Image Display Device Diffraction Grating Color Uniformity
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Solution Overview
Problem
Existing image display devices suffer from color irregularities and changes in brightness due to pupil position, primarily caused by variations in diffraction wavelengths across the diffraction grating members, leading to suboptimal image quality.
Innovation Solution
The image display device employs a configuration with a first diffraction grating member and a second diffraction grating member, where the second diffraction grating member is thinner and has a maximum diffraction efficiency less than 50%, while the first diffraction grating member has an efficiency of 50% or greater, both with constant refractive index modulation, to maintain image quality and brightness uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the second diffraction grating member has high diffraction efficiency (≥50%), then more light is emitted from the light guide plate, but color irregularities occur and brightness uniformity deteriorates
Solution Approach 1:
The patent applies parameter changes by setting the maximum diffraction efficiency of the second diffraction grating member to be less than 50%, which is a specific parameter adjustment. This efficiency control prevents excessive diffraction that causes color irregularities while maintaining sufficient light emission. The diffraction efficiency parameter is optimized to balance light output and color uniformity.
Solution Approach 2:
The patent implements local quality by making the second diffraction grating member thinner than the first diffraction grating member. This local structural modification (reducing thickness) creates a region with controlled diffraction characteristics that emits light with reduced color irregularities. The varying thickness across different grating members creates local quality differences in diffraction efficiency.
2Power
If the second diffraction grating member is thicker, then diffraction efficiency increases, but Bragg wavelength variations increase causing color irregularities
Solution Approach 1:
The patent changes the physical parameter of the second diffraction grating member by reducing its thickness compared to the first diffraction grating member. This thickness parameter adjustment directly controls the diffraction efficiency and Bragg wavelength characteristics, ensuring uniformity across the grating member while maintaining adequate light emission.
3Illumination intensity
If multiple diffraction gratings with high efficiency are used, then light emission is enhanced, but pupil position sensitivity increases causing brightness changes
Solution Approach 1:
The patent optimizes the diffraction efficiency parameter of the second diffraction grating member to be less than 50%, which reduces the system's sensitivity to pupil position variations. This parameter adjustment ensures that brightness remains relatively uniform across different viewing positions while maintaining adequate overall light emission.
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 effectively reduces color irregularities and maintains high brightness uniformity across the display, enhancing the overall image quality by minimizing changes in Bragg wavelengths and diffraction efficiency with pupil position.
Implementation Method 1
a first diffraction grating member made up of a volume hologram diffraction grating for diffracting and reflecting light input to the light guide plate
Implementation Method 2
light input to the light guide plate is subjected to total reflection within the light guide plate
Implementation Method 3
a second diffraction grating member made up of a volume hologram diffraction grating for diffracting and reflecting light propagated within the light guide plate by total reflection, and emitting the light from the light guide plate
Implementation Method 4
light propagated within the light guide plate by total reflection
Data Source
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AI summary
An image display device includes an image forming device, collimating optical system, and optical device, with the optical device including a light guide plate, first diffraction grating member and second diffraction grating member which are made up of a volume hologram diffraction grating, and with central light emitted from the pixel of the center of the image forming device and passed through the center of the collimating optical system being input to the light guide plate from the near side of the second diffraction grating member with a certain angle. Thus, the image display device capable of preventing occurrence of color irregularities, despite the simple configuration, can be provided.