Birefringent Grating Waveguide for Uniform Illuminance

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Solution Overview

Problem

Waveguide display systems face a challenge in maintaining uniform illuminance over the expanded exit pupil, as the luminance of the exit light decreases along the exit pupil-expanding direction due to repeated diffraction by the out-coupler.

Innovation Solution

The implementation of a waveguide display assembly with an out-coupling element featuring a grating with a diffraction efficiency gradient along a predetermined direction, specifically oriented to compensate for the luminance decrease along the exit pupil-expanding direction, ensuring uniform illuminance across the expanded exit pupil.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Area of stationary object

If the waveguide expands the exit pupil along the direction of propagating light, then the field of view and eye-box size are increased, but the luminance of the exit light decreases along the exit pupil-expanding direction

Engineering Contradiction:

Improveexit pupil areaVSAvoidluminance of exit light

Core Design Contradiction:

Area of stationary objectVSIllumination intensity

Solution Approach 1:

The out-coupling grating is designed with spatially varying diffraction efficiency, where the diffraction efficiency increases along the exit pupil-expanding direction. This local variation in grating properties compensates for the luminance decrease, ensuring uniform illuminance across the expanded exit pupil while maintaining the enlarged eye-box and field of view

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The diffraction efficiency parameter of the out-coupling grating is modified to create a gradient distribution. By changing the grating period, depth, or other parameters across the waveguide surface, the diffraction efficiency is increased in regions where luminance has decreased, thereby compensating for the brightness loss and achieving uniform illuminance over the expanded exit pupil

Inventive Principle:

Principle #35Parameter changes

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 effectively compensates for the luminance decrease along the exit pupil-expanding direction, achieving uniform illuminance over the expanded exit pupil, thereby maintaining consistent image brightness throughout the display area.

Implementation Method 1

The out-coupling element includes a grating having a diffraction efficiency gradient along a predetermined direction at a plane of the grating

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 2

a waveguide optically coupled with the display and configured to guide the image light to an exit pupil of the optical device

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS12204136B2Optical combiner with uniform illuminance throughput

Publication Date: 2025.01.21 META PLATFORMS TECHNOLOGIES LLC

AI summary

A device includes a display configured to generate an image light. The device also includes a waveguide optically coupled with the display and configured to guide the image light to an exit pupil of the device. The waveguide includes a grating including a birefringent material, and a birefringence of the grating is configured to increase along a pupil-expanding direction of the device.