Study On Silicon-based Waveguide Phase Shifter

Silicon-based optical modulator is the key component of silicon photonic systems,and has to meet the requirements of high-speed transmission bandwidth,low power consumption and CMOS compatible with existing technologies and processes.While optical modulator has been mired since silicon or silicon nitride cannot utilize thermo-optical or free carrier dispersion effect effectively to satisfy all the requirements such as high-speed modulation,compactness and low-cost.So,the technology of heterogeneously integrated of nonlinear optical materials has become a research hotspot in recent years.Transparent conductive oxides?TCOs? are expected to solve this problem for their tunability of the permittivity under a gate voltage.In this paper,two kinds of electro-optical modulators based on TCO materials are designed by numerical simulation method,which are optical switches and optical phase shifters based on silicon or silicon nitride,respectively;and we have develop the process of low-loss silicon nitride optical waveguide and the integration process of TCO materials with SiN platform.The main work is divided into the following two parts.1.Generally,the relative high absorption loss in TCOs has limited their application in electro-optical phase shifters.Here,we propose a compact and low insertion loss silicon waveguide phase shifter based on high electron mobility TCO materials.We demonstrate the mobility of TCOs is closely related to the device insertion loss.We propose a silicon waveguide optical phase shifter based on high mobility cadmium oxide(?=300 cm²V^-1s^-1)by the Drude model,Thomas-Fermi theory and and numerical simulation with Comsol.For?-phase shift at 1550 nm,phase shifters show great performance parameters with a modulation bandwidth of 300 GHz.Specifically,silicon waveguide phase shifter based on CdO shows insertion loss of 1.4 dB,device length of127?m;silicon nitride waveguide phase shifter based on CdO shows insertion loss of 1dB,device length of 176?m.Our work provides a new strategy for the development of high speed silicon waveguide phase shifters in silicon photonics.The other modulation method is induced an epsilon-near-zero?ENZ? effect in TCOs by controlling the electron concentration.Optical switch with high-efficiency modulation,strong optical absorption based on TCO's structure could be achieved at ENZ state for the discontinuity of the electric field.Here,we also design a silicon waveguide optical switch through ring resonator based on ITO,which shows a phase shift of 0.15? and the extinction ration of7 dB by Lumerical.2.At the same time,we adjust the process condition of low-loss silicon waveguide systematically,including PECVD,contact-mode photolithography and etching.The transmission loss of 4?m straight waveguide is 4.98±0.57 dB/cm through the cut-off method,Based on the low-loss SiN waveguide process and the lift-off process,we also develop a silicon nitride waveguide optical switch through ring resonator based on ITO preliminarily.