Study of Integrated Optical Phased Array System

Abstract

This dissertation comprises three research projects focused on the Integrated Optical Phased Array (OPA) device, which has been extensively researched for its potential applications in LiDAR. Chapter 1 in this dissertation serves as an introduction of the OPA research. The first project is introduced in Chapter 2, it examines the waveguide grating coupler in SOI-based OPA devices and identifies a limitation in beam steering range of approximately 15° per 100nm wavelength range. To overcome this challenge, the author proposes a compound period grating coupler structure that generates a second beam by combining two electrical field perturbations. The simulation results indicate that this approach can achieve a combined beam steering range of over 26° per 100nm wavelength range. Furthermore, the addition of a DBR structure at the device's bottom can also reduce the leakage of light power through the substrate. The study also investigates the device's fabrication tolerance. The second research project is introduced in Chapter 3, it deals with a conflict between the need for a large emitter aperture and the excessive number of phase shifters required to suppress the aliasing effect associated with such an aperture. To address this issue, the author proposes a phase-combining unit (PCU) structure that utilizes the phase interference between two identical light modes with different phases. This structure allows for using N phase shifters to control 2N-1 emitters. Simulation results suggest that a PCU-assisted device with N phase shifters performs similarly to a non-PCU-assisted device with 2N-1 phase shifters. Experimental results also support this finding. Chapter 4-6 introduces the third project, which focuses on addressing the optical efficiency challenges that have hindered the industry-level maturity of OPA. Chapter 4 presents an end-fire 3-D OPA device based on a multi-layer SiN/SiO platform, the phase shifting and emitting parts are numerically investigated. The findings reveal that the edge-coupler for emitters can achieve an impressive light emitting efficiency of around 80%, with the beam's wavelength tuning capability and steering sensitivity customizable based on the specific application. In Chapter 5, the author designs the input coupling portion of the whole 3-D OPA device, and an experimental proof-of-concept whole device is fabricated and tested. The results demonstrate that the optical efficiency at both the input and output ends is significantly improved using the multi-waveguide-layer configuration. Finally, in Chapter 6, the author proposes and experimentally verifies a new fabrication method for the 3-D OPA using a single-lithography deep etching process. This method overcomes the limitations of the traditional multi-layer fabrication process, such as back control on gap thickness and layer misalignment.