Homogenous light intensity output from a waveguide combiner
Techniques for an optical waveguide with homogenous light intensity output are described herein. In an example, an optical waveguide system includes an optical waveguide substrate and a first holographic layer coupled to the optical waveguide substrate and configured to inject light into the optical waveguide substrate as injected light. The optical waveguide system also includes a second holographic layer coupled to the optical waveguide substrate and configured to receive the injected light and output the injected light as output lights in a direction. The second holographic layer is characterized by a varying diffraction efficiency and the output lights have a homogenous intensity at a distance from the second holographic layer.
1 . An optical waveguide system comprising:
an optical waveguide substrate characterized by a maximum diffraction efficiency;
a first holographic layer coupled to the optical waveguide substrate and configured to inject light into the optical waveguide substrate; and
a second holographic layer coupled to the optical waveguide substrate and configured to receive the light and output first light rays in a first direction,
wherein:
the second holographic layer includes extraction sites,
the second holographic layer is characterized by a varying diffraction efficiency,
the varying diffraction efficiency at an extraction site of the extraction sites is different from the maximum diffraction efficiency of the optical waveguide substrate and is defined as a function of the maximum diffraction efficiency, and
the first light rays have a homogenous intensity at a first distance from the second holographic layer.
2 . The optical waveguide system of claim 1 , wherein the second holographic layer includes a plurality of regions, wherein a first region of the plurality of regions is characterized by a first diffraction efficiency value that is based at least in part on a location of the first region and on a maximum efficiency of the optical waveguide substrate.
3 . The optical waveguide system of claim 2 , wherein the light represents an image, wherein the first region outputs a first duplicate of the image, wherein a second region of the plurality of regions outputs a second duplicate of the image, wherein the first duplicate and the second duplicate have brightness in luminosity.
4 . The optical waveguide system of claim 2 , wherein a second region of the plurality of regions includes a surface relief grating (SRG) or a volume holographic optical element (VHOE) and is characterized by a second diffraction efficiency value that is different from the first diffraction efficiency value, and wherein the first diffraction efficiency value is constant across the first region.
5 . The optical waveguide system of claim 1 , wherein a region of the second holographic layer is characterized by a diffraction efficiency value that is based at least in part on a number of bounces of the light due to total internal reflection (TIR) up to the region and on a maximum diffraction efficiency of the optical waveguide substrate.
6 . The optical waveguide system of claim 1 , wherein the second holographic layer includes a volume holographic optical element (VHOE) recorded in the optical waveguide substrate based at least in part on incoherent light illumination, wherein the varying diffraction efficiency is modulated by the incoherent light illumination.
7 . The optical waveguide system of claim 1 , wherein a first region of the second holographic layer is characterized by a first diffraction efficiency value, wherein a second region of the second holographic layer is characterized by a second diffraction efficiency value, wherein the second diffraction efficiency value is based at least in part on a distance between the first region and the second region and on a maximum diffraction efficiency of the optical waveguide substrate.
8 . The optical waveguide system of claim 7 , wherein the second holographic layer defines an eye box, and wherein the second diffraction efficiency value is further based at least in part on a width of the eye box.
9 . An apparatus comprising:
a light source configured to emit light; and
an optical waveguide system that is characterized by a maximum diffraction efficiency and that comprises:
an optical waveguide substrate;
a first holographic layer coupled to the optical waveguide substrate and configured to inject the light into the optical waveguide substrate; and
a second holographic layer coupled to the optical waveguide substrate and configured to receive the light and output first lights rays in a first direction,
wherein:
the second holographic layer includes extraction sites,
the second holographic layer is characterized by a varying diffraction efficiency,
the varying diffraction efficiency at an extraction site of the extraction sites is different from the maximum diffraction efficiency of the optical waveguide substrate and is defined as a function of the maximum diffraction efficiency, and
the first light rays have a homogenous intensity at a first distance from the second holographic layer.
10 . The apparatus of claim 9 , wherein the varying diffraction efficiency and the homogenous intensity, are a first varying diffraction efficiency and a first homogenous intensity, respectively, and wherein the apparatus further comprises:
a third holographic layer coupled to the optical waveguide substrate and configured to receive the first light rays and output second light rays in a second direction,
wherein:
the third holographic layer is characterized by a second diffraction efficiency, and
the second light rays have a second homogenous intensity at a second distance from the third holographic layer.
11 . The apparatus of claim 9 , wherein a first region of the second holographic layer comprises a first extraction site and is characterized by a first diffraction efficiency value, wherein a second region of the second holographic layer comprises a second extraction site and is characterized by a second diffraction efficiency value, wherein the second diffraction efficiency value is based at least in part on a location of the second extraction site and on the maximum diffraction efficiency of the optical waveguide substrate.
12 . The apparatus of claim 11 , wherein the varying diffraction efficiency is defined based at least in part on a non-linear function expressed as
η
(
n
)
=
1
1
η
max
+
N
-
n
,
wherein “n” corresponds to an n-th extraction site, “N” represents the total number of extraction sites, and “η max ” represents the maximum diffraction efficiency.
13 . The apparatus of claim 9 , wherein the second holographic layer comprises a first region comprising a first surface relief grating (SRG) diffraction element and a second region comprising a second SRG diffraction element, wherein a first height of the first SRG diffraction element is different than a second height of the second SRG diffraction element and is based at least in part on a location of the first region within the second holographic layer and on a maximum diffraction efficiency of the optical waveguide substrate.
14 . The apparatus of claim 9 , wherein the second holographic layer comprises a first volume holographic optical element (VHOE) region and a second VHOE region, wherein a first refractive index of the first VHOE region is different than a second refractive index of the second VHOE region and is based at least in part on a location of the first VHOE region within the second holographic layer and on a maximum diffraction efficiency of the optical waveguide substrate.
15 . The apparatus of claim 9 , wherein the second holographic layer is recorded in a photopolymer film, wherein the varying diffraction efficiency is set during a recording of the second holographic layer in the photopolymer film by at least varying light intensity of a recording light source emitting incoherent light, wherein a value of the light intensity for a region of the second holographic layer is based at least in part on a location of the region within the second holographic layer and a maximum diffraction efficiency of the optical waveguide substrate.
16 . The apparatus of claim 9 , wherein the second holographic layer comprises a plurality of surface relief grating (SRG) diffraction elements etched in the optical waveguide substrate, wherein a first SRG diffraction element is etched to have a height that is based at least in part on a location of the first SRG diffraction element within the second holographic layer and a maximum diffraction efficiency of the optical waveguide substrate.
17 . The apparatus of claim 9 , wherein the second holographic layer comprises a plurality of regions and forms an eye box, wherein each one of the plurality of regions corresponds to a pupil location to view an image within the eye box, and wherein a brightness of the image in luminosity is homogenous across the eye box.