A wavelength and time multiplexed image transfer by employing multiple light sources and volume hologram grating expands the field-of-view of the image guide combiner for near-to-eye beyond its total internal reflection limit.
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.
We propose and demonstrate a Field of View (FOV) expander, realized by wavelength-division multiplexing (WDM) by using volume holographic gratings (VHG). This holographic based FOV expander is low cost and easy to manufacture, which we demonstrate through our updated in-plane writing setup. We present our experimental results of diffraction efficiency measurements and image analysis which show high SNR and angular resolution. This holographic based FOV expander based on VHGs have potentials and can be implemented into AR/VR systems.
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.
The recently reported “Angular Spatial Light Modulator” (ASLM) light engine, using pulsed illumination synchronized to a Digital Micromirror Device (DMD), shows significant promise to enhance pixel counts of Near-to-Eye Displays (NED) without increasing package volume, but requires an uncommon illumination driver. We present a field effect transistor based constant-current driver that is fast, compact, and scalable to RGB illumination. The digital-to-analog convertor modulates intensity on-the-fly for illumination-based multiplexing. The driver outputs 100 ns pulses, up to 24 kHz repetition rate. The circuit is demonstrated for two laser diodes and for two LEDs in an ASLM-enhanced pixel count display.
A holographic lidar concept established on the Digital Micromirror Mirror (DMD)-based hybrid light modulation is reported, which multiplexes coarse-steering by sawtooth phase modulation and fine-steering by binary amplitude modulation. The hybrid steering is achieved by overlaying displayed Computer-Generated Holograms (CGHs) with a sawtooth blazed grating phase mask, which the blaze angle programmed by synchronized short-pulse illumination of transitioning micromirrors creating the CGHs. The steering principle is demonstrated as a 2D beam steering scheme with a 532 nm visible pulse laser, and implemented into a 905 nm lidar system with a 44° field-of-view, 0.9°×0.4° angular resolution, 7.8 FPS video frame rate, and 1 m detection distance.
The “Angular Spatial Light Modulator” (ASLM) utilizes digital micromirror device (DMD) as a binary patterned programmable blazed grating to increase number of output pixels of a DMD by merging geometric and diffractive optical capabilities of the DMD. We demonstrate series of capabilities of the ASLM for beam and pattern steering. In particular, a single-chip beam steering lidar, an extended FOV display, a light-field projector, and a multi-view display which can be implemented into AR/VR systems. We also present our metrology results of wavefront distortion of DMD while micro mirrors are transitioning over between on and off states.
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