Augmented reality is still in its infancy and is projected to grow substantially over the next few years. Grating-based waveguides are now established as the key enabling display technology for merging the physical and digital worlds in implementations as diverse as near eye displays, auto HUDs and large-scale retail displays. Despite significant design effort, delivering wide field-of-view (FoV) color, daylight-compatible brightness and ultra-compact glasses-like form factors at an acceptable price remain major development hurdles for consumer AR displays. The form factor challenge is only partially met using thin waveguides; current picture generation units, comprising the microdisplay beam splitter and projection optics, are increasingly seen as too bulky to satisfy the aesthetic requirements of consumer eyewear, while traditional input, fold and output grating architectures occupy too much waveguide real estate. Brightness and power consumption are compromised by losses of typically 95% incurred in coupling light from a picoprojector into a waveguide. DigiLens is prototyping a compact wide angle, full-color laser-illuminated consumer AR waveguide based on its Integrated Dual Axis (IDA) waveguide architecture which uses Digilens’s proprietary Switchable Bragg Grating (SBG) technology. An IDA waveguide multiplexes beam expansion and extraction gratings using a high index modulation holographic LC-photopolymer material system optimized for wide angle multiplex grating applications. A 50-degree diagonal FoV, full-color, low-cost IDA waveguide lens was demonstrated at the Consumer Electronics Show (CES) in Las Vegas (January 2020). As shown in Figure 1, DigiLens’s current waveguide display range includes helmet (25° diagonal), smart glass (30° diagonal) and head-worn (50° diagonal) color waveguide displays.
Wide field of view color waveguide display reference designs for low-cost consumer AR displays using high index modulation photopolymer and liquid crystal material for providing compact wide-angle, displays are presented.
Waveguide technology for providing compact wide-angle, low-cost HUDs for partially autonomous road vehicles with scalability to meet future HUD requirements, extending beyond safety and vehicle informatics, to fully autonomous vehicles will be presented.
DigiLens Switchable Bragg Grating (SBG) waveguide technology for transportation AR HUD consumer products enables switchable, tunable and digitally reconfigurable color HUDs with a field of view, brightness and form factor surpassing those of competing technologies. DigiLens waveguide gratings are printed into a proprietary polymer and liquid crystal mixture that can provide any required combination of diffraction efficiency and angular bandwidth in a thin waveguide with high transparency and very low haze. DigiLens waveguides can be laminated to integrate multiple optical functions into a thin transparent device. Our current reference designs for dashboard mounted and wearable ARHUDs will be presented.
DigiLens’s Switchable Bragg Grating (SBG) waveguides enable switchable, tunable and digitally reconfigurable color waveguide displays with a field of view, brightness and form factor surpassing those of competing technologies. DigiLens waveguides can be laminated to integrate multiple optical functions into a thin transparent device. DigiLens waveguide gratings are printed into a proprietary polymer and liquid crystal mixture that can provide any required combination of diffraction efficiency and angular bandwidth in a thin waveguide with high transparency and very low haze. The waveguide combines two key components: an image generation module, essentially a pico projector, and a holographic waveguide for propagating and expanding the image vertically and horizontally. Color is provided by a stack of monochrome waveguides each capable of addressing the entire field of view, incorporating an input rolled K-vector grating, a fold grating, and an output grating. Rolling the K-vectors expands the effective angular bandwidth of the waveguide. Fold gratings enable two-dimensional beam expansion in a single waveguide layer, which translates into lower manufacturing cost, reduced haze, and improved image brightness. The design of these complex SBGs is complicated by their birefringent properties, taking the design of DigiLens waveguides well beyond the frontiers of established ray-tracing codes. Our paper summarizes the key features of DigiLens waveguide technology and discusses our optical design methodology, with examples from DigiLens’s current waveguide HUD products.
Digilens is developing a new class of optical components based on the combination of Electrically Switchable Bragg Grating (ESBG) and waveguide technology. One or more optical waveguides are formed on a substrate which is used as one wall of a cell filled with an ESBG. The ESBG layer forms part of the waveguide cladding, such that the grating can interact with the evanescent field of the light energy traveling in the waveguide. This device architecture has been used to make Electrical Variable Optical Attenuators with more than 50 db of controllable range, flat attenuation over the optical communications C band, fast (<100 msecond) switching speed, and encouragingly low polarization dependent loss. Initial results on a variable wavelength-selective filter are also reported.
DigiLens Inc. (Sunnyvale, California) has developed the Application Specific Optical Element (ASOE) based on Electrically Switchable Bragg Gratings (ESBGs) using an advanced Holographic Polymer Dispersed Liquid Crystal material system. One of the embodiments of this fundamental technology is a customizable white light color sequential filter system which aims to replace traditional color wheel assemblies in microdisplay-based display applications such as business projectors, HDTV and large computer monitors. ASOEs are essentially stacks or laminates of intrinsically thin ESBGs encapsulated using transparent substrates. ASOEs have no moving parts; they are completely solid state and silent in operation. They offer the benefits of holographic optical elements in terms of being able to compress conventional optical systems into compact and lightweight form factors. Their switching speed is fast enough for color sequential display applications. They will have a major impact on the complexity and cost of a broad gamut of microdisplay applications, including projection and near- eye. This paper reviews the role of reflective ASOE filters in projection systems, with reference to design concepts currently in development.
A new solid state optical device technology - Electrically Switchable Bragg Grating (ESBG) technology - based on holographic polymer dispersed liquid crystal (H-PDLC), is being applied in Application Specific Integrated Lenses (ASILs) and Filters (ASIFs). These devices, also referred to as E-Lenses and E-Filters, are essentially stacks or laminates of intrinsically thin ESBGs encapsulated using transparent substrates. ASILs and ASIFs provide a basic colour sequential switching technology that directly challenges optical mechanical solutions such as color wheels. ASILs and ASIFs have no moving parts; they are completely solid state and silent in operation. They offer the benefits of holographic optical elements in terms of being able to compress conventional optical systems into compact and lightweight form factors. Since their switching speed is fast enough for colour sequential operation, colour dispersion can be controlled. They will have a major impact on the complexity and cost of a broad gamut of microdisplay applications, including projection and near-eye. The paper reviews the role of ASILs and ASIFs in both areas, with reference to design concepts currently in development.
Holographic polymer-dispersed liquid crystal, a new class of composite electro-optic materials, has rapidly matured as a technology for electronically switchable Bragg gratings. Recent progress in H-PDLC materials science has improved basic understanding of the mechanisms of diffusion, nanodroplet formation, and the morphology underlying switchable holograms, leading to practical improvements in key parameters such as the switching ratio, speed and operating voltage and an ability to optimize formulations for varied device functions such a switchable lenses and switchable waveguide Bragg gratings. Combining lens, filter or holographic optical functions with switchability leads to reduced parts count and simplified designs for projection displays and compact wearable microdisplays. H-PDLC technology is now approaching the performance and stability requirements that will enable photonic applications such as low cost WDM switches for optical networks.
Application Specific Integrated Filters (ASIFs), based on a unique holographic polymer dispersed liquid crystal (H-PDLC) material system offering high efficiency, fast switching and low power, are being developed for microdisplay based projection applications. A new photonics technology based H-PDLC materials combined with the ability to be electrically switched on and off offers a new approach to color sequential filtering of a white light source for microdisplay-based front and rear projection display applications. Switchable Bragg gratings created in the PDLC are fundamental building blocks. Combined with the well- defined spectral and angular characteristics of Bragg gratings, these selectable filters can provide a large color gamut and a dynamically adjustable white balance. These switchable Bragg gratings can be reflective or transmissive and in each case can be designed to operate in either additive or subtractive mode. The spectral characteristics of filters made from a stack of these Bragg gratings can be configured for a specific lamp spectrum to give high diffractive efficiency over the broad bandwidths required for an illumination system. When it is necessary to reduce the spectral bandwidth, it is possible to use the properties of reflection Bragg holograms to construct very narrow band high efficiency filters. The basic properties and key benefits of ASIFs in projection displays are reviewed.
Application Specific Integrated Lenses (ASILs), based on a unique holographic polymer dispersed liquid crystal material system, which offer high efficiency, fast switching and low power are being developed for display and telecommunication applications. The basic properties and key benefits of ASILs in wearable displays are reviewed.
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