Intermediate DOE Rotates Polarization to Uncouple Grating Loops

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Solution Overview

Problem

Optical interference, known as 'banding,' occurs in diffractive optical element (DOE) systems due to closed-loop coupling, which is exacerbated by the use of polymeric materials and manufacturing defects, leading to reduced optical resolution, uniformity, and color fidelity in display systems.

Innovation Solution

The implementation of an intermediate DOE with grating features that rotate the polarization state of light perturbations orthogonally relative to the main beam, uncoupling closed loops and reducing interference, while varying the direction of depth modulation in the grating structure to control interference as constructive or destructive.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Weight of moving object

If polymeric materials are used in volume production of the DOE to minimize system weight, then weight is reduced, but optical interference (banding) is exacerbated due to less optimal optical properties

Engineering Contradiction:

Improvesystem weightVSAvoidoptical interference

Core Design Contradiction:

Weight of moving objectVSObject-affected harmful factors

Solution Approach 1:

The patent converts the harmful effect of closed-loop coupling into a beneficial outcome by introducing an intermediate DOE that rotates the polarization state of perturbed light. This polarization rotation transforms the interfering light paths into non-interfering paths, converting the harmful banding effect into improved optical performance while maintaining the use of lightweight polymeric materials.

Inventive Principle:

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

2Manufacturing precision

If small nanometer-scale variations in fabricated DOEs are present, then manufacturing tolerance is improved, but optical interference is exacerbated

Engineering Contradiction:

Improvemanufacturing toleranceVSAvoidoptical interference

Core Design Contradiction:

Manufacturing precisionVSObject-affected harmful factors

Solution Approach 1:

The patent introduces an intermediate DOE as a mediator between the in-coupling and out-coupling DOEs. This intermediate element rotates the polarization state of light perturbations, acting as a buffer that decouples the manufacturing variations from the final optical interference. The polarization rotation ensures that nanometer-scale variations in grating depth or width do not propagate as harmful interference patterns.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If closed-loop coupling is present in the intermediate DOE, then light paths are coupled, but optical interference is generated reducing resolution and uniformity

Engineering Contradiction:

Improvelight path couplingVSAvoidoptical resolution

Core Design Contradiction:

Adaptability or versatilityVSMeasurement precision

Solution Approach 1:

The patent changes the polarization state parameter of the light passing through the intermediate DOE. By rotating the polarization state of perturbed light to be orthogonal to the main beam, the system transforms coupled light paths into independent paths. This parameter change eliminates the interference that would otherwise reduce optical resolution and uniformity.

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 configuration enhances optical resolution, uniformity, and color fidelity, increasing the tolerance to manufacturing errors and reducing banding, thereby improving the overall performance of the optical display system.

Implementation Method 1

The intermediate DOE includes grating features that are configured to rotate a state of polarization of light perturbations in the intermediate DOE that would otherwise generate optical interference through a closed-loop coupling phenomenon

Methodology Applied

Scientific EffectPolarization rotation: Polarisation

Implementation Method 2

an intermediate DOE provides exit pupil expansion in a first direction

Methodology Applied

Scientific EffectDiffraction: Diffraction

Data Source

PatentUS9946072B2Diffractive optical element with uncoupled grating structures

Publication Date: 2018.04.17 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

In an optical display system having a waveguide and 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 intermediate DOE includes grating features that are configured to rotate a state of polarization of light perturbations in the intermediate DOE that would otherwise generate optical interference through a closed-loop coupling phenomenon. The polarization state of a perturbed beam is rotated in the intermediate DOE to be orthogonal relative to the polarization state of the main beam used for image display to thereby uncouple the closed loops and make the perturbed beam non-interfering with the imaging beam.