Waveguide Output DOE Layout for Uniform AR/VR Brightness
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Solution Overview
Problem
Conventional augmented reality displays suffer from non-uniform brightness of light coupled out of the waveguide, leading to degraded user experience due to visible non-uniformity in the displayed image.
Innovation Solution
The optical device incorporates a planar waveguide with an output diffractive optical element (DOE) featuring optical structures oriented in a third direction non-parallel to the first and second periodic directions, allowing for tuning of diffraction efficiency to enhance light output uniformity, using polygon or parallelogram shapes and varying slopes or offsets to control light coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light is coupled into the waveguide using a conventional output element, then light can be extracted from the waveguide, but the brightness is non-uniform across the output area
Solution Approach 1:
The output element is divided into multiple diffractive regions, each responsible for different portions of the output area. Each region can be independently designed and optimized to achieve uniform brightness distribution across the entire output area, while maintaining manufacturability through modular construction.
Solution Approach 2:
Different regions of the output element are assigned different diffractive properties and orientations. The first diffractive region has a first orientation and the second diffractive region has a second orientation, allowing each region to be locally optimized for its specific function in achieving uniform overall brightness.
2Productivity
If a single diffractive optical element is used, then the structure is simple, but the light expansion and coupling efficiency is limited
Solution Approach 1:
Multiple diffractive regions are combined within a single output element structure. The first and second diffractive regions work together to expand light in different directions and improve overall coupling efficiency, while remaining integrated into one manufacturable component.
Solution Approach 2:
The patent introduces a third orientation dimension for the optical structures within the diffractive regions. This additional degree of freedom allows for enhanced light expansion control and coupling efficiency without significantly increasing manufacturing complexity, as the structures remain planar.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution improves light output uniformity by reducing relative brightness in bright regions and increasing it in dim regions, resulting in a more uniformly bright image for the user.
Implementation Method 1
Light from the projector is coupled into the waveguide by an input structure (for example via diffraction or reflection)
Implementation Method 2
The projected light is totally internally reflected within the waveguide
Implementation Method 3
an output diffractive optical element, configured to receive light from the input diffractive optical element in an input direction, expand the light in two dimensions
Implementation Method 4
each optical structure is oriented in a third direction that is non-parallel to the first and second directions of periodicity, and is configured to couple light out of the waveguide towards the user
Data Source
Figure 1
Figure 2A~2C
Figure 3
AI summary
An optical device for use in an augmented reality or virtual reality display, comprising: a planar waveguide; an input diffractive optical element, DOE, configured to receive light from a projector and couple the light into the waveguide; an output DOE configured to receive light from the input diffractive optical element in an input direction, expand the light in two dimensions and couple the light out of the waveguide towards a user, the output DOE comprising a first diffractive region configured to diffract light within the waveguide, the first diffractive region having a first direction of periodicity and a second direction of periodicity , wherein an angle between the input direction and the first direction of periodicity is equal and opposite to an angle between the input direction and the second direction of periodicity, wherein the first diffractive region comprises an array of optical structures, wherein each optical structure is oriented in a third direction that is non-parallel to the first and second directions of periodicity, and is configured to couple light out of the waveguide towards the user.