Plate Waveguide Mirror Image Elimination
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Solution Overview
Problem
Helmet-mounted displays (HMDs) face issues with image sharpness due to the formation of opposite mirror images during light transmission through plate waveguides, affecting the clarity of the displayed images.
Innovation Solution
A plate waveguide design incorporating cascaded splitting films with specific refractive index, field of view, and angle configurations to eliminate mirror images, ensuring that the mirror image does not overlap with the ideal image and maintaining high transmissivity for ideal image light while reducing mirror image brightness to less than 5% of the ideal image.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If light is continuously reflected and transmitted on the upper and lower surfaces of the waveguide, then the transmitted image can reach the eye, but opposite mirror images are formed which affect image sharpness
Solution Approach 1:
The waveguide is divided into multiple functional zones with different reflection characteristics. The upper surface has a first reflection region and a second reflection region with different reflection rates, while the lower surface has corresponding regions. This segmentation allows different parts of the waveguide to handle different aspects of light transmission, separating the ideal image path from the mirror image path.
Solution Approach 2:
Different regions of the waveguide surfaces are assigned different reflection rates. Specifically, the first reflection region on the upper surface and its corresponding region on the lower surface have a first reflection rate, while the second reflection region and its corresponding region have a second reflection rate. This local differentiation enables precise control over light paths to eliminate mirror images while maintaining image transmission.
2Manufacturing precision
If cascaded splitting films are used to eliminate mirror images, then image sharpness is improved, but the system complexity increases
Solution Approach 1:
The waveguide surfaces serve multiple functions: they act as both transmission paths for ideal images and as reflection surfaces for eliminating mirror images. The same upper and lower surfaces that transmit the transmitted image also contain the reflection regions that eliminate opposite images, eliminating the need for separate components.
Solution Approach 2:
The reflection rate parameter is varied across different regions of the waveguide surfaces. By changing the reflection rate from the first reflection rate to the second reflection rate in different zones, the system achieves mirror image elimination while maintaining a relatively simple overall structure without requiring additional complex components.
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 eliminates mirror images in near-eye display systems, maintaining image sharpness without increasing system volume or weight, and enhances energy threshold for high-energy laser applications by ensuring high uniformity of the adhesive layer.
Implementation Method 1
Based on the principle of total reflection, a light beam needs to be continuously reflected and transmitted on the upper and lower surfaces of the waveguide and finally transmitted to the eye
Implementation Method 2
a refractive index of the parallel plate, a field of view, an angle of the splitting films, and an angle of the incident light are required to satisfy following relationships: a condition of total reflection transmission: 90°−b−ω>arcsin(1/n); a condition where the mirror image does not overlap with the ideal image, and there is no ghosting: |arcsin(n×sin(90°−4a+b))−arcsin(n×sin(90°−2a−b))|>2ω
Data Source
AI summary
A slab waveguide, comprising a plate having parallel surfaces and a cascade light splitting film. The plate is used for receiving and transmitting incident waveguide light which bears a transmitted image. The splitting film is disposed in the plate, intersects the upper and lower surface of the plate, and is used for reflecting the incident waveguide light out of the slab waveguide to form an actual image. In order to avoid mirror image coincidence, the waveguide needs to satisfy: |arcsin(n×sin(90°−4a+b))−arcsin(n×sin(90°−2a−b))1>2ω, wherein a is an inclined angle between the cascade light splitting film and the lower surface of the plate, b is an inclined angle between central image light of the incident waveguide light and the lower surface of the plate, ω is an image display viewing angle of the transmitted image, and n is the refractive index of the plate.