Two-Dimensional Light Homogenization in Optical Waveguides
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Solution Overview
Problem
Optical waveguides often suffer from spatially-inhomogeneous power distribution of light, leading to performance deficits in applications like head-mounted displays, where non-uniform intensity profiles result in reduced image resolution and brightness due to mode inhomogeneity.
Innovation Solution
The implementation of light homogenizing structures, including substrates with partial reflective layers and holograms, which redirect and refract light to achieve uniform power distribution across the waveguide, effectively homogenizing light in one or two dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If light is propagated through a waveguide using total internal reflection, then light can be guided to an output, but spatially-inhomogeneous power distribution occurs leading to non-uniform intensity profile
Solution Approach 1:
The patent applies local quality by varying the reflectivity of the partial reflector at different longitudinal positions along the waveguide. The reflectivity is higher at positions where light intensity is lower and lower at positions where light intensity is higher, creating a spatially-dependent reflection characteristic that compensates for the non-uniform intensity distribution and achieves uniform power distribution across the waveguide.
2Measurement precision
If light coupling devices are used to redirect light towards exit pupil, then projected image is formed, but mode inhomogeneity broadens point spread function reducing resolution
Solution Approach 1:
The patent introduces a partial reflector as an intermediary element between the propagating light modes and the output coupling mechanism. This partial reflector mediates the interaction by selectively reflecting portions of the light beam at different longitudinal positions, thereby homogenizing the power distribution before the light reaches the output coupler, which narrows the point spread function and improves image resolution.
3Stability of the object's composition
If partial reflector with spatially-varying reflectivity is used to homogenize light, then uniform power distribution is achieved, but device structure becomes more complex
Solution Approach 1:
The patent implements parameter changes by varying the reflectivity parameter of the partial reflector along the longitudinal dimension of the waveguide. The reflectivity is engineered to decrease at positions where light intensity is higher and increase where light intensity is lower, creating a spatially-dependent parameter profile that actively compensates for intensity non-uniformity and achieves homogeneous power distribution.
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
This approach enhances the resolution and brightness of projected images by minimizing the point spread function and ensuring a uniform intensity profile, thereby improving the overall performance of optical waveguide-based devices.
Implementation Method 1
a partial reflector that reflects a portion of a light beam while allowing a remainder of the light beam to pass through the partial reflector
Implementation Method 2
An optical waveguide can use total internal reflection (TIR) to guide light to an output
Implementation Method 3
The cross-coupler may include holograms that diffract light on both upwards and downward passes
Data Source
AI summary
An optical reflective device including a waveguide and longitudinal light homogenizing structures mounted to a surface of the waveguide are disclosed. The light homogenizing structures may receive input light and produce longitudinally homogenized light by homogenizing the input light along a longitudinal dimension of the waveguide. A cross-coupler in the waveguide may receive the longitudinally homogenized light from the light homogenizing structures and may produce two-dimensionally homogenized light by redirecting the longitudinally homogenized light along a lateral dimension of the waveguide. The light homogenizing structures may include partially reflective layers, stacked substrate layers with refractive index mismatches, and/or a combination of partially and fully reflective layers. The cross coupler and/or partially reflective layer may be formed using sets of holograms. A prism or a slanted substrate surface may couple the input light into the substrate.