Polarization Filters for Stray Light Reduction in Eye Tracking
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Solution Overview
Problem
Stray light in near-eye devices with eye/face tracking capabilities poses significant challenges, causing glare, unwanted reflections, and optical artifacts that degrade image quality and complicate accurate gaze direction determination.
Innovation Solution
The use of infrared (IR) filters, neutral density filters, and polarization-sensitive behind-the-lens cameras in conjunction with polarized light sources to mitigate stray light in eye/face tracking systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If eye/face tracking systems are implemented in near-eye devices, then user interaction capabilities are enhanced, but stray light causes glare and optical artifacts that degrade image quality
Solution Approach 1:
A polarization filter is introduced as an intermediary component in the optical path between the eye/face tracking camera and the external environment. This filter selectively transmits polarized light from the eye while blocking stray light reflections, thereby maintaining tracking functionality while eliminating harmful optical artifacts
Solution Approach 2:
The system utilizes polarization state changes of light as it reflects from the eye versus stray light sources. By detecting and filtering based on these polarization differences, the system distinguishes between useful tracking signals and harmful stray light, resolving the contradiction between enhanced interaction and reduced interference
2Object-affected harmful factors
If polarization filters are added to reduce stray light, then image quality improves, but device complexity increases
Solution Approach 1:
The polarization filter serves multiple functions simultaneously: it acts as a stray light rejection mechanism, a polarization state analyzer for eye reflection identification, and an optical path element that maintains system compactness. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity while achieving effective stray light reduction
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 enhances the accuracy and efficiency of eye/face tracking in near-eye devices by reducing stray light, thereby improving image quality and maintaining user interaction reliability.
Implementation Method 1
a polarization-sensitive behind-the-lens camera in conjunction with polarized light sources to mitigate stray light
Implementation Method 2
The use of infrared (IR) filters, neutral density filters, and polarization-sensitive behind-the-lens cameras
Implementation Method 3
The use of infrared (IR) filters, neutral density filters, and polarization-sensitive behind-the-lens cameras
Data Source
AI summary
Systems, methods, and apparatuses to reduce stray light in eye/face tracking systems of near-eye devices are presented. In one aspect, an IR filter may minimize stray light when suitably disposed in-frame, in-lens (as, e.g., a localized in-lens IR filter), and/or coupled to a waveguide. In another aspect, configurations of linearly-polarized IR light sources and polarization-sensitive IR light sensors may be effective for stray light reduction in eye/face tracking systems. In yet another aspect, polarization-sensitive pre-processing methods and/or stray light reduction methods may be beneficial for eye/face tracking systems in near-eye devices. In an example, a near-eye AR/VR device includes a display screen to display AR/VR content through an optical stack, which includes a light source to project linearly-polarized IR light onto the user's eye, and a polarization-sensitive IR light sensor filters received IR light using polarization to separate out stray light from the linearly-polarized eye/face tracking light.