast to the reported ordinary Kerr lattices, vortex solitons in the proposed fractional-space lattices are stable only in the intermediate region of propagation constant, and this region widens rapidly with the increase of Lévy index. Under the same Lévy index, the stability range of on-site vortices is larger than that of off-site ones. Especially, for on-site vortex solitons, the upper edge of stability range appears at where the maximum of soliton power is located, which provides an effective way to identify the stability range of on-site vortices. Our results extend the study of vortex solitons into space-fractional systems and deepen the understanding of Kerr lattices in fractional dimensions.

Free-Running Mode-Locked Laser Based Dual-Comb Spectroscopy

Md Imrul Kayes, Nurmemet Abdukerim, Alexandre Rekik, and Martin Rochette

Doc ID: 346581 Received 24 Sep 2018; Accepted 27 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: We present a real-time dual-comb spectrometer operated from a bi-directional mode-locked fiber laser in the wavelength range of 1.9 μm. Two pulsed signals emitted from a common cavity ensures mutual coherence and common mode noise rejection. The resulting spectrometer operates without any complex electronic feedback system.

Multi-carrier channeled polarimetry for photoelastic modulator systems

Andrey Alenin, Farhana Bashar, Michael Gehm, and J. Scott Tyo

Doc ID: 346727 Received 25 Sep 2018; Accepted 26 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Photoelastic modulator-based polarimeters use multi-carrier modulation schemes that are more complicated than the single carriers of rotating optics. Current state-of-the-art reconstruction implementations favor mathematical simplicity by using significantly abridged subsets of channels. In this Letter, we extend our generalized channeled polarimetry principles to address the challenges associated with multi-carrier modulation schemes. We demonstrate the performance forfeited by existing systems through the use of an incomplete set of information channels, as well as propose a set of more optimal system parameters that achieve better reconstruction noise characteristics. The overall improvement corresponds to an up to a factor of six better sensitivity.

Narrowing spectral linewidth in passively mode-locked solid-state lasers

Tzu-Lin Huang, S. C. Li, C. H. Tsou, Hsing-Chih Liang, K. F. Huang, and Yung-Fu Chen

Doc ID: 346968 Received 28 Sep 2018; Accepted 25 Oct 2018; Posted 30 Oct 2018  View: PDF

Abstract: A novel scheme to realize a mode-locked laser with narrow spectral linewidth is demonstrated by exploiting a reflected Fabry-Perot cavity to introduce intense Fabry-Perot effect. Stable continuous-wave mode-locked operation is achieved with the repetition rate of 48 MHz and the maximum average output power of 2.6 W under an incident pump power of 11.9 W. The mode-locked pulse width is systematically investigated by varying the optical thickness of the reflected Fabry-Perot cavity. The pulse duration is experimentally found to be in a range from 0.8 ns to 2.6 ns. Experimental results reveal that the reflected Fabry-Perot cavity is the key factor leading to the pulse generation in nanosecond regime. This work is believed to provide a promising method for generating optical pulses with narrow spectral linewidth.

Dispersion Engineering of Hyperbolic Plasmons in Bilayer 2D Materials

Maturi Renuka, Xiao Lin, zuojia wang, Lian Shen, Bin Zheng, Huaping Wang, and Hongsheng Chen

Doc ID: 346675 Received 08 Oct 2018; Accepted 25 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: Recent progress on anisotropic 2D materials brings new technologies for directional guidance of hyperbolic plasmons. Here, we investigate the plasmonic modes in twisted bilayer 2D materials. Calculated dispersion curves show that two hyperbolas split as the twisted angle increases. The topological transition from closed ellipses to open hyperbolas is achieved by varying the frequency, indicating switching between highly directional and omnidirectional plasmons. These findings will provide potential applications in the design of tunable field effect transistors and waveguides.

Optical rectification of a 100 W average power mode-locked thin-disk oscillator

Frank Meyer, Negar Hekmat, Samira Mansourzadeh Ashkani, Felix Fobbe, Farhad Aslani, Martin Saraceno, and Clara Saraceno

Doc ID: 347364 Received 04 Oct 2018; Accepted 25 Oct 2018; Posted 01 Nov 2018  View: PDF

Abstract: We demonstrate THz generation at MHz repetition rate by optical rectification in GaP crystals, using excitation average power levels exceeding 100 W. The laser source is a state-of-the-art diode-pumped Yb:YAG SESAM-mode-locked thin-disk laser, capable of generating 580 fs pulses at an average power up to 120 W and a repetition rate of 13.4 MHz directly from a one-box oscillator, without the need for any extra amplification stages. In this first demonstration, we measure a maximum THz average power of 78 µW at a central frequency of 0.8 THz. Our result shows that optical rectification of state-of-the-art high average power ultrafast sources in nonlinear crystals is within reach, and paves the way towards high average power, ultrafast laser pumped THz sources.

Wavelength tunable gain-switched fiber laser around 1.7-μm-band and its application to spectroscopic photoacoustic imaging

Can Li, Jiawei Shi, Xiaojing Gong, Cihang Kong, Zhi-Chao Luo, Liang Song, and Kenneth Kin-Yip Wong

Doc ID: 345579 Received 11 Sep 2018; Accepted 24 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Recently demonstrated bond-selective photoacoustic imaging has revealed the importance of 1.7-μm laser sources, which are currently accessed through nonlinear conversion from shorter wavelengths with compromised performances. In this letter, we demonstrate a gain-switched thulium-doped fiber laser with continuous tuning from 1690 nm to 1765 nm by using an electrically driven acousto-optical tunable filter. Micro-joule laser pulses with a shot-to-shot intensity variation of 1.6% and a pulse duration of 150 ns are achieved. The laser source is then harnessed to implement a photoacoustic microscopy system, of which the lateral resolution is estimated to be 17.8 μm by scanning a resolution target. The photoacoustic spectra of butter, rapeseed oil, and adipose tissue are measured and show a consistent absorption peak of around 1720 nm. Photoacoustic microscopy imaging of the adipose tissue demonstrates a desirable optical absorption contrast of lipids and the superiority of the laser for spectroscopic photoacoustic detection.

Non-evolving spatial coherence function

Aristide Dogariu and CRISTIAN ACEVEDO

Doc ID: 347526 Received 08 Oct 2018; Accepted 21 Oct 2018; Posted 29 Oct 2018  View: PDF

Abstract: We present a general model for the spatial coherence function of random fields created by scattering elliptical, perfect vortex beams. Remarkably, as opposed to the free-space propagation of typical random fields, there are regimes were the spatial coherence function does not evolve. We demonstrate analytically, numerically, and experimentally that both the size and the shape of the spatial correlations can be precisely controlled in a manner that is independent of the propagation distance.

Monochromatic NIR UC emission in Tm3+/Yb3+ co-doped GdVO4 phosphor: Effect of Bi3+ ion concentration and pump power of diode laser

abhishek dwivedi, Devendra Kumar, and S Rai

Doc ID: 334376 Received 08 Jun 2018; Accepted 20 Oct 2018; Posted 31 Oct 2018  View: PDF

Abstract: Tm3+/Yb3+/Bi3+ co-doped GdVO4 phosphor sample has been synthesized using high temperature solid state reaction technique. The X-ray diffraction patterns reveal pure phase formation and crystalline behavior of the synthesized samples. Intense blue and NIR upconversion (UC) emissions have been observed on excitation with 980 nm diode laser. It is found that addition of Bi3+ ion to the phosphor reduces the intensity of blue emission and enhances the NIR emission intensity to the extent so that NIR emission is nearly monochromatic [(INIR/IBlue) ~ 14]. This ratio is further improved upto 70 times [almost monochromatic] by varying the pump power of the diode laser. This value is observed for the composition GdVO4: 0.01Tm3+, 0.05Yb3+, 0.10Bi3+ phosphor at 1.0 W pump power. Thus this sample can be used as a cheap source of monochromatic ‘Red LED’ and also in bioimaging.OCIS Keywords: Optical materials (Materials), Rare-earth-doped materials (Materials), Energy transfer (Physical optics), Luminescence (Physical optics), Emission (Spectroscopy), Fluorescence, laser-induced (Spectroscopy)

Mapping complex polarization states of light on a solid

Mariam Alameer, Ashish Jain, Mitra Rahimian, Hugo Larocque, Paul Corkum, Ebrahim Karimi, and Ravi-Bhardwaj Vedula

Doc ID: 346986 Received 28 Sep 2018; Accepted 17 Oct 2018; Posted 26 Oct 2018  View: PDF

Abstract: Polarization states of light, represented by different points on a Poincar\'e sphere, can be readily analyzed for a Gaussian beam by a combination of waveplates and polarizers. However, this method cannot be extended to higher order Poincar\'e spheres and complex polarization patterns produced by coherent superpositions of vector vortex beams. We demonstrate visualization of complex polarization patterns by imprinting them on to a solid surface in the form of periodic nano-gratings oriented parallel to the local structure of the electric field of light. We design unconventional surface structures by controlling the superposition of vector vortex beams. Our method is of potential interest to the production of sub-wavelength nano-structures.

Cavity induced tunable perfect infrared absorption in imprinted coupled complementary hole-disk array

alireza safaei, Sushrut Modak, Abraham Vázquez-Guardado, Daniel Franklin, and Debashis Chanda

Doc ID: 344258 Received 29 Aug 2018; Accepted 17 Oct 2018; Posted 17 Oct 2018  View: PDF

Abstract: Photonic microcavity coupling of a subwavelength hole-disk array, a two-element metal/dielectric composite structure with enhanced extraordinary transmission, leads to 100% coupling of incident light to the cavity system and subsequent absorption. This light-funneling process arises from the temporal and spatial coupling of the broadband localized surface plasmon resonance on the coupled hole-disk array and the photonic modes of the optical cavity, which induces spectral narrowing of the perfect absorption of light. A simple nanoimprint lithography-based large area fabrication process paves the path towards practical implementation of plasmonic cavity-based devices and sensors.

Efficient design of random metasurfaces

Hadiseh Nasari, Matthieu Dupre, and Boubacar Kante

Doc ID: 343216 Received 27 Aug 2018; Accepted 15 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: Random media introduce large degrees of freedom in device design and can thus address challenges in manipulating optical waves. Wave shaping with metasurfaces has mainly utilized periodic or quasi-periodic grids, and, the potential of random arrangement of particles for devices has only come under investigation recently. The main difficulty in pursuing random metasurfaces is the identification of the degrees of freedom that optimize their efficiencies and functions. They can also encode information using the statistics of particles distribution. We propose a phase-map that accounts for the statistical nature of random media. The method takes into account effects of random near-field couplings that introduce phase errors by affecting the phase shift of elements. The proposed approach increases the efficiency of our random metasurface devices by up to ~20%. This work paves the way towards the efficient design of random metasurfaces with potential applications in highly secure optical cryptography and information encoding.

Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser

Ying Han, J. Partington, Rabi Chhantyal-Pun, Manju Henry, O. Auriacombe, T. Rawlings, Lian He Li, James Keeley, M. Oldfield, N. Brewster, R. Dong, Paul Dean, Giles Davies, Brian Ellison, Edmund Linfield, and Alex Valavanis

Doc ID: 344578 Received 31 Aug 2018; Accepted 10 Oct 2018; Posted 07 Nov 2018  View: PDF

Abstract: A multimode self-mixing terahertz-frequency gas absorption spectroscopy is demonstrated based on a quantum cascade laser. A double-metal device configuration is used to expand the laser’s frequency tuning range and a precision-micromachined external waveguide module is used to enhance the optical feedback. Methanol spectra are measured using two laser modes at 3.362 THz and 3.428 THz simultaneously, with more than 8 absorption peaks resolved over a 15 GHz bandwidth, which provide the minimum detectable absorption coefficient of 2.7×10-4 cm−1 and 4.9×10−4 cm−1, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth and duty cycle significantly.

Fast Raman spectral mapping of highly fluorescing samples by time-gated spectral multiplexed detection

Christopher Corden, Dustin Shipp, Pavel Matousek, and Ioan Notingher

Doc ID: 335878 Received 11 Sep 2018; Accepted 07 Oct 2018; Posted 16 Oct 2018  View: PDF

Abstract: We present a time-gated Raman micro-spectroscopy technique suitable for fast Raman mapping of samples eliciting large laser-induced fluorescence backgrounds. To achieve the required time resolution for effective fluorescence rejection, a pico-second pulsed laser and a single photon avalanche diode were used. A module consisting of a spectrometer, digital micromirror device (DMD) and two prisms was used for high-resolution spectral filtering and multiplexing, required for a high chemical specificity and short integration times. With this instrument, we demonstrated time-gated Raman imaging of highly fluorescent samples, achieving acquisition times as short as 3 minutes for 40x40 pixels resolution images.

Image reversal reactive immersion lithography improves the detection limit of focal molography

Andreas Frutiger, Yves Blickenstrofer, Cla Tschannen, Andreas Reichmuth, Christof Fattinger, and Janos Vörös

Doc ID: 341991 Received 04 Sep 2018; Accepted 29 Sep 2018; Posted 01 Oct 2018  View: PDF

Abstract: Focal molography is a label-free optical biosensing method that relies on a coherent pattern of binding sites for biomolecular interaction analysis. Reactive immersion lithography (RIL) is central to the patterning molographic chips but has potential for improvements. Here, we show that applying the idea of image reversal to RIL enables the fabrication of coherent binding patterns of increased quality (i.e., higher analyte efficiency). Thereby the detection limit of focal molography in biological assays can be improved.

Photonics in highly dispersive media: The exact modal expansion

Frederic Zolla, Andre Nicolet, and Guillaume Demesy

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

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

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