RGB Diffractive Waveguide Stacks With Matched Refractive Index

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Solution Overview

Problem

Existing augmented reality/mixed reality devices face challenges in optical performance due to the use of a single material for all layers, which affects modulation transfer function, efficiency, field of view, and uniformity, primarily because of variations in refractive index and yellowness index across different wavelengths.

Innovation Solution

Customized diffractive waveguide stacks are designed using different materials and optical properties tailored for each color layer (RGB) to optimize refractive index and yellowness index, employing combinations of glass and polymer waveguides to achieve optimal performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If a single material is used for all waveguide layers, then manufacturing complexity is reduced, but optical performance deteriorates due to wavelength-dependent refractive index variations

Engineering Contradiction:

Improvematerial selection simplicityVSAvoidoptical performance consistency

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent applies local quality by selecting different materials with optimized optical properties for each wavelength range (red, green, blue layers). Each layer uses a material specifically tailored to its operational wavelength, ensuring optimal refractive index and minimal absorption for that specific color range, thereby resolving the contradiction between manufacturing simplicity and optical performance consistency.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent employs composite materials by combining multiple different materials in a single waveguide stack. Each material is selected for its specific optical characteristics at different wavelengths, creating a multi-material composite structure that achieves superior overall optical performance compared to using a single material for all layers.

Inventive Principle:

Principle #40Composite materials

2Loss of energy

If high refractive index materials are used, then light guiding efficiency is improved, but yellowness index increases causing light absorption

Engineering Contradiction:

Improvelight guiding efficiencyVSAvoidlight absorption due to yellowness

Core Design Contradiction:

Loss of energyVSObject-generated harmful factors

Solution Approach 1:

The patent applies parameter changes by carefully selecting materials with specific refractive index values optimized for different wavelength ranges. For each color layer, a material is chosen that provides the necessary refractive index for efficient light guiding while maintaining acceptable yellowness index levels, thus balancing light guiding efficiency with minimal light absorption.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent addresses this contradiction by applying local quality through wavelength-specific material selection. Each layer (red, green, blue) uses a material whose refractive index and yellowness characteristics are optimized for its specific operational wavelength, ensuring high light guiding efficiency without excessive light absorption at each particular wavelength.

Inventive Principle:

Principle #3Local quality

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 customized waveguide stacks enhance optical performance by improving modulation transfer function, efficiency, and field of view, while minimizing light absorption, thereby enhancing the overall efficiency of the eyepiece.

Implementation Method 1

diffractive waveguide for guiding light

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 2

first refractive index differs from the second refractive index

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

diffractive waveguide stack comprising a first diffractive waveguide and a second diffractive waveguide

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentEP3987330B1Customized polymer/glass diffractive waveguide stacks for augmented reality/mixed reality applications

Publication Date: 2026.01.21 MAGIC LEAP INC

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AI summary

A diffractive waveguide stack includes first, second, and third diffractive waveguides for guiding light in first, second, and third visible wavelength ranges, respectively. The first diffractive waveguide includes a first material having first refractive index at a selected wavelength and a first target refractive index at a midpoint of the first visible wavelength range. The second diffractive waveguide includes a second material having a second refractive index at the selected wavelength and a second target refractive index at a midpoint of the second visible wavelength range. The third diffractive waveguide includes a third material having a third refractive index at the selected wavelength and a third target refractive index at a midpoint of the third visible wavelength range. A difference between any two of the first target refractive index, the second target refractive index, and the third target refractive index is less than 0.005 at the selected wavelength.