Optical Stack Reflective Polarizer Off-Axis Color
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Solution Overview
Problem
Conventional multilayer optical films used in display applications suffer from color distortions at high view angles due to manufacturing variations, leading to off-axis colors and reduced uniformity and brightness in reflective polarizers.
Innovation Solution
The use of an optical stack comprising a first reflective polarizer and a partially reflective component, where the partially reflective component is a second reflective polarizer with adjusted reflection properties, including a non-parallel pass axis orientation and refractive index differences, to achieve improved color properties and reduced off-axis colors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional multilayer optical films are used in display applications, then the reflective polarizer provides basic light transmission and reflection, but color distortions and off-axis colors occur at high view angles due to manufacturing variations
Solution Approach 1:
The optical film is divided into multiple distinct layers including a first reflective polarizer layer, a second reflective polarizer layer, and a circular polarizer layer. Each layer has specific optical properties and functions that work together to reduce off-axis color variations while maintaining brightness
Solution Approach 2:
The invention uses a composite structure combining multiple polarizer types (linear reflective polarizers and circular polarizers) with different optical characteristics. This composite approach allows the system to achieve both high brightness and reduced color distortions at high view angles
2Reliability
If the number of microlayers is increased to ensure high reflectivity for polarized light, then reflection performance improves, but the complexity of the optical film increases
Solution Approach 1:
Instead of using an excessive number of thin microlayers, the invention uses a moderate number of layers with optimized thicknesses and materials. The first and second reflective polarizer layers are designed with sufficient thickness to achieve high reflectivity without requiring excessive layer counts
Solution Approach 2:
The invention optimizes parameters such as layer thickness, refractive index, and material composition to achieve high reflectivity. By changing these parameters strategically, the system achieves reliable reflection performance with a manageable number of layers
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 provides enhanced color accuracy and uniformity by reducing off-axis color variations and improving brightness, especially in display applications like liquid crystal displays and head-mounted displays.
Implementation Method 1
the reflection and transmission characteristics of the optical film are determined in large part by constructive and destructive interference of light reflected from the layer interfaces
Implementation Method 2
the reflection and transmission characteristics of the optical film are determined in large part by constructive and destructive interference of light reflected from the layer interfaces
Implementation Method 3
Reflective polarizers composed of a plurality of microlayers whose in-plane refractive indices are selected to provide a substantial refractive index mismatch between adjacent microlayers along an in-plane block axis and a substantial refractive index match between adjacent microlayers along an in-plane pass axis
Implementation Method 4
Depending on the amount of birefringence (if any) exhibited by the individual microlayers
Data Source
Figure 1A~2A
Figure 2B~3
Figure 4~5
AI summary
Optical stacks including a first reflective polarizer and a partially reflective component are described. The partially reflective component may be a second reflective polarizer or a collimating reflector. The first reflective polarizer has a first average visible light reflectance for light polarized along the first block axis at normal incidence of at least 90 percent and a first average visible light transmittance for light polarized along the first pass axis at normal incidence of at least 85 percent. The second reflective polarizer has a second block axis and a second average visible light reflectance for light polarized along the second block axis at normal incidence being no more than the first average visible light reflectance minus 10 percent. The first and second block axes are not parallel and the first and second reflective polarizers have different f-ratios.