Optical: systems and elements – Polarization without modulation – Polarizarion by dichroism
Reexamination Certificate
1998-08-03
2001-01-09
Nguyen, Thong (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarizarion by dichroism
C359S483010, C362S035000, C349S065000
Reexamination Certificate
active
06172809
ABSTRACT:
BACKGROUND ART
1. Technical Field
The present invention relates to a surface light source device having a function for generating a polarized light flux from a polarization-free light or a function for generating a much polarized light flux from a less polarized light (hereinafter called polarization function). The surface light source device of the invention is employed in applications requiring polarized light flux, and is particularly applied beneficially to backlight of a liquid crystal display.
2. Description of the Related Art
It has been hitherto known well to apply a surface light source device comprising a light guide plate having light scattering ability on the surface or inside, and a light source (such as fluorescent lamp) disposed at the side to backlight of a liquid crystal display or the like (for example, Japanese Laid-open Patents No. H2-221926 and No. H4-145485, and Japanese Laid-open Utility Model No. 51-89888).
In these “conventional” surface light source devices, the principle is based on the idea that the quantity of light emitted from the light exit surface is maintained by making the light propagation direction as random as possible by the light scattering action in the light guide or surface region. Therefore, the presented illuminating light is free from evident directivity, and does not have function for generating the light possessing polarization in a specific direction.
By contrast, the present inventor previously proposed a light flux parallelizing apparatus by making use of light flux parallelizing function of a wedge-shaped light scattering light guide having characteristic parameters for defining the scattering characteristic (effective scatter irradiation parameter E and correlation distance a; detail given later) determined in a specific range (Japanese Patent Application No. H5-349479, filed Dec. 28, 1993). When a modified surface light source device is constituted by combining the light flux parallelizing apparatus with a light source, the illuminating light flux has a definite directivity, but polarization polarized in a specific direction cannot be generated.
As the means for obtaining polarized light from a polarization free light emitted from an ordinary light source, polarizing plates and beam splitter type polarizer are known. These polarizing elements eliminate the polarized components in a direction orthogonal to a specific direction in order to obtain a polarized light.
As a result, about half of the light energy is lost. Therefore, if the polarizing element is combined with any one of the surface light source devices mentioned above, it is difficult to obtain polarized illuminating light flux efficiently.
On the other hand, when a polarization-free illuminating light flux is entered from behind a liquid crystal display panel of a liquid crystal display, by the polarizing plate provided at the light incident side of the liquid crystal display panel in order to enter the light polarized in a specific direction into the liquid crystal layer, about half of the light energy of the illuminating light flux generated in the surface light source device is wasted. Accordingly, the brightness of the display of the liquid crystal display is sacrificed.
If the surface light source device having a capability of generating a light flux polarized in a specific direction having a suppressed light energy loss is presented, by employing it in the backlight of the liquid crystal display, the loss of the liquid crystal display panel when passing through the polarizing plate can be lowered (The polarizing direction of the illuminating light flux from the backlight and the polarizing axis direction of the polarizing plate are set parallel.). From such viewpoint, realization of a surface light source device having a capacity of generating a light flux polarized in a specific direction with a suppressed light energy loss has been waited for.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the invention to present a surface light source device with polarization function capable of suppressing the lowering of efficiency of use of light energy in polarization, and obtaining a bright polarized light flux.
It is another object of the invention to present a surface light source device with polarization function suited to backlight of a liquid crystal display.
To achieve the objects, the invention presents a surface light source device comprising, as a basic constitution, a light flux parallelizer made of a light scattering light guide plate having a wedge-shaped section, light feed means disposed at the thicker end side of the light flux parallelizer, and light permeable polarization separating means having reflection characteristic dependent on the polarization components, being disposed so as to extend along the light exit surface of the light flux parallelizer. The polarization separating means may include the following.
[1] A polarization separating plate made of a transparent optical material having a refractive index in a range of 1.3 to 2.0
[2] A plurality of polarization separating plate disposed in laminates across air layer, each having a refractive index in a range of 1.3 to 2.0
[3] A polarization separating plate having a refractive index in a range of 1.3 to 2.0, wherein repetitive slopes for approximately satisfying the Brewster's angle condition for the exit direction of the parallel light flux emitted from the light exit surface of the light flux parallelizer are formed on the light incident surface of the polarization separating plate
[4] A polarization separating plate having a multilayer film made of an optical material having a refractive index in a range of 1.3 to 2.3
By directing the light turned back from the light permeable polarization separating means, after modifying the polarized state of the light the light flux parallelizer from the light permeable polarization separating means again, in order to obtain light of higher degree of polarization, a polarization scrambler or polarization converting means may be provided along the surface opposite to the light exit surface of the light flux parallelizer.
The polarization converting means may include the following.
[1] Polarization converting means having a phase difference plate and light reflecting means disposed the outside of the phase difference plate
[2] Polarization converting means containing a region of multiple one-body compound prism regions arranged parallel by sequentially coupling three volume region elements of triangular columnar shape with both ends in right-angled isosceles triangles so that the axial directions of the triangular column corresponding to the elements respectively may be directed in three mutually orthogonal directions
[3] Polarization converting means containing a region of multiple one-body compound prism regions arranged parallel by coupling a plurality of unit volume regions, the unit volume region being a one-body volume region sequentially coupling volume region elements of triangular columnar shape with both ends in right-angled isosceles triangles so that the axial directions of the triangular column corresponding to the elements respectively may be directed in three mutually orthogonal directions
[4] Polarization converting means containing a region of multiple one-body compound prism regions arranged parallel by coupling a plurality of unit volume regions, the unit volume region being a one-body volume region sequentially coupling volume region elements of triangular columnar shape with both ends in right-angled isosceles triangles so that the axial directions of the triangular column corresponding to the elements respectively may be directed in three mutually orthogonal directions, and a substrate region made of an optical material by repeatedly forming slopes on both face and back surfaces, wherein the compound prism region arranging region is provided on the repeated slopes on one of the face and back surfaces, and is optically and mechanically coupl
Arai Takayuki
Koike Yasuhiro
Cherry Euncha
Enplas Corporation
Nguyen Thong
Staas & Halsey , LLP
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