Waveguide with diffractive optical element
A holographic projector includes a waveguide that includes a pair of opposing reflective surfaces arranged to receive and waveguide a hologram/holographic wavefront therebetween. A first surface of the pair of complementary surfaces is partially reflective-partially transmissive such that a plurality of replicas of the hologram/holographic wavefront are emitted therefrom. The holographic projector further includes a diffractive optical element arranged to receive the plurality of replicas of the hologram/holographic wavefront from the first surface of the waveguide and principally redirect each replica into a respective non-zero diffractive order defined by a diffraction angle. The holographic projector also includes an array of louvres arranged to receive the hologram/holographic wavefront from the diffractive optical element, where the array of louvres is substantially transmissive at the non-zero diffraction angle and substantially non-transmissive at a zeroth diffraction angle of the diffractive optical element.
1 . A holographic projector comprising:
a spatial light modulator arranged to spatially modulate incident light;
a waveguide comprising a pair of complementary surfaces arranged to receive a wavefront comprising modulated light from the spatial light modulator, waveguide the wavefront therebetween, and emit a plurality of replicas of the wavefront from a first surface of the pair of complementary surfaces that is partially reflective-partially transmissive;
a diffractive optical element arranged to receive the plurality of replicas of the wavefront from the first surface of the waveguide and principally redirect each replica into a respective non-zero diffractive order defined by a non-zero diffraction angle; and
an array of louvres arranged to receive the plurality of replicas of the wavefront from the diffractive optical element, wherein the array of louvres is transmissive at the non-zero diffraction angle and non-transmissive at a zeroth diffraction angle of the diffractive optical element.
2 . The holographic projector as claimed in claim 1 , wherein the array of louvres are arranged to absorb the zeroth diffractive order.
3 . The holographic projector as claimed in claim 1 , wherein, in a first plane, an angle between the zeroth diffraction order and the non-zero diffractive order is in the range 40 to 70 degrees at a first wavefront wavelength.
4 . The holographic projector as claimed in claim 3 , wherein, in the first plane, the angle between the zeroth diffraction order and the non-zero diffractive order is in the range 40 to 70 degrees at a second and third wavefront wavelength.
5 . The holographic projector as claimed in claim 1 , wherein, in a second plane, an angle between the zeroth diffraction order and the non-zero diffractive order is in the range 10 to 20 degrees.
6 . The holographic projector as claimed in claim 1 , wherein the non-zero diffractive order into which the replicas of the wavefront are principally redirected is the first diffractive order.
7 . The holographic projector as claimed in claim 1 , wherein the waveguide comprises an input port arranged to receive the wavefront.
8 . The holographic projector as claimed in claim 7 , wherein the input port is positioned at or towards an end of the waveguide that is closest to an eye-box of the holographic projector.
9 . The holographic projector as claimed in claim 7 , wherein each louvre of the array of louvres is angled towards the input port.
10 . The holographic projector as claimed in claim 9 , wherein a distal end/edge of each louvre is closer to the input port than the respective proximal end/edge of the louvre and wherein the distal end/edge is furthest from the first surface.
11 . The holographic projector as claimed in claim 7 , wherein the louvres are angled with respect to a normal of a plane of the first surface.
12 . The holographic projector as claimed in claim 1 , wherein the holographic projector the array of louvres is part of a reflection suppression layer of the holographic projector.
13 . The holographic projector as claimed in claim 1 , wherein the diffractive optical element is a holographic optical element.
14 . The holographic projector as claimed in claim 1 , wherein the diffractive optical element comprises a volume hologram.
15 . The holographic projector as claimed in claim 14 , wherein the volume hologram is a volume Bragg grating.
16 . The holographic projector as claimed in claim 1 , wherein the diffractive optical element is arranged such that a ratio of the brightness of the non-zero diffraction order and a sum of the brightness of other diffraction orders for each of the replica wavefronts varies with distance from the input port.
17 . A display system comprising the holographic projector of claim 1 and further comprising an optical combiner, wherein the holographic projector is arranged such that the plurality of replicas of the holographic wavefront emitted by the waveguide are redirected from the optical combiner to form a virtual image that is viewable from an eye-box.
18 . The display system according to claim 17 , wherein the waveguide comprises a first end and a second end, the first end being closest to the optical combiner, and wherein the waveguide further comprises an input port arranged to receive the wavefront, the input port positioned at or towards the second end of the waveguide.
19 . The holographic projector as claimed in claim 1 , wherein the wavefront is encoded with a hologram.
20 . The holographic projector as claimed in claim 1 , wherein
the diffractive optical element is arranged to, while principally redirecting each replica into the respective non-zero diffractive order to provide the plurality of replicas of the wavefront, the plurality of replicas of the wavefront being a plurality of diffracted replicas, transmitting a plurality of zeroth-order replicas of the wavefront at a zeroth diffraction angle of the diffractive optical element; and
the array of louvres is arranged to transmit the plurality of diffracted replicas of the wavefront and to block the zeroth-order replicas of the wavefront.
21 . A method for holographic projection, the method comprising
spatially modulating light from a spatial light modulator;
receiving a wavefront comprising a wavefront comprising modulated light from the spatial light modulator by a waveguide comprising a pair of complementary surfaces;
waveguiding the wavefront in the waveguide between the pair of complementary surfaces;
emitting a plurality of replicas of the wavefront from a first surface of the pair of complementary surfaces that is partially reflective-partially transmissive;
receiving the plurality of replicas of the wavefront from the first surface of the waveguide by a diffractive optical element;
principally redirecting with the diffractive optical element each replica into a respective non-zero diffractive order defined by a non-zero diffraction angle to provide a plurality of diffracted replicas of the wavefront, while transmitting with the diffractive optical element a plurality of zeroth order replicas at a zeroth diffraction angle of the diffractive optical element;
receiving the plurality of diffracted replicas and the plurality of zeroth-order replicas of the wavefront at an array of louvres; and
transmitting through the array of louvres the plurality of diffracted replicas, while blocking by the array of louvres the plurality of zeroth order replicas.