Large etendue laser beam steering by 2D MEMS resonant mirror and digital micromirror device for time-of-flight lidar and AR display

Abstract

Resonant MEMS mirror has been recognized as one of the solid-state laser beam steering (LBS) solutions for AR display and lidar. Such MEMS resonant mirrors’ large angular throw achieves over tens of degrees in scanning field of view (FOV) with operation speed exceeding tens of kHz in resonant frequency. In LBS, beam area is critical especially for lidar to access targets located at a far distance. Having both a large angular throw and beam area, or large Etendue, it is feasible to simultaneously satisfy requirement. For Time of Flight (ToF) lidar transmitter, we proposed and experimentally characterized a large Etendue LBS architecture employing a 2-dimensional MEMS mirror and diffractive LBS by Digital Micromirror Device (DMD). The beam area of MEMS resonant mirror is matched to DMD with relay optics while DMD diffractively increases the Etendue by factor of 5, which is equal to the number of diffraction orders supported by DMD. Along with beam steering, we address laser pulses’ timing to MEMS mirror’s movement to enable raster scanning that eliminates re-sorting of ToF data required for LBS employing a Lissajous pattern.