Light Guide Plate Uniforming Brightness via Partially Reflective Surface Array
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Solution Overview
Problem
Conventional light guide plates used in image display apparatuses face challenges in projecting image light of uniform brightness while maintaining high light use efficiency, as the amount of image light propagating through the plate decreases, leading to nonuniform brightness and reduced light use efficiency when trying to increase reflectivity.
Innovation Solution
A light guide plate design featuring internal reflective surfaces and a partially reflective surface array with varying inter-surface spacings and reflectivity along the direction of image light propagation, including a uniforming element to adjust the intensity distribution of image light, allowing for uniform brightness projection with high light use efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the reflectivity of the partially reflective surfaces is increased to achieve high light use efficiency, then light use efficiency is improved, but the nonuniformity of brightness of the image becomes increasingly salient
Solution Approach 1:
The patent applies local quality by varying the spacing between partially reflective surfaces at different locations within the light guide plate. Specifically, the spacing is made non-uniform, with closer spacing in regions where more light extraction is needed and wider spacing where less extraction is required. This local variation in structural parameters enables different parts of the plate to have optimized light extraction characteristics, simultaneously achieving high overall light use efficiency while maintaining uniform brightness distribution across the projected image.
Solution Approach 2:
The patent employs parameter changes by modifying the geometric parameters of the partially reflective surfaces arrangement. The key parameter changed is the inter-surface spacing, which is varied continuously or in steps across the light guide plate. By changing this spatial parameter, the patent optimizes the balance between light extraction efficiency and brightness uniformity, resolving the technical contradiction between these two competing requirements.
2Use of energy by moving object
If the amount of image light propagating through the light guide plate is increased, then light use efficiency is improved, but the brightness uniformity deteriorates due to gradual light loss during propagation
Solution Approach 1:
The patent addresses this contradiction by implementing local quality through position-dependent spacing of partially reflective surfaces. In regions closer to the light source where more light is available, the spacing is optimized to extract appropriate amounts of light. In regions farther from the light source where less light remains, the spacing is adjusted to extract less light, compensating for the cumulative light loss during propagation. This local optimization maintains brightness uniformity while maximizing overall light use efficiency.
Solution Approach 2:
The patent applies preliminary action by pre-designing the non-uniform spacing pattern of partially reflective surfaces before light propagation occurs. The spacing configuration is calculated in advance to anticipate and compensate for the gradual light loss that will occur during propagation through the plate. This preliminary structural design ensures that even though light intensity decreases during propagation, the extracted light distribution remains uniform across the output.
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 design enables the projection of image light with uniform brightness and improved light use efficiency, extending the eye box and maintaining see-through characteristics, even with higher reflectivity, thus enhancing the performance of head-mounted and head-up displays.
Implementation Method 1
first and second internal reflective surfaces that are approximately parallel to each other and propagate incoming image light while totally reflecting the incoming image light
Implementation Method 2
a partially reflective surface array that is placed in an interior sandwiched between the first and second internal reflective surfaces, and has a plurality of partially reflective surfaces arranged therein in a direction of propagating image light, the plurality of partially reflective surfaces being inclined at a predetermined angle and partially reflecting the image light
Data Source
AI summary
A light guide plate includes: first and second internal reflective surfaces that are approximately parallel and propagate incoming image light while totally reflecting the image light; a partially reflective surface array that has a plurality of partially reflective surfaces arranged in a direction of propagating image light, the partially reflective surfaces being inclined at a predetermined angle and partially reflecting the image light; and a uniforming element that uniforms intensity distribution of image light which is reflected by the partially reflective surface array to be projected from the light guide plate. As the uniforming element, the partially reflective surface array is divided into a plurality of segments along a direction of propagating image light, and the inter-surface spacing of the partially reflective surfaces or the reflectivity of the partially reflective surfaces is configured to vary from segment to segment.