Optical Waveguide Grating Design for Continuous Exit Pupil Expansion
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Solution Overview
Problem
Holographic optical waveguides face challenges in ensuring continuous exit pupil expansion without secondary diffraction at the in-coupling grating, which is contradictory to preventing energy loss due to secondary diffraction, and this requires complex light path designs that increase system cost and complexity.
Innovation Solution
The optical waveguide incorporates a transmissive out-coupling grating and a reflective out-coupling grating, with specific misalignment and positioning to ensure no secondary diffraction at the in-coupling grating and continuous exit pupil expansion, using optimized parameters for the grating width, period, and refractive index to achieve efficient energy use and observation continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single out-coupling grating is used, then the structure is simple, but continuous exit pupil expansion cannot be achieved
Solution Approach 1:
The out-coupling grating is divided into multiple independent grating regions (first out-coupling grating, second out-coupling grating, third out-coupling grating) with different orientations and positions. Each grating region contributes to expanding the exit pupil in a specific direction, and their combined effect achieves continuous 360-degree exit pupil expansion without requiring a single complex grating structure.
Solution Approach 2:
The patent transitions from a single-plane grating configuration to a multi-dimensional arrangement by placing out-coupling gratings on different surfaces (front surface and side surfaces) of the optical waveguide. This spatial distribution across multiple dimensions enables continuous exit pupil expansion in all directions around the user's eye.
2Loss of energy
If the beam width is increased to prevent secondary diffraction, then energy loss is reduced, but the field of view is limited
Solution Approach 1:
The patent resolves the trade-off between beam width and field of view by transitioning from a single-direction beam expansion approach to a multi-dimensional beam distribution. Multiple out-coupling gratings oriented at different angles (0 degrees, 45 degrees, 90 degrees) distribute the beam in multiple spatial dimensions, achieving both sufficient beam width to prevent secondary diffraction and a wide 360-degree field of view.
Solution Approach 2:
The field of view is segmented into multiple directional zones, each served by a specific out-coupling grating region. The first out-coupling grating handles one direction, the second handles another direction at 45 degrees, and the third handles a third direction at 90 degrees. This segmentation allows each grating to optimize beam width for its specific direction while collectively providing a comprehensive wide field of view.
3Loss of energy
If complex light path designs are used to prevent secondary diffraction, then energy efficiency is improved, but system cost and complexity increase
Solution Approach 1:
The patent combines multiple functions into the out-coupling grating structure itself. The same grating regions that couple light out of the waveguide also serve to expand the exit pupil and control beam direction. This merging eliminates the need for separate components or complex light path designs, achieving high energy efficiency while maintaining relatively simple system structure and lower cost.
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 configuration allows for efficient energy use and continuous exit pupil expansion without secondary diffraction, optimizing the optical waveguide's performance and reducing system complexity and cost.
Implementation Method 1
have the beam propagate in a total reflection manner in the optical waveguide body
Implementation Method 2
couple the light beam propagating to the beam coupling-out region out of the optical waveguide body, such that the beam does not undergo secondary diffraction at the coupling grating
Data Source
AI summary
An optical waveguide includes an optical waveguide body having a beam in-coupling region and a beam coupling-out region, wherein: the beam in-coupling region is provided with a coupling grating configured to couple a beam into the optical waveguide body, and have the beam propagate in a total reflection manner in the optical waveguide body; the beam coupling-out region is provided with an out-coupling grating configured to couple the light beam propagating to the beam coupling-out region out of the optical waveguide body, such that the beam does not undergo secondary diffraction at the coupling grating and have continuous exit pupil expansion; and the out-coupling grating includes a transmissive out-coupling grating and a reflective out-coupling grating disposed on two sides of the optical waveguide body parallel to a beam propagation direction.