# US 7,746,555 B2 · Polarizer, polarization light source and image display unit using them

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- Number: US 7,746,555 B2
- Document ID: US7746555B2
- Status: Granted
- Kind: B2
- Application number: 12/236,976
- Filed: 2008-09-24
- Published: 2009-02-05
- Granted: 2010-06-29
- Earliest claimed: 2002-04-23
- Assignees: Nitto Denko Corporation
- Inventors: Kazutaka Hara; Minoru Miyatake
- Web page: https://patentgrep.com/patent/US7746555B2

## CPC

- G02B 5/3025: {Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state (G02B5/3008, G02B5/3016 take precedence)}
- G02B 5/3016: {involving passive liquid crystal elements (optical properties of liquid crystals G02F1/0063; polarising elements associated with active liquid crystal devices G02F1/133528)}
- G02B 5/3083: {Birefringent or phase retarding elements (G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001)}
- G02F 1/133536: {Reflective polarizers (G02F1/13362 takes precedence)}
- G02F 1/133634: {the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis}
- H10K 59/8791: {Arrangements for improving contrast, e.g. preventing reflection of ambient light}
- G02F 1/133543: {Cholesteric polarisers}
- G02F 1/13362: {providing polarized light, e.g. by converting a polarisation component into another one}
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02F: OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- H10K: ORGANIC ELECTRIC SOLID-STATE DEVICES

## Abstract

A polarization component, capable of efficiently reflecting an obliquely transmitted light beam toward a light source without degrading the transmission-polarization property of a perpendicular incident light beam, is provided. A C-plate having an oblique retardation of at least λ/8 with respect to a light beam inclined by at least 30° is disposed between at least two reflective circular polarizer layers whose selective reflection wavelength bands of polarized light overlapping each other. A combination of a reflective linear polarizer and a quarter wavelength plate may be used instead of the reflective circular polarizer. Alternatively, a combination of two reflective linear polarizer layers and two quarter wavelength plate layers (Nz≧2) disposed therebetween can provide a similar effect. Further, a combination of two reflective linear polarizer layers and a half wavelength plate (Nz≧1.5) disposed therebetween may be used. When reflective linear polarizer layers are used, they must be bonded together with their axial directions set at a certain angle. The polarization component is preferably used in various image display apparatuses such as liquid crystal display apparatuses and organic EL display apparatuses.

## Claims

### Claim 1

A polarization component comprising at least two reflective linear polarizer layers, a retardation layer and two quarter wavelength plate layers disposed between the reflective linear polarizer layers, wherein
one of the quarter wavelength plate layers is disposed between one of the reflective linear polarizer layers and the retardation layer, and the other quarter wavelength plate layer is disposed between the other reflective linear polarizer layer and the retardation layer,
the two reflective linear polarizer layers have selective reflection wavelength bands for selective reflection of polarized light, the selective reflection wavelength bands overlapping each other at least partially,
the quarter wavelength plate layer positioned on one surface of the retardation layer has an in-plane slow axis that forms an angle of 40° to 50° with respect to a polarization axis of the reflective linear polarizer layer positioned on the same side of the retardation layer,
the quarter wavelength plate layer positioned on the other surface of the retardation layer has an in-plane slow axis that forms an angle of −40° to −50° with respect to a polarization axis of the reflective linear polarizer layer on the same side of the retardation layer,
an angle formed by the in-plane slow axes of the two quarter wavelength plate layers is determined arbitrarily, and
the retardation layer satisfies the conditions of formula (I) and formula (III) below:
R≦λ/10 (I)
R′≧λ/4 (III)
wherein, in formula (I) and formula (III), λ denotes a wavelength of light entering the retardation layer;
R denotes an absolute value of an in-plane retardation in a X-axis direction and in a Y-axis direction with respect to incident light from a Z-axis direction, where the X-axis direction is a direction showing a maximum refractive index within the plane of the retardation layer, the Y-axis direction is a direction perpendicular to the X-axis direction within the plane of the retardation layer, and the Z-axis direction is a thickness direction of the retardation layer and perpendicular to the X-axis direction and the Y-axis direction;
R′ denotes an absolute value of retardation between a X′-axis direction and a Y′-axis direction with respect to incident light from a direction inclined by at least 30° with respect to the Z-axis direction, where the X′-axis direction is an axial direction within a plane of the retardation layer perpendicular to the incidence direction of the incident light inclined by at least 30° with respect to the Z-axis direction, and the Y′ axis direction is a direction perpendicular to the incidence direction and to the X′ axis direction.

### Claim 2 (depends on 1)

The polarization component according to claim 1, wherein the overlapping region of the selective reflection wavelength bands in the two reflective linear polarizer layers comprises a wavelength range of 540 to 560 nm.