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Optics (physics.optics)

Wed, 12 Apr 2023

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1.Universal Polarization Transformations: Spatial programming of polarization scattering matrices using a deep learning-designed diffractive polarization transformer

Authors:Yuhang Li, Jingxi Li, Yifan Zhao, Tianyi Gan, Jingtian Hu, Mona Jarrahi, Aydogan Ozcan

Abstract: We demonstrate universal polarization transformers based on an engineered diffractive volume, which can synthesize a large set of arbitrarily-selected, complex-valued polarization scattering matrices between the polarization states at different positions within its input and output field-of-views (FOVs). This framework comprises 2D arrays of linear polarizers with diverse angles, which are positioned between isotropic diffractive layers, each containing tens of thousands of diffractive features with optimizable transmission coefficients. We demonstrate that, after its deep learning-based training, this diffractive polarization transformer could successfully implement N_i x N_o = 10,000 different spatially-encoded polarization scattering matrices with negligible error within a single diffractive volume, where N_i and N_o represent the number of pixels in the input and output FOVs, respectively. We experimentally validated this universal polarization transformation framework in the terahertz part of the spectrum by fabricating wire-grid polarizers and integrating them with 3D-printed diffractive layers to form a physical polarization transformer operating at 0.75 mm wavelength. Through this set-up, we demonstrated an all-optical polarization permutation operation of spatially-varying polarization fields, and simultaneously implemented distinct spatially-encoded polarization scattering matrices between the input and output FOVs of a compact diffractive processor that axially spans 200 wavelengths. This framework opens up new avenues for developing novel optical devices for universal polarization control, and may find various applications in, e.g., remote sensing, medical imaging, security, material inspection and machine vision.

2.Sensitivity-Tunable Terahertz Liquid/Gas Biosensor Based on Surface Plasmon Resonance with Dirac Semimetal

Authors:Mengjiao Ren Hunan Normal University, Chengpeng Ji Hunan Normal University, Xueyan Tang Hunan Normal University, Haishan Tian Hunan Normal University, Leyong Jiang Hunan Normal University, Xiaoyu Dai Hunan University, Xinghua Wu Jiujiang University

Abstract: In this paper, we study the sensitivity-tunable Terahertz (THz) liquid/gas biosensor in a coupling prism-three-dimensional Dirac semimetal (3D DSM) multilayer structure. The high sensitivity of the biosensor originates from the sharp reflected peak caused by surface plasmon resonance (SPR) mode. This structure achieves the tunability of sensitivity due to that the reflectance could be modulated by the Fermi energy of 3D DSM. Besides, it is found that the sensitivity curve depends heavily on the structural parameters of 3D DSM. After parameter optimization, we obtained sensitivity over 100{\deg}/RIU for liquid biosensor. We believe this simple structure provides a reference idea for realizing high sensitivity and tunable biosensor device.

3.Radically Uniform Spike Trains in Optically Injected Quantum Cascade Oscillators

Authors:Yibo Peng School of Information Science and Technology, ShanghaiTech University, Shanghai, China Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai, China University of Chinese Academy of Sciences, Beijing, China, Siting Liu School of Information Science and Technology, ShanghaiTech University, Shanghai, China Shanghai Engineering Research Center of Energy Efficient and Custom AI IC, ShanghaiTech University, Shanghai, China, Vassilios Kovanis Bradley Department of Electrical and Computer Engineering, Virginia Tech Research Center, Arlington, Virginia, USA, Cheng Wang School of Information Science and Technology, ShanghaiTech University, Shanghai, China Shanghai Engineering Research Center of Energy Efficient and Custom AI IC, ShanghaiTech University, Shanghai, China

Abstract: It has been found that noise-induced excitability in quantum well and quantum dot semiconductor laser systems usually produces spike patterns of non-uniform amplitude. In this letter, we experimentally record that an inter-subband quantum cascade laser injected with a monochromatic laser exhibits a series of highly-uniform spike trains in the time domain. Theoretical analysis demonstrates that such high uniformity has its origin in the ultrashort carrier lifetime of the quantum cascade laser gain medium that is typically close to one picosecond.

4.Suppression of optical absorption with a bound state in the continuum

Authors:Radoslaw Kolkowski, Andriy Shevchenko

Abstract: Optical bound states in the continuum (BICs) have enabled suppression of radiation loss in various photonic structures. However, their quality ($Q$) factors can be limited by the intrinsic absorption loss, if present. We propose a type of BICs in which both the radiation and absorption losses are suppressed. The underlying mechanism is based on mutual coupling between three optical modes without explicitly restricting their symmetry. We numerically demonstrate such BICs in periodic metasurfaces made of resonant gold nanoparticles on a slab waveguide, showing $Q$ factors approaching $10^7$ in the visible spectral range. Our findings suggest that the $Q$ factors have no upper limit even in lossy plasmonic systems.