Overlapping Grating Image Light Guide for Expanded Eyebox
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Solution Overview
Problem
Conventional image light guides for Head-Mounted Displays (HMDs) face constraints in eyebox size, leading to limited movement tolerances and uneven light distribution, resulting in hot spots and increased manufacturing complexity and cost.
Innovation Solution
The design incorporates an out-coupling diffractive optic with overlapping grating patterns that expand both dimensions of image-bearing beams within an eyebox, allowing for more compact and well-corrected virtual image presentation by diffracting light in both angularly encoded and decoded forms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If separate beam expansion stages are used for orthogonal dimensions, then beam expansion is achieved, but waveguide size and manufacturing complexity increase
Solution Approach 1:
The patent combines multiple beam expansion functions into a single out-coupling diffractive optic by overlapping multiple grating patterns (first grating pattern for primary beam expansion, second grating pattern for orthogonal dimension expansion, and third grating pattern for additional beam control). This merging of functions into one component achieves the same effect as separate stages while reducing waveguide size and manufacturing complexity.
Solution Approach 2:
The out-coupling diffractive optic is designed to perform multiple functions simultaneously: it expands beams in the primary dimension, expands beams in the orthogonal dimension, and controls light distribution across the eyebox. This multi-functional design eliminates the need for separate dedicated components for each function.
2Area of moving object
If beam management functions are added to expand beams in multiple dimensions, then eyebox size increases, but waveguide size increases
Solution Approach 1:
The patent merges multiple beam expansion operations into a single out-coupling diffractive optic with overlapping grating patterns. The first grating pattern expands beams in one dimension while the second grating pattern expands beams in the orthogonal dimension, both within the same optical component and waveguide area, preventing waveguide size increase.
3Illumination intensity
If conventional out-coupling diffractive optics are used, then light is diffracted out of the waveguide, but light distribution is uneven causing hot spots
Solution Approach 1:
The patent applies different grating patterns in different regions of the out-coupling diffractive optic to achieve uniform light distribution. The first grating pattern addresses one region's beam expansion needs, the second grating pattern addresses another region's orthogonal expansion needs, and the third grating pattern provides additional local control. This localized optimization eliminates hot spots by ensuring even light distribution across the entire eyebox.
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
This solution enhances the eyebox size and light distribution uniformity, reducing sensitivity to viewer position and manufacturing complexity while maintaining desired angular relationships for improved virtual image presentation.
Implementation Method 1
An in-coupling diffractive optic formed along the waveguide diffracts the image-bearing light beams from an image source into the waveguide for propagating the image-bearing light beams along the length of the waveguide in an angularly encoded form
Implementation Method 2
An out-coupling diffractive optic spaced apart from the in-coupling diffractive optic along the length of the waveguide diffracts the image-bearing light beams from the waveguide in an angularly decoded form toward an eyebox for viewing the image from the image source
Data Source
AI summary
An image light guide for conveying a virtual image has a waveguide that conveys image-bearing light, formed as a flat plate having an in-coupling diffractive optic with a first grating vector diffracting an image-bearing light beam into the waveguide and directing diffracted light. An out-coupling diffractive optic is formed as a plurality of overlapping diffraction gratings including a first grating pattern having first grating vector k1 and a second grating pattern having a second grating vector k2 for expanding and ejecting the expanded image bearing beams from the waveguide into an expanded eyebox within which the virtual image can be seen.