Multi-Layer Waveguide Coating to Minimize Phase Shifts

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Solution Overview

Problem

Refractive head mount displays face challenges in maintaining optical resolution due to phase shifts caused by light propagating through different materials, leading to beam quality deterioration and reduced image quality.

Innovation Solution

Implement a multi-layer coating structure within waveguides to control and minimize phase shifts by using materials with refractive indices close to the ambient medium, and employing additional layers to mitigate phase differences, ensuring high transmittance and low reflectivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If light propagates through different materials in the waveguide, then the light is guided and reflected to form images, but phase shifts accumulate leading to beam quality deterioration and reduced optical resolution

Engineering Contradiction:

Improveimage qualityVSAvoidoptical resolution

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent converts the harmful phase shifts accumulated through the multi-layer coating into a beneficial effect by carefully designing the layer thicknesses and refractive indices to induce phase shifts that compensate for each other. The first layer induces a phase shift, while the second layer is specifically designed to induce an opposing phase shift, thereby canceling out the net phase error and improving beam quality and optical resolution.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Solution Approach 2:

The patent changes the physical parameters of the coating layers, specifically the thickness and refractive index of each layer, to control the phase shift characteristics. By adjusting these parameters, the design achieves minimal net phase shift while maintaining the desired reflective properties for waveguide operation.

Inventive Principle:

Principle #35Parameter changes

2Reliability

If multi-layer coating structures are used to achieve specific reflection and polarization characteristics, then the waveguide functionality is improved, but phase shifts are induced that affect beam quality

Engineering Contradiction:

Improvewaveguide functionalityVSAvoidphase shifts

Core Design Contradiction:

ReliabilityVSObject-generated harmful factors

Solution Approach 1:

The patent segments the coating structure into multiple distinct layers, each with specific thickness and refractive index properties. The first layer provides initial reflective characteristics, while the second layer is specifically designed to counteract the phase shifts introduced by the first layer, thereby separating the function of achieving reflection from the function of controlling phase.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent applies local quality by giving different layers distinct optical properties tailored to their specific functions. The first layer is optimized for reflection, while the second layer is optimized for phase compensation, with each layer's thickness and refractive index locally adjusted to achieve its specific role in the overall system performance.

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 solution effectively reduces phase shifts to enhance image quality, maintaining high optical resolution and minimizing diffraction artifacts in head mount displays.

Implementation Method 1

As light propagates in a medium or in free space it accumulates phase. Light propagating a certain distance through different materials would accumulate different phases.

Methodology Applied

Scientific EffectPhase shift:

Implementation Method 2

using materials with refractive indices close to the ambient medium

Methodology Applied

Scientific EffectRefraction: Refraction

Implementation Method 3

Refractive head mount displays are based on partially reflective surfaces that are embedded inside a waveguide

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS12449664B2Multi-layer coating structure to minimize phase shifts, method of manufacture, waveguide and head mount display

Publication Date: 2025.10.21 LUMUS LTD

AI summary

An apparatus includes a waveguide and one or more partially reflective surfaces embedded inside the waveguide, wherein each of the one or more partially reflective surfaces includes a multi-layer coating structure, wherein a first portion of the multi-layer coating structure induces an overall phase shift of light propagating through the first portion of the multi-layer coating structure and wherein a second portion of the multi-layer coating structure is selected to decrease the overall phase shift.