Balancing and improving holographic waveguide efficiency
Techniques for improving holographic waveguide efficiency are described. In an example, a waveguide includes a substrate having a first surface and a second surface. The waveguide includes a holographic layer configured to inject, into the substrate as first light, light received at the first surface, diffract a first portion of the first light such that the first portion propagates in a first propagation direction, and diffract a second portion of the first light such that the second portion propagates in a second propagation direction. The waveguide includes a reflective component configured to reflect a remaining portion of the first light as second light from the second surface toward the first surface. The holographic layer is further configured to diffract a first portion of the second light such that the first portion of the second light propagates within the substrate in the first propagation direction.
1 . A bi-ocular system comprising:
a display light engine configured to emit first light that represents an image; and
a bio-ocular waveguide comprising:
a substrate having a first surface and a second surface, wherein the first light is received at the first surface;
an injection holographic layer disposed between the first surface and the second surface and comprising:
a first volume holographic optical element (VHOE) configured to diffract a first portion of the first light such that the first portion propagates within the substrate in a first propagation direction;
a second VHOE configured to diffract a second portion of the first light such that the second portion propagates within the substrate in a second propagation direction, wherein the second propagation direction is parallel to and opposite of the first propagation direction; and
a reflective material coupled to the second surface and configured to reflect a remaining portion of the first light as second light reflected toward the second surface,
wherein the second VHOE is further configured to diffract a first portion of the second light such that the first portion of the second light propagates within the substrate in the first propagation direction, and
wherein the injection holographic layer and the display light engine are aligned such that an offset exists between a reference point of the injection holographic layer and a reference point of the display light engine, wherein the offset is along the second propagation direction;
a first redirection holographic layer configured to redirect the first portion of the first light and the first portion of the second light as a third portion propagating in a third propagation direction;
a second redirection holographic layer configured to redirect the second portion as a fourth portion propagating in a fourth propagation direction;
a first extraction holographic layer configured to extract the third portion as a fifth portion propagating in a fifth propagation direction, wherein the fifth portion represents the image; and
a second extraction holographic layer configured to extract the fourth portion as a sixth portion propagating in a sixth propagation direction, wherein the sixth portion represents the image.
2 . The bi-ocular system of claim 1 , wherein:
the first VHOE is further configured to diffract a second portion of the second light such that the second portion of the second light propagates within the substrate in the second propagation direction,
the second redirection holographic layer is configured to redirect the second portion of the first light and the second portion of the second light as the fourth portion propagating in the fourth propagation direction, and
the fifth portion and the sixth portion have a same brightness.
3 . The bi-ocular system of claim 1 , wherein the injection holographic layer has a width defined along a direction parallel to the first propagation direction, and wherein the offset is within a range of twenty percent of the width.
4 . A waveguide comprising:
a substrate having a first surface and a second surface;
a holographic layer coupled to the substrate and configured to:
diffract a first portion of first light incident upon the first surface such that the first portion of the first light propagates within the substrate in a first propagation direction;
diffract a second portion of the first light such that the second portion of the first light propagates within the substrate in a second propagation direction, wherein an angle between the second propagation direction and the first propagation direction is larger than or equal to one-hundred twenty degrees; and
a reflective component configured to reflect a remaining portion of the first light as second light incident upon the second surface,
wherein the holographic layer is further configured to diffract a first portion of the second light such that the first portion of the second light propagates within the substrate in the first propagation direction.
5 . The waveguide of claim 4 , wherein the holographic layer is aligned with a light source such that an offset exists between a reference point of the holographic layer and a reference point of the light source, wherein the offset is along the second propagation direction.
6 . The waveguide of claim 4 , wherein the holographic layer is disposed between the first surface and the second surface and comprises a first volume holographic optical element (VHOE) and a second VHOE, and wherein:
the first VHOE is configured to diffract the first portion of the first light such that the first portion of the first light propagates within the substrate in the first propagation direction,
the first VHOE is further configured to diffract a second portion of the second light such that the second portion of the second light propagates within the substrate in the second propagation direction,
the second VHOE is configured to diffract the second portion of the first light such that the second portion of the first light propagates within the substrate in the second 10 propagation direction, and
the second VHOE is further configured to diffract the first portion of the second light such that the first portion of the second light propagates within the substrate in the first propagation direction.
7 . The waveguide of claim 4 , wherein the holographic layer comprises a first optical element and a second optical element, and wherein:
the first optical element is configured to diffract the first portion of the first light at a diffraction angle and comprises at least one of: a first volume holographic optical element (VHOE) or a first surface relief grating (SRG), and
the second second optical element is configured to diffract the first portion of the second light at the same diffraction angle and comprises at least one of: a second VHOE or a second SRG.
8 . The waveguide of claim 4 , wherein the holographic layer comprises a first optical element and a second optical element, and wherein:
the first optical element is configured to outcouple a third portion of the first light toward the second surface,
the reflective component is configured to reflect the third portion as third light toward the first surface, and
the second optical element is configured to diffract a second portion of the third light such that the second portion of the third light propagates within the substrate in the first propagation direction.
9 . The waveguide of claim 4 , wherein the holographic layer comprises a first volume holographic optical element (VHOE) and a second VHOE arranged in a stack, and wherein:
the first VHOE is configured to diffract the first portion of the first light, and pass a third portion of the first light toward the second VHOE,
the second VHOE is configured to receive the third portion, diffract the second portion of the first light, and pass the remaining portion of the first light toward the reflective component, and
the second VHOE is further configured to receive the second light and diffract the first portion of the second light.
10 . The waveguide of claim 4 , wherein the holographic layer has a first edge and a second edge, and wherein the reflective component is a reflective material disposed on the second surface and has a width that extends between the first edge and the second edge or that extends to a predefined distance from the first edge.
11 . The waveguide of claim 4 , wherein the reflective component comprises a dielectric mirror disposed at a predefined distance away from the second surface and arranged to be parallel to the second surface.
12 . A device comprising:
a light source configured to emit first light; and
a waveguide comprising:
a substrate having a first surface and a second surface; and
a holographic layer coupled to the substrate and configured to:
diffract a first portion of the first light such that the first portion propagates within the substrate in a first propagation direction, the first light being incident upon the first surface, and
diffract a second portion of the first light such that the second portion propagates within the substrate in a second propagation direction, wherein an angle between the second propagation direction and the first propagation direction is larger than or equal to one-hundred twenty degrees,
wherein the holographic layer and the light source are aligned such that an offset along the second propagation direction exists between a reference point of the holographic layer and a reference point of the light source.
13 . The device of claim 12 , wherein the waveguide further comprises:
a reflective component configured to reflect a remaining portion of the first light as second light incident upon the second surface, wherein the holographic layer is further configured to diffract a first portion of the second light such that the first portion of the second light propagates within the substrate in the first propagation direction.
14 . The device of claim 13 , wherein the holographic layer comprises a plurality of volume holographic optical elements (VHOEs) that are arranged in a stack and that are aligned to have the same reference point of the holographic layer, or a multiplexed hologram that includes a plurality of diffraction gratings.
15 . The device of claim 12 , wherein the holographic layer comprises a first volume holographic optical element (VHOE) and a second VHOE, wherein the first VHOE and the second VHOE overlap at least partially, wherein the first VHOE or the second VHOE differs at least in thickness or index modulation.
16 . The device of claim 12 , wherein the holographic layer comprises a first volume holographic optical element (VHOE) and a second VHOE that overlap and that are arranged in a stack, wherein the waveguide further comprises a reflective component configured to reflect a remaining portion of the first light as second light incident upon the second surface, and wherein the light source and the reflective component are arranged on opposite sides of the stack.
17 . The device of claim 12 , wherein the holographic layer is a first holographic layer and is configured to output the first portion as a first output light toward a second holographic layer and output the second portion as a second output light toward a third holographic layer, wherein the first output light and the second output light have a same brightness.
18 . The device of claim 12 , wherein the holographic layer comprises a first volume holographic optical element (VHOE) and a second VHOE, and wherein:
the first VHOE is configured to diffract the first portion of the first light such that the first portion propagates in the first propagation direction,
the second VHOE is configured to diffract the second portion of the first light such that the second portion propagates in the second propagation direction, and
the first VHOE and the second VHOE partially overlap and are parallel to each other.
19 . The device of claim 12 , wherein the holographic layer and the light source are aligned according to an alignment procedure, wherein the offset is predefined prior to the alignment procedure as a target alignment for the alignment procedure.
20 . The device of claim 12 , wherein the holographic layer and the light source are aligned according to an alignment procedure that measures light brightness, and wherein the alignment procedure sets the offset based on light brightness measurements.