Cholesteric Liquid Crystal Diffraction Element with Tilted Alignment
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Solution Overview
Problem
The existing methods for producing cholesteric liquid crystal diffraction elements face challenges in adjusting the angle of liquid crystal domains, leading to increased scattering components and low sharpness of diffracted light due to the difficulty in aligning the helical axis of the cholesteric liquid crystal layer with respect to the substrate surface.
Innovation Solution
A liquid crystal diffraction element is developed with a periodic pattern alignment film and a cholesteric liquid crystal layer where the molecular axis of the liquid crystal compound is tilted with respect to the substrate surface, and the arrangement of bright and dark portions is tilted with respect to the surface, achieved by using a liquid crystal composition containing chiral agents whose helical twisting power changes with light irradiation or temperature, and a photo-alignment film formed by interfering light from different directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the temperature of a coating film including a liquid crystal compound is lowered to form a cholesteric liquid crystalline phase, then the liquid crystal compound transitions from isotropic phase to cholesteric liquid crystalline phase, but it becomes extremely difficult to adjust the angle of liquid crystal domain with respect to the normal direction of the film plane
Solution Approach 1:
The alignment film is prepared in advance with a predetermined periodic pattern of alignment elements having different tilt angles or azimuth directions before the liquid crystal layer is formed. This preliminary structure guides the liquid crystal molecules to achieve the desired angular orientation during the phase transition, solving the problem of difficulty in adjusting the liquid crystal domain angle after the cholesteric phase is formed.
Solution Approach 2:
The alignment film incorporates spatial variation in alignment element properties (different tilt angles or azimuth directions at different locations) to create local differences in liquid crystal orientation. This allows precise control over the angular distribution of liquid crystal domains in specific regions, enabling adjustment of the overall domain angle while maintaining the cholesteric phase structure.
2Reliability
If the helical axis main direction is tilted by a predetermined angle with respect to the normal direction of the layer plane, then reflection anisotropy is achieved, but the angle of the reflecting surface cannot be adjusted, leading to increased scattering components
Solution Approach 1:
The alignment film creates local variations in alignment element orientation (different tilt angles or azimuth directions) that translate to corresponding variations in the cholesteric liquid crystal layer's helical axis orientation. This allows the reflecting surface angle to be precisely adjusted in different regions while maintaining reflection anisotropy, thereby reducing scattering components.
Solution Approach 2:
By changing the parameters of the alignment elements (tilt angles and azimuth directions) in the alignment film, the orientation of the helical axis and consequently the angle of the reflecting surface can be adjusted. This parameter control enables optimization of the reflecting surface angle to minimize scattering while preserving the essential reflection anisotropy property.
3Illumination intensity
If light is incident from a normal direction of the cholesteric liquid crystal layer, then reflection occurs, but the diffracted light is diffracted in various directions leading to low sharpness
Solution Approach 1:
The periodic pattern of alignment elements with different orientations creates corresponding periodic variations in the cholesteric liquid crystal layer structure. This results in well-defined, localized diffraction features rather than scattered diffraction, thereby improving the sharpness of diffracted light while maintaining strong reflection.
Solution Approach 2:
The alignment film employs asymmetric or chiral periodic patterns of alignment elements that induce corresponding asymmetric structures in the cholesteric liquid crystal layer. This asymmetry produces well-defined diffraction patterns with high sharpness, converting the previously scattered diffraction into directed, sharp diffracted beams.
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 configuration results in a diffraction element with low scattering and high sharpness of diffracted light, as the periodic pattern alignment ensures consistent diffraction angles and reduces fluctuations in the liquid crystal alignment pattern, enhancing the optical properties of the cholesteric liquid crystal layer.
Implementation Method 1
A cholesteric liquid crystal layer is known as a layer having properties of selectively reflecting either dextrorotatory circularly polarized light or levorotatory circularly polarized light in a specific wavelength range
Implementation Method 2
the temperature of a coating film including a liquid crystal compound and heated to a temperature equal to or higher than a first phase transition temperature (that is, a temperature at which the liquid crystal compound exhibits an isotropic phase) is lowered to a temperature equal to or lower than the first phase transition temperature
Implementation Method 3
a photo-alignment film formed by interfering light from different directions
Data Source
AI summary
Provided are a liquid crystal diffraction element which exhibits low scattering and high sharpness of diffracted light, and a method for producing the same. A liquid crystal diffraction element having an alignment film which has a periodic pattern and also having a cholesteric liquid crystal layer, in which: the periodic pattern is imparted to the alignment film as a result of alignment elements having different tilt angles being periodically arranged in the alignment film or the alignment elements being arranged in a manner such that the azimuth direction thereof swings in one in-plane direction; the direction of the molecular axis of a liquid crystal compound changes while continuously rotating and in at least one in-plane direction on at least one main surface among the pair of main surfaces of the cholesteric liquid crystal layer; the molecular axis of the liquid crystal compound is tilted with respect to the main surfaces of the cholesteric liquid crystal layer; and an arrangement direction of bright portion and dark portion derived from the cholesteric liquid crystalline phase observed by a scanning electron microscope in a cross section perpendicular to the main surfaces is tilted with respect to the main surfaces of the cholesteric liquid crystal layer.