Design And Optimization Of Silica-based 90 Degree Optical Hybrid

90-degree optical hybrid can mix the two optical signals,and then recover the original signal after being processed by balance detector and DSP.It is an integrated optical device extensively applied in coherent optical communication,coherent imaging,optical sensing,coherent laser radar,etc.Integrated optical technology can effectively reduce device size and improve device performance.90-degree optical hybrid based on planar optical waveguide has the advantages of small size,low loss,therefore it becomes a research hotspot in the field of optical communication in recent years.In this thesis,the silica-based planar optical waveguide 90-degree optical hybrid is intensively studied,including the design and optimization of 90-degree optical hybrid,as well as the fabrication and testing of devices.The main contents of this paper are composed of four parts.1.Theoretical analysis of three commonly used planar optical waveguide 90-degree optical hybrid is carried out,and a 90-degree optical hybrid is designed by combining a 3dB coupler and a 90-degree phase shifter.Simulation analysis is carried out on the structure to obtain optimized device parameters.2.To improve the bandwidth of 90-degree phase shifter and reduce the size of 90-degree optical hybrid,theoretical analysis and simulation are carried out on two design schemes of the 90-degree phase shifter in terms of wavelength dependence and error sensitivity.Results show that bandwidth of the phase shifter designed with refractive index difference scheme is 2.2-3.6 times that of the length difference scheme(varying with the waveguide width),and the error sensitivity is considerably higher than that of the length difference scheme(when there is an error in waveguide width,phase error of the phase shifter designed with refractive index difference scheme is about 590-780 times that of the length difference scheme);influence of the increase of waveguide refractive index difference on cross waveguide is analyzed.Results show that loss and crosstalk are less than 0.12dB and 49.2dB respectively when the relative refractive index difference is 0.75%and intersection angle is greater than 24 degrees.3.To verify the wavelength dependence difference between two phase shifters,180 degree MZI device was fabricated using two phase shifter structures.Experimental results show that bandwidth of the phase shifter designed with refractive index difference scheme is 1.9 times that of the length difference scheme,which is consistent with the simulation results.4.Test results of 90 degree optical hybrid show that output phase deviation is within 4 degree,split ratio of signal light and local oscillator light I/Q branch is 49.75%:50.25%and 50.11%:49.89%,respectively.Insertion loss at the In-phase and Quadrature port is less than 1.18dB and 1.26dB,respectively.Insertion loss of the whole device is less than 1.22dB,performance of the device is equivalent to that of the existing optical hybrid,and the size is smaller,the insertion loss is lower.