Tunable Lens Eye Sensor for HMD Wavefront Sensing
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) fail to accurately compensate for aberrations introduced by headset optics, leading to sub-optimal rendering of content in virtual and augmented reality environments due to indirect estimation of the user's accommodative state, resulting in incorrect blur and depth cues.
Innovation Solution
An HMD system incorporating an electronic display, optics block, and eye sensor assembly with a tunable lens capable of wavefront sensing and eye tracking, which directly measures the accommodative state of the user's eye by emitting infrared light and using a Shack-Hartmann wavefront sensor to determine the shape of the crystalline lens, allowing for accurate positioning of the focal plane and anatomically correct rendered blur.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If vergence-based estimation is used to determine accommodation state, then the system can infer accommodation from vergence tracking, but the measurement accuracy is insufficient for optimal focal plane positioning
Solution Approach 1:
The patent replaces the indirect mechanical/ computational estimation method (vergence-based inference) with a direct optical measurement system (wavefront sensor using Shack-Hartmann technique). This substitution enables precise measurement of the eye's wavefront aberrations to directly determine accommodation state, eliminating the inaccuracies of population-average-based estimation.
Solution Approach 2:
The patent introduces an intermediary optical system consisting of infrared light delivery optics and a wavefront sensor. This intermediary system mediates between the user's eye and the HMD control system, providing accurate real-time accommodation data that enables dynamic focal plane adjustment and improved depth cue rendering.
2Reliability
If a variable focus element is added to the volumetric display to improve image quality, then the accommodative state can be better compensated, but the device complexity increases
Solution Approach 1:
The patent employs a variable focus element (tunable lens or deformable mirror) that can dynamically adjust its optical power in real-time based on the measured accommodation state. This dynamic adjustment allows the system to maintain optimal image quality across different viewing distances and accommodation levels without requiring multiple fixed-focus optical paths.
Solution Approach 2:
The patent changes the optical parameters (focal length, curvature) of the variable focus element based on the measured accommodation state. By adjusting these parameters in real-time, the system compensates for aberrations and maintains sharp focus across different depths, improving image quality without adding substantial structural complexity.
3Measurement precision
If the eye sensor assembly operates in wavefront sensing state to measure accommodation, then accurate accommodative state data is obtained, but eye tracking functionality is lost
Solution Approach 1:
The patent implements periodic switching between wavefront sensing mode and eye tracking mode. The system alternates between these two operational states, using the tunable lens to either measure wavefront aberrations (for accommodation) or track eye position (for gaze). This periodic action ensures both functions are maintained over time, though not simultaneously.
Solution Approach 2:
The patent uses a dynamically reconfigurable optical system where the tunable lens can switch between different operational modes. The system dynamically adjusts the lens state to either focus for wavefront sensing or maintain neutrality for eye tracking, enabling the sensor assembly to perform both functions sequentially with optimal performance in each mode.
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 system achieves accurate positioning of the focal plane and inclusion of anatomically correct blur in virtual scenes, enhancing the perceived quality and contrast of the displayed content by directly measuring the user's accommodative state and higher-order aberrations in real-time.
Implementation Method 1
the eye sensor operates as an accommodation sensor, such as a Shack-Hartmann wavefront sensor
Implementation Method 2
IR light emitted from electronic display is delivered to the eye through the lens to the retina and detected after the IR light is reflected from the retina
Implementation Method 3
The tunable lens is capable of operating in a wavefront sensing state (or micro-lens state) and an eye tracking state (or neutral state)
Data Source
AI summary
A head mounted display (HMD) includes an eye sensor, an optics block, and a display. The eye sensor includes a detector and a tunable lens. The tunable lens has a micro-lens state (e.g., acts as a micro-lens array) and a neutral state. In the micro-lens state the eye sensor acts as an accommodation sensor, and in the neutral state the eye sensor acts as an eye tracking sensor. The eye sensor can alternate functioning as an eye tracking or an accommodation sensor by adjusting the state of the tunable lens. In alternate embodiments, the accommodation sensor is separate from the eye tracker and a beam splitter is used to split the reflected light toward the two sensors.