Optical Polarizer Stack for Uniform High-Brightness Displays
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Solution Overview
Problem
Conventional absorbing polarizers exhibit high spatial variation in block state transmittance and polarization efficiency, leading to optical defects in displays.
Innovation Solution
Combining a high contrast reflective polarizer with a weaker absorbing polarizer, such as one made with thinner polyvinyl alcohol layers and lower iodine concentration, to form an optical stack that minimizes spatial variation and enhances transmission efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional absorbing polarizer is used, then the display can achieve polarization function, but high spatial variation in block state transmittance and polarization efficiency occurs leading to optical defects
Solution Approach 1:
The patent combines a reflective polarizer and an absorbing polarizer into a composite optical stack. The reflective polarizer provides high polarization efficiency with low spatial variation, while the absorbing polarizer contributes to overall polarization function. This merging allows the system to achieve both high reliability (optical uniformity) and adequate manufacturing precision by compensating for the weaknesses of each individual component.
Solution Approach 2:
The optical stack uses a composite structure consisting of multiple polarizer layers with different characteristics. The reflective polarizer layer (e.g., multilayer optical film) is combined with an absorbing polarizer layer (e.g., iodine-stained PVOH), creating a composite material system that leverages the high polarization efficiency and spatial uniformity of the reflective layer while maintaining the functional polarization properties of the absorbing layer.
2Productivity
If a high contrast reflective polarizer is combined with a weaker absorbing polarizer, then spatial variation is minimized and transmission efficiency is enhanced, but device complexity increases
Solution Approach 1:
The patent merges a high contrast reflective polarizer with a weaker absorbing polarizer in a composite optical stack. This combination enhances transmission efficiency by leveraging the high polarization efficiency of the reflective polarizer while using a thinner, lower-concentration absorbing polarizer that contributes to polarization without excessive absorption. The merging allows the system to achieve high productivity through improved light transmission.
Solution Approach 2:
The patent changes key parameters of the absorbing polarizer, specifically reducing the thickness and iodine concentration compared to conventional absorbing polarizers. This parameter change creates a 'weaker' absorbing polarizer that has reduced spatial variation and works synergistically with the reflective polarizer. The parameter changes enable enhanced transmission efficiency while maintaining adequate polarization function.
3Illumination intensity
If the absorbing polarizer has high average transmittance and high standard deviation of block state transmittance, then more light is transmitted, but optical defects are generated
Solution Approach 1:
The patent combines a high contrast reflective polarizer with a weaker absorbing polarizer having high average transmittance and high standard deviation of block state transmittance. The reflective polarizer compensates for the spatial variation (high standard deviation) of the absorbing polarizer, ensuring that the overall optical stack maintains high reliability and optical uniformity. This merging allows the system to achieve high illumination intensity through the high average transmittance while the reflective polarizer ensures uniformity across the optical output.
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 combination results in higher brightness and maintained contrast ratio in liquid crystal displays without noticeable optical defects, improving display efficiency.
Implementation Method 1
each interference layer reflects or transmits light primarily by optical interference
Implementation Method 2
the absorbing polarizer has a first optical transmittance for the first polarization state, an optical absorption greater than about 50% for the second polarization state
Data Source
AI summary
An optical stack includes a reflective polarizer including a plurality of interference layers and an absorbing polarizer disposed on the reflective polarizer. The plurality of interference layers transmits at least about 85% of an incident light having a first polarization state, reflects at least about 80% of the incident light having a second polarization state, and transmits less than about 0.1% of the incident light having the second polarization state. The absorbing polarizer has a first transmittance for the first polarization state and a second transmittance for the second polarization state. An average of the first and second transmittances is greater than about 0.46. The second transmittance has a first standard deviation. The optical stack has a transmittance for the second polarization state having a second standard deviation which is less than the first standard deviation by at least about 10%. A display includes the optical stack.