Off-axis DOE eye imaging for HMDs
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Solution Overview
Problem
Existing imaging systems for head-mounted displays face challenges in efficiently imaging the eyes due to the short distance between the display and the eyes, conflicting requirements for gaze tracking and biometric identification, and occlusion by eyelids and eyelashes.
Innovation Solution
The use of a reflective off-axis Diffractive Optical Element (DOE) or Holographic Optical Element (HOE) positioned near the wearer's temple to image the eye, allowing for a larger depth of field and improved imaging capabilities despite occlusions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a backward-facing imager is used to image the eye, then the imager can be positioned close to the eye, but the depth of field is limited and the system is heavier
Solution Approach 1:
A reflective optical element (such as a mirror or beam splitter) is introduced as an intermediary between the eye and the forward-facing imager. This reflective element redirects light from the eye into the imager, enabling off-axis imaging with extended depth of field while allowing the imager to be positioned away from the eye, thereby reducing the weight burden on the eye area.
Solution Approach 2:
The imaging system transitions from a direct axial configuration to an off-axis configuration using reflective elements. This dimensional change in the optical path allows the imager to be positioned forward-facing rather than directly behind the eye, extending the depth of field and redistributing weight away from the eye area while maintaining imaging capability.
2Reliability
If the imager is positioned forward-facing away from the eye, then the depth of field increases and weight distribution improves, but the imaging path becomes more complex
Solution Approach 1:
A reflective optical element serves as a compact intermediary that folds the optical path, allowing the imager to be positioned forward-facing while maintaining a manageable optical configuration. This intermediary enables the off-axis imaging geometry needed for extended depth of field without requiring excessively complex optical arrangements.
3Measurement precision
If a reflective element is introduced to enable forward-facing imaging, then imaging capabilities improve, but the optical system becomes more complex
Solution Approach 1:
A reflective optical element (mirror or beam splitter) is introduced as a relatively simple intermediary component to redirect light from the eye to the forward-facing imager. This single reflective element enables off-axis imaging with improved depth of field and eye tracking capability while adding minimal complexity compared to more sophisticated optical systems.
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 effective eye tracking, biometric identification, and multiscopic reconstruction of the eye shape, while also being easier to wear due to the reduced weight and improved depth of field.
Implementation Method 1
a reflective element disposed in or on one of the pair of optical elements, the reflective element configured to reflect infrared light toward the forward-facing imager
Implementation Method 2
The use of a reflective off-axis Diffractive Optical Element (DOE) or Holographic Optical Element (HOE) positioned near the wearer's temple to image the eye
Data Source
AI summary
Examples of an imaging system for use with a head mounted display (HMD) are disclosed. The imaging system can include a forward-facing imaging camera and a surface of a display of the HMD can include an off-axis diffractive optical element (DOE) or hot mirror configured to reflect light to the imaging camera. The DOE or hot mirror can be segmented. The imaging system can be used for eye tracking, biometric identification, multiscopic reconstruction of the three-dimensional shape of the eye, etc.