Varifocal Pancake Lens Block for VR Vergence-Accommodation Conflict
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Solution Overview
Problem
Virtual reality headsets fail to correctly render depth and focus, leading to visual fatigue and nausea due to vergence and accommodation conflicts, as they cannot adjust focal length to match the user's changing gaze within a virtual scene.
Innovation Solution
A pancake lens block with a back curved optical element and a front smaller curved optical element, featuring a partially reflective surface and polarized reflector, allows for adjustable focal lengths by altering the shape of optical elements or changing their distance, synchronized with eye tracking to maintain user comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed focal length is used in the VR headset, then the optical system is simple and stable, but the user experiences visual fatigue and nausea due to vergence-accommodation conflict when viewing objects at different depths
Solution Approach 1:
The patent implements a varifocal optical system where the focal length can be dynamically adjusted based on the user's gaze point. The optical system transitions from a fixed focal length design to a variable focal length design, allowing the focus to change as the user looks at different virtual objects at different depths, thereby resolving the vergence-accommodation conflict and improving user comfort.
Solution Approach 2:
The patent changes the optical parameter (focal length) of the lens system to match the vergence depth of the user's gaze. By adjusting the focal length parameter dynamically, the system ensures that the accommodation state of the user's eyes matches the vergence state, eliminating visual fatigue and nausea while maintaining system stability through controlled parameter adjustment.
2Ease of operation
If the focal length is adjusted to match user gaze, then visual comfort is improved, but the device complexity increases due to additional optical elements and control mechanisms
Solution Approach 1:
The patent employs a dynamic focus adjustment mechanism that automatically varies the focal length of the optical system based on real-time tracking of the user's gaze point. This dynamic adjustment allows the system to maintain optimal focus without requiring manual intervention, improving ease of operation while managing complexity through automation.
Solution Approach 2:
The patent implements a feedback control system where the user's gaze point is tracked and used to determine the appropriate focal length setting. The system continuously monitors the user's viewing direction and adjusts the focus accordingly, creating a closed-loop control mechanism that simplifies operation while managing device complexity through intelligent control algorithms.
3Adaptability or versatility
If multiple optical elements are used to achieve variable focus, then focal length adjustment capability is improved, but the manufacturing precision requirements increase
Solution Approach 1:
The patent divides the optical system into multiple discrete optical elements (lens elements) that can be independently adjusted. By segmenting the optical system, the patent enables variable focus capability through the coordinated adjustment of multiple elements, allowing for a broader focus range while managing manufacturing precision through modular assembly and adjustment mechanisms.
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 pancake lens block effectively mitigates vergence-accommodation conflicts by dynamically adjusting focus to match the user's gaze, reducing visual fatigue and nausea by ensuring accurate alignment of vergence depth and focal length.
Implementation Method 1
The back optical element includes a surface that is partially reflective to allow a portion of light from the display screen to travel through the back optical element, while another portion of light is reflected
Implementation Method 2
The front optical element includes a polarized reflector that reflects light waves with electric fields oriented perpendicular to a polarization direction of the polarized reflector and allows light waves with electric fields parallel to the polarization direction to travel through
Implementation Method 3
one or more waveplates or other optical elements with the back curved optical element and the front curved optical element that alter the polarization state of light waves travelling through the waveplates
Implementation Method 4
A pancake lens block for a virtual reality headset includes a back curved optical element and a front smaller curved optical element in optical series
Data Source
AI summary
A virtual scene presented on a display of a virtual reality headset can be adjusted using a varifocal element by changing the shape of one or more optical elements of a pancake lens block, by varying the distance between the two optical elements, or both, based on where in a virtual scene a user is looking. The headset tracks a user's eyes to determine a vergence depth from gaze lines in order to accommodate the user's eye for the determined vergence depth. Accordingly, the shape of one or more optical elements is adjusted, the distance between the two optical elements, or both, is changed to focus light from the display of the virtual reality headset at the vergence depth to keep the user's eye in a zone of comfort as vergence and accommodation change.