Waveguide Display Grating Surface Variations for Banding Elimination
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Solution Overview
Problem
Waveguide-based display systems often suffer from a visible banding effect due to equal or nearly equal optical path lengths of incoherent light propagating through the fold zone, leading to intensity variations across the eye box, affecting image quality.
Innovation Solution
Introducing surface variations on the first and/or second surfaces of the intermediate grating to create an optical path length difference between the respective optical paths, ensuring that the banding effect is eliminated by varying the thickness of the fold zone, thereby preventing destructive and constructive interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the optical waveguide uses a conventional design with uniform thickness in the fold zone, then the manufacturing process is simple, but a visible banding effect occurs due to equal optical path lengths causing intensity variations
Solution Approach 1:
The patent applies local quality by introducing surface variations specifically in the fold zone of the optical waveguide. The thickness of the fold zone is varied locally rather than uniformly, creating different optical path lengths in specific regions. This localized modification eliminates the banding effect caused by equal optical path lengths while maintaining uniform thickness in other zones, thus resolving the contradiction between manufacturing simplicity and eliminating the banding effect.
2Object-affected harmful factors
If surface variations are introduced to eliminate the banding effect, then image quality improves, but the manufacturing precision requirements increase
Solution Approach 1:
The patent applies parameter changes by modifying the thickness parameter of the fold zone to create surface variations. By changing the thickness parameter locally in the fold zone, the optical path length is varied to eliminate the banding effect. This approach transforms the uniform thickness parameter into a varied parameter, achieving improved image quality while the precision requirements are managed through controlled variations rather than extreme precision demands.
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 surface variations effectively eliminate the banding effect by introducing an optical path length difference of at least 50 nanometers, ensuring consistent image intensity across the eye box and enhancing image quality.
Implementation Method 1
the incoupling grating is arranged to couple each beam into the intermediate grating
Implementation Method 2
the exit grating is arranged to diffract the two versions of that beam outwardly
Implementation Method 3
Such systems can incorporate diffraction gratings, which cause effective beam expansion so as to output expanded versions of the beams provided by the light engine
Data Source
AI summary
A display system comprises an optical waveguide and a light engine. The light engine generates multiple input beams which form a virtual image. An incoupling grating of the waveguide couples each beam into an intermediate grating of the waveguide, in which that beam is guided onto multiple splitting regions. The intermediate grating splits that beam at the splitting regions to provide multiple substantially parallel versions of that beam. Those multiple versions are coupled into an exit grating of the waveguide, in which the multiple versions are guided onto multiple exit regions. The exit grating diffracts the multiple versions of that beam outwardly. The multiple input beams thus cause multiple exit beams to exit the waveguide which form a version of the virtual image. One or more surfaces of the intermediate grating comprise surface variations such that a visible banding effect is eliminated from the version of the virtual image.