Compact head-up display
Disclosed embodiments include a display system comprising a first waveguide pupil expander comprising an input port, output port, a first pair of parallel surfaces, and a second pair of parallel surfaces. The first pair of parallel surfaces is orthogonal to the second pair of parallel surfaces and arranged to light guide a diffracted or diverging (e.g. holographic) light field from the input port to the output port by internal reflection therebetween. A first surface of the first pair of parallel surfaces is partially transmissive-reflective such that the light field is divided at each internal reflection and a plurality of replicas of the light field is transmitted through a region of the first surface that forms the output port. The second pair of parallel surfaces is also arranged to light guide the light field from the input port to the output port by at least one internal reflection.
1 . A display system comprising:
a first waveguide pupil expander comprising an input port, output port, a first pair of parallel surfaces and a second pair of parallel surfaces, wherein the first pair of parallel surfaces is orthogonal to the second pair of parallel surfaces;
wherein the first pair of parallel surfaces is arranged to light guide a diffracted light field comprising diverging ray bundles from the input port to the output port by internal reflections therebetween, wherein the diffracted light field is spatially-modulated in accordance with a hologram displayed on a spatial light modulator and comprises an expanding light cone such that the light field size increases with propagation distance within the first waveguide pupil expander, wherein the diffracted light field has a light field size defined in a direction substantially orthogonal to a propagation direction of the light field, and wherein a first surface of the first pair of parallel surfaces is partially transmissive-reflective such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted through a region of the first surface that forms the output port; and
wherein the second pair of parallel surfaces is also arranged to light guide the light field from the input port to the output port by at least one total internal reflection, wherein the light field size is substantially equal to or greater than a second spacing size, defined between first and second surfaces of the second pair of parallel surfaces during internal reflection of the light field within the first waveguide pupil expander, and wherein the second pair of parallel surfaces are arranged to retain the diffracted light field within the first waveguide pupil expander and such that the diffracted light field is directed to exit the first waveguide pupil expander via the output port.
2 . The display system of claim 1 , wherein the light field size is substantially equal to or greater than a first spacing size, defined between the first and second surfaces of the first pair of parallel surfaces.
3 . The display system of claim 1 , wherein the hologram comprises a computer-generated hologram.
4 . The display system of claim 1 , wherein the output port of the first waveguide pupil expander is coupled to an input port of a second waveguide pupil expander.
5 . The display system of claim 4 , wherein the second waveguide pupil expander is arranged to guide the diffracted light field from its input port to a respective output port by internal reflection between a third pair of parallel surfaces on the second waveguide pupil expander, wherein a first surface of the third pair of parallel surfaces is partially transmissive-reflective such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted through a region of the first surface on the second waveguide pupil expander, which forms its output port.
6 . The display system of claim 1 , further comprising a waveguide coupler having a receiving face, comprising an input port, which is configured to receive the light field output by the first waveguide pupil expander.
7 . The display system of claim 6 , wherein the waveguide coupler has a fourth pair of parallel reflective surfaces substantially corresponding to the second pair of parallel surfaces of the first waveguide pupil expander.
8 . The display system of claim 7 , wherein the output port of the first waveguide pupil expander is coupled to an input port of a second waveguide pupil expander, and wherein the fourth pair of parallel surfaces are arranged to guide the light field from the first waveguide pupil expander to the second waveguide pupil expander by at least one internal reflection.
9 . The display system of claim 7 , wherein a size of a separation between first and second surfaces of the fourth pair of parallel surfaces is substantially equal to the second spacing size, defined between first and second surfaces of the second pair of parallel surfaces.
10 . The display system of claim 6 , wherein the waveguide coupler has a substantially triangular shape that substantially fills a space between the first and second waveguide pupil expanders.
11 . The display system of claim 4 , wherein the first waveguide pupil expander is substantially elongated and the second waveguide pupil expander is substantially planar.
12 . The display system of claim 4 , wherein the first and second waveguide pupil expanders collectively provide pupil expansion in a first direction and in a second direction perpendicular to the first direction, wherein a plane containing the first and second direction is substantially parallel to a plane of the second waveguide pupil expander.
13 . The display system of claim 4 , wherein (i) the first and second directions of pupil expansion define a viewing plane and (ii) an area of pupil expansion defined by the first and second exit pupil expansion defines an eye-box area.
14 . The display system of claim 4 , further comprising a fold mirror between the first waveguide pupil expander and the second waveguide pupil expander, wherein the fold mirror is arranged to fold an optical path of the light field between the first waveguide pupil expander and the second waveguide pupil expander.
15 . The display system of claim 14 , further comprising a waveguide coupler having a receiving face, comprising an input port, which is configured to receive the light field output by the first waveguide pupil expander, wherein the fold mirror is arranged to fold an optical path of the light field between the waveguide coupler and the second waveguide pupil expander.
16 . The display system of claim 4 , further comprising a control device disposed between the first waveguide pupil expander and second waveguide pupil expander, wherein the control device comprises an array of apertures, each aperture selectively operable between a transmissive state and a non-transmissive state.
17 . The display system of claim 16 , wherein the array of apertures of the control device extends in an elongate direction of the first waveguide pupil expander.
18 . The display system of claim 16 , further comprising:
a waveguide coupler having a receiving face, comprising an input port, which is configured to receive the light field output by the first waveguide pupil expander; and
a fold mirror between the first waveguide pupil expander and the second waveguide pupil expander, wherein the fold mirror is arranged to fold an optical path of the light field between the first waveguide pupil expander and the second waveguide pupil expander; and
wherein the control device is one of (i) disposed between the first waveguide pupil expander and the waveguide coupler, (ii) disposed between the waveguide coupler and the second waveguide pupil expander, or (iii) disposed between the fold mirror and the second waveguide pupil expander.
19 . The display system of claim 16 , wherein the display system is, or is comprised within, a head-up display (HUD) system.
20 . The display system of claim 19 , wherein the HUD system is arranged in cooperation with an optical combiner such as a windscreen of a vehicle.
21 . The display system of claim 19 , wherein the output port of the first waveguide pupil expander is coupled to an input port of a second waveguide pupil expander, and wherein the HUD system defines a user eye-box that is substantially orthogonal to a plane defined by the second waveguide pupil expander.
22 . A method of providing pupil expansion for a diffracted light field comprising diverging ray bundles, wherein the diffracted light field is spatially-modulated in accordance with a hologram displayed on a spatial light modulator and comprises an expanding light cone such that the light field size increases with propagation distance within the first waveguide pupil expander and has a light field size defined in a direction substantially orthogonal to a propagation direction of the light field, and wherein the method comprises:
directing the diffracted light field into a first waveguide pupil expander, wherein the first waveguide pupil expander comprises an input port, output port, a first pair of parallel surfaces and a second pair of parallel surfaces, wherein the first pair of parallel surfaces are orthogonal to the second pair of parallel surfaces;
guiding the diffracted light field from the input port to the output port by internal reflection between the first pair of parallel surfaces;
wherein a first surface of the first pair of parallel surfaces is partially transmissive-reflective such that the light field is divided at each internal reflection and a plurality of replicas of the light field are transmitted through a region of the first surface that forms the output port; and
wherein the second pair of parallel surfaces are also arranged to light guide the light field from the input port to the output port by at least one total internal reflection, wherein the light field size is substantially equal to or greater than a second spacing size, defined between first and second surfaces of the second pair of parallel surfaces during internal reflection of the light field within the first waveguide pupil expander, and wherein the second pair of parallel surfaces retain the diffracted light field within the first waveguide pupil expander and ensure that the diffracted light field only leaves the first waveguide pupil expander via the output port.