Eye Tracking Illuminator Using P-Polarized Light at Brewster's Angle

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Solution Overview

Problem

Existing eye tracking systems in Head Mounted Devices (HMDs) face challenges in accurately determining eye direction and gaze due to unwanted reflections from optic arrangements, such as glasses, which can obscure pupil identification and reduce the reliability of gaze estimation.

Innovation Solution

The implementation of an eye tracking system with an illuminator arrangement that emits p-polarized light at an angle corresponding to Brewster's angle to minimize reflections from optic arrangements in the light beam path, utilizing p-polarized light sources and polarizers to reduce unwanted reflections.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional illuminators are used to illuminate the user's eyes for eye tracking, then the pupil and corneal reflections can be identified, but unwanted reflections from optic arrangements (such as glasses) create false glints that reduce the accuracy of eye tracking

Engineering Contradiction:

Improveaccuracy of pupil and corneal reflection identificationVSAvoidunwanted reflections from optic arrangement

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The patent applies parameter changes by modifying the polarization state of the illuminator light from unpolarized to p-polarized. This parameter change in the light properties causes reflections from optic arrangements to be minimized when light strikes at Brewster's angle, thereby reducing false glints while maintaining the ability to identify the pupil and corneal reflections for accurate eye tracking

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent converts the harmful effect of reflections from optic arrangements into a beneficial outcome by utilizing Brewster's angle phenomenon. By orienting the illuminator at Brewster's angle relative to the optic arrangement surface and using p-polarized light, the reflections that would normally create false glints are transformed into minimal or eliminated reflections, thereby improving eye tracking accuracy

Inventive Principle:

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

2Object-affected harmful factors

If the illuminator is oriented to minimize reflections from the optic arrangement, then false glints are reduced, but the intensity of light reaching the eye and being reflected back to the sensor may be reduced

Engineering Contradiction:

Improvefalse glints from optic arrangementVSAvoidintensity of light reflected from eye

Core Design Contradiction:

Object-affected harmful factorsVSIllumination intensity

Solution Approach 1:

The patent uses parameter changes by switching from unpolarized to p-polarized light and adjusting the illuminator orientation to Brewster's angle. This dual parameter change simultaneously achieves two objectives: minimizing false glints from optic arrangements while maintaining sufficient light intensity for eye tracking, because p-polarized light at Brewster's angle penetrates the optic arrangement with minimal reflection loss

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 approach effectively reduces unwanted reflections, allowing for more accurate pupil and corneal reflection identification, thereby enhancing the reliability of eye direction and gaze estimation in HMDs like VR and AR devices.

Implementation Method 1

The illuminator arrangement is configured to emit p-polarized light

Methodology Applied

Scientific Effectp-polarized light: Polarisation

Implementation Method 2

the illuminator arrangement is configured to emit p-polarized light to be incident on a surface of the optic arrangement at an angle corresponding to, or substantially corresponding to, Brewster's angle

Methodology Applied

Scientific EffectBrewster's angle: Brewster's Angle

Implementation Method 3

emit p-polarized light to be incident on a surface of the optic arrangement at an angle corresponding to, or substantially corresponding to, Brewster's angle. By emitting p-polarized light to be incident on the surface of the optic arrangement at this angle it is possible to minimize or at least reduce (unwanted) reflections from an optic arrangement

Methodology Applied

Scientific EffectReflection: Reflection

Data Source

PatentUS11966047B2Eye tracking system for reducing unwanted reflections from an optic arrangement

Publication Date: 2024.04.23 TOBII TECH AB

AI summary

The present disclosure generally relates to the field of eye tracking systems. An eye tracking system is provided. The eye tracking system comprises an illuminator arrangement, including at least one light source, configured to illuminate an eye of a user. The eye tracking system is configured to enable a reduction of reflections from an optic arrangement (e.g., a pair of glasses) that is located in a light beam path between the illuminator arrangement and the eye when the eye tracking system is in use. The illuminator arrangement is configured to emit p-polarized light to be incident on a surface of the optic arrangement at an angle corresponding to, or substantially corresponding to, Brewster's angle.