Eye Tracking Waveguide Polarization Noise Reduction
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Solution Overview
Problem
There is a need for a compact and lightweight eye-tracking system in head-mounted display devices that can effectively steer and demagnify light for accurate pupil detection without noise interference, while being compatible with augmented reality operations.
Innovation Solution
The use of waveguides and polarization-dependent optical elements, such as polarization volume holographic elements and geometric phase lenses, to steer and demagnify light within the waveguide, allowing for the placement of optical elements away from the user's view and reducing noise by filtering specific polarizations, thereby enabling a smaller and more efficient detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional eye-tracking optical elements are placed close to the user's view (on-axis position), then accurate pupil detection can be achieved, but the device becomes bulky and heavy
Solution Approach 1:
The patent moves the eye-tracking optical elements from the on-axis position (close to user's view) to an off-axis position using a waveguide structure. This spatial reconfiguration in another dimension allows the optical elements to be placed away from the user's direct line of sight while maintaining optical functionality, thereby reducing the overall device size and weight without compromising pupil detection accuracy
Solution Approach 2:
The waveguide acts as an intermediary optical component that relays light from the off-axis optical elements to the detector. This intermediary structure enables the separation of the optical elements from the user's view while maintaining the optical path, allowing compact integration of eye-tracking functionality without adding bulk to the front of the device
2Measurement precision
If larger detectors are used to capture sufficient light for accurate eye tracking, then detection precision improves, but the device size and weight increase
Solution Approach 1:
The waveguide serves as an optical intermediary that efficiently relays and concentrates light from the off-axis optical elements to the detector. This intermediary optical path maximizes light delivery to a compact detector, enabling accurate eye tracking with a smaller detector area, thereby reducing device size while maintaining detection precision
3Use of energy by moving object
If all polarizations of light are allowed to reach the detector, then maximum light intensity is received, but noise increases and performance deteriorates
Solution Approach 1:
The patent introduces a polarization-dependent optical element that creates local quality differentiation in the optical path. This element selectively processes different polarizations: it directs the desired polarization (e.g., p-polarized light from the eye) toward the detector while directing unwanted polarizations (e.g., s-polarized ambient light) away from the optical path. This local quality control at a specific point in the optical system enables noise rejection while maintaining sufficient light intensity for accurate detection
Solution Approach 2:
The polarization-dependent optical element converts potentially harmful ambient light (unwanted polarization) into a beneficial filtering mechanism. By exploiting the polarization difference between the desired eye-reflected light and unwanted ambient light, the system uses the harmful factor (ambient light interference) as a basis for selective rejection, thereby improving signal-to-noise ratio and eye-tracking performance
4Adaptability or versatility
If the eye-tracking system is integrated into augmented reality operations, then versatility improves, but optical complexity increases
Solution Approach 1:
The waveguide structure serves multiple functions simultaneously: it acts as both the augmented reality display waveguide (guiding virtual image light to the user's eye) and the eye-tracking optical relay (guiding reflected eye light to the detector). This multi-functionality integrates eye-tracking capability into the existing augmented reality optical path without adding separate, complex optical subsystems, thereby maintaining versatility while controlling optical complexity
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 allows for a compact and efficient eye-tracking system that improves performance by reducing noise and enabling the use of smaller detectors, while maintaining compatibility with augmented reality operations by transmitting visible light.
Implementation Method 1
direct a first ray, having a first circular polarization and impinging on the first optical element at a first incidence angle, in a first direction so that the first ray propagates through the optical waveguide via total internal reflection toward a second optical element
Implementation Method 2
a first optical element configured to: i) direct a first ray, having a first circular polarization and impinging on the first optical element at a first incidence angle, in a first direction so that the first ray propagates through the optical waveguide via total internal reflection toward a second optical element, and ii) direct a second ray, having a second circular polarization that is distinct from the first circular polarization and impinging on the first optical element at the first incidence angle, in a second direction that is distinct from the first direction so that the second ray propagates away from the second optical element
Data Source
AI summary
An optical system includes an optical waveguide, and a first optical element configured to direct a first ray, having a first circular polarization and impinging on the first optical element at a first incidence angle, in a first direction so that the first ray propagates through the optical waveguide via total internal reflection toward a second optical element. The first optical element is configured to also direct a second ray, having a second circular polarization that is distinct from the first circular polarization and impinging on the first optical element at the first incidence angle, in a second direction that is distinct from the first direction so that the second ray propagates away from the second optical element. The second optical element is configured to direct the first ray propagating through the optical waveguide toward a detector.