Polarization Multiplexing Silicon-photonic Optical Phased Array For 2D Optical Beam Steering

Optical phased arrays(OPA)is a beam output system with a set of array output arrangements that work in the optical frequency band,which realizes the beam steering by controlling the phase of the array elements.This solid-state beam steering capability has made it widely studied,and it has good application prospects in the fields of light detection and ranging(Lidar),free-space optical communication,and laser display.The rapid development of photonic integration technology has made silicon-based OPAs an effective solution for realizing chip-level fast beam scanning control devices.For the current integrated OPAs,although the size of the array and the number of components continue to increase,the beam quality and steering angle are still limited,and there are still many challenges.This thesis is aimed at improve the scanning angle of silicon-based OPA.We propose a scheme combining OPA with the polarization multiplexing,which is used to extend the steering angle with the same wavelength bandwidthFirstly,this thesis theoretically analyzes the factors that affect the performance of the OPA.According to the mode coupling theory,related devices for polarization control are designed.Then,an OPA chip based on polarization multiplexing is designed,in which a polarization control system is composed of a Mach-Zehnder interferometer(MZI)switch,a polarization rotator(PR),and a polarization beam splitter(PBS).The beams are divided equally by the multimode interference(MMI)couplers and then the phases are controlled by the thermo-optic effect of silicon,which is finally emitted from the waveguide grating array.Through the analysis of the polarization sensitivity of silicon-on-insulator(SOI)waveguide gratings with different top silicon layer thickness,the 340 nm SOI platform was chosen to implement the designed OPA system Then the structures of PBS,PR,MMI couplers are optimized to ensure high performances.The simulation results show that the loss of PBS is less than 1 dB,the loss of PR is less than 0.3 dB,and the 1×2MMI can achieve efficient split beam splitting for both polarization modes.A 1×16 phased array with 1.2 ?m pitch is designed,and the simulation results show that a scanning angle of 77.4° × 28.2° can be obtained under the introduction of the two polarization modes,which is almost doubled compared to the conventional structures based on single polarization.The proposed device is then fabricated and characterized,the measurement results show good agreement with the simulations.