Waveguide Diffractive Optical Elements for AR Exit Pupil Spacing
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Solution Overview
Problem
Conventional augmented reality and virtual reality displays face challenges in reducing the spacing between exit pupils on a waveguide without increasing the size of the input grating or projector, while also achieving high efficiency in light coupling and minimizing transitions between exit pupils.
Innovation Solution
The use of two input diffractive optical elements on opposing surfaces of a waveguide, with one element configured to capture light and allow it to pass through, and the other to couple it into the waveguide, creating overlapping patterns of exit pupils that reduce spacing and increase in-coupling efficiency, along with a two-dimensional output diffractive optical element for exit pupil expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the size of each exit pupil is increased to reduce perception of transitions between exit pupils, then the spacing between exit pupils is reduced, but the size of the input grating and projector must be increased
Solution Approach 1:
The single input grating is segmented into multiple input gratings positioned at different locations on the waveguide. Each input grating couples light to create a portion of the overall exit pupil pattern. By segmenting the input coupling function across multiple smaller gratings, the patent achieves reduced exit pupil spacing without requiring any single grating to be excessively large.
Solution Approach 2:
The patent transitions from a one-dimensional arrangement (single input grating) to a two-dimensional arrangement (multiple input gratings positioned at different locations on the waveguide surface). This spatial distribution across multiple dimensions allows for denser exit pupil spacing while keeping individual grating sizes manageable.
2Adaptability or versatility
If multiple exit pupils are coupled towards the user at different points within the eyebox to provide augmented reality images regardless of gaze direction, then the eyebox coverage is improved, but the spacing between exit pupils creates perceptible transitions
Solution Approach 1:
Multiple exit pupils generated by different input gratings are merged into a combined pattern where they overlap. This merging creates a continuous or near-continuous distribution of exit pupils across the eyebox, maintaining gaze independence while eliminating perceptible transitions between discrete pupils.
Solution Approach 2:
The patent uses a two-dimensional array of input gratings positioned at different locations on the waveguide surface. This two-dimensional spatial distribution creates a correspondingly dense two-dimensional pattern of exit pupils, ensuring coverage across the entire eyebox while minimizing spacing to prevent perceptible transitions.
3Manufacturing precision
If the spacing between points on the waveguide where exit pupils are coupled out is reduced, then transitions between exit pupils are minimized, but the input grating size must be increased
Solution Approach 1:
The function of coupling exit pupils across the entire waveguide surface is segmented into multiple smaller input gratings, each responsible for a portion of the overall pattern. This segmentation allows for reduced spacing between coupling points while keeping individual grating areas small and manageable.
Solution Approach 2:
The patent distributes input gratings across two dimensions on the waveguide surface rather than using a single extended grating. This two-dimensional distribution achieves fine spacing between exit pupils through spatial multiplication of smaller grating elements rather than expanding a single grating's dimensions.
4Loss of energy
If high efficiency diffraction is achieved using blazed or slanted grating structures, then light coupling efficiency is improved, but the device complexity increases
Solution Approach 1:
The patent modifies the geometric parameters of the input gratings by introducing slanted or blazed structures with specific angles. These parameter changes optimize the diffraction efficiency of each grating element, maximizing light coupling into the waveguide while maintaining a relatively simple overall device architecture through the use of multiple identical or similar grating elements.
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 reduced spacing between exit pupils, increased in-coupling efficiency, and uniform brightness, enhancing the user's experience by minimizing transitions and power consumption, while maintaining efficient light delivery and projector power usage.
Implementation Method 1
Light from the projector is coupled into the waveguide by an input diffraction grating
Implementation Method 2
The projected light is totally internally reflected within the waveguide
Data Source
AI summary
An optical device for an augmented reality or virtual reality display. A first input diffractive optical element is arranged on a waveguide to receive light from a projector, couple a first portion of the light into the waveguide along a first path, and allow a second portion of the light to pass through. A second input diffractive optical element is arranged to receive the second portion of the light and couple a third portion of the received light along a second path. An output diffractive optical element receives light along the first and second paths and couples the received light out of the waveguide towards a viewer at a first pattern of positions for light along the first path and at a second pattern of positions for light along the second path, providing a first and second plurality of exit pupils corresponding to the first and second pattern of positions.