Multilayer Reflective Polarizer Film for High-Contrast Displays
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Solution Overview
Problem
Transflective liquid crystal displays (LCDs) suffer from inefficiencies in backlighting, which reduces brightness under ambient light conditions due to randomization of polarization, making them less effective compared to traditional brushed aluminum surfaces.
Innovation Solution
A reflective polarizer film with a multi-layer structure of alternating high and low refractive index layers, optimized for optical interference, achieves high transmission and reflection of specific polarization states, reducing the need for absorbing polarizers and enhancing brightness while maintaining a thin profile.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a traditional brushed aluminum reflector is used in reflective displays, then the display can utilize ambient light effectively, but the display cannot provide sufficient brightness in low ambient light conditions
Solution Approach 1:
The optical system is segmented into distinct functional layers: a reflective polarizer film with alternating high and low refractive index layers for ambient light utilization, and a separate backlight assembly with optical cavity for low ambient light conditions. This segmentation allows each component to optimize its function for specific lighting conditions without compromising the other.
Solution Approach 2:
The display system is designed to perform multiple functions through a single integrated structure that can operate in both reflective mode (using ambient light) and transmissive mode (using backlight). The polarizer film serves dual purposes: reflecting ambient light while also allowing controlled light transmission to the liquid crystal layer, enabling the display to adapt to varying ambient light conditions.
2Illumination intensity
If a backlight assembly is added to provide illumination in low ambient light, then brightness under ambient light improves, but the polarization of light is randomized and contrast ratio decreases
Solution Approach 1:
The harmful effect of the backlight randomizing polarization is extracted and isolated by positioning the reflective polarizer film between the backlight and the liquid crystal layer. The polarizer film selectively transmits only the desired polarization state while blocking the randomized polarization components, thereby maintaining contrast ratio while still allowing the backlight to provide illumination when needed.
Solution Approach 2:
The reflective polarizer film acts as an intermediary element between the backlight assembly and the liquid crystal layer. It mediates the light from the backlight by selectively transmitting specific polarization states while blocking others, thus preserving the polarization integrity required for high contrast ratio while still enabling backlight illumination functionality.
3Reliability
If absorbing polarizers are used to achieve high contrast ratio, then polarization selectivity improves, but light transmission is reduced and brightness decreases
Solution Approach 1:
The absorbing polarizer mechanism is replaced with a reflective polarizer mechanism. Instead of absorbing unwanted polarization states and converting them to heat, the reflective polarizer uses optical interference in a multi-layer film structure to reflect unwanted polarization states while transmitting desired states. This substitution maintains high polarization selectivity and contrast ratio while significantly improving light transmission and brightness.
Solution Approach 2:
The approach converts the harmful effect of light absorption into a beneficial reflective process. Rather than absorbing unwanted polarization states which loses light energy, the system reflects these states back, converting the loss into a useful function that maintains contrast ratio while preserving light transmission through the desired polarization path.
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 film provides a contrast ratio of at least 1000:1 with over 85% transmission and 80% reflection for desired polarization states, significantly improving display brightness and efficiency without increasing thickness.
Implementation Method 1
each interference layer reflecting or transmitting light primarily by optical interference
Data Source
AI summary
Optical films are disclosed that include a plurality of interference layers. Each interference layer reflects or transmits light primarily by optical interference. The total number of the interference layers is less than about 1000. For a substantially normally incident light in a predetermined wavelength range, the plurality of interference layers has an average optical transmittance greater than about 85% for a first polarization state, an average optical reflectance greater than about 80% for an orthogonal second polarization state, and an average optical transmittance less than about 0.2% for the second polarization state.