Multilayer Retarder for Circularly Polarizing Plate

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Solution Overview

Problem

Existing circularly polarizing plates for OLEDs and LCDs face challenges in reducing thickness while maintaining wide-range functionality and a wide viewing angle, as current methods either fail to achieve the desired optical properties or are difficult to thin effectively.

Innovation Solution

A multilayer retarder is created by stacking a first retardation layer with negative refractive index anisotropy and a second retardation layer with positive refractive index anisotropy, both having parallel optical axes, to provide a circularly polarizing plate with in-plane retardations that satisfy specific wavelength-dependent conditions, allowing for a thinner design with wide-range functionality and a wide viewing angle.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If a conventional single-layer retardation structure is used, then the circularly polarizing plate can be made thin, but it fails to achieve both wide-range functionality and wide viewing angle

Engineering Contradiction:

Improvethickness of circularly polarizing plateVSAvoidwide-range functionality and wide viewing angle

Core Design Contradiction:

Length of moving objectVSAdaptability or versatility

Solution Approach 1:

The patent divides the single retardation layer into multiple retardation layers with different optical characteristics. Specifically, it uses a first retardation layer with negative refractive index anisotropy and a second retardation layer with positive refractive index anisotropy, each having different wavelength dispersibilities. This segmentation allows each layer to contribute differently to the overall optical performance, enabling both thinness and wide-range functionality with wide viewing angle to be achieved simultaneously.

Inventive Principle:

Principle #1Segmentation

2Adaptability or versatility

If a λ/4 plate and λ/2 plate are stacked with crossing optical axes, then wide-range functionality is achieved, but the viewing angle becomes narrow

Engineering Contradiction:

Improvewide-range functionalityVSAvoidviewing angle

Core Design Contradiction:

Adaptability or versatilityVSEase of operation

Solution Approach 1:

The patent inverts the conventional approach by using parallel optical axes instead of crossing optical axes for the stacked retardation layers. The first and second retardation layers are disposed with their optical axes parallel to each other, which fundamentally changes the optical path and interference characteristics. This inversion allows the combination to achieve both wide-range functionality and wide viewing angle, resolving the contradiction present in conventional crossing-axis designs.

Inventive Principle:

Principle #13The other way round (Inversion)

3Adaptability or versatility

If a reverse wavelength dispersion material is used, then wide-range functionality is achieved, but the plate thickness cannot be reduced

Engineering Contradiction:

Improvewide-range functionalityVSAvoidthickness of circularly polarizing plate

Core Design Contradiction:

Adaptability or versatilityVSLength of moving object

Solution Approach 1:

The patent employs a composite structure combining two different types of retardation materials: a first retardation layer with negative refractive index anisotropy and normal wavelength dispersion, and a second retardation layer with positive refractive index anisotropy and reverse wavelength dispersion. This composite material approach allows the beneficial properties of both material types to work together, achieving wide-range functionality while maintaining reduced thickness that is suitable for flexibilization.

Inventive Principle:

Principle #40Composite materials

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 multilayer retarder achieves a circularly polarizing plate that is thinner, with improved wide-range functionality and a wide viewing angle, effectively reducing internal reflection and enhancing display visibility, particularly in organic electroluminescent and liquid crystal display devices.

Implementation Method 1

a first retardation layer having negative refractive index anisotropy; a second retardation layer having positive refractive index anisotropy

Methodology Applied

Scientific EffectBirefringence: Birefringence

Data Source

PatentUS10802187B2Circularly polarizing plate, display device, and multilayer retarder

Publication Date: 2020.10.13 SHARP KK

AI summary

A circularly polarizing plate includes: a first retardation layer having negative refractive index anisotropy; a second retardation layer having positive refractive index anisotropy; and a linear polarizer, the first retardation layer and the second retardation layer being disposed such that their optical axes are parallel to each other, the first retardation layer providing an in-plane retardation whose absolute value is |R1(λ)| to light having a wavelength of λ nm, the second retardation layer providing an in-plane retardation whose absolute value is |R2(λ)| to light having a wavelength of λ nm, the first retardation layer and the second retardation layer satisfying the following formulas (1) to (4):|R1(450)|>|R1(550)|>|R1(650)| (1)|R2(550)|>|R1(550)| (2)|R2(550)|−|R1(550)|>|R2(450)|−|R1(450)| (3)|R2(650)|−|R1(650)|>|R2(550)|−|R1(550)| (4).