Liquid Crystal Alvarez Lens for HMD Vergence-Accommodation Conflict
Solution Overview
Problem
Existing head-mounted displays (HMDs) and near-eye displays (NEDs) suffer from visual fatigue and nausea due to their limited ability to compensate for the vergence-accommodation conflict, which occurs when the eye vergence and visual distance accommodation are not properly aligned, leading to discomfort during immersive virtual or augmented reality experiences.
Innovation Solution
The implementation of liquid crystal (LC) Alvarez lenses with optically coupled components that can adjust their optical power by laterally displacing each other, utilizing a spatial optical phase delay profile defined by a cubic polynomial, allowing for dynamic focus adjustment to match changing gaze directions and virtual object distances, thereby reducing the vergence-accommodation conflict.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional fixed-focus lenses are used in HMDs, then the device structure is simple, but the vergence-accommodation conflict cannot be compensated, causing visual fatigue and nausea
Solution Approach 1:
The patent implements a dynamic lens system using liquid crystal Alvarez lenses that can change focal length in real-time. The liquid crystal layers are controlled by voltage signals to dynamically adjust the optical power, enabling the lens to adapt to different vergence requirements and compensate for the vergence-accommodation conflict, thus resolving the contradiction between adaptability and device complexity
Solution Approach 2:
The patent changes the optical parameters of the lens by varying the refractive index of the liquid crystal material through voltage control. By adjusting the voltage applied to the liquid crystal layers, the focal length and optical power of the lens can be continuously modified, enabling dynamic accommodation compensation without mechanical movement, thereby improving adaptability while maintaining relatively simple device structure
2Speed
If mechanically movable lenses are used to adjust focus, then focal length adjustment is achievable, but the adjustment speed is slow and reliability is reduced
Solution Approach 1:
The patent replaces the mechanical lens movement system with an electrically controlled liquid crystal optical system. Instead of physically moving lenses mechanically, the focal length is adjusted by applying voltage to change the liquid crystal's refractive index. This substitution eliminates mechanical wear, reduces adjustment time to milliseconds, and improves reliability by removing moving parts, thus simultaneously improving both speed and reliability
3Productivity
If liquid crystal Alvarez lenses are implemented, then quick and reliable focus adjustments are achieved, but the device complexity increases
Solution Approach 1:
The patent extracts the focus adjustment function from the mechanical lens system and implements it separately using liquid crystal layers with specific Alvarez lens profiles. By separating the optical power adjustment function from the structural support function, the system achieves quick and reliable focus adjustments through electrical control of the liquid crystal layers, while the overall device structure remains manageable through functional decomposition
Solution Approach 2:
The liquid crystal Alvarez lens structure serves multiple functions simultaneously: it provides the Alvarez lens optical profile for focus adjustment, enables dynamic focal length change through voltage control, and integrates the liquid crystal material's electro-optic properties for rapid response. This multi-functionality improves productivity by combining several capabilities in a single component, thereby reducing the need for additional separate components and mitigating the increase in device complexity
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 enables quick and reliable focus adjustments, reducing user fatigue by ensuring that the optical power of the lens system aligns with the changing vergence of the eyes, providing a more comfortable and immersive experience in virtual and augmented reality applications.
Implementation Method 1
Each of the first and second Alvarez lens components may comprise a liquid crystal (LC) layer having an azimuthal angle of LC molecules spatially varying in a plane of the LC layer, such that the azimuthal angle defines a spatial optical phase delay profile of an Alvarez lens
Implementation Method 2
The LC layer may have an azimuthal angle of LC molecules spatially varying in plane of the LC layer such that a spatial variation of theta is defined by a cubic polynomial
Data Source
AI summary
A varifocal liquid crystal lens in Alvarez configuration is disclosed. A head mounted or near-eye display may include a liquid crystal Alvarez lens for focus adjustment for user sight accommodation, vergence accommodation, etc. The liquid crystal Alvarez lens may be of various types, such as Pancharatnam-Berry phase (PBP) lens or a polarization volume holographic lens.