Cholesteric Liquid Crystal Layer with Pitch Gradient for Dual-Wavelength Reflection
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Solution Overview
Problem
Cholesteric liquid crystal layers can only selectively reflect light in one wavelength range, requiring multiple layers for broader wavelength coverage, limiting their application in reflecting light components across distant wavelength ranges such as red and blue or infrared and red light.
Innovation Solution
A cholesteric liquid crystal layer with a refractive index ellipsoid structure, where nx>ny, and a pitch gradient (PG) structure, allowing selective reflection of light components in two distant wavelength ranges, including the selective reflection center wavelength and its half, within a single layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a single cholesteric liquid crystal layer with uniform helical pitch is used, then the structure is simple and easy to manufacture, but it can only selectively reflect light in one wavelength range
Solution Approach 1:
The cholesteric liquid crystal layer is divided into multiple regions with different helical pitches along the thickness direction. Each region reflects light at different wavelength ranges, enabling a single layer to cover multiple wavelength bands (e.g., visible and infrared regions) without requiring multiple separate layers.
Solution Approach 2:
The invention introduces variation in the helical pitch across the thickness dimension of the liquid crystal layer. By making the helical pitch dependent on the depth from the front surface, the layer achieves wavelength selectivity in the vertical dimension, allowing simultaneous reflection of different wavelengths without increasing lateral complexity.
2Adaptability or versatility
If multiple cholesteric liquid crystal layers with different helical pitches are used to reflect light in distant wavelength ranges, then the wavelength coverage is expanded, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Multiple functional regions with different helical pitches are merged into a single cholesteric liquid crystal layer. The front surface region has a first helical pitch for reflecting visible light, while the rear surface region has a second helical pitch for reflecting infrared light, combining what would traditionally require separate layers into one manufacturable component.
Solution Approach 2:
Different regions of the liquid crystal layer are assigned different helical pitch characteristics tailored to their specific functions. The front region optimizes for visible wavelength reflection while the rear region optimizes for infrared wavelength reflection, allowing each zone to perform its designated function efficiently within a unified structure.
3Adaptability or versatility
If the helical pitch is increased to reflect longer wavelengths, then the reflection wavelength range extends to infrared, but the visible light reflection capability is reduced
Solution Approach 1:
The liquid crystal layer is segmented into a front surface region with a first helical pitch optimized for visible light reflection and a rear surface region with a second helical pitch optimized for infrared light reflection. This segmentation allows both wavelength ranges to be reflected effectively without compromising either capability.
Solution Approach 2:
The solution moves the wavelength selection mechanism into the thickness dimension rather than relying solely on lateral pitch variation. By varying the helical pitch along the depth of the layer, the invention achieves wavelength differentiation without sacrificing the intensity of reflected light in either visible or infrared regions.
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
Enables the selective reflection of light components across two distant wavelength ranges, expanding the reflection wavelength range and enhancing the versatility of cholesteric liquid crystal layers in applications like decorative sheets and projection systems.
Implementation Method 1
A cholesteric liquid crystal layer that is obtained by immobilizing a cholesteric liquid crystalline phase has wavelength selectivity where only light in a specific wavelength range is selectively reflected
Implementation Method 2
a reflection wavelength range where the cholesteric liquid crystal layer selectively reflects light depends on a helical pitch of a cholesteric liquid crystalline phase. As the helical pitch increases, the cholesteric liquid crystal layer selectively reflects light having a longer wavelength
Implementation Method 3
in which the cholesteric liquid crystal layer has a region where a refractive index nx in a slow axis direction and a refractive index ny in a fast axis direction in a plane satisfy nx>ny
Implementation Method 4
a helical pitch in the cholesteric alignment gradually changes in the thickness direction of the cholesteric liquid crystal layer
Data Source
AI summary
An optical element includes a cholesteric liquid crystal layer obtained by cholesterically aligning a liquid crystal compound, in which the cholesteric liquid crystal layer has a region where a refractive index nx in a slow axis direction and a refractive index ny in a fast axis direction in a plane satisfy nx>ny, a helical axis of the cholesteric alignment is parallel to a thickness direction of the cholesteric liquid crystal layer, and a helical pitch in the cholesteric alignment gradually changes in the thickness direction of the cholesteric liquid crystal layer.