Holographic Image Guide with Chirped Grating for HMD Luminance
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Solution Overview
Problem
Existing image guides for head-mounted displays suffer from signal light loss due to diffraction at hologram areas, leading to decreased luminance and luminance uniformity, and current solutions using liquid crystal polymer or double-side diffractive optical elements increase costs.
Innovation Solution
An image guide with a glass or plastic planar substrate featuring multiple hologram areas with a diffraction efficiency chirping structure, where the sum of grating vectors of the first, second, and third hologram areas is zero, and the depth of the diffraction structure is uniform or chirped, enhancing luminance and uniformity while reducing manufacturing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If liquid crystal polymer or double-side diffractive optical element is used to improve luminance uniformity, then luminance uniformity is improved, but manufacturing cost increases
Solution Approach 1:
The patent applies local quality by creating a chirped diffraction structure where the grating period varies locally across different regions of the hologram area. This local variation in grating period compensates for the non-uniform light distribution, achieving improved luminance uniformity without requiring expensive liquid crystal polymer or double-side diffractive optical elements
Solution Approach 2:
The patent changes the physical parameter of the grating period across the hologram area to create a chirped structure. By systematically varying the grating period from one region to another, the diffraction efficiency is optimized across different spatial locations, achieving uniform luminance distribution while using a simpler, lower-cost single-side surface relief grating structure
2Ease of operation
If signal light propagates through multiple hologram areas, then virtual image is formed, but light loss due to diffraction decreases luminance
Solution Approach 1:
The patent converts the harmful effect of diffraction-induced light loss into a beneficial effect by designing a chirped grating structure. The varying grating period is specifically engineered to control and optimize diffraction efficiency, transforming what was previously a source of light loss into a mechanism that enhances overall diffraction efficiency and luminance while maintaining virtual image formation
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 provides high luminance and luminance uniformity at a lower cost by minimizing light loss and improving diffraction efficiency through the strategic arrangement and depth modulation of hologram areas on the image guide substrate.
Implementation Method 1
Signal light propagating in the substrate of the image guide encounters a hologram area several times
Data Source
AI summary
An image guide comprising glass or plastic planar substrate, a first hologram area, a second hologram area, and a third hologram area which are formed on the substrate as surface relief grating, period and direction of diffraction structure of the first, second, and third hologram areas have a relationship which is a sum of grating vectors of the first, second, and third hologram areas becomes zero, depth of diffraction structure on the first hologram area is a uniform in the own hologram area, and depth of diffraction structure on the second or third hologram area is chirped in the own hologram area increases luminance and uniformity of virtual image.