Polarizer, polarization light source and image display unit using them
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.
1. A polarization component comprising at least two reflective polarizer layers and a retardation layer disposed between the reflective polarizer layers, wherein
the two reflective polarizer layers are reflective circular polarizer layers that selectively transmit one of clockwise circularly polarized light or counterclockwise circularly polarized light while selectively reflecting the other, wherein
the two reflective circular polarizer layers have selective reflection wavelength bands for selective reflection of polarized light, the bands overlapping each other at least partially, and
the retardation layer satisfies conditions of Formulae (I) and (II) below:
R≦λ/ 10 (I)
R≧λ/ 8 (II)
wherein in Formulae (I) and (II), λ denotes a wavelength of light entering the retardation layer;
R denotes an absolute value of retardation 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 (normal direction), where the X-axis direction is a direction showing a maximum refractive index within the plane of the retardation layer (in-plane slow axis direction), the Y-axis direction is a direction perpendicular to the X-axis direction within the plane of the retardation layer (in-plane fast axis direction), 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.
2. The polarization component according to claim 1 , wherein circularly polarized light beams passing through the two reflective circular polarizer layers rotate in a same direction.
3. The polarization component according to claim 1 , wherein an overlapping region of the selective reflection wavelength bands in the two reflective circular polarizer layers comprises a wavelength range of 540 to 560 nm.
4. The polarization component according to claim 1 , wherein the retardation layer comprises a cholesteric liquid crystal compound fixed in a planar alignment state, and a selective reflection wavelength band of the retardation layer is present in a wavelength region other than a visible light region of 380 nm to 780 nm.
5. The polarization component according to claim 1 , wherein the retardation layer comprises a rodlike liquid crystal compound fixed in a homeotropic alignment state.
6. The polarization component according to claim 1 , wherein the retardation layer comprises a discotic liquid crystal compound fixed in a nematic phase or columnar phase alignment state.
7. The polarization component according to claim 1 , wherein the retardation layer comprises a biaxially-aligned non-liquid crystal polymer.
8. The polarization component according to claim 1 , wherein the retardation layer comprises an inorganic layered compound having a negative uniaxiality, the inorganic layered compound is in an alignment state where an optical axis direction of the retardation layer is fixed in a direction (normal direction) perpendicular to the plane.
9. The polarization component according to claim 1 , the polarization component further comprising at least one additional layer having a function of a quarter wavelength plate at least in a front direction, the layer is disposed outside of at least one of the two reflective circular polarizer layers and positioned at the visible side.
10. The polarization component according to claim 9 , the polarization component further comprising an absorptive dichroic polarizing plate, the absorptive dichroic polarizing plate is disposed outside the additional layer having a function of a quarter wavelength plate at least in the front direction.
11. The polarization component according to claim 1 , wherein the respective layers are laminated through translucent layers of an adhesive or a pressure-sensitive adhesive.
12. An image display apparatus comprising a polarization component according to claim 1 .