Beam and image steering by Micro Electro Mechanical System (MEMS) Spatial Light Modulators decouples trade-offs between resolution, field of view, and size of displays and optics that are a common challenge found in optical designs. We overview solid state lidar and augmented reality display engine employing MEMS SLMs, Texas Instruments Digital Micromirror Device and Phase Light Modulators.
Micro Mechanical Electronics System based Spatial Light Modulators (MEMS-SLM) enables unique capability “Just in time photon delivery” or steering beam images to where and when they are needed. The beam and image steering solves challenges commonly found in both lidar and AR optical engines dominated by classical tradeoffs, such as image FOV, resolution and SLM size or form factor of optical engine. As a novel beam and image steering device, we transformed Texas Instruments Digital Micromirror Device (TI-DMD) into a diffractive beam and image steering device. TI-DMD is known as a binary spatial light modulator. Micromirros’ tilt re-directs light into on- or off-states. Without modifying TIDMD, but with employing a nano-second pulse illumination synchronized to the transitional movement of micromirrors between the of- and off-states turns DMD into a diffractive beam and image steering device.
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.
By employing Talbot self-imaging, phase modulation depth of a Spatial Light Modulator (SLM) is doubled without employing relay optics and/or multiple SLMs. The proposed optical architecture enables laser beam steering of infrared light with enhanced diffraction efficiency while using a single SLM designed for visible wavelength.
By combining a Micro Electro Mechanical System based resonant mirror and a Digital Micromirror Device, we demonstrated a large scan angle, fast scan rate, and high resolution beam steering for the lidar applications. The proposed optical architecture preserves a large Etendue of DMD-based diffractive beam steering with a synchronized short pulsed laser to transition of micromirror array while increasing angular resolution.
A novel method of beam steering, utilizing a mass-produced Digital Micromirror Device (DMD), enables a reliable single chip Light Detection and Ranging (LIDAR) with a large field of view while having minimum moving components. In the single-chip LIDAR, a short-pulsed laser is fired in a synchronous manner to the micromirrors rotation during the transitional state. Since the pulse duration of the laser pulse is substantially short compared to the transitional time of the mirror rotation, virtually the mirror array is frozen in transition at several discrete points, which forms a programmable and blazed grating. The programmable blazed grating efficiently redirects the pulsed light to a single diffraction order among several while employing time of flight measurement. Previously, with a single 905nm nanosecond laser diode and Si avalanche photo diode, a measurement accuracy and rate of <1 cm and 3.34k points/sec, respectively, was demonstrated over a 1m distance range with 48° full field of view and 10 angular resolution. We have also increased the angular resolution by employing multiple laser diodes and a single DMD chip while maintaining a high measurement rate of 3.34k points/s. In addition, we present a pathway to achieve 0.65° resolution with 60° field of view and 23k points/s measurement rate.
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