Liquid Crystal Diffraction Element for VR Ghost Suppression
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Solution Overview
Problem
In head-mounted displays like VR glasses, despite the use of liquid crystal diffraction elements to suppress zero-order light, diffracted light other than first-order light still occurs, causing ghost images due to variations in the liquid crystal alignment pattern, leading to multiple image recognition issues.
Innovation Solution
A liquid crystal diffraction element with an optically-anisotropic layer featuring a liquid crystal alignment pattern where the optical axis rotates continuously in a radial shape, with a gradually changing period and controlled ratios of bright and dark line widths, suppresses high-order diffracted light by maintaining small variations in the single periods, thereby reducing ghost occurrences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a liquid crystal diffraction element is used to suppress zero-order light, then front light is incident into eyes as appropriate image light, but high-order diffracted light is generated causing ghost images
Solution Approach 1:
The patent applies local quality by creating a liquid crystal alignment pattern where the optical axis rotates continuously in at least one in-plane direction with a gradually changing period. This non-uniform, locally varied alignment structure selectively suppresses high-order diffracted light while maintaining first-order diffraction, thereby reducing ghost images without compromising the main image quality
Solution Approach 2:
The patent utilizes parameter changes by controlling the rotation period of the optical axis to gradually change in the in-plane direction. By adjusting this periodic parameter and ensuring it satisfies specific conditions (period gradually changes, ratio of maximum to minimum period within specified range), the diffraction characteristics are optimized to eliminate high-order diffraction components that cause ghost images
2Object-generated harmful factors
If the optical axis rotation period is varied to suppress high-order diffraction, then ghost images are reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies dynamics by implementing a continuous rotation pattern of the optical axis where the rotation period gradually changes in the in-plane direction. This dynamic, continuous variation approach is more robust to manufacturing tolerances compared to sharp discontinuities, as gradual changes are easier to achieve with standard liquid crystal alignment techniques while still effectively suppressing high-order diffraction
Solution Approach 2:
The patent uses partial action by applying the continuous rotation pattern only in the necessary regions to suppress high-order diffraction, rather than requiring perfect control throughout the entire device. The gradual period change and specified ratio constraints provide sufficient suppression without demanding extreme manufacturing precision across all parameters
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 minimizes the occurrence of ghost images in head-mounted displays by controlling the diffraction angles and line width variations, ensuring that only first-order diffracted light is predominantly observed, thus enhancing image clarity.
Implementation Method 1
a liquid crystal diffraction element including an optically-anisotropic layer that is formed of a liquid crystal composition including a liquid crystal compound... the optically-anisotropic layer has a liquid crystal alignment pattern in which an orientation of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction
Data Source
AI summary
Provided are a liquid crystal diffraction element, an image display apparatus, and a head mounted display where occurrence of a ghost in a head mounted display such as VR glasses can be suppressed. The liquid crystal diffraction element includes at least an optically-anisotropic layer that is formed of a liquid crystal composition including a liquid crystal compound, in which the optically-anisotropic layer has a liquid crystal alignment pattern in which an orientation of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction, in a case where a length over which the optical axis rotates by 180 degrees in the one direction is set as a single period, the single period gradually changes in the one direction, and in a case where an average period of 50 periods in the one direction from a period having a longest length of the single period is represented by Λa and a main surface of the optically-anisotropic layer in a region having a period shorter than or equal to the average period Λa is observed with an optical microscope, both of a ratio between a maximum value and a minimum value among widths of 30 continuous bright lines and a ratio between a maximum value and a minimum value among widths of 30 continuous dark lines in the region are 1.2 or less.