Multifocal HMD with Switchable Half Waveplate for Vergence-Accommodation Conflict
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) for virtual reality systems often cause vergence-accommodation conflict, leading to double vision, visual fatigue, and nausea in users due to their inability to compensate for the discrepancy between vergence depth and focal length when rendering three-dimensional content.
Innovation Solution
A multifocal block within the HMD that includes switchable half waveplate (SHWP) optical components, allowing for adjustment of focal distances by switching the SHWP states, and an eye tracking system to determine the appropriate focal distance for each user, thereby aligning the vergence depth with the focal length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional HMDs present stereoscopic images on an electronic display, then the illusion of depth is simulated, but vergence and accommodation conflict occurs causing double vision, visual fatigue, and nausea
Solution Approach 1:
The patent implements dynamic focal length adjustment by switching between multiple focal planes (first focal plane for near content, second focal plane for far content) based on the depth of virtual objects. This dynamic adaptation allows the display to match the focal length with vergence depth, eliminating the static mismatch that causes visual discomfort while maintaining depth perception.
Solution Approach 2:
The system changes the optical parameter of focal length by activating different optical paths through the multifocal block. When viewing near objects, the system switches to the first focal plane with appropriate focal length; when viewing far objects, it switches to the second focal plane. This parameter change aligns the focal length with the vergence depth required for different depth perceptions.
2Adaptability or versatility
If multiple multifocal structures are cascaded to increase focal distance options, then more potential focal distances are available, but device complexity increases
Solution Approach 1:
The multifocal block is segmented into multiple independent multifocal structures, each handling specific focal distance ranges. Each multifocal structure contains its own set of optical components (waveplates, polarizers, mirrors) that can be independently controlled. This segmentation allows the system to provide multiple focal distance options while keeping each individual structure relatively simple and manageable.
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 solution effectively reduces user discomfort by aligning the vergence depth with the focal length, minimizing fatigue and nausea by presenting images at appropriate focal distances, thereby enhancing the virtual reality experience.
Implementation Method 1
The SHWP has a first state that causes the multifocal structure to output image light at the first focal distance, and a second state that causes the multifocal structure to output the image light at another focal distance
Data Source
AI summary
A head-mounted display (HMD) includes a multifocal block having one or more possible focal distances and includes a multifocal structure. The multifocal structure has a first focal distance and a second focal distance of the one or more possible focal distances. The multifocal structure includes one or more optical components positioned in series such that light from an electronic display is received and passes through each of the one or more optical components at least once before being output from the multifocal structure. The one or more optical components includes a switchable half waveplate (SHWP). The SHWP has a first state that causes the multifocal structure to output image light at the first focal distance, and a second state that causes the multifocal structure to output the image light at the first focal distance.