Bifocal Optical Assembly for HMD Vergence-Accommodation Conflict
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Solution Overview
Problem
Vergence-accommodation conflict in virtual reality systems causes discomfort and nausea due to decoupling of vergence and accommodation processes, particularly affecting users with different accommodative ranges, as their eyes struggle to focus on virtual objects at incorrect distances.
Innovation Solution
An optical assembly with a bifocal optical element is integrated into the head-mounted display, generating two image planes at different distances to accommodate users with varying accommodative ranges, allowing them to focus comfortably on both near and far objects by adjusting the optical power, thereby coupling the accommodation process with vergence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-focus display is used in HMD, then the optical structure is simple, but the accommodation stimulus is incorrect for near objects causing image blur and user discomfort
Solution Approach 1:
The display is divided into multiple focal zones (near, intermediate, far) with each zone having its own optical path and imaging characteristics. This segmentation allows different portions of the display content to be focused at different distances, resolving the contradiction between simple optical structure and accurate focus by creating a multi-focal system rather than a single fixed-focus system.
Solution Approach 2:
The optical system transitions from a static fixed-focus design to a dynamic multi-focal system where the focal plane can be adjusted. The display can dynamically switch between different focal distances or provide continuous focal adjustment, allowing the accommodation stimulus to match the vergence distance for different viewing scenarios.
2Adaptability or versatility
If the display is positioned to accommodate younger users with larger accommodative range, then younger users can focus comfortably, but older users with smaller accommodative range experience discomfort and nausea
Solution Approach 1:
The HMD optical system is designed to serve multiple user groups (different ages and accommodative ranges) through a single unified platform. By implementing multi-focal capability, the system can adapt its focal planes to match the specific accommodative needs of different users, making the device universally applicable while preventing discomfort in any user group.
Solution Approach 2:
The system changes the optical parameters (focal distance, optical power) based on the user's accommodative characteristics. By adjusting these parameters, the HMD can optimize the accommodation stimulus for each user's specific needs, ensuring comfortable viewing for both younger users with large accommodative ranges and older users with smaller ranges.
3Device complexity
If Vergence and Accommodation are decoupled in fixed-focused HMD, then the optical design is simplified, but users experience discomfort, disorientation, or nausea
Solution Approach 1:
The system pre-establishes multiple focal planes corresponding to different vergence distances before the user views content. By having the accommodation focal planes ready in advance and properly aligned with the vergence distances, the system eliminates the need for real-time dynamic adjustment while still maintaining the coupling between vergence and accommodation, thus simplifying the optical design compared to fully dynamic 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 mitigates vergence-accommodation conflict, expanding the user base by allowing users of different ages to comfortably view content without experiencing discomfort or nausea, as the bifocal optical element provides a broader accommodative range and reduces optical power where needed.
Implementation Method 1
The optical assembly is configured to direct the image light to an eye-box of the HMD
Data Source
AI summary
A head-mounted display (HMD) presented herein comprises an electronic display and an optical assembly. The electronic display is configured to emit image light. The optical assembly is configured to direct the image light to an eye-box of the HMD corresponding to a location of a user's eye. The electronic display is positioned with respect to an optical axis of the HMD such that a first portion of the image light emitted by a first portion of the electronic display and a second portion of the image light emitted by a second portion of the electronic display appear to originate at different distances from the optical assembly such that the optical assembly generates at least a first image plane associated with the first portion of the electronic display and a second image plane associated with the second portion of the electronic display.