HMD Optical Element Stray Infrared Light Reduction

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Solution Overview

Problem

Conventional head-mounted displays (HMDs) with eye-tracking systems face interference from optics, leading to reduced accuracy and increased power consumption due to stray infrared light caused by surface imperfections and total internal reflection within the optically transparent layers.

Innovation Solution

An optical element for HMDs featuring an illumination layer emitting infrared light, an optical combiner to direct reflected light to a camera, an optically transparent layer to pass infrared light, and a confinement layer with a lower refractive index to induce waveguiding, combined with an infrared extractor on the side-edge to absorb or frustrate confined infrared light, reducing stray light occurrences.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If an optically transparent layer is used to pass infrared light, then infrared transmission is improved, but stray infrared light is generated due to surface imperfections and total internal reflection

Engineering Contradiction:

Improveinfrared light transmissionVSAvoidstray infrared light

Core Design Contradiction:

Illumination intensityVSObject-generated harmful factors

Solution Approach 1:

The patent extracts and removes stray infrared light from the optical system by introducing an infrared-absorbing layer that selectively absorbs the harmful stray light while allowing the main infrared illumination path to pass through the optically transparent layer unaffected

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The infrared-absorbing layer acts as an intermediary element between the optically transparent layer and the eye-tracking camera, mediating the infrared light paths by absorbing stray reflections while permitting the primary illumination to reach the eye and reflect back for detection

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If conventional optics are used in HMD, then the structure is simple, but eye-tracking accuracy is reduced due to interference from stray infrared light

Engineering Contradiction:

Improveoptical structureVSAvoideye-tracking accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent applies local quality by introducing the infrared-absorbing layer only in specific regions where stray light reflections occur, rather than modifying the entire optical system. This targeted approach maintains overall structural simplicity while locally eliminating the harmful effects that degrade eye-tracking precision

Inventive Principle:

Principle #3Local quality

3Adaptability or versatility

If illumination sources are added for eye-tracking, then eye-tracking capability is enabled, but power consumption increases due to stray light interference

Engineering Contradiction:

Improveeye-tracking capabilityVSAvoidpower consumption

Core Design Contradiction:

Adaptability or versatilityVSUse of energy by moving object

Solution Approach 1:

The patent converts the harmful stray infrared light into a beneficial configuration by using the infrared-absorbing layer to selectively remove only the problematic reflected paths while preserving the primary illumination-reflection-detection cycle, thereby enabling eye-tracking functionality with optimized power consumption rather than requiring excessive illumination power to overcome the stray light interference

Inventive Principle:

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

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

Enhances the signal-to-noise ratio of the eye-tracking system by minimizing stray infrared light, improving accuracy and reducing power requirements, while maintaining transparency for augmented or virtual reality applications.

Implementation Method 1

a confinement layer disposed on a surface of the optically transparent layer to induce waveguiding of confined infrared light propagating within the optically transparent layer

Methodology Applied

Scientific EffectWaveguiding: Waveguide (optics)

Implementation Method 2

total internal reflection within the optically transparent layers

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Implementation Method 3

an infrared extractor disposed on a side-edge of the optically transparent layer to absorb or frustrate the confined infrared light

Methodology Applied

Scientific EffectAbsorption: Absorption (EM radiation)

Data Source

PatentEP3980837B1Optical element for reducing stray infrared light

Publication Date: 2023.03.29 META PLATFORMS TECHNOLOGIES LLC

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Figure 3~4B

AI summary

An optical element for a head mounted display (HMD) includes an illumination layer, an optical combiner, and an optically transparent layer. The illumination layer is configured to emit infrared light towards an eyeward side of the optical element. The optical combiner is configured to receive reflected infrared light that is reflected by an eye of a user and to direct the reflected infrared light towards an infrared camera. The optically transparent layer is disposed between the illumination layer and the eyeward side of the optical element. The optical element may further include one or both of a confinement layer and an infrared extractor. The confinement layer is disposed on a surface of the optically transparent layer to induce waveguiding of confined infrared light propagating within the optically transparent layer. The infrared extractor is disposed on a side-edge of the optically transparent layer to absorb or frustrate the confined infrared light.