Light Guide Plate with Variable Pitch Diffraction Grating for Wide Angle Display
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Solution Overview
Problem
Existing image display devices face challenges in enlarging the display angle-of-view region while suppressing color unevenness, particularly when using a single light guide plate with diffraction gratings for RGB colors, which often result in ghosting and increased cost due to the need for multiple light guide plates and complex configurations.
Innovation Solution
An image display device and method utilizing a single light guide plate with a first diffraction grating for incident image light and a second diffraction grating for emitting image light, where the gratings have the same pitch and are designed to diffract and reflect image light to enhance the angle-of-view while minimizing color unevenness by dividing the image light into color beams and optimizing diffraction efficiency across RGB wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If multiple light guide plates with different diffraction grating pitches are used for RGB colors, then color accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple light guide plates with different diffraction grating pitches into a single light guide plate by using a variable pitch diffraction grating structure. The pitch of the diffraction grating varies in the direction of the normal line of the light guide plate surface, allowing different pitch regions to handle different colors (R, G, B) within the same plate, thus combining multiple functions into one component.
Solution Approach 2:
The patent applies local quality by creating regions with different diffraction grating pitches within the same light guide plate. Each region has a pitch optimized for specific color wavelengths, with the pitch value changing according to the position in the normal direction. This allows each local region to be optimized for its specific function while maintaining overall system integration.
2Device complexity
If a single light guide plate with uniform diffraction grating is used, then device complexity is reduced, but color crosstalk and ghosting occur
Solution Approach 1:
The patent changes the pitch parameter of the diffraction grating in the normal direction to prevent color crosstalk. By varying the pitch according to position, the diffraction angles for different colors are optimized at different depths, ensuring proper color separation without requiring multiple plates. This parameter variation eliminates ghosting while maintaining a single-plate structure.
3Manufacturing precision
If diffraction grating pitch varies in the surface direction, then color separation is improved, but viewable angle decreases
Solution Approach 1:
The patent introduces asymmetry in the diffraction grating structure by varying the pitch in the normal direction rather than in the surface direction. This asymmetric configuration allows color separation to be achieved through depth-based pitch variation while maintaining symmetric light extraction in the surface direction, thereby preserving a wide viewable angle.
Solution Approach 2:
The patent moves the pitch variation from the surface plane to the normal direction (depth dimension). Instead of varying pitch along the surface which would narrow the viewing angle, the pitch varies through the thickness of the plate, utilizing the third dimension to achieve color separation without compromising angular coverage.
4Ease of manufacture
If incident angle center is tilted to the output side for single grating RGB diffraction, then manufacturing is simplified, but angle of view decreases
Solution Approach 1:
The patent creates a universal diffraction grating structure that handles multiple colors (R, G, B) simultaneously with a single grating element. The variable pitch design allows the same grating to diffract different colors at appropriate angles without requiring separate gratings or tilted configurations, maintaining both ease of manufacture and wide angle of view.
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 enlarges the display angle-of-view region while maintaining color accuracy and reducing costs by simplifying the configuration, avoiding crosstalk, and utilizing a single light guide plate, thus providing a more efficient and cost-effective means of displaying information.
Implementation Method 1
a first diffraction grating that is provided on the light guide plate, diffracts and reflects the image light incident on the light guide plate, and propagates the image light inside the light guide plate
Implementation Method 2
a first diffraction grating that is provided on the light guide plate, diffracts and reflects the image light incident on the light guide plate
Implementation Method 3
parallel light flux groups having different traveling orientations from each other are incident thereon, propagate therein by total reflection
Data Source
AI summary
There is provided an image display device capable of displaying more information by enlarging a display angle-of-view region while suppressing color unevenness with a simple configuration. An image display device 10 includes: an image forming unit 13 that has a plurality of pixels and emits image light from the plurality of pixels; an optical system 12 that converts each beam of the image light having an image height emitted from the image forming unit into a parallel beam having an angle of view; a light guide plate 11 on which the image light converted by the optical system is incident, in which the image light propagates, and from which the image light is emitted to the outside; a first diffraction grating 14 that is provided on the light guide plate, diffracts and reflects the image light incident on the light guide plate, and propagates the image light inside the light guide plate; and a second diffraction grating 15 that is provided on the light guide plate, diffracts and reflects the image light that has propagated inside the light guide plate, and emits the image light from the light guide plate to the outside. The image forming unit 13 divides the image light into a plurality of color beams.