Eye-Tracking Optical System Stray Light Suppression
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Solution Overview
Problem
Existing optical systems for eye-tracking face challenges in capturing images with sufficient contrast due to stray light propagation, which increases background noise and reduces image quality.
Innovation Solution
The optical system incorporates anti-reflection (AR) coatings and ghost suppression components strategically positioned to enhance the transmission of visible and infrared light, even at wide angles of incidence, thereby suppressing stray light and improving image contrast.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If anti-reflection coatings are applied to reduce stray light, then image contrast improves, but manufacturing complexity increases
Solution Approach 1:
The patent applies multi-layer anti-reflection coatings composed of different materials with varying refractive indices (e.g., silicon dioxide, titanium dioxide, magnesium fluoride) to achieve superior stray light suppression. These composite coating structures enable broader spectral coverage and higher transmission efficiency compared to single-layer coatings, directly improving image contrast while managing manufacturing complexity through standardized deposition processes.
Solution Approach 2:
The anti-reflection coatings are applied selectively to specific optical surfaces where stray light generation is most problematic, such as the cornea and lens interfaces. By targeting only critical surfaces rather than coating all optical elements uniformly, the system achieves effective stray light reduction while minimizing overall manufacturing complexity and material usage.
2Illumination intensity
If anti-reflection coatings are designed for wide angle of incidence, then light transmission improves, but coating complexity increases
Solution Approach 1:
The patent transitions from designing coatings optimized for normal incidence to engineering multi-layer AR coatings that maintain low reflectance across wide angles of incidence (up to 60 degrees or more). This is achieved by carefully selecting layer thicknesses and refractive indices to create interference patterns that suppress reflections at oblique angles, thereby improving light transmission from the eye across the full field of view while managing coating complexity through computational optimization.
3Illumination intensity
If infrared illumination intensity is increased to improve image quality, then stray light increases, but image contrast worsens
Solution Approach 1:
The patent acknowledges that increased infrared illumination intensity generates more stray light, but converts this harmful effect into a benefit by implementing specialized anti-reflection coatings that are optimized for infrared wavelengths. These coatings selectively suppress stray light reflections while maintaining high transmission of the desired infrared illumination, thereby allowing the system to use higher illumination intensities to improve signal strength without sacrificing image contrast.
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 effectively reduces stray light reflections, increases the intensity of the desired infrared imaging light, and boosts the contrast of eye-tracking images, leading to more efficient identification of eye features for accurate eye-tracking analysis.
Implementation Method 1
anti-reflection (AR) coatings and ghost suppression components strategically positioned to enhance the transmission of visible and infrared light
Implementation Method 2
The illumination source emits infrared (IR) light that illuminates the coated surface and reflects towards the user's eye
Data Source
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AI summary
The disclosure includes optical systems and near-eye optical elements (110) configured to suppress stray infrared light. Infrared illuminators (126, 237) illuminate an eyebox area with narrow-band infrared illumination light for eye-tracking. A combiner layer (240) receives reflected infrared light reflected of an eye of the user and directs the reflected infrared light to a camera (108) configured to capture eye-tracking images of an eye of a user. An anti-reflection (AR) coating (723) may be disposed on a base curvature to reduce Fresnel reflections that generate stray light. A ghost suppression component (533) may be paired with the infrared illuminators to reduce stray light becoming incident on the camera (108).