Eye Tracking Volume Grating with Spatially Varying K-Vectors
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Solution Overview
Problem
Conventional eye tracking systems face limitations in achieving high diffraction efficiency and reducing aberrations across the entire field of view, leading to poor image quality and limited angular bandwidth, especially when trying to image objects off-axis or at varying distances.
Innovation Solution
The use of a volume grating optical element with spatially varying k-vectors, each optimized for specific portions of the field of view, ensures high diffraction efficiency and reduces aberrations by aligning with the Bragg matching conditions at different incident angles, thereby improving imaging quality and inducing optical power where needed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional diffraction grating is used in eye tracking systems, then the structure is simple, but the diffraction efficiency is low and aberrations are high across the field of view
Solution Approach 1:
The patent applies local quality by making the grating period spatially variable across the optical element. Different regions of the grating have different periods optimized for their respective fields of view, allowing high diffraction efficiency and reduced aberrations across the entire field of view rather than being uniform throughout. This resolves the contradiction by accepting increased optical element complexity to achieve significantly improved diffraction efficiency.
Solution Approach 2:
The patent changes the physical parameter of grating period from a constant value to a spatially varying value. By adjusting the grating period parameter across different regions to match local Bragg conditions, the system achieves high diffraction efficiency across the entire field of view, resolving the contradiction between simple structure and high performance.
2Manufacturing precision
If a uniform grating is used, then the manufacturing is easy, but the imaging quality is poor for off-axis objects
Solution Approach 1:
The patent implements local quality by optimizing the grating period for different spatial regions. Each region's grating period is tailored to achieve optimal imaging quality for objects in that specific portion of the field of view, particularly improving off-axis imaging. This approach accepts increased fabrication complexity to achieve superior localized imaging performance across the entire field.
Solution Approach 2:
The patent segments the grating into multiple regions with different grating periods. Rather than using a single uniform grating, the optical element is divided into zones, each with optimized parameters for its local field of view requirements, improving overall imaging quality across the entire field.
3Adaptability or versatility
If the field of view is extended to include off-axis objects, then the angular bandwidth is increased, but the diffraction efficiency decreases
Solution Approach 1:
The patent resolves this contradiction by applying local quality through spatially varying grating periods. Each region of the grating is optimized for its local angular range, allowing the system to maintain high diffraction efficiency across a wide angular bandwidth. The grating period varies to match Bragg conditions for different incident angles across the extended field of view.
4Reliability
If a single k-vector is used for the grating, then the optical element is simple, but aberrations increase across the field of view
Solution Approach 1:
The patent applies local quality by using spatially varying k-vectors instead of a single uniform k-vector. Different regions of the optical element have different k-vectors optimized for their local field of view, which reduces aberrations and improves image quality across the entire field. This accepts increased optical element complexity to achieve superior imaging performance.
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 diffraction efficiency to over 80% across the field of view, reduces aberrations, and allows for accurate imaging of objects at various distances and angles, improving the overall performance of eye tracking systems in wearable devices and virtual/augmented reality applications.
Implementation Method 1
the volume grating configured to direct light from portions of the eyebox within a field of view to the detector
Implementation Method 2
each portion has a Bragg matching condition at a respective incident angle of impinging light
Implementation Method 3
the first portion has a Bragg matching condition at a first incident angle of a first impinging light relative to the optical element in the field of view
Data Source
AI summary
Systems and method for eye tracking are provided. In some embodiments, the eye tracking system includes a light source configured to generate light and project the light toward an object in a field of view, a detector configured to receive reflected portions of the light from the field of view in order to image the object, and a combiner including a volume grating configured to direct light reflected from different points in a field of view to the light detector. The volume grating includes a plurality of portions along a first area and each of the portions comprising a unique k-vector that is dependent on a respective portion of the field of view.