Optical Stack with Birefringent Layer for Polarizing Efficiency
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Solution Overview
Problem
Existing multilayer reflective polarizers in display devices face challenges in achieving high reflectivity of s-polarized light and high transmission of p-polarized light with minimal color artifacts, due to refractive index mismatches in the y- and z-directions, which affect backlight efficiency and power consumption.
Innovation Solution
An optical stack comprising alternating birefringent and isotropic layers with semi-crystalline polymers, where the birefringent layers exhibit optically symmetrical crystallites aligned to minimize refractive index differences in the y- and z-directions, and the isotropic layers maintain consistent refractive indices, enabling high polarizing efficiency with reduced off-axis reflectivity and color issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multilayer reflective polarizers are designed to reflect s-polarized light and transmit p-polarized light, then polarizing efficiency is improved, but refractive index mismatches in the y- and z-directions cause color artifacts and reduce backlight efficiency
Solution Approach 1:
The patent applies local quality by creating optically symmetrical crystallites with specific refractive index characteristics in the birefringent layers. The crystallites are oriented to provide n1y ≈ n1z, creating local optical symmetry that eliminates color artifacts while maintaining high polarizing efficiency through the alternating layer structure.
Solution Approach 2:
The patent uses composite materials by combining birefringent layers with isotropic layers in an alternating multilayer structure. The birefringent layers provide polarization functionality while the isotropic layers compensate for refractive index variations, creating a composite structure that achieves both high polarizing efficiency and minimal color artifacts.
2Stability of the object's composition
If refractive index differences in the y- and z-directions are minimized to reduce color artifacts, then optical symmetry is improved, but the complexity of controlling crystallite alignment increases
Solution Approach 1:
The patent applies parameter changes by controlling the refractive index parameters of the crystallites during polymer stretching. By adjusting the stretching conditions and polymer composition, the crystallites develop specific refractive index characteristics (n1y ≈ n1z) that provide optical symmetry while maintaining manufacturability through standard processing techniques.
3Reliability
If alternating birefringent and isotropic layers are used to achieve high reflectivity and transmission, then polarizing performance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent applies segmentation by dividing the optical stack into alternating birefringent and isotropic layers with specific thickness ratios. This segmentation allows each layer to perform its specific function while the overall structure achieves high polarizing performance. The thickness of each layer can be optimized independently to balance manufacturing precision requirements with performance goals.
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 optical stack achieves high reflectivity of s-polarized light and high transmission of p-polarized light with minimal color artifacts, improving backlight efficiency and reducing power consumption in display devices.
Implementation Method 1
the birefringent layers have refractive indices n1x, n1y and n1z in the x-, y- and z-directions, respectively... the difference between n1x and n1y is greater than about 0.10
Implementation Method 2
the birefringent layers comprising semi-crystalline polymer having optically symmetrical crystallites, wherein the optically symmetrical crystallites being substantially aligned
Data Source
AI summary
An optical stack (400) having a plurality of alternating polymeric layers (401, 402) is described. The alternating layers may be alternating birefringent (syndiotactic polystyrene, sPS) and isotropic (CoPENa) layers, or alternating positively and negatively birefringent layers. Birefringent layers are made using polymers which form optically symmetrical crystallites upon stretching of the polymer. The optical stack has a large refractive index difference in the x-direction (the stretching direction) and small refractive index differences in the y- and z-directions (the non-stretching directions). The optical stack can be made using standard film tentering methods and may be a multilayer reflective polarizer.