Reflective Micro Electro Mechanical System (MEMS) display as a spatial light modulator with synchronized nano-second pulse effectively diffracts light into one of multiple diffraction orders with high efficiency. Beam and image steering in a time sequential manner by this principle is applied for optical systems such as lidar, near-to-eye display and high-framerate cameras. We overview diffractive MEMS based beam and image steering by using a concept Time-to-Angle Conversion.
An ideal Near-to-Eye display (NED) requires high-resolution images, a large field of view (FOV) and depth cues. Sometimes, those performances are degraded due to optical aberrations of optics. To correct for aberrations, in this work, we utilize digital phase conjugation (DPC) with a Texas Instruments phase light modulator (TI-PLM) to generate a 3D image with TIR/geometrical image guide. TI-PLM is a type of MEMS device that modulates the phase of the incoming light by moving the micromirrors in a piston motion, thereby modulating the phase. To measure aberration induced by the image guide combiner, we employed an off-axis holography, capturing the off-axis fringes using a camera sensor. Subsequently, image processing on the captured fringes, involving Fourier transform and cropping of +1st order, to extract the final field information while reducing low-frequency noise. Computer-generated hologram (CGH) was generated to negate the phase aberration, which is then displayed on the PLM. Through phase conjugation, we reconstruct the wavefront, resulting in a series of point sources displayed at different depths, and producing a 3D point images. This method allows us to generate multiple point sources with different depths, contributing to the 3D image in our Near-to-Eye display even via aberrated medium.
Automotive Light Detection and Ranging (LiDAR) modules, wearable augmented reality display engines, and field-deployable free-space optical communication systems all require fast and robust solid-state beam and image steering solutions with a wide 2-dimensional field of view, as mechanical laser beam scanning is prone to mechanical failure. Diffractive beam steering with a digital micromirror device provides a robust solid-state beam steering solution to these problems and has been show to increase the field of view in 1-dimension for LiDAR and display systems. By extension, two Digital Micromirror Devices arranged orthogonally can be synchronized with a pulsed laser to diffractively steer a beam arbitrarily in 2-dimensions. This technique enables all-solid-state 2-dimensional beam steering solutions for beam steering and image steering applications.
To facilitate Augmented Reality (AR) displays suitable for all-day-long usage, technologies are anticipated to realize compact form factor, low power consumption without compromising key aspects such as field-of-view (FOV), brightness, resolution, and uniformity. The balance among those requirements is crucial for creating a better AR experiences that are both comfortable and visually appealing for extended use. One of the challenges, FOV-resolution-form factor trade-off is addressed by using a MEMS based micro display panel, Digital Micromirror Device (DMD) in diffractive image steering mode. The DMD is paired with synchronized and short laser pulse illumination and a prism array expands FOV. This setup facilitates steering images into one of the multiple diffraction orders in a time sequential manner. The FOV is horizontally increased by fivefold. The vertical FOV is increased by twofold by incorporating illumination multiplexing. The resulting FOV reaches 30 degrees horizontally and 12 degrees vertically, all while sustaining a resolution of 1.86 arc minutes per pixel. This method increases FOV without sacrificing resolution nor increasing the form factor of micro display panel.
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.
Enabling all-day-wearable augmented reality (AR) displays require compact engineering solutions that still satisfy requirements like wide field-of-view (FOV) and high resolution. By using a Digital Micromirror Device (DMD) and a pulsed laser in synchronization we are able to perform diffractive image steering which decouples the FOV of the projected image from the display size while not sacrificing image resolution. This approach reduces, by several factors, the lateral extent of the display panel while retaining image resolution. The diffractive-steering-enabled FOV expansion by the DMD, paired with a prism array placed at the exit pupil of the projection lens, maintains a small form factor by re-distributing a part of the volume from the projector engine to the image transfer optics. Together with diffractive image steering and the prism array we demonstrate a 5x increase in field-of-view. This approach decreases the requirement on the number of pixels to maintain high resolution across a wide FOV, which makes it suitable for eventually installing it in small form factor head mounted displays.
Diffractive image steering using a Micro Electro Mechanical System (MEMS) Spatial Light Modulator (SLM) with pulsed illumination decouples display size from field of view (FOV), that reduces a form factor of augmented reality (AR) and virtual reality (VR) display engine, while not sacrificing the resolution of image. In the image steering, pulsed illumination is necessary to access to the transitional period of MEMS SLM. Correlation of average laser power of laser diode driven in a pulsed mode operation is evaluated and compared to the power of the laser diode driven in continuous mode.
Micro Electro Mechanical System (MEMS) spatial light modulators enables adaptive and fast beam and image steering. For lidar applications, Texas Instruments Phase Light Modulator (TI-PLM) is paired with real-time calculation and display of Computer Generated Holograms (CGH) by CUDA-OpenGL interoperability assisted by YOLOv4-tiny network model for object detection and recognition. The real-time object recognition, CGH calculation, and display framework replaces conventional raster scanning with camera-input based and foveated beam steering while having a beam scan rate beyond the frame rate of TI-PLM. For Augmented Reality (AR) application, the same framework is used for image steering based on gaze information of eye. With Texas Instruments Digital Micromirror Device (TI-DMD), image is steered into a part of field of view by following movement of eye. The diffractive image steering enabled by TI-DMD increases FOV while not sacrificing resolution of the image displayed.
We demonstrated a real-time lidar system applying a Digital Micromirror Device (DMD) as a field of view (FOV) expander of a lidar receiver employing a 2D Multi-Pixel Photon Counter (MPPC). By temporally synchronizing the transitional state of micromirrors with returning photons from lidar, receiver FOV is diffractively steered to the targets’ direction enabled by nano-second pulse laser. With a nanosecond 905nm laser transmitter, time-of-flight (ToF) lidar images were captured across seven diffraction orders with the expanded 35 degrees full field of view lidar scanning range.
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.
We demonstrated a real-time lidar system that utilizes a Digital Micromirror Device (DMD) as a field of view (FOV) expander and a 2D Multi-Pixel Photon Counter (MPPC) as a lidar sensor. By synchronizing the dynamic transition of DMD micromirrors between on- and off-states with the MPPC and a nanosecond pulse laser, the receiver FOV is diffractively steered to expected direction enabled by timing the delay of micromirrors transition to the laser. The DMD-MPPC lidar can capture up to 7 diffraction orders of high-resolution geospatial data. By applying the laser beam steering technique, this system is able to span over 35 degrees FOV, which is 10 times expansion of FOV compared to the single lidar detector FOV. In this work, as a preliminary demonstration towards diffractive FOV expansion, we presented the high resolution lidar images while DMD is switching between on and off state. Also, we performed distance resolution testing to validate the functionality of DMD-MPPC flash lidar system.
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 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.
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.
CUDA-OpenGL interoperability enables to drastically reduce the computational time for CGH calculation and display on Spatial Light Modulators via HDMI display channel. The fast calculation method enables on-the-fly diffractive beam steering by Micro Electro Mechanical System based phase light modulator with YOLOv4-tiny model based object recognition to do AI-based dynamic beam tracking in order to trace the object of interest.
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.
Digital Micromirror Device (DMD) is a commercial and mass-produced Micro Electromechanical System (MEMS) spatial light modulator (SLM) consisting of millions of mirrors that spatially modulate lights by switching it between on and off states. Between the on- and off-states, transitional states exist where micromirror changes tilt angle. We report a method to control the transitional time of the mirror array by controlling the pressure of the ambient air. The increased air pressure to 100 psi increases mirrors transitional time by 20%. We also address the possibility of controlling the transitional time electrically.
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