Image Display Device Spacer Plate Interference Fringe Reduction
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Solution Overview
Problem
Image display devices using diffraction gratings and functional films in light guide plates suffer from image deterioration due to components of image light propagating inside adhesive layers, causing image blur and uneven brightness.
Innovation Solution
The image display device incorporates a first and second spacer plate with specific thickness and refractive index relationships to control the diffraction and propagation of image light, reducing interference fringes caused by zero-order diffraction light and enhancing image quality by ensuring the light and dark pitch of interference fringes is below the threshold of human visibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a diffraction grating is used to extract image light from the light guide plate, then the exit pupil is expanded, but interference fringes are generated causing image deterioration
Solution Approach 1:
A polarization beam splitting film is introduced as an intermediary component between the light guide plate and the diffraction grating. This film separates the light paths and controls the polarization state of light, preventing the direct interaction that causes interference fringes while maintaining the diffraction grating's pupil expansion function
Solution Approach 2:
The invention changes the optical parameters by introducing polarization control through the polarization beam splitting film. By manipulating the polarization state of light before it reaches the diffraction grating, the system modifies how light interacts with the grating structure, thereby eliminating interference fringes while preserving the expanded exit pupil
2Productivity
If a functional film is attached on the diffraction grating side of the light guide plate, then light extraction efficiency is controlled, but image light components propagate inside the adhesive layer causing image blur
Solution Approach 1:
The polarization beam splitting film serves as an intermediary that redirects light paths, preventing image light components from propagating through the adhesive layer. This mediator maintains the functional film's light extraction efficiency while eliminating the harmful propagation path that causes image blur
Solution Approach 2:
The optical path is segmented into separate channels by the polarization beam splitting film. Image light and other light components are separated and directed along different paths, preventing the mixing and propagation that occurs in the adhesive layer, thereby maintaining image clarity while preserving light extraction efficiency
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 reduces image deterioration by minimizing the visibility of interference fringes, thereby improving image clarity and contrast sensitivity, ensuring that the image display device provides a clearer and more stable image projection.
Implementation Method 1
a diffraction grating, part of the image light which has propagated inside the light guide plate being diffracted by the diffraction grating being extracted
Implementation Method 2
a light guide plate having a first plane and a second plane opposing to each other, allowing image light to be repeatedly reflected between the first plane and the second plane, so as to propagate therethrough
Data Source
AI summary
Provided is an image display device, including: an image projection optical system projecting, at infinity, image light corresponding to an arbitrary image; a first light guide portion formed like a plate having a first plane and a second plane, in which the image light projected from the image projection optical system is transmitted in part through the first plane with the rest being reflected between the first plane and the second plane, so as to be propagated in the x-direction by repeating the transmission and the reflection; a first spacer plate formed like a plate having a third plane and a fourth plane, the third plane being bonded to the first plane; and a first output deflector formed on or bonded to the fourth plane, the first output deflector diffracting part of the image light transmitted through the first plane, in a direction substantially perpendicular to the first plane.