Research On Silicon-Based Optical Waveguide Mode Switch Based On MZI Structure

With the advent of the 5G information era,the demand for information transmission speed and capacity of people is also increasing.However,due to factors such as the Shannon limit and nonlinear effects of optical fibers,the transmission capacity of single-mode optical fiber has reached its theoretical limit,which has been unable to meet the urgent needs of people for high-speed and large-capacity data transmission in the future.In this context,mode division multiplexing technology,as a powerful solution to improve the capacity of optical communication,has received widespread attention from researchers.Mode division multiplexing technology is mainly based on the orthogonality of spatial modes,using different spatial modes as independent transmission channels,which can effectively improve communication capacity and also help reduce system power consumption.In the mode division multiplexing system,mode optical switch is one of the most critical devices,mainly used to complete the conversion between multiple modes or mode channel switching,which can greatly improve the flexibility of the mode division multiplexing system,and have broad application prospects in the mode division multiplexing system.Silicon photonic technology is based on a standard complementary metal oxide semiconductor（CMOS）platform,compatible with integrated circuit technology,and has the advantages of large-scale,high-precision,high-speed,and low power consumption.It is one of the most promising solutions for on-chip integrated optical applications.Under this research background,this thesis mainly focuses on the research of silicon based waveguide mode optical switching devices based on Mach Zehnder interferometer（MZI）structure.The main content includes the following parts:Firstly,the research progress and development trend of silicon based photonics are introduced,as well as the advantages of silicon based photonics in current optical communication systems.The research background and progress of mode optical switches in recent years are summarized,and the optical waveguide mode theory and the working principle of MZI structures are analyzed.Secondly,a 1×1 electro mode optical switch based on MZI structure is designed and fabricated.The mode switching and switching functions between TE₀ and TE₁ modes have been achieved,theoretical simulation loss is less than 4.5 dB and extinction ratios greater than 16.2 dB.Tests on the prepared devices have shown that the extinction ratio of the device is greater than 14.8 dB,the rise time is 37 ns,and the fall time is 50ns;On this basis,a 2×2 mode insensitive mode optical switch realizes insensitive transmission and switching functions for TE₀,TE₁,and TE₂ modes.Based on this structure,a reconfigurable non-blocking multimode optical switch array based on the Benes architecture is further designed as a switching unit.In the"All Cross"state,the insertion loss of TE₀ and TE₁ modes is less than 3.3 dB and 13.3 dB,and the crosstalk is less than-38.9 dB and-13.8 dB,respectively,In the"All Bar"state,the insertion loss of TE₀and TE₁ modes is less than 3.7 dB and 11.1 dB,respectively,and the crosstalk is less than-17.5 dB and-14.9 dB,respectively.Finally,based on the silicon based planar optical waveguide structure,a silicon based three-dimensional waveguide mode optical switch is proposed by introducing phase change materials to achieve self maintaining optical switching states.This device can achieve the reconfigurable mode multiplexing/demultiplexing function of TE₀ mode in the upper silicon based single mode waveguide and TE₂₁ mode and TE₁₂ mode in the lower few mode waveguide,with a loss of less than 2.64 dB and crosstalk of less than-15.4 dB in all states.