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.
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.
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.
Augmented Reality (AR) devices optically superimpose information over the real world through an optical channel which angular resolution is limited by total internal reflection in the image guide. This limitation is governed by packaging size, Field of View, resolution, and the brightness. We discuss two multiplexing and de-multiplexing methods to address this challenge. By applying wavelength and time multiplexing, like, what is used in optical communication. Along with diffraction multiplexing via an array of facets, an increase in the effective optical bandwidth for the AR display is demonstrated. The demonstrated hybrid approach NED projection system combines multiple domains of multiplexing to enhance the FOV of displays without the typical package volume and energy consumption trade-offs. Showing the untapped potential of multiplexing on Digital Micro-mirror Devices based near-to-eye displays.
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 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.
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