Waveguide Grating Area Variation for Uniform Luminance
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Solution Overview
Problem
Prior art projection displays using waveguides suffer from irregular brightness distribution along the light path, resulting in varying intensity of image-bearing light pupils, which affects the perceived brightness by the observer.
Innovation Solution
A waveguide element with a grating element whose area increases with distance along the propagation axis, allowing for uniform luminance of image-bearing light pupils, achieved by varying the grating element's interaction with image-bearing light, ensuring consistent brightness perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a constant area grating element is used in the waveguide, then the structure is simple and manufacturing is easier, but the brightness distribution along the light path becomes irregular
Solution Approach 1:
The grating element's area is varied along the propagation direction to create different local properties. Specifically, the area of the grating element increases with distance along the propagation axis, which compensates for the decreasing light intensity along the path and achieves uniform brightness distribution.
Solution Approach 2:
The physical parameter of the grating element (its area) is changed along the propagation direction. By increasing the grating element area with distance, the interaction between light and grating is optimized at different positions, resulting in uniform luminance of image-bearing light pupils along the entire light path.
2Illumination intensity
If the grating element area increases with distance, then uniform brightness distribution is achieved, but manufacturing precision requirements increase
Solution Approach 1:
The grating element is designed with spatially varying area to achieve uniform brightness. This local variation in grating area allows each section to contribute appropriately to the overall uniform luminance, with the area increasing systematically along the propagation axis.
Solution Approach 2:
The grating element area is systematically changed along the propagation direction according to a controlled pattern. This parameter change enables compensation for light intensity decay while maintaining manufacturability through predictable geometric progression.
3Area of stationary object
If a small image-providing light source is used, then the device size is reduced, but the field of view and exit pupil size are limited
Solution Approach 1:
The waveguide structure transforms the light propagation from a point-source limited geometry to a planar waveguide geometry. By injecting light into a plate-like waveguide and using total internal reflection, the system expands the effective light distribution area while maintaining a compact device footprint.
Solution Approach 2:
The optical system is divided into multiple functional components: an image-providing light source, a waveguide with propagation paths, and multiple grating elements positioned along the propagation axis. This segmentation allows each component to be optimized independently while achieving overall system goals of compact size and large exit pupil.
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 ensures a more even brightness distribution along the waveguide, providing uniform luminance of image-bearing light pupils, thereby enhancing the observer's viewing experience by maintaining consistent intensity across the display.
Implementation Method 1
a grating element carried on or within the layer of material that is arranged such that image-bearing light propagating through the layer of transmissive material may interact with the grating element to allow at least some of the image bearing light to exit the layer of material or to direct at least some of the image bearing light within the layer of material
Implementation Method 2
a layer of light transmissive material arranged to allow propagation of image bearing light along a predefined propagation axis of the layer of material by total internal reflection of the image bearing light within the layer of material
Data Source
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AI summary
A waveguide (60) formed of material (6)2 allows propagation of image bearing light along a light pathway (64) by total internal reflection of the image bearing light. The layer of material (62) is a light transparent material arranged to allow an observer, not illustrated, to look through the layer of material (62) whilst also arranged to carry image bearing light. A grating element (66) carried within the layer of material (62) is arranged such that impinging image bearing light following the light pathway (64) is either diffracted out of the layer of material (62) as a pupil of image bearing light (68a to 68n) or is reflected by either surface (70) or surface (72). The efficiency of the grating element (66) is varied along the length of the layer of material (62) to achieve the desired pupils of image bearing light (68a to 68n) along the length of the layer of material (62). This results in a more even brightness of pupils of image bearing light (68a to 68n), as perceived by the observer looking through the layer of material (62).