Multifocal HMD Optics for Vergence-Accommodation Conflict
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Solution Overview
Problem
Head-mounted displays (HMDs) suffer from vergence accommodation conflict (VAC), causing discomfort due to mismatched optical and intended depth in stereoscopic displays, leading to double images and eyestrain.
Innovation Solution
An optical display system with a multifocal assembly that has at least two optical powers and is programmable to adjust focal depth, using a Pancharatnam-Berry liquid crystal lens and a synchronized local backlight device to dynamically change accommodation cues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If fixed optical depth is used in stereoscopic display, then device complexity is reduced, but viewer comfort deteriorates due to vergence accommodation conflict
Solution Approach 1:
The patent applies a multifocal assembly that can dynamically adjust optical power between multiple fixed focal lengths (e.g., +2.00D, +4.00D, +6.00D) to match the intended depth of 3D content. This dynamic adjustment resolves the VAC by allowing the accommodation cue to vary with the displayed depth, transforming a static optical system into one that adapts to different viewing conditions.
Solution Approach 2:
The patent changes the optical power parameter of the imaging system by introducing a multifocal assembly with variable optical power. The assembly switches between discrete focal lengths based on the intended depth of the displayed content, thereby changing the accommodation requirement from a fixed value to a variable parameter that matches the 3D scene depth.
2Object-affected harmful factors
If adjustable display depth is implemented, then viewer comfort is improved by reducing VAC, but device complexity increases due to additional optical components
Solution Approach 1:
The multifocal assembly serves multiple functions: it acts as a focusing element, a depth-coding device, and an accommodation-adjustment mechanism. By consolidating these functions into a single programmable assembly rather than using separate optical components, the patent reduces the overall system complexity while achieving adjustable depth functionality.
Solution Approach 2:
The multifocal assembly acts as an intermediary between the display device and the viewer's eye. It processes the light from the display and transforms it into the appropriate focal configuration, mediating the conflict between fixed display geometry and variable viewing requirements without requiring fundamental changes to either the display or the eye model.
3Adaptability or versatility
If multiple optical powers are provided, then adaptability to different depths is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the optical power adjustment into discrete, pre-manufactured focal length options (e.g., +2.00D, +4.00D, +6.00D) rather than requiring continuous precision. Each focal length is implemented as a separate optical element or state within the multifocal assembly, allowing for standardized manufacturing of discrete components that can be switched between, thereby reducing the precision requirements for each individual element.
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
Relieves VAC by dynamically adjusting focal depth to match viewer's vergence distance, reducing discomfort and improving visual clarity in 3D displays.
Implementation Method 1
using a Pancharatnam-Berry liquid crystal lens and a synchronized local backlight device to dynamically change accommodation cues
Implementation Method 2
using a Pancharatnam-Berry liquid crystal lens
Data Source
AI summary
An optical display system and a head-mounted display electronics apparatus are disclosed. The optical display system comprises: an image-generating apparatus, which generates image light; and an image-viewing apparatus, which guides the image light to eyes of a viewer, wherein the image-viewing apparatus comprises an imaging optical assembly and a multifocal assembly placed, the multifocal assembly has at least two optical powers and is programmable to choose at least one of the optical powers at a given time.