Waveguide Input Grating Layout to Reduce AR Display Stray Light
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Solution Overview
Problem
Existing image display devices suffer from reduced light utilization efficiency due to light beams being diffracted at the input grating of the light input unit, which can reflect back into the light-guiding plate, leading to stray light and decreased efficiency.
Innovation Solution
The virtual-image display device incorporates a diffraction optical element that covers the incident region of the light-guiding member, with the diffraction region set to reflect diffracted light onto the opposing surface of the light-guiding plate, preventing it from entering the diffraction optical element again, thereby optimizing light utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the size of the light input unit is increased to uniformly duplicate image light, then brightness uniformity is improved, but light utilization efficiency deteriorates due to light beams being reflected back into the light-guiding plate
Solution Approach 1:
The patent extracts and removes the problematic reflected light beams from the system by designing the diffraction optical element to direct diffracted light outside the light-guiding plate, preventing it from re-entering and causing stray light. This resolves the contradiction by eliminating the harmful reflection path while maintaining the light input unit size needed for brightness uniformity.
Solution Approach 2:
The patent converts the harmful reflected light into a beneficial configuration by using the diffraction optical element to redirect the diffracted light outside the light-guiding plate. The diffraction that previously caused stray light is now utilized to steer light away from the problematic reflection path, transforming the harmful effect into a solution that maintains brightness uniformity while improving light utilization efficiency.
2Stability of the object's composition
If the light input unit size is increased, then light distribution uniformity is improved, but device size and weight increase
Solution Approach 1:
The patent removes the need for excessive light input unit size by extracting the problematic reflected light paths through diffraction. The diffraction optical element enables effective light distribution with a more compact light input unit by preventing stray light formation, thus achieving light distribution uniformity without increasing device weight.
3Stability of the object's composition
If the light input unit size is increased, then light distribution uniformity is improved, but device complexity increases
Solution Approach 1:
The patent merges the functions of light diffusion and stray light prevention into a single diffraction optical element. This integrated approach achieves light distribution uniformity without requiring separate components for each function, thereby maintaining optical system simplicity while improving light distribution uniformity.
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 configuration enhances light utilization efficiency by minimizing stray light and maintaining image quality, while reducing the device's size and weight.
Implementation Method 1
an input diffraction optical element configured to cause the image light to enter the light-guiding plate
Implementation Method 2
a light-guiding plate configured to guide the image light
Implementation Method 3
an output diffraction optical element configured to cause the image light to be outputted from the light-guiding plate
Data Source
AI summary
A virtual-image display device includes a display panel configured to output image light, a projection optical system configured to collimate the image light from the display panel, and a light-guiding member including a light-guiding plate configured to guide the image light, an input diffraction optical element configured to cause the image light to enter the light-guiding plate, and an output diffraction optical element configured to cause the image light to be outputted from the light-guiding plate. A diffraction region of the input diffraction optical element covers an incident region of the image light at the light-guiding member, and the diffraction region is set at a region in which the image light diffracted at the input diffraction optical element is reflected on an opposing surface of the light-guiding plate, and enters an outside of the input diffraction optical element.