One-Dimensional MEMS Optical Phased Array Systems Based on Surface Micro-Machined Silicon Mirrors for Scanning LiDAR Applications

Optical phased array (OPA) systems are an emerging technology for lightweight and miniature LiDAR scanners due to their compact size and construction that eliminate the need for robust physical moving parts, leading to a fast response, high reliability, and low power requirements. MEMS based OPA systems generally demand narrow and tightly spaced suspended microstructures with high-aspect-ratios in the lateral dimensions, rendering some significant challenges in the system design, fabrication, and integration. This thesis presents the first MEMS based OPA system that is fabricated using a conventional surface micromachining process, leading to a simplified design for the OPA technology. The one-dimensional OPA device utilizes an array of piston-type micromirrors which act as optical phase shifters. Each metal coated polysilicon micromirror is suspended by a pair of serpentine springs and is individually actuated at low voltage by a separate electrostatic parallel plate actuator. The field of view obtained by the prototype is measured as 4.76°. The low-mass micromirrors have a response time of 6.5 µs and an out of plane actuation stroke of 0.16 µm at a dc bias voltage of 55 V which is equal to one-quarter of the laser wavelength (650 nm) used, translating into the desired optical phase shift of π radian. LiDAR scanners are usually required to generate hundreds to thousands of scan points along a far-field scan line which leads to a large number of active phase shifters in the arrays and high complexity in control. A novel one-dimensional OPA system based on a limited number of pitch tunable silicon micromirrors is presented for laser steering with high angular resolution. The in-plane pitch tuning of all the physically connected micromirrors is realized by a pair of lateral electrostatic comb-drive actuators which require only one conductive layer. The longitudinal motion of the actuators is linearly guided by a group of mirror-positioned flexures. During the fabrication steps, an optical path difference is realized by slightly elevating every other suspended micromirror along the array in order to form the required phase shift pattern. A pitch tuning of the prototype at 30 V results in an optical steering range of 0.04° with an angular resolution of 0.002°.

Department dc:contributor.department

Mechanical and Industrial Engineering

Year dc:date.issued

2021

Author dc:creator

• Mohammad, Tarek

Advisors dc:contributor.advisor

• Ben Mrad, Ridha
• He, Siyuan

• Autonomous Vehicles
• LiDAR Scanner
• Micro Electromechanical Systems
• Optical Phased Array
• Silicon Micromirror
• Surface Micromachining

Handle dc:identifier.uri

http://hdl.handle.net/1807/109255

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/109255