A Monolithic Forward-View Optical Scanner by a Pair of Upright MEMS Mirrors on a SiOB for LiDAR Applications

A forward-view optical scanner made of a MEMS mirror typically needs a second mirror to fold the optical beam forward, and thus an assembly structure is required, which drastically increases the overall size and weight of the scanner. This paper reports an ultra-small forward-view optical scanner with two vertically oriented micromirrors integrated on a silicon optical bench (SiOB). A new latch structure is proposed to secure the mirror frame at its vertical position and an array of meander thin-film stripes is designed to assist the latching process. The new design has been successfully fabricated and shows much-improved verticality with a maximum deviation of less than ±2° from 90°. With an optical aperture of 0.7 mm, the form factor of the MEMS chip is 4.9 mm (length) by 4.7 mm (width) by 1.8 mm (height). The measured forward field of view (FoV) of the vertical micromirrors reaches 21° in both axes at non-resonance with the voltage amplitude less than 4 V. The first resonant frequency (corresponding to the mirror frame rotation mode) of the micromirror is about 630 Hz. A fiber-pigtail bonded forward scanner is assembled with a footprint of 2 cm by 1.2 cm and a weight of 0.6 g. A forward scanning LiDAR has been built with this new MEMS scanner. The non-resonant scanning capability enables forward-view adaptive resolution and zoom-in scanning capability.