US-12619070-B2 - Hologram waveguiding

US12619070B2US 12619070 B2US12619070 B2US 12619070B2US-12619070-B2

Abstract

A projection system comprising a display device, a hologram engine and a waveguide. The display device is arranged to display a hologram of an image and spatially modulate light in accordance with the hologram to form a holographic wavefront. The hologram engine is arranged to calculate the hologram. The hologram is arranged to angularly distribute light within the holographic wavefront in accordance with spatial position within the image such that continuous angular ranges of the holographic wavefront respectively correspond with continuous regions of the image. The waveguide comprising a pair of parallel reflective surfaces arranged to waveguide the holographic wavefront therebetween. A first surface of the pair of parallel reflective surfaces is partially reflective-transmissive so as to form an output comprising a plurality of emission zones for the holographic wavefront. The hologram engine is arranged to modify the hologram to at least partially compensate for a decrease in intensity of the emission from each successive emission zone of the waveguide caused by the partial reflection-transmissions at the first surface during waveguiding.

Inventors

Jamieson Christmas

Assignees

ENVISICS LTD

Dates

Publication Date: 20260505
Application Date: 20230830

Claims (20)

1 . A projection system comprising: a display device arranged to display a hologram of an image and spatially modulate light in accordance with the hologram to form a holographic light field; a hologram engine arranged to calculate the hologram, wherein the hologram is arranged to angularly distribute light within the holographic light field in accordance with spatial position within the image such that continuous angular ranges of the holographic light field respectively correspond with continuous regions of the image; a waveguide comprising a pair of parallel reflective surfaces arranged to waveguide the holographic light field therebetween, wherein a first surface of the pair of parallel reflective surfaces is partially reflective-transmissive so as to form an output comprising a plurality of emission zones for the holographic light field, wherein the hologram engine is arranged to modify the hologram to at least partially compensate for a decrease in intensity of the emission from each successive emission zone of the waveguide caused by the partial reflection-transmissions at the first surface during waveguiding.
2 . A projection system as claimed in claim 1 arranged to form a plurality of viewing positions within a viewing region, wherein the entire holographic light field is receivable through a viewing pupil at each viewing position but different continuous angular ranges of the holographic light field are receivable through the viewing pupil from different emission zones of the waveguide.
3 . A projection system as claimed in claim 1 wherein at least partially compensating for the decrease in intensity of the emission from each successive emission zone comprises changing the intensity of at least one angular channel of the holographic light field.
4 . A projection system as claimed in claim 1 wherein at least partially compensating for the decrease in intensity of the emission from each successive emission zone comprises changing the intensity of at least one continuous region of a target image of the hologram prior to calculation of the hologram.
5 . A projection system as claimed in claim 3 wherein changing the intensity comprises applying a gain or loss factor.
6 . A projection system as claimed in claim 1 wherein calculation of the hologram comprises a plurality of iterations of a phase retrieval algorithm.
7 . A projection system as claimed in claim 1 wherein calculation of the hologram comprises a point cloud method.
8 . A projection system as claimed in claim 1 wherein a second surface of the pair of parallel reflective surfaces is substantially fully reflective.
9 . A projection system as claimed in claim 1 further comprising a viewer tracking system arranged to determine a location of a viewer within a viewing window downstream of the waveguide, wherein the hologram engine is arranged to determine a correlation between angular channels of the holographic light field and the emission zones based on the determined location of the viewer.
10 . A projection system as claimed in claim 1 wherein the transmissivity of the first surface at each emission zone, T(n), in the direction of waveguiding satisfies the following equation: T ⁡ ( n ) = T ⁡ ( n - 1 ) [ 1 - T ⁡ ( n - 1 ) ] × [ 1 - L ] wherein L is an optical loss factor of the waveguide material.
11 . A method of replicating a holographic light field using a waveguide, wherein the waveguide comprises a pair of parallel reflective surfaces arranged to waveguide the holographic light field therebetween, wherein a first surface of the pair of parallel reflective surfaces is partially reflective-transmissive so as to form an output comprising a plurality of emission zones for the holographic light field in the direction of waveguiding and the method comprises: calculating a hologram arranged to angular distribute light within the holographic light field in accordance with image position such that angular channels within the holographic light field respectively correspond with continuous regions of the image; modifying the hologram to at least partially compensate for a decrease in intensity of the emission from each successive emission zone of the waveguide caused by the partial reflection-transmissions at the first surface during waveguiding; and displaying the hologram and spatially modulating light in accordance with the hologram to form the holographic light field.
12 . A method as claimed in claim 11 further comprising receiving, by a viewer disposed within a viewing window downstream of the waveguide, through a pupil thereof, different angular channels of the holographic light field from different emission zones of the waveguide.
13 . A method as claimed in claim 11 further comprising modifying the global intensity of at least one angular channel of the holographic light field.
14 . A method as claimed in claim 11 further comprising changing the global intensity of at least one continuous region of a target image of the hologram prior to calculation of the hologram.
15 . A method as claimed in claim 11 further comprising determining a location of a viewer within a viewing window downstream of the waveguide and determining a correlation between angular channels of the holographic light field and the emission zones based on the determined location of the viewer.
16 . A method as claimed in claim 11 wherein the waveguide is arranged to form a plurality of viewing positions within a viewing region, wherein the entire holographic light field is receivable through a viewing pupil at each viewing position but different continuous angular ranges of the holographic light field are receivable through the viewing pupil from different emission zones of the waveguide.
17 . A method as claimed in claim 11 wherein at least partially compensating for the decrease in intensity of the emission from each successive emission zone comprises changing the intensity of at least one angular channel of the holographic light field.
18 . A method as claimed in claim 11 wherein at least partially compensating for the decrease in intensity of the emission from each successive emission zone comprises changing the intensity of at least one continuous region of a target image of the hologram prior to calculation of the hologram.
19 . A method as claimed in claim 11 wherein calculation of the hologram comprises a plurality of iterations of a phase retrieval algorithm.
20 . A method as claimed in claim 11 wherein calculation of the hologram comprises a point cloud method.

Description

FIELD The present disclosure relates to a light engine and a method of relaying a diffracted light field. More specifically, the present disclosure relates a projection system and a method of replicating a hologram using a waveguide. Some embodiments relate to a holographic projector, picture generating unit or head-up display. 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, there is disclosed herein a display system comprising a display device, a pattern generator and a waveguide. The display device is arranged to display a diffractive pattern corresponding to an image and spatially modulate light in accordance with the diffractive pattern to form a diffracted light field. The pattern generator is arranged to determine the diffractive pattern. The diffractive pattern is arranged to angularly distribute light within the diffracted light field in accordance with spatial position within the image such that continuous angular ranges (i.e. angular channels) of the diffracted light field respectively correspond with continuous regions of the image. The waveguide comprising a pair of parallel reflective surfaces arranged to waveguide the diffracted light field therebetween. A first surface of the pair of parallel reflective surfaces is partially reflective-transmissive so as to form an output comprising a plurality of emission or replication zones for the diffracted light field (in the direction of waveguiding). The pattern generator is arranged to modify the diffractive pattern to at least partially compensate for a decrease in intensity of the emission from each successive emission or replication zone of the waveguide caused by the partial reflection-transmissions at the first surface during waveguiding. More specifically, there is disclosed herein a projection system comprising a display device, a hologram engine and a waveguide. The display device is arranged to display a hologram of an image and spatially modulate light in accordance with the hologram to form a holographic wavefront (or holographic light field). The hologram engine is arranged to calculate the hologram. The hologram is arranged to angularly distribute light within the holographic wavefront in accordance with spatial position within the image such that continuous angular ranges (i.e. angular channels) of the holographic wavefront respectively correspond with continuous regions of the image. The waveguide comprising a pair of parallel reflective surfaces arranged to waveguide the holographic wavefront therebetween. A first surface of the pair of parallel reflective surfaces is partially reflective-transmissive so as to form an output comprising a plurality of emission zones for the holographic wavefront (in the direction of waveguiding). The hologram engine is arranged to modify the hologram to at least