EP-4202533-B1 - COMPACT HEAD-UP DISPLAY AND WAVEGUIDE THEREFOR

EP4202533B1EP 4202533 B1EP4202533 B1EP 4202533B1EP-4202533-B1

Inventors

LIN, Ruisheng
Smeeton, Timothy
XIA, YIREN
CHRISTMAS, JAMIESON

Dates

Publication Date: 20260506
Application Date: 20221213

Claims (13)

A waveguide comprising: a pair of opposing surfaces (910, 920) arranged to guide a diffracted light field therebetween by internal reflection; an input port arranged to receive light from a display system; an output port formed by a first transmissive-reflective element of a first surface (910) of the pair of opposing surfaces (910, 920), wherein 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, wherein the waveguide further comprises a reflective element (970) arranged to internally reflect within the waveguide the diffracted light field, wherein the input port comprises a second transmissive-reflective element (960) extending across part of an area of the input port and arranged to receive, and partially transmit and partially reflect, at least a portion of the light from the display system, characterised in that the input port further comprises a transmissive element (950) arranged to receive a portion of the light from the display system, wherein the transmissive element (950) adjoins the second transmissive-reflective element (960) and the second transmissive-reflective element (960) adjoins the reflective element (970), and wherein the second transmissive-reflective element (960) comprises a partially transmissive and partially reflective surface coating.
A waveguide as claimed in claim 1 wherein the second transmissive-reflective element (960) is arranged to internally reflect within the waveguide at least some of the diffracted light field.
A waveguide as claimed in claim 1 or 2 wherein the second transmissive-reflective element (960) is configured such that at least some of the diffracted light field is incident thereon only once, optionally, configured such that all light rays of the diffracted light field are incident thereon only once.
A waveguide as claimed in any preceding claim wherein the input port is formed on a second surface (920) of the pair of opposing surfaces (910, 920).
A waveguide as claimed in any preceding claim wherein the second transmissive-reflective element (960) has a transmissivity of 0.1 to 0.5 such as 0.2 to 0.4.
A waveguide as claimed in claim 1 wherein the reflective element (970) is disposed on the second surface (920) immediately adjacent the input port.
A waveguide as claimed in claim 1 or 6 wherein: the transmissivity of the second surface from the start of the second transmissive-reflective element (960) to the end of the reflective element (970) is continuous, optionally, continuously decreasing, and/or the transmissivity of the reflective element (970) is less than 0.1 such as less than 0.07 or less than 0.05.
A waveguide as claimed in any preceding claim wherein the second transmissive-reflective element (960) is arranged to receive all the light from the display system.
A waveguide as claimed in any preceding claim wherein the input port has a length in the direction of waveguiding and the second transmissive-reflective element (960) extends over at least a part of the length of the input port.
A waveguide as claimed in any preceding claim wherein the display system comprises a spatial light modulator arranged to display a hologram and/or the diffracted light field is spatially modulated in accordance with the hologram.
A waveguide as claimed in any preceding claim wherein the display system comprises a display device having a pixel area defining the exit pupil of the display system that is expanded by the waveguide.
A system comprising the waveguide of any preceding claim wherein the waveguide is a second one-dimensional pupil expander of a pair of waveguide pupil expanders arranged to expand the pupil of the display system in a first direction and second, perpendicular direction, respectively.
A system comprising: a display system arranged to form a diffractive light field for viewing by a viewing system, and a waveguide as claimed in any preceding claim for receiving the diffractive light field at an input port thereof, wherein the diffractive 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.

Description

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). A different implementation of a pupil expander is described in US 2010/321781 A1. BACKGROUND AND 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 zero to the maximum diffractive angle) from the LCoS, towards a viewing entity/system such as a camera or an eye. In some embodiments, magnification techniques may be used to increase the range of available diffraction angles beyond t