Bifocal Optical Assembly for Head-Mounted Displays
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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, such as older individuals who have a smaller accommodative range compared to younger users.
Innovation Solution
A bifocal optical element is integrated into the head-mounted display (HMD) with different optical powers for two image planes, allowing users with varying accommodative ranges to focus on content presented in these planes, thereby mitigating the conflict and expanding the user base.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed-focused display is used in HMD, then the optical system is simple, but vergence-accommodation conflict occurs causing user discomfort
Solution Approach 1:
The display surface is segmented into multiple focal planes (first image plane and second image plane at different distances). Different regions of the display correspond to different virtual depths, allowing the optical system to present content at multiple accommodation distances simultaneously, thereby resolving the vergence-accommodation conflict while maintaining a relatively simple optical structure.
Solution Approach 2:
The patent adds a depth dimension to the display by creating multiple image planes at different focal distances along the optical axis. This transforms a traditional 2D fixed-focus display into a multi-planar display system, enabling content to be presented at various virtual depths without complicating the lateral optical path.
2Adaptability or versatility
If multiple image planes are provided for different accommodative ranges, then adaptability to different users is improved, but device complexity increases
Solution Approach 1:
The optical assembly is designed to serve multiple functions simultaneously: it provides both near and far focal planes within a single integrated structure. This multi-functional design allows the same optical assembly to accommodate users with different accommodative ranges (including older users with presbyopia) without requiring separate optical systems for different user groups.
Solution Approach 2:
Multiple image planes that would traditionally require separate optical paths are merged into a single integrated optical assembly. The first and second image planes are combined in one optical structure, allowing users to view content at different virtual distances through the same eyepiece without adding multiple separate optical components.
3Ease of manufacture
If the display focuses at a fixed distance, then manufacturing is simple, but it causes image blur for users needing different accommodation
Solution Approach 1:
Different regions of the display surface are assigned different focal qualities. The display is divided into areas corresponding to different image planes, with each region optimized for its specific focal distance. This allows the manufacturing process to maintain simplicity while achieving precise focus control for different user needs through spatial differentiation of optical properties.
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 bifocal optical element enables users of different ages to comfortably view content by providing separate image planes for near and far focal distances, effectively coupling accommodation with vergence, reducing discomfort and nausea associated with vergence-accommodation conflict.
Implementation Method 1
The optical assembly includes a multifocal optical element, e.g., a bifocal optical element. A first portion of the multifocal optical element has a first optical power that is associated with a first image plane, and a second portion of the multifocal optical element has a second optical power different than the first optical power and the second optical power is associated with a second image plane.
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 optical assembly includes a multifocal optical element, e.g., a bifocal optical element. A first portion of the multifocal optical element has a first optical power that is associated with a first image plane. The second portion of the multifocal optical element has a second optical power different than the first optical power, the second portion associated with a second image plane.