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.
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.
Laser beam steering is an essential function for LiDAR. Phase Spatial Light Modulator (SLM) provides a capability of steering beam in a fast and random-access manner but suffers from limited FOV and side lobes. In this paper, we present a DMD (Digital Micromirror Device)-PLM hybrid beam steering concept that features high resolution, large-FOV, and side-lobe free beam steering.
The recent development of the MEMS Phase Light Modulator (PLM) enables fast laser beam steering for lidar applications by displaying Computer Generated Hologram (CGH) on-the-fly without resorting to iterative CGH calculation algorithm. We discuss application of MEMS PLM (Texas Instruments PLM) for quasi continuous laser beam steering by deterministically calculated CGHs.
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 concept of Texas Instrument (TI)-Phase-only Spatial Light Modulator (PLM) is reported which utilizing the dynamic piston motion of PLM pixels to form a discretized blazed grating. By fully manipulating the piston motion of pixels and increasing the available discretization level of the quasi-blazed grating, the Diffraction Efficiency (DE) can achieve close to 99%, which qualifies PLM an ideal candidate for beam steering functionality combining with its MEMS based high refresh rate and large aperture. The DE of the discretized blazed grating is proven to have 86% with 633 nm monochromatic light incident at 25° with 16 discretization levels and 2𝜋 round-trip phase modulation by RCWA algorithm. Furthermore, additional factors which lead to the degradation of diffraction efficiency is also analyzed.
Diffractive beam steering by Digital Micromirror Device enables an efficient way to simultaneously manipulate light both in the spatial and angular domain by spatial and time multiplexing while keeping large area and angular throw product. Long-term stability and susceptibility of beam and image steering rely on how synchronization of ns laser pulse and transition of micromirrors is maintained over time and through variation of device temperature. The long-term performance of the beam steering is evaluated by monitoring diffraction efficiency over 350 hrs. with a 360 Hz repetition rate. Also, diffraction efficiency was monitored while increasing the temperature of the mirror array from 45 to 75 degrees C. Over the period, stable beam steering was observed. A decrease in diffraction efficiency under high temperature was observed. We confirmed readjusting synchronization timing recovered the diffraction efficiency to the level of room temperature. The experimental results show a stable operation of diffractive beam steering by DMD is feasible for the long term, and even under variation of temperature by adaptively adjusting synchronization timing of laser pulse to starting timing of DMD mirror transition.
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