US-12619077-B2 - Compact head-up display and waveguide therefor

US12619077B2US 12619077 B2US12619077 B2US 12619077B2US-12619077-B2

Abstract

A display system comprises a waveguide forming a pupil expander. The waveguide comprises a pair of opposing surfaces arranged to guide a diffracted light field therebetween by internal reflection. An input port of the waveguide is arranged to receive light from a display system. An output port of the waveguide is formed by a first transmissive-reflective element of a first surface of the pair of opposing surfaces. The first transmissive-reflective element is such that the diffracted light field is divided at each internal reflection and a plurality of replicas of the diffracted light field are transmitted out of the waveguide through the output port. The input port comprises a second transmissive-reflection element arranged to receive at least a portion of the light from the display system.

Inventors

Ruisheng Lin
Timothy Smeeton
Yiren Xia
Jamieson Christmas

Assignees

ENVISICS LTD

Dates

Publication Date: 20260505
Application Date: 20221206
Priority Date: 20211221

Claims (20)

1 . A waveguide comprising: a pair of opposing surfaces arranged to guide a light field therebetween by internal reflection; an input port arranged to receive light from a display system, wherein the input port comprises a first transmissive-reflective element disposed on a first surface of the pair of opposing surfaces and configured to (i) receive, and partially transmit and partially reflect, at least a portion of the light from the display system and (ii) internally reflect within the waveguide at least some of the light field; a reflective element disposed on the first surface of the pair of opposing surfaces, wherein the reflective element is adjacent to the first transmissive-reflective element and configured to internally reflect the light field within the waveguide, and wherein a transmissivity of the first surface from a start of the first transmissive-reflective element to an end of the reflective element is one of (i) continuous or (ii) continuously decreasing; and an output port formed by a second transmissive-reflective element disposed on a second surface of the pair of opposing surfaces, wherein the second transmissive-reflective element is such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted out of the waveguide through the output port.
2 . The waveguide of claim 1 , wherein the first transmissive-reflective element is at least one of (i) configured such that at least some of the light field is incident thereon only once or (ii) configured such that all light rays of the light field are incident thereon only once.
3 . The waveguide of claim 1 , wherein the input port is formed on the first surface of the pair of opposing surfaces.
4 . The waveguide of claim 1 , wherein the first transmissive-reflective element has a transmissivity of between 0.1 to 0.5.
5 . The waveguide of claim 1 , wherein the reflective element is disposed on the first surface immediately adjacent to the input port.
6 . The waveguide of claim 1 , wherein a transmissivity of the reflective element is one of (i) less than 0.1, (ii) less than 0.07, or (iii) less than 0.05.
7 . The waveguide of claim 1 , wherein the first transmissive-reflective element is arranged to receive all the light from the display system.
8 . The waveguide of claim 1 , wherein the input port further comprises a transmissive element arranged to receive a portion of the light from the display system, and wherein one of (i) the transmissive element adjoins the first transmissive-reflective element and (ii) the first transmissive-reflective element adjoins the reflective element.
9 . The waveguide of claim 1 , wherein the first transmissive-reflective element comprises a partially transmissive and partially reflective surface coating.
10 . The waveguide of claim 1 , wherein the input port has a length in a direction of waveguiding and the first transmissive-reflective element extends over at least a part of the length of the input port.
11 . The waveguide of claim 1 , wherein one or both of (i) the display system comprises a spatial light modulator arranged to display a hologram and (ii) the light field is spatially modulated in accordance with the hologram.
12 . The waveguide of claim 1 , wherein the display system comprises a display device having a pixel area defining an exit pupil of the display system that is expanded by the waveguide.
13 . A system comprising a waveguide, wherein the waveguide comprises: a pair of opposing surfaces arranged to guide a light field therebetween by internal reflection; an input port arranged to receive light from a display system, wherein the input port comprises a first transmissive-reflective element disposed on a first surface of the pair of opposing surfaces and configured to (i) receive, and partially transmit and partially reflect, at least a portion of the light from the display system and (ii) internally reflect within the waveguide at least some of the light field; a reflective element disposed on the first surface of the pair of opposing surfaces, wherein the reflective element is adjacent to the first transmissive-reflective element and configured to internally reflect the light field within the waveguide, and wherein a transmissivity of the first surface from a start of the first transmissive-reflective element to an end of the reflective element is one of (i) continuous or (ii) continuously decreasing; and an output port formed by a second transmissive-reflective element disposed on a second surface of the pair of opposing surfaces, wherein the second transmissive-reflective element is such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted out of the waveguide through the output port; and wherein the waveguide is a second one-dimensional pupil expander of a pair of waveguide pupil expanders arranged to expand a pupil of the display system in a first direction and a second, perpendicular direction, respectively.
14 . A system comprising: a display system arranged to form a light field for viewing by a viewing system; and a waveguide configured to receive the light field at an input port thereof, wherein the light field increases in size with propagation distance from the display system such that the viewing system can perceive a virtual image at a finite virtual image distance, and wherein the waveguide comprises: a pair of opposing surfaces arranged to guide a light field therebetween by internal reflection; an input port arranged to receive light from a display system, wherein the input port comprises a first transmissive-reflective element disposed on a first surface of the pair of opposing surfaces and configured to (i) receive, and partially transmit and partially reflect, at least a portion of the light from the display system and (ii) internally reflect within the waveguide at least some of the light field; a reflective element disposed on the first surface of the pair of opposing surfaces, wherein the reflective element is adjacent to the first transmissive-reflective element and configured to internally reflect the light field within the waveguide, and wherein a transmissivity of the first surface from a start of the first transmissive-reflective element to an end of the reflective element is one of (i) continuous or (ii) continuously decreasing; and an output port formed by a second transmissive-reflective element disposed on a second surface of the pair of opposing surfaces, wherein the second transmissive-reflective element is such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted out of the waveguide through the output port.
15 . The waveguide of claim 1 , wherein the light field comprises a diffracted light field.
16 . The waveguide of claim 1 , wherein the light field comprises an image formed by holographic reconstruction.
17 . The system of claim 13 , wherein the light field comprises a diffracted light field.
18 . The system of claim 13 , wherein the light field comprises an image formed by holographic reconstruction.
19 . The system of claim 14 , wherein the light field comprises a diffracted light field.
20 . The system of claim 14 , wherein the light field comprises an image formed by holographic reconstruction.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119 to UK Patent Application GB 2118613.5, titled “Compact Head-Up Display and Waveguide Therefor,” filed on Dec. 21, 2021, and currently pending. The entire contents of GB 2118613.5 are incorporated by reference herein for all purposes. FIELD The present disclosure relates to pupil expansion or replication, in particular, for a diffracted light field comprising diverging ray bundles. More specifically, the present disclosure relates a display system comprising a waveguide pupil expander and to a method of pupil expansion using a waveguide. Some embodiments relate to two-dimensional pupil expansion, using first and second waveguide pupil expanders. Some embodiments relate to a picture generating unit and a head-up display, for example an automotive head-up display (HUD). INTRODUCTION Light scattered from an object contains both amplitude and phase information. This amplitude and phase information can be captured on, for example, a photosensitive plate by well-known interference techniques to form a holographic recording, or “hologram”, comprising interference fringes. The hologram may be reconstructed by illumination with suitable light to form a two-dimensional or three-dimensional holographic reconstruction, or replay image, representative of the original object. Computer-generated holography may numerically simulate the interference process. A computer-generated hologram may be calculated by a technique based on a mathematical transformation such as a Fresnel or Fourier transform. These types of holograms may be referred to as Fresnel/Fourier transform holograms or simply Fresnel/Fourier holograms. A Fourier hologram may be considered a Fourier domain/plane representation of the object or a frequency domain/plane representation of the object. A computer-generated hologram may also be calculated by coherent ray tracing or a point cloud technique, for example. A computer-generated hologram may be encoded on a spatial light modulator arranged to modulate the amplitude and/or phase of incident light. Light modulation may be achieved using electrically-addressable liquid crystals, optically-addressable liquid crystals or micro-mirrors, for example. A spatial light modulator typically comprises a plurality of individually-addressable pixels which may also be referred to as cells or elements. The light modulation scheme may be binary, multilevel or continuous. Alternatively, the device may be continuous (i.e. is not comprised of pixels) and light modulation may therefore be continuous across the device. The spatial light modulator may be reflective meaning that modulated light is output in reflection. The spatial light modulator may equally be transmissive meaning that modulated light is output in transmission. A holographic projector may be provided using the system described herein. Such projectors have found application in head-up displays, “HUD”. SUMMARY Aspects of the present disclosure are defined in the appended independent claims. Broadly, the present disclosure relates to image projection. It relates to a method of image projection and an image projector which comprises a display device. The present disclosure also relates to a projection system comprising the image projector and a viewing system, in which the image projector projects or relays light from the display device to the viewing system. The present disclosure is equally applicable to a monocular and binocular viewing system. The viewing system may comprise a viewer's eye or eyes. The viewing system comprises an optical element having optical power (e.g., lens/es of the human eye) and a viewing plane (e.g., retina of the human eye/s). The projector may be referred to as a ‘light engine’. The display device and the image formed (or perceived) using the display device are spatially separated from one another. The image is formed, or perceived by a viewer, on a display plane. In some embodiments, the image is a virtual image and the display plane may be referred to as a virtual image plane. In other embodiments, the image is a real image formed by holographic reconstruction and the image is projected or relayed to the viewing plane. The image is formed by illuminating a diffractive pattern (e.g., hologram) displayed on the display device. The display device comprises pixels. The pixels of the display device may display a diffractive pattern or structure that diffracts light. The diffracted light may form an image at a plane spatially separated from the display device. In accordance with well-understood optics, the magnitude of the maximum diffraction angle is determined by the size of the pixels and other factors such as the wavelength of the light. In embodiments, the display device is a spatial light modulator such as liquid crystal on silicon (“LCoS”) spatial light modulator (SLM). Light propagates over a range of diffraction angles (for example, from ze