Optical Element with Birefringent Mask for High-Efficiency Diffraction
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Solution Overview
Problem
Existing optical elements face challenges in achieving high diffraction efficiency while maintaining a large diffraction angle, and the accuracy of patterning using polymerizable liquid crystal mask layers is thickness-dependent.
Innovation Solution
An optical element with a first optically-anisotropic layer made from a cured composition containing a liquid crystal compound, featuring a refractive index anisotropy of 0.24 or more, a liquid crystal alignment pattern with a rotational period of 1.6 μm or less, and a film thickness of 1 μm or less, is used as a birefringent mask to form a photo-alignment pattern, which is then coated with a second optically-anisotropic layer to enhance diffraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the diffraction angle is increased, then the light can be directed to a wider area, but the diffraction efficiency decreases and the intensity of diffracted light decreases
Solution Approach 1:
The patent changes the refractive index anisotropy parameter (Δn) to 0.24 or more, which is a significant increase from conventional liquid crystal materials. This parameter change enables the optical element to achieve both large diffraction angles and high diffraction efficiency by enhancing the optical modulation capability of the liquid crystal layer
Solution Approach 2:
The patent creates a liquid crystal alignment pattern where the optical axis direction continuously changes rotationally in the plane, with a period of 1.6 μm or less. This local variation in optical axis orientation enables different regions to contribute to both wide angular distribution and efficient light modulation
2Strength
If the thickness of the polymerizable liquid crystal mask layer is increased, then the mask strength may be improved, but the formation accuracy of the photo-alignment pattern becomes inconsistent
Solution Approach 1:
The patent optimizes the thickness parameter of the optically-anisotropic layer to be 1 μm or less, which balances the mask strength and formation accuracy. This thin film thickness ensures sufficient mechanical strength while maintaining uniform light transmission for accurate photo-alignment pattern formation
Solution Approach 2:
The patent replaces conventional photolithography methods with a holographic exposure method using an optical element as a mask. This substitution eliminates the need for thick mask layers and achieves high formation accuracy through optical interference patterns
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 enables the production of optical elements with improved diffraction efficiency and accuracy, capable of producing diffracted light with a large diffraction angle and high efficiency, while also improving the formation accuracy of photo-alignment patterns.
Implementation Method 1
an optical element which has 0.24 or more of a refractive index anisotropy Δn550... the first optically-anisotropic layer has a first liquid crystal alignment pattern in which a direction of an optical axis derived from the first liquid crystal compound continuously changes rotationally... capable of obtaining diffracted light with a large diffraction angle and high diffraction efficiency
Implementation Method 2
a first optically-anisotropic layer consisting of a cured layer of a composition including a first liquid crystal compound... refractive index anisotropy Δn550 which is measured with light having a wavelength of 550 nm
Implementation Method 3
a method for forming a photo-alignment pattern using an optical element... irradiating the photo-alignment film with light through the birefringent mask to form, on a surface of the photo-alignment film, a photo-alignment pattern
Data Source
AI summary
Provided are an optical element including a first optically-anisotropic layer consisting of a cured layer of a composition including a first liquid crystal compound, in which the first optically-anisotropic layer has 0.24 or more of a refractive index anisotropy Δn550 which is measured with light having a wavelength of 550 nm, the first optically-anisotropic layer has a first liquid crystal alignment pattern in which a direction of an optical axis derived from the first liquid crystal compound continuously changes rotationally in at least one in-plane direction, and in the first liquid crystal alignment pattern, in a case where a length Λ over which the direction of the optical axis rotates 180° in a plane is defined as a single period, the length Λ of the single period is 1.6 μm or less; a method for forming a photo-alignment pattern; and a method for manufacturing an optical element.