Waveguide DOE Layout for Uniform AR Display Brightness
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Solution Overview
Problem
Conventional augmented reality displays exhibit non-uniform brightness in the central strip of the output image due to uneven light coupling, resulting in a higher-brightness or lower-brightness central strip that degrades the user experience.
Innovation Solution
The optical device employs multiple diffractive optical elements offset in different directions within the waveguide to guide light along multiple paths, ensuring overlapping patterns of light are coupled out, thereby smoothing out brightness variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If light is coupled into the waveguide along a single optical path, then the device structure is simple, but a central strip with non-uniform brightness appears in the output image
Solution Approach 1:
The single optical path is segmented into multiple optical paths (first optical path and second optical path) by introducing a turning diffractive optical element. This segmentation allows light to reach the output DOE through different routes, preventing the formation of a bright central strip and achieving more uniform brightness distribution in the output image.
Solution Approach 2:
A turning diffractive optical element is introduced as an intermediary component between the input DOE and the output DOE. This intermediary element redirects portions of light along alternative paths, enabling multiple optical paths to coexist and thereby solving the brightness uniformity problem without significantly complicating the overall device structure.
2Area of stationary object
If multiple diffractive optical elements are overlaid to expand light in two dimensions, then space utilization on the waveguide is improved, but a central strip with abnormal brightness appears
Solution Approach 1:
The light expansion function is segmented across multiple diffractive optical elements arranged in sequence rather than overlaid simultaneously. The first DOE expands light in one dimension, the turning DOE redirects light, and the second DOE expands light in another dimension, achieving two-dimensional expansion while maintaining brightness uniformity through sequential optical path segmentation.
Solution Approach 2:
The patent transitions from a two-dimensional overlay arrangement to a three-dimensional sequential arrangement of diffractive optical elements. By distributing the light expansion function across multiple elements positioned at different locations and orientations within the waveguide, the patent achieves two-dimensional light expansion while avoiding the central strip brightness issue caused by direct overlay.
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 effectively reduces or eliminates the visible dim central strip, enhancing the uniformity and quality of the displayed image.
Implementation Method 1
an input diffractive optical element, DOE, configured to receive light from a projector and to couple the received light into the waveguide along a plurality of optical paths
Implementation Method 2
The projected light is totally internally reflected within the waveguide
Data Source
AI summary
An optical device for use in an augmented reality or virtual reality display includes a waveguide and an input diffractive optical element (DOE) that receives light from a projector and couples it into the waveguide along multiple optical paths. The device includes an output DOE offset along a first direction to couple light towards a viewer, and a first turning DOE offset along a second different direction. The input DOE couples a first portion of light directly towards the output DOE in the first direction, while coupling a second portion in the second direction towards the first turning DOE, which then diffracts it towards the output DOE. The input DOE may comprise first and second gratings for diffracting the respective light portions. The device may include additional turning DOEs to handle light coupled in other directions.