Polarization Rotating Grating In-Coupling DOE for Waveguide Banding

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Solution Overview

Problem

Diffractive optical elements (DOEs) in optical display systems face issues with banding due to polymeric materials' suboptimal optical properties, manufacturing variations, and back-coupling, leading to reduced display uniformity and efficiency.

Innovation Solution

Incorporating an in-coupling DOE with a polarization rotating grating that separates light into different polarization states, reducing back-coupling and enhancing manufacturing tolerance by using asymmetric grating profiles, which improves light coupling efficiency and reduces banding.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If polymeric materials are used to minimize system weight, then weight is reduced, but optical properties deteriorate leading to banding and reduced display uniformity

Engineering Contradiction:

Improvesystem weightVSAvoiddisplay uniformity

Core Design Contradiction:

Weight of moving objectVSReliability

Solution Approach 1:

The patent introduces a polarization rotating grating as an intermediary element within the in-coupling DOE. This grating rotates the polarization state of coupled light, serving as a mediator that transforms the optical properties of the light entering the waveguide. By doing so, it compensates for the suboptimal optical properties of polymeric materials, reducing banding effects and improving display uniformity while maintaining the weight advantages of using polymeric materials.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of manufacture

If manufacturing variations in submicron range occur, then manufacturing tolerance is exceeded, but optical performance deteriorates due to interference patterns

Engineering Contradiction:

Improvemanufacturing toleranceVSAvoidoptical performance

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent employs parameter changes by modifying the polarization state of light through the polarization rotating grating. This parameter transformation (from linear to circular or elliptical polarization) fundamentally alters how light interacts with manufacturing variations in the waveguide. The changed polarization parameter makes the system less sensitive to submicron-scale manufacturing variations, thereby maintaining optical performance despite relaxed manufacturing tolerances.

Inventive Principle:

Principle #35Parameter changes

3Productivity

If in-coupling efficiency is increased, then light coupling improves, but back-coupling increases due to reciprocity of light propagation

Engineering Contradiction:

Improvein-coupling efficiencyVSAvoidback-coupling

Core Design Contradiction:

ProductivityVSLoss of energy

Solution Approach 1:

The patent applies the inversion principle by using the polarization rotating grating to fundamentally reverse or alter the polarization state of light propagating through the waveguide. This inversion of the polarization parameter creates an asymmetric optical path that breaks the reciprocity relationship. Light that couples in efficiently with one polarization state returns with a different polarization state, preventing it from efficiently coupling back out, thus reducing back-coupling losses.

Inventive Principle:

Principle #13The other way round (Inversion)

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 increases display uniformity, reduces banding, and enhances manufacturing tolerance, particularly when using polymeric materials, by rotating the polarization state of in-coupled light and combining it with non-rotated light, resulting in improved optical resolution and reduced back-coupling.

Implementation Method 1

a first portion includes a grating to rotate a polarization state of in-coupled light

Methodology Applied

Scientific EffectPolarization rotation: Polarisation

Implementation Method 2

Diffractive optical elements (DOEs) are optical elements with a periodic structure

Methodology Applied

Scientific EffectDiffraction: Diffraction

Implementation Method 3

The in-coupled light beams with different polarization states are combined in the waveguide after undergoing total internal reflection

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS10073278B2Diffractive optical element using polarization rotation grating for in-coupling

Publication Date: 2018.09.11 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

In an optical display system that includes a waveguide with multiple diffractive optical elements (DOEs), an in-coupling DOE couples light into the waveguide, an intermediate DOE provides exit pupil expansion in a first direction, and an out-coupling DOE provides exit pupil expansion in a second direction and couples light out of the waveguide. The in-coupling DOE is configured with two portions—a first portion includes a grating to rotate a polarization state of in-coupled light while a second portion couples light into the waveguide without modulation of the polarization state. The in-coupled light beams with different polarization states are combined in the waveguide after undergoing total internal reflection. However, as the difference in optical path lengths of the constituent light beams exceeds the coherence length, the combined light has random polarization (i.e., a degree of polarization equal to zero).