A high-order mode converter and multiplexer based on silicon waveguide is designed. According to the principle of mode coupling, the conversion between high-order modes in different polarization states can be realized, including TM01 toTE11 mode conversion and TE01 to TM11mode conversion. Using the FDTD method, we analyze in detail the influence of the waveguide width W on the mode refractive index N, as well as the influence of the waveguide width W, the gap G and the coupling length L between different waveguides on the polarization extinction ratio and insertion loss. The results show that the polarization extinction ratio of the designed mode converter is 23.17dB and 24.9dB, the loss is 0.27dB and 0.589dB, and the coupling length is 14µm and 9.7µm, respectively. Besides, we proposed a 10-channel simultaneous polarization and mode division multiplexing system by the cascade of 10 mode converters, which can further increase the communication capacity.
A double-trench silicon waveguide based on SOI chip is proposed to generate high-order OAM modes (OAM±2). The double-trench structure excites two high-order orthogonal modes with π/2 (or 3π/2) phase difference, and can couple into high-order OAM±2 modes at the output terminal. The FDTD simulation results show that the mode conversion efficiency is greater than 95% and the intersection loss is less than 0.22dB during the wavelength range of 1.3 μm to 1.8 μm. The proposed method to generate OAM beams in SOI waveguide would be interesting for on-chip integrated optical communication, optical trapping and quantum information processing.
Based on an integrated silicon platform, we propose a device for generating and multiplexing optical orbital angular momentum modes(OAM), which is consisted of asymmetric directional couplers and trench waveguides. Asymmetric directional coupler is composed of single-mode and multi-mode waveguides . According to the principle of phase matching, the fundamental mode TE00 is coupled to the second-order mode via an asymmetric directional coupler. Single-trench waveguide can support two orthogonal eigenmodes. By adjusting the phase difference of two orthogonal eigenmodes to make them degenerate, they can be converted into orbital angular momentum modes with topological charges of +1, 0, -1, and multiplexed in the second trench. We simulate and analyze the characteristics of the device using three-dimensional finite difference domain method (3D-FDTD). The simulation results show that the device can realize the generation and multiplex of orbital angular momentum modes with topological charges +1, 0, -1. The proposed device is very compact with a footprint of 92 μm×5.3 μm and an insertion loss of 0.359 dB. The structure woks on a wavelength range from 1.48 μm to 1.57 μm. The structure is simple and easy to integrate, having a good application in OAM multiplexing system.
A simple optical orbital angular momentum (OAM) mode generator based on silicon-on-insulator (SOI) strip waveguides is proposed, which is consisted of a coupled waveguide and a trench waveguide. The fundamental mode TE00 is coupled to the second-order mode via an asymmetric directional coupler. Single-trench waveguide can support two orthogonal LP-like modes whose optical axes are rotated by around 45° with respect to the horizontal and vertical directions. We simulate and analyze the mode properties and propagation effects of OAM modes with charge numbers of 1or -1 by FDTD. When the phase difference between two LP-like eigenmodes is π/2,the second-order mode is further converted to the OAM mode over a wide wavelength range from 1.43μm to 1.58μm.The simulation results indicate that the loss can achieve approximately 0.16 dB. The proposed device is very compact with footprint of <47μm×2μm and the mode conversion efficiency is over 97%. Thus, such structure of OAM mode generator is a promising candidate for applying in OAM multiplexing system and other fields.
A two rings, triangular lattice photonic crystal fiber sensor element using surface plasma resonance phenomenon is proposed. The performance of the sensor is analyzed by finite element (FEM) analysis software Multiphysics COMSOL. The influence of structural parameters on the performance of the sensor is discussed. The results show that the maximum sensitivity is 6000nm/RIU, when refractive index is in the range of 1.31 to 1.38. The sensor can be directly placed in the liquid and platinum layer is placed outer surface of the photonic crystal fiber, which can simplify the manufacturing process and the measurement process , has important practical value.
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