Cholesteric Liquid Crystal Reflective Layer Sidelobe Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing optical elements with cholesteric liquid crystal layers face challenges in suppressing sidelobe occurrence and achieving high reflectivity, as they tend to reflect light outside the intended wavelength range, leading to undesirable reflections.
Innovation Solution
The optical element incorporates a pair of reflective layers with cholesteric liquid crystal layers, where the rotation direction of optical axes is opposite between layers, and the birefringence varies across the layers' thickness, with specific depth positions defining regions of different birefringence to minimize sidelobe formation and enhance reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cholesteric liquid crystal layer is used for selective reflection, then reflectivity in a specific wavelength range is achieved, but sidelobe occurs causing reflection of light outside the intended wavelength range
Solution Approach 1:
The reflective layer is segmented into multiple cholesteric liquid crystal layers (first, second, and third layers) with different helical pitch numbers. Each layer reflects a specific wavelength range, and by combining them, the overall reflectivity is enhanced while sidelobe is suppressed through careful selection of pitch ratios
Solution Approach 2:
Different regions of the reflective layer (first, second, and third layers) are assigned different local qualities in terms of helical pitch numbers. The first layer has pitch number N1, the second layer has N2, and the third layer has N3, where specific relationships between these numbers create the desired optical characteristics and suppress sidelobe
Solution Approach 3:
The reflective layer is constructed as a composite structure combining multiple cholesteric liquid crystal layers with different optical properties. This composite approach allows the system to achieve both high reflectivity in the target wavelength range and suppression of reflections in unwanted wavelength ranges
2Quantity of substance
If the reflection wavelength range is broadened, then more light is reflected, but sidelobe becomes more prominent
Solution Approach 1:
The reflective layer is segmented into multiple cholesteric liquid crystal layers (first, second, and third layers) with different helical pitch numbers. Each layer reflects a specific wavelength range, and by combining them, the overall reflectivity is enhanced while sidelobe is suppressed through careful selection of pitch ratios
Solution Approach 2:
The helical pitch numbers of the cholesteric liquid crystal layers are precisely controlled with specific relationships (N1:N2:N3 ratios) to optimize the reflection characteristics. By adjusting these parameters, the system achieves both broad wavelength coverage and sidelobe suppression
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 effectively suppresses sidelobe occurrence and increases reflectivity by ensuring that only light within the desired wavelength range is reflected, improving the optical performance of the element.
Implementation Method 1
A layer (hereinafter, also referred to as 'cholesteric liquid crystal layer') obtained by immobilizing a cholesteric liquid crystalline phase is known as a layer that selectively reflects at least either right circularly polarized light or left circularly polarized light in a specific wavelength range
Implementation Method 2
an optical element in which a reflection direction of reflected light is reflected obliquely instead of specular reflection by finely controlling an alignment state of the cholesteric liquid crystal layer
Implementation Method 3
at least one of birefringences in the first region and the third region is less than a birefringence in the second region
Data Source
AI summary
The present invention provides an optical element in which the occurrence of sidelobe is suppressed and a reflectivity is high, an image display apparatus, a head-mounted display, a sensing apparatus, and an eye tracking apparatus. The optical element according to the present invention includes: at least one reflecting layer pair that is a combination of two reflective layers where turning directions of circularly polarized light to be reflected are opposite to each other and at least a part of reflection wavelength ranges is an overlapping part, in which the reflective layer includes a cholesteric liquid crystal layer obtained by immobilizing a cholesteric liquid crystalline phase, the cholesteric liquid crystal layer has a liquid crystal alignment pattern in which a direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction, and in a case where a depth position corresponding to 10% of a total helical pitch number of the reflective layer from one surface to another surface side of the reflective layer is set as a depth position X, a depth position corresponding to 90% of the total helical pitch number of the reflective layer from the one surface to the other surface side of the reflective layer is set as a depth position Y, a region from the one surface to the depth position X is set as a first region, a region from the depth position X to the depth position Y is set as a second region, and a region from the depth position Y to the other surface is set as a third region, at least one of birefringences in the first region and the third region is less than a birefringence in the second region.