Virtual Image Display Ridge Line Reflection Unit Brightness Uniformity
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Solution Overview
Problem
Virtual image display devices experience stripe-shaped brightness unevenness due to light flux changes and multiple reflections in light guide plates, leading to decreased brightness and image quality.
Innovation Solution
A virtual image display device with a light guide device featuring a reflection unit that covers the ridge line vicinity area on the third face, forming an obtuse angle with the second face, ensuring non-transparent reflection and preventing light leakage, thereby maintaining high reflectance and reducing brightness unevenness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a light guide plate uses total reflection to direct image light, then the image light can be guided to the viewer's eyes, but stripe-shaped brightness unevenness occurs due to light extinction in the opening periphery of the folded mirror
Solution Approach 1:
The patent applies local quality by making the reflection unit protrude specifically in the ridge line vicinity area where brightness unevenness occurs. This localized structural modification ensures that the reflection unit covers the peripheral portion near the boundary with the adjacent face, providing enhanced reflection precisely where needed without altering the entire light guide plate structure. This resolves the contradiction by maintaining high reflectance in critical areas while preserving overall system functionality.
Solution Approach 2:
The reflection unit is designed to protrude in advance before light incidence, covering the ridge line vicinity area proactively. This preliminary structural arrangement ensures that even light rays that would normally strike the peripheral portion near the boundary are reflected effectively, preventing brightness unevenness before it occurs. The protrusion width is specifically controlled to be equal to or more than 0.1mm to ensure sufficient coverage.
2Reliability
If the reflection unit is made to cover the ridge line vicinity area to prevent light leakage, then brightness uniformity improves, but the device complexity increases
Solution Approach 1:
Rather than making the entire light guide plate complex, the invention applies local quality by modifying only the reflection unit in the specific ridge line vicinity area. The protrusion is localized to where it is needed (peripheral portion near the boundary with adjacent face), keeping the rest of the light guide plate structure simple and maintaining ease of manufacture while improving brightness uniformity.
3Reliability
If the protrusion width of the reflection unit is increased to ensure sufficient reflection coverage, then brightness uniformity improves, but the amount of protrusion may affect total reflection efficiency on the second face
Solution Approach 1:
The patent applies parameter changes by precisely controlling the protrusion width of the reflection unit to be equal to or more than 0.1mm. This specific parameter range ensures sufficient coverage of the ridge line vicinity area to prevent light leakage and improve brightness uniformity, while simultaneously maintaining total reflection efficiency on the second face. The parameter is optimized to balance both requirements without excessive protrusion.
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 effectively prevents stripe-shaped brightness unevenness, ensuring a bright and uniform image by securing sufficient reflection even in peripheral areas, thus enhancing image quality and reducing light loss.
Implementation Method 1
a light guide unit directing the image light received from the light incident unit by total reflection on first and second faces opposed to each other and extending in parallel
Implementation Method 2
a third face that reflects the image light by a reflection unit forming an obtuse angle with respect to the second face
Data Source
AI summary
In a virtual image display device, a mirror layer has a thickness of 50 nm or more to perform non-transparent reflection in a second ridge line vicinity area on a third reflection face side in a ridge line portion extending between the third reflection face and a second reflection face. Accordingly, reflectance of image light can be prevented from being decreased by the second ridge line vicinity area (that is, a peripheral portion on a light guide unit in the third reflection face), and thus stripe-shaped brightness unevenness extending in a longitudinal direction can be prevented from occurring on the viewed image. That is, in the image display device, it is possible to secure sufficient reflection even in the peripheral portion close to a boundary with the second reflection face with respect to the third reflection face, and also to display a bright image with little brightness unevenness.