Design And Research Of Silicon-based Photonic Crystal Thermo-optic Modulator And Its Coupling Devic

Over the past few years,advancements in technology such as the Internet,5G communications,and artificial intelligence have resulted in a significant increase in the amount of data being transmitted and a greater demand for high-quality network performance.Photonic integrated circuits(PICs)have become one of the promising industrial platforms in SiliconOn-Insulator(SOI)due to the demand for high data rates and low power consumption.The perfect compatibility of SOI with CMOS technology enables large-scale fabrication and application of PICs.Outstanding research results have been achieved for C-band photonic devices.Siliconbased modulators are the important part of optical communications,which are the hot topic and focus of research.In this thesis,we focus on how to use silicon-based photonic crystal microcavities and apodized grating to achieve a thermo-optical tuning system with low loss,high tuning efficiency and small size.The specific research results are summarized as follows:1.A apodized grating coupler has been designed in C-band TE mode.The method of linearly changing the effective refractive index of the grating is used to improve the coupling efficiency,and the performance of the grating is improved by using the particle swarm optimization algorithm.The performance of grating coupling on different top silicon thicknesses is investigated.The grating optimised has a coupling efficiency of 60%on standard 220 nm-thick SOI and a 3-dB optical bandwidth of 63.5 nm.On standard 340 nm-thick SOI,the coupling efficiency of 80%and a 3-dB optical bandwidth of 51.3 nm.At the same time,the scattering process of the grating unit and the leakage factor of the grating were studied by using the finite-difference time domain method.In addition,the method of linearly changing the effective refractive index can be used for the design of any grating,as a widely applicable technique.2.A photonic crystal microcavity modulator based on graphene heater is investigated.Photonic crystal microcavity with ultra-small mode field volume is to select wavelength.In 3D simulation,the resonance peak at 1555 nm in the PhC nanocavity exhibits the transmission of 30%,quality factor of 663,and a mode field volume of 0.103 μm3.Ultra-small mode field volume is beneficial to the interaction of light and master.Thermal tuning efficiency ηd of 2.5 nm/mW after adding graphene thermal electrodes above the microcavity.In addition,the optical transmission of the device(combined grating coupler and thermo-optic modulator)is calculated using the finite-difference time domain method.The overall loss of the obtained device is-8.2dB,and the area is 30 μm × 80 μm.The structure exhibits excellent performance with low insertion loss,ultracompact,and has good research value and application prospect.3.Two tapered structures are used to improve the coupling performance between the devices.In grating couplers,the taper structure solves the problem of mode mismatch at the interface between the strip waveguide and the grating.After adding the tapered structure,the coupling efficiency improves by 16%on the 220 nm SOI and by 7%on the 340 nm SOI.In the thermo-optical modulator,the tapered structure solves the mismatch of group index of refraction between the strip waveguide and the photonic crystal waveguide,increasing coupling efficiency by 32%.