Optics Letters

Mohsen Kamandar Dezfouli, Yuri Grinberg, Daniele Melati, Pavel Cheben, Jens H Schmid, Alejandro Sánchez-Postigo, Alejandro Ortega-Moñux, Gonzalo Wangüemert-Pérez, Ross Cheriton, Siegfried Janz, Dan-Xia Xu
We present perfectly vertical grating couplers for the 220 nm silicon-on-insulator platform incorporating subwavelength metamaterials to increase the minimum feature sizes and achieve broadband low back-reflection. Our study reveals that devices with high coupling efficiencies are distributed over a wide region of the design space with varied back-reflections, while still maintaining minimum feature sizes larger than 100 nm and even 130 nm. Using 3D-finite-difference time-domain simulations, we demonstrate devices with broadband low back-reflection of less than -20 d B over more than 100 nm bandwidth centered around the C-band...
July 1, 2020: Optics Letters
Jiayi Yu, Xinlei Zhu, Shuqin Lin, Fei Wang, Greg Gbur, Yangjian Cai
We introduce a general strategy for the synthesis of vector partially coherent beams (PCBs) with a prescribed non-uniform correlation structure. With it, we characterize a specific family of such beams, termed radially polarized Hermite non-uniformly correlated (RPHNUC) beams. These beams possess unusual propagation properties compared to vector PCBs with uniform correlation structure; for example, they maintain their dark hollow core and evolve multi-ring structures. These beams may prove useful in free-space optical communications, optical trapping, and polarization-sensitive imaging...
July 1, 2020: Optics Letters
Xavier Audier, Wei-Wen Chen, Marcus T Cicerone
We describe a simple approach to dispersion-free optical delay line design that provides very low aberration over an extended delay range. In this approach, we minimize aberrations by directing non-axial beam displacements along a line of symmetry built into the apparatus. We show improved performance and significant reduction of wavefront aberrations by comparing simulation and experimental results with a similar delay line that lacks this line of symmetry. The new design facilitates transform-limited recovery of spectral resolution in Fourier transform coherent anti-Stokes Raman scattering, and accordingly, we demonstrate 3...
July 1, 2020: Optics Letters
Rui Ma, Zhao Wang, Hua Hui Zhang, Wei Li Zhang, Yun Jiang Rao
Memory-effect-based speckle correlation is one of the most practical techniques for imaging through scattering opaque media, where a light source with low spatial coherence and moderate bandwidth plays a pivotal role. Usually, a rapidly rotating diffuser is applied to make the light source spatially decoherent. Here, an all-fiber-based low-spatial-coherence light source is proposed and demonstrated for such speckle-correlated imaging. The illumination structure is greatly simplified, the lightening efficiency is enhanced, and the wavelength is extended to the near-infrared band, which is favorable for a larger memory effect range and deeper penetrating depth through opacity...
July 1, 2020: Optics Letters
Ugaitz Elu, Luke Maidment, Lenard Vamos, Tobias Steinle, Florian Haberstroh, Valentin Petrov, Valeriy Badikov, Dmitrii Badikov, Jens Biegert
B a G a 2 G e S e 6 (BGGSe) is a newly developed nonlinear material that is attractive for ultrabroad frequency mixing and ultrashort pulse generation due to its comparably low dispersion and high damage threshold. A numerical study shows the material's capacity for octave-spanning mid-infrared pulse generation up to 18 µm. In a first experiment, we show that a long crystal length of 2.6 mm yields a pulse energy of 21 pJ at 100 MHz with a spectral bandwidth covering 5.8 to 8.5 µm. The electric field of the carrier-envelope-phase stable pulse is directly measured with electro-optical sampling and reveals a pulse duration of 91 fs, which corresponds to sub-four optical cycles, thus confirming some of the prospects of the material for ultrashort pulse generation and mid-infrared spectroscopy...
July 1, 2020: Optics Letters
In-Goo Lee, Chang-Hwan Yi, Ji-Won Lee, Jinhyeok Ryu, Sunjae Gwak, Kwang-Ryong Oh, Chil-Min Kim
We study a lasing of mode groups in a fully chaotic rounded D-shape InGaAsP semiconductor microcavity laser when an electrode is smaller than a cavity (inward gap). Although there are numerous unstable periodic orbits supporting resonances, a mode group localized on period-5 unstable periodic orbit is more competitive than the others for our laser configuration of the inward gap. By means of theoretical and numerical analyses with ray and wave dynamics, we show that the analyses well agree with our experimental results...
July 1, 2020: Optics Letters
Gaoyou Liu, Yi Chen, Zhuang Li, Ke Yang, Baoquan Yao, Jiyong Yao, Ruixue Wang, Chao Yang, Shuyi Mi, Tongyu Dai, Xiaoming Duan
We firstly demonstrated a tunable 2.1 µm pumped mid-infrared type-II phase-matching B a G a 4 S e 7 (BGSe) optical parametric oscillator (OPO). A signal tuning range of 3.82-3.99 µm was achieved. With a signal light produced by the BGSe OPO serving as seed, the Z n G e P 2 (ZGP) optical parametric amplifier (OPA) was first introduced. A 4.35 W mid-infrared laser was obtained in the novel type-II BGSe OPO with a ZGP OPA system, which was pumped by a 24 W 1 kHz Q -switched Ho:YAG laser. The beam quality factor M 2 of the whole system is ∼2...
July 1, 2020: Optics Letters
Anhu Li, Xingsheng Liu, Zusheng Zhao
We present a three-dimensional (3D) computational imaging architecture based on the imaging principle of a dynamic virtual camera, which enables the spatial reconstruction using a single camera and a compact wedge prism device. By rotating the prism for camera boresight adjustment, the proposed system can capture an object from different viewpoints. Each captured image appears to be recorded directly with one virtual camera moving in a certain path, facilitating the computational process for stereo matching and profile reconstruction...
July 1, 2020: Optics Letters
Yaotian Zhao, Xuhan Guo, Yong Zhang, Jinlong Xiang, Kangnian Wang, Hongwei Wang, Yikai Su
Ultra-compact mode-order converters with dielectric slots are demonstrated on a silicon-on-insulator platform. We propose a mode converter that converts the TE0 mode into the TE1 mode with an ultra-small footprint of only 0.8×1.2µ m 2 . The measured insertion loss is less than 1.2 dB from 1520 nm to 1570 nm. To reduce the insertion loss, we further optimize the structure and design two mode converters that convert the TE0 mode into the TE1 mode and the TE2 mode with footprints of 0.88×2.3µ m 2 and 1.4×2...
July 1, 2020: Optics Letters
David R Gozzard, Lyle E Roberts, James T Spollard, Paul G Sibley, Daniel A Shaddock
Optical phased arrays (OPAs) are devices that use the coherence of light to control the interference pattern in the far field, which enables them to steer a laser beam with no moving parts. As such, OPAs have potential applications in laser communications, target acquisition and tracking, metrology, and directed energy. In this Letter, we present a control architecture for an actively phase-locked OPA, capable of steering a laser beam at speeds limited by the actuation bandwidth of electro-optic modulators...
July 1, 2020: Optics Letters
Jia-Yang Chen, Chao Tang, Zhao-Hui Ma, Zhan Li, Yong Meng Sua, Yu-Ping Huang
Thin-film lithium-niobate-on-insulator (LNOI) has emerged as a superior integrated-photonics platform for linear, nonlinear, and electro-optics. Here we combine quasi-phase-matching, dispersion engineering, and tight mode confinement to realize nonlinear parametric processes with both high efficiency and wide wavelength tunability. On a millimeter-long, Z-cut LNOI waveguide, we demonstrate efficient (1900±500 % W -1 c m -2 ) and highly tunable (-1.71 n m / K ) second-harmonic generation from 1530 to 1583 nm by type-0 quasi-phase-matching...
July 1, 2020: Optics Letters
Qiang Zhang, Hui Yu, Penghui Xia, Zhilei Fu, Xiaofei Wang, Jianyi Yang
In this Letter, we demonstrate an ultra-high linearity silicon carrier-depletion-based modulator by integrating a dual-parallel Mach-Zehnder modulator (DP-MZM) with a 1×2 thermo-optical switch. The operation principle is to manipulate power distributions of RF and optical signals among the two sub-MZMs, so their third-order nonlinearities can cancel each other. Spurious-free dynamic ranges (SFDRs) for the third-order intermodulation distortion (IMD3) are measured to be 123/120 d B ⋅ H z 6/7 at 1/10 GHz, which represents a record-high linearity achieved with silicon-based modulators...
July 1, 2020: Optics Letters
D Dolinina, A Yulin
The dynamics of one-dimensional periodically modulated optical cavities are studied in the framework of coupled counterpropagating wave approximation. It is shown that in these systems, a spontaneous symmetry breaking bifurcation can occur, resulting in the formation of the dynamically stable asymmetric states with nonzero energy flux. Bright cavity solitons nestling on the spatially uniform backgrounds with broken symmetry are found and investigated in detail. One of the distinguishing features of the solitons on the asymmetric background is that they can exist at the pump powers much less than those needed for the formation of the solitons on the symmetric backgrounds...
July 1, 2020: Optics Letters
Chin-Hao Tseng, Sheng-Kwang Hwang
This Letter studies a photonic approach for chaotic microwave generation through destabilization of period-one (P1) nonlinear dynamics in a semiconductor laser subject to intensity-modulated (IM) optical injection. Chaos can be excited when the modulation sideband perturbation carried by the IM optical injection is a few gigahertz higher than the lower oscillation sideband of the P1 dynamics. As a result, chaotic microwaves with a spectral distribution of more than 50 GHz and a bandwidth of about 33 GHz are generated without any time-delay signature or modulation-induced peak...
July 1, 2020: Optics Letters
Qi Dai, Zile Li, Liangui Deng, Nan Zhou, Juan Deng, Jin Tao, Guoxing Zheng
Under the government of Malus's law, metasurfaces composed of anisotropic nanostructures acting as nano-polarizers have shown their precise optical manipulation of polarization profile of incident light at the nanoscale. The orientation degeneracy implied in Malus's law provides a new design degree of freedom for polarization multiplexing, which can be employed to design amplitude-modulated multiplexing meta-devices. Herein, we experimentally demonstrate this concept by encoding two independent amplitude profiles into a single metasurface under different polarization controls, merely with a single-size nanostructure design approach...
July 1, 2020: Optics Letters
Chaonan Yao, Amer Kotb, Bin Wang, Subhash C Singh, Chunlei Guo
Nanostructure and nanoantenna-based all-optical (AO) devices have attracted significant research interests in recent years due to their small size, high information capacity, ultrafast processing, low power consumption, and overall practicality. Here, in this Letter, we propose a novel metasurface having quasi-rhombus-shaped antennas to modulate optical modes in a dielectric-loaded waveguide for the realization of a complete family of logic gates including NOT, AND, OR, XOR, NAND, NOR, and XNOR. These logic operations are realized using destructive and constructive interferences between the input optical signals...
July 1, 2020: Optics Letters
Yiming Li, Elena Buglakova, Yongdeng Zhang, Jervis Vermal Thevathasan, Joerg Bewersdorf, Jonas Ries
Interferometric single-molecule localization microscopy (iPALM, 4Pi-SMS) uses multiphase interferometry to localize single fluorophores and achieves nanometer isotropic resolution in 3D. The current data analysis workflow, however, fails to reach the theoretical resolution limit due to the suboptimal localization algorithm. Here, we develop a method to fit an experimentally derived point spread function (PSF) model to the interference 4Pi-PSF. As the interference phase is not fixed with respect to the shape of the PSF, we decoupled the phase term in the model from the 3D position of the PSF...
July 1, 2020: Optics Letters
Xu Cao, Cuiping Yao, Shudong Jiang, Jason Gunn, Austin C Van Namen, Petr Bruza, Brian W Pogue
Fluorescence imaging is severely limited by the background and autofluorescence of tissues for in vivo detection of circulating tumor cells (CTCs). Time-gated luminescence (TGL) imaging, in combination with luminescent probes that possess hundreds of microsecond emission lifetimes, can be used to effectively suppress this background, which has predominantly nanosecond lifetimes. This Letter demonstrates the feasibility of TGL imaging using luminescent probes for the in vivo real time imaging and tracking of single CTCs circulating freely in the blood vessels with higher accuracy given by substantially higher signal-to-noise ratio...
July 1, 2020: Optics Letters
Guillaume Vanderhaegen, Pascal Szriftgiser, Corentin Naveau, Alexandre Kudlinski, Matteo Conforti, Stefano Trillo, Nail Akhmediev, Arnaud Mussot
We report the first, to the best of our knowledge, experimental observation of doubly periodic first-order solutions of the nonlinear Schrödinger equation in optical fibers. We confirm, experimentally, the existence of A -type and B -type solutions. This is done by using the initial conditions that consist of a strong pump and two weak sidebands. The evolution of power and phase of the main spectral components is recorded using heterodyne time-domain reflectometry. Another important part of our experiment is active loss compensation...
July 1, 2020: Optics Letters
Stirling Scholes, Andrew Forbes
Laser brightness is crucial in many optical processes, and is optimized by high power, high beam quality (low M 2 ) beams. Here we show how to improve the laser beam quality factor (reducing the M 2 ) of arbitrary structured light fields in a lossless manner using continuous phase-only elements, thus allowing for the increase in brightness by a simple linear optical transformation. We demonstrate the principle with four high M 2 initial beams, converting each to a Gaussian ( M 2 ≈1) with a dramatic increase in brightness of >10×...
July 1, 2020: Optics Letters
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