Polychromatic Object Imager for HMD Eye Tracking
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Solution Overview
Problem
Current head-mounted displays (HMDs) and near-eye displays are bulky and uncomfortable due to their large size and weight, and they lack the necessary fidelity and reliability in 3D imaging and eye tracking, particularly in reducing the size and weight of eye tracker devices and overall optics blocks.
Innovation Solution
A 3D object imager using a fan of infrared light beams at different wavelengths for illumination, combined with an array of detector pixels having sub-arrays with varying spectral responsivities, and an image forming assembly to determine object distance by comparing signals from these sub-arrays, along with a wavelength-selective reflector to redirect light and enhance imaging capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional eye tracking and 3D imaging systems are used in HMDs, then imaging fidelity and reliability are maintained, but device size and weight increase making it cumbersome and uncomfortable
Solution Approach 1:
The detector array is divided into multiple sub-arrays, each with different spectral sensitivities (e.g., short-wavelength, mid-wavelength, long-wavelength infrared detectors). This segmentation allows the system to capture spectral information across different wavelength ranges using smaller, specialized detector elements rather than requiring a single large detector, thereby reducing overall device weight while maintaining imaging fidelity.
Solution Approach 2:
The system uses a polychromatic light source that emits multiple wavelengths simultaneously, and the detector sub-arrays are tuned to different spectral parameters. By changing the operational parameter from monochromatic to polychromatic illumination with spectrally-resolved detection, the system achieves accurate 3D imaging with reduced hardware size, as each sub-array can be optimized for its specific wavelength range.
2Reliability
If traditional eye tracking systems are used, then reliable gaze direction determination is achieved, but the optics block size and weight increase
Solution Approach 1:
The eye tracking system uses multiple detector sub-arrays with different spectral sensitivities to simultaneously capture reflected infrared light from the eye. This segmentation allows the system to determine gaze direction and vergence through spectral analysis of the reflected light, eliminating the need for bulky traditional optical tracking components and reducing optics block volume while maintaining tracking reliability.
Solution Approach 2:
The polychromatic infrared light source and segmented detector array serve multiple functions: they enable both 3D depth mapping of the eye and determination of gaze direction and vergence. This multi-functionality consolidates what would traditionally require separate optical systems into a single compact unit, reducing optics block volume while maintaining reliable eye tracking.
3Measurement precision
If spectral information is resolved using multiple detectors, then depth accuracy is improved, but device complexity increases
Solution Approach 1:
The detector array is segmented into sub-arrays with different spectral sensitivities, where each sub-array is optimized for detecting specific wavelength ranges. This segmentation simplifies the design of individual detector elements while achieving comprehensive spectral coverage, as each sub-array can be independently optimized rather than requiring a single complex broadband detector, thereby improving depth measurement accuracy without proportionally increasing device 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 solution enables more accurate and reliable 3D imaging and eye tracking, reducing the size and weight of the display device while maintaining high fidelity, allowing for improved user experience in virtual and augmented reality applications.
Implementation Method 1
an infrared light source comprising a polychromatic light source for emitting polychromatic light and a dispersive element for receiving the polychromatic light from the polychromatic light source and angularly disperse the polychromatic light into a fan of light beams
Implementation Method 2
a wavelength-selective reflector for placing in front of the eye and the wavelength-selective reflector being configured to redirect light in the infrared wavelength range and to transmit towards the eye outside light in a visible wavelength range
Implementation Method 3
an array of detector pixels including first and second sub-arrays of detector pixels having first and second overlapping different wavelength dependencies of responsivity in the infrared wavelength range
Data Source
AI summary
A three-dimensional object imager uses infrared light at different wavelengths to triangulate depth information of the object from wavelength-dependent detection of the infrared image of the object. The depth information is obtained by determining wavelength of infrared light impinging on different pixels of the array. The wavelength may be determined by breaking each pixel into a plurality of sub-pixels, each sub-pixel having its own spectral selectivity to light at different infrared wavelength. For eye imaging or eye tracking applications, this enables the preservation of an unobstructed field of view of the eye while obtaining real-time, dynamic information about eye position and orientation in an non-intrusive, inconspicuous manner.