Lightguide Outcoupling Structures for Near-Eye Displays
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Solution Overview
Problem
Near-to-eye optical systems in head mountable displays face limitations in field of view and image quality due to the reliance on internal reflection and outcoupling structures like diffraction gratings, angle-sensitive dichroic mirrors, and mirrors, which result in limited field of view and susceptibility to degradation from environmental conditions.
Innovation Solution
A lightguide assembly with a corrugated surface structure and selectively applied optical coatings that redirect light, allowing for improved light emission angles and reduced reflections, enhancing the field of view and image quality by using a combination of reflective and transmissive materials and coatings to manage light propagation and emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If internal reflection structures and diffraction gratings are used for outcoupling, then light can be redirected within the lightguide, but the field of view is limited and image quality degrades due to ghosting effects and power loss
Solution Approach 1:
The patent changes the geometric parameters of the outcoupling structure by using prismatic surfaces with specific angles (e.g., 45-degree angles) and varying depths instead of conventional diffraction gratings. This parameter change enables broader field of view and reduced ghosting while maintaining light redirection functionality
Solution Approach 2:
The outcoupling structure is segmented into multiple discrete prismatic elements with different orientations and depths rather than using a continuous diffraction grating pattern. This segmentation allows independent optimization of each prism to reduce ghosting effects while maintaining overall light redirection
2Adaptability or versatility
If angle-sensitive dichroic mirrors and mirrors are used for light redirection, then light propagation can be controlled, but the system becomes susceptible to degradation from environmental conditions and has limited field of view
Solution Approach 1:
The patent merges the light redirection function previously performed by separate dichroic mirrors and mirrors into an integrated set of prismatic outcoupling structures formed directly on the lightguide. This integration eliminates multiple optical interfaces that are susceptible to environmental degradation while maintaining light propagation control
Solution Approach 2:
The patent replaces the mechanical mirror system with a purely optical prismatic structure that uses refraction and internal reflection at controlled angles. This substitution eliminates the need for separate mirror components that can degrade environmentally while achieving the same light redirection function
3Productivity
If conventional outcoupling structures are used, then light can be emitted from the lightguide, but power loss occurs and ghosting effects reduce user experience
Solution Approach 1:
Different regions of the lightguide surface are given different local qualities through prisms of varying depths and orientations. Each local region is optimized to redirect light at specific angles while minimizing ghosting, allowing high overall emission efficiency without uniform ghosting across the entire surface
Solution Approach 2:
The prismatic outcoupling structures use asymmetric geometries with different angles and depths rather than uniform symmetric patterns. This asymmetry allows precise control over light redirection angles to maximize emission efficiency while minimizing ghosting effects that arise from symmetric diffraction grating patterns
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 provides a more robust and efficient near-to-eye optical system with improved field of view and reduced image artifacts, simplifying fabrication and enhancing user experience by minimizing ghosting effects and power loss, while allowing for both virtual reality and augmented reality applications.
Implementation Method 1
A lightguide assembly with a corrugated surface structure and selectively applied optical coatings that redirect light
Implementation Method 2
A lightguide assembly with a corrugated surface structure and selectively applied optical coatings that redirect light, allowing for improved light emission angles
Data Source
AI summary
A lightguide assembly including structures to provide for outcoupling of light from an internal reflection structure. In an embodiment, a lightguide assembly includes light transmissive bodies forming respective corrugations which are coupled to one another. Optical coatings are variously disposed between the respective corrugations, wherein the optical coatings provide for redirection of light from the lightguide assembly. In another embodiment, optical coatings are each applied to a respective one of alternate facets of a corrugation. Polymer film portions provide mechanical support for the optical coatings during application to the corrugation.