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.
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.
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.
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.
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.
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 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.
We demonstrate a hologram-based image projector that expands the field of view (FOV) via wavelength multiplexing while retaining the flexibility of the high-resolution image displayed by a Digital Micromirror Device (DMD). Current Near-to-Eye Displays (NED) for AR/VR/MR applications are often limited in Etendue of the display devices and of the image transfer optics. Moreover, angular resolution and FOV are typically coupled, therefore a large physical package volume is also needed for large FOV optics. Our group previously reported increasing Etendue by custom pulsed illumination sources synchronized to a single DMD. To effectively utilize the increased Etendue along with the often angularly band-limited optical channels, for example, a TIR image guide, additional means to effectively increase Etendue of image transfer medium is needed. To address this challenge, wavelength multiplexed image transfer with extraction volume holograms proved to effectively increase the FOV at least by factor of 2. Along with the volume hologram, the prototype projector system employed 100ns pulsed dual lasers as sources, with a 0.7” DMD operating at 20kHz, coupled with a reflection type extraction volume hologram. In this talk, we address the optical architecture of wavelength multiplexed and FOV expanded projector, and are undergoing quantitative assessments of image quality, such as uniformity, resolution, contrast, and crosstalk.
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.
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.
Desirable fields-of-view, angular resolutions, and form factors of near-to-eye AR/VR/MR displays require order-ofmagnitude increases in pixel count and pixel density of spatial light modulators (SLM). We present an in-plane angularspatial light modulation technique to increase the independent output display pixels of a DMD by three orders of magnitude to achieve gigapixel output from a sub-megapixel device. Pulsed illumination synchronized to a DMD’s micromirror actuation realizes pixel-implemented and diffraction-based angular modulation, and fine source array control increases angular selectivity. The gigapixel output is demonstrated in a 1440-perspective display, each perspective having the DMD’s full native XGA resolution, across a 43.9°×1.8° FOV viewing angle. 8-bit multi-perspective videos at 30 FPS are demonstrated, and pixel-implemented multi-focal-plane image generation is realized. Implications for near-to-eye displays are discussed.
We introduce our recent work on the occlusion-capable near-to-eye display. Our implementation uses only a single digital micromirror device (DMD) both for the real scene masking and virtual image display. The real scene imaging onto the DMD and the mixed scene projection toward the eye are achieved using a single optics of polarization-based double-path configuration. These single DMD and the shared optics feature contributes to the reduction of the overall system volume. In the presentation, we explain the principle and introduces our recent experimental results demonstrating 60Hz display of color virtual images with per-pixel occlusion in over 90% maximum occlusion ratio.
A single Digital Micromirror Device with a single illumination source projects multiple, independent patterns into corresponding directions across a nearly-doubled angular extent by time multiplexing and by nanosecond illumination pulse synchronization for a binary patterned programmable blazed grating. The resulting “Angular Spatial Light Modulator” (ASLM) system nearly-doubles the étendue of a DMD-type SLM and creates a multiplication factor for the output pixel count and effective pixel density. We demonstrate an extended FOV display, a light-field projector, and a multi-view display which can be implemented into AR/VR systems. We present an implementation update using the DLP7000 DMD, increasing output pixel count by and effective pixel density orders-of-magnitude beyond traditional SLM systems while achieving an extended field-of-view and/or eye-box size due to the increased étendue.
Bullet-shaped LEDs are commonly used in self-luminous traffic signs as LED-dotted matrices due to their low cost, simplicity, robustness, and ease of installation. We proposed a simple low-cost method that creates a model suitable for the high manufacturing tolerance found in bullet-shaped LEDs. The method starts from measuring multiple one-dimensional angular intensity patterns at interested distances from multiple LEDs to form a database, including distances at 10, 15, 20, 25, 35, 50, and 100 mm. Their normalized cross-correlations are then calculated to find the batch that has the most similarity and base our model off that batch. Finally, we validate the model via Monte Carlo simulations in comparison to the original one-dimensional angular intensity patterns in the database. The platform demonstrated to obtain an average of 99% in normalized cross correlation between different batches of the same model LED, and a model of that LED is currently under development.
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