Segmented EPE Grating for Waveguide Interference Reduction
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Solution Overview
Problem
Existing Exit Pupil Expanders for optical waveguide arrangements suffer from interference caused by light rays, leading to non-uniformities in the out-coupled image, and lack the ability to independently tune the phase of diffracted light rays without altering the amplitude response of the gratings.
Innovation Solution
The Exit Pupil Expander grating is divided into multiple segments with misaligned grating bars, allowing for different phase shifts in each segment, controlled according to Lohmann's detour-phase principle, to minimize interference while maintaining the amplitude of light rays unaltered.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a uniform grating is used in the EPE, then the structure is simple and easy to manufacture, but light rays interfere in the grating causing non-uniformities in the out-coupled image
Solution Approach 1:
The EPE grating is divided into multiple segments (first segment, second segment, third segment) with different grating bar configurations. Each segment introduces different path length differences for light rays passing through it, thereby reducing interference effects while maintaining manufacturing feasibility through modular design
Solution Approach 2:
Different segments of the grating have different local properties - specifically, different grating bar positions and orientations in each segment. This local variation in grating structure allows different phase shifts to be introduced at different locations, reducing interference while keeping the overall system manufacturable
2Object-affected harmful factors
If grating parameters are varied at different locations to reduce wave interference, then luminance uniformity improves, but the ability to independently tune phase without altering amplitude response is lost
Solution Approach 1:
The grating is segmented into multiple sections where each segment can independently control the phase of diffracted light rays. By dividing the grating into distinct segments with different bar configurations, the system achieves both interference reduction and independent phase tuning capability
Solution Approach 2:
The grating bars in different segments are positioned asymmetrically relative to each other, with each segment having a unique bar configuration. This asymmetry enables independent phase control for each segment while the overall periodic structure maintains amplitude response consistency
3Object-affected harmful factors
If the EPE grating is divided into multiple segments with misaligned grating bars, then interference effects are reduced and phase tuning is enabled, but the device complexity increases
Solution Approach 1:
The grating is divided into a limited number of segments (typically 2-3 segments) rather than continuously varying the structure. This segmentation reduces interference effects and enables phase tuning while avoiding excessive complexity by maintaining a discrete, manageable number of segments with periodic structures
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 approach reduces interference effects and provides more degrees of freedom for modifying the optical waveguide operation, enhancing luminance uniformity and image quality by controlling phase shifts without altering the amplitude of light rays.
Implementation Method 1
said multiple grating bars of the first segment and said multiple grating bars of the second segment are misaligned to cause light rays propagating along different paths in the EPE grating to undergo different phase shifts
Implementation Method 2
Light rays typically interfere in the EPE grating and hence cause non-uniformities into an out-coupled image
Implementation Method 3
an EPE grating for expanding the exit pupil of an image on the out-coupling grating
Data Source
AI summary
According to an example aspect of the present invention, there is provided an Exit Pupil Expander, EPE, grating which is divided into at least two segments, wherein the EPE grating comprises multiple grating bars in a first segment and multiple grating bars in a second segment, said multiple grating bars of the first segment being directed about to a same direction as said multiple grating bars of the second segment and misaligned in a direction which is perpendicular to the direction of the grating bars.