Tapered Anti-reflection Coating for Waveguide Combiner Image Sharpness

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Solution Overview

Problem

Waveguide combiners with high-refractive index substrates or coatings suffer from low transmission and unwanted reflections due to the reflection of incoming light, degrading the modulation transfer function and virtual image sharpness in augmented reality applications.

Innovation Solution

A waveguide combiner design featuring a coating with a tapered portion over the waveguide layer, which reduces phase tears and reflections by minimizing the boundary discontinuity between the grating and waveguide regions, using a refractive index mismatch between the coating and grating materials to enhance light propagation and reduce aberrations.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If high-refractive index substrates or coatings are used in waveguide combiners, then light guidance and grating efficiency are improved, but unwanted reflections and low transmission occur due to refractive index mismatch at boundaries

Engineering Contradiction:

Improvelight guidance efficiencyVSAvoidunwanted reflections

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent applies a tapered coating with a gradual curvature transition at the boundary between the grating region and waveguide region. This curved/tapered structure replaces the sharp angular boundary, creating a gradual refractive index transition that reduces phase tears and unwanted reflections while maintaining light guidance efficiency.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent changes the physical parameter of the coating thickness gradually across the boundary region. The coating transitions from a certain thickness at the grating edge to zero thickness at the waveguide edge, creating a continuous refractive index transition that eliminates abrupt boundary effects and reduces reflections.

Inventive Principle:

Principle #35Parameter changes

2Loss of energy

If a coating is applied over the waveguide layer, then transmission is improved, but phase tears and boundary discontinuity occur at the interface between grating and waveguide regions

Engineering Contradiction:

Improvelight transmissionVSAvoidboundary continuity

Core Design Contradiction:

Loss of energyVSStability of the object's composition

Solution Approach 1:

The tapered coating introduces a curved transition profile at the boundary rather than a sharp discontinuity. This curvature creates a smooth phase transition for light waves passing through the boundary, eliminating phase tears while maintaining the protective and transmissive functions of the coating.

Inventive Principle:

Principle #14Spheroidality (Curvature)

3Reliability

If exterior grating structures are placed at outer edges of the grating, then grating functionality is maintained, but boundary discontinuity and image sharpness degradation occur

Engineering Contradiction:

Improvegrating functionVSAvoidimage sharpness

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The tapered coating smooths the abrupt transition at the exterior grating structures by creating a gradual thickness reduction. This curved transition prevents sharp boundary effects that would otherwise degrade image sharpness, while the grating structures maintain their diffraction functionality.

Inventive Principle:

Principle #14Spheroidality (Curvature)

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

The tapered coating architecture improves the modulation transfer function and virtual image sharpness, increasing transmission and reducing unwanted reflections, thereby enhancing the user experience in augmented reality by minimizing distractions from ambient light.

Implementation Method 1

using a refractive index mismatch between the coating and grating materials to enhance light propagation and reduce aberrations

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 2

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS20250012960A1Tapered Anti-reflection coating that preserves image sharpness in waveguide combiners

Publication Date: 2025.01.09 APPLIED MATERIALS INC

AI summary

Embodiments of the disclosure provided herein include waveguide combiners. More specifically, embodiments described herein provide for waveguide combiners with a waveguide layer and a coating having a tapered portion disposed thereover. The waveguide includes one or more gratings, the one or more gratings including a plurality of grating structures disposed over a waveguide substrate, wherein the grating structures include a waveguide material, and the plurality of grating structures include exterior grating structures at outer edges of the one or more gratings. A waveguide layer is disposed over the waveguide substrate between the exterior grating structures and an edge of the waveguide substrate, the waveguide layer including the waveguide material, and a coating disposed over the waveguide layer, the coating having a tapered portion that is tapered from at least one of the exterior grating structures to a planar portion of the coating.