JPH0263005A - Polarizing element - Google Patents

Abstract

PURPOSE:To obtain a small-sized system of good uniformity by arranging units each consisting of a specific birefringent lens and a rotatory polarization layer provided selectively nearby one focal line of the birefringent lens in the same plane. CONSTITUTION:This polarizing element consists of the birefringent lens array formed by orienting nematic liquid crystal 304 uniaxially in an X direction and sandwiching the liquid crystal between a transparent substrate 301 and a transparent substrate 303 which has a cylindrical concave array 302 and the rotary polarization layer formed by installing 1/2-wavelength layers 105 made of polycarbonate on the transparent support substrate 305 in stripes nearby the focal line on the optical axis of the birefringent lens array in parallel to the lens array. Units each consisting of the birefringent lens and rotatory polarization layer are arranged in the same plane. Consequently, the bright, compact, and inexpensive polarizing element which provides substantially no absorption is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to the structure of a polarizing element with high light transmittance useful for displays, photodetectors, etc.

[Prior art] Conventional polarizing elements include, for example, those that combine birefringent crystal prisms such as Glan-Thompson prisms, or those that combine birefringent crystal prisms such as Glan-Thompson prisms, or optical absorption A typical example was a stretched oriented film that utilized the dichroism of .

[Problem to be solved by the invention] However, since the above-mentioned oriented film type essentially utilizes dichroism of light absorption, those with a high degree of polarization have low absolute transmittance, making it difficult to achieve high definition. When used in liquid crystal displays or highly sensitive polarization detectors, 1. a high output light source is required; 2. There were problems such as the polarizing element breaking down due to heat generation. 3. The cross-crystal prism type requires a depth that is approximately equal to or greater than the size of the light-receiving surface. It had problems such as being difficult to handle in terms of layout, the system incorporating 40° being heavy, and 5° being expensive.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bright, compact, and inexpensive polarizing element that is essentially free from absorption in order to solve this problem.

[Means for Solving the Problems] The polarizing element of the present invention comprises a birefringent lens in which the surface of an optically uniaxial material has a curvature in a plane perpendicular to its principal optical axis;
and an optical rotation layer selectively provided near one focal line of the birefringent lens.

In general, light from an incoherent light source such as a lamp is naturally polarized light with an arbitrary polarization plane, and has two orthogonal components (
For example, it can be divided isometrically into Px, Py). P
When using x acid component, remove Py by absorption or
It is necessary to separate the py from the optical path using a polarizing beam splitter, etc., and the light intensity will be reduced to 1/2 as it is.
It becomes below. Therefore, a polarizing element with essentially little light attenuation separates the -degree light beam using a birefringent lens, then selectively imparts a phase difference to only one side, rotates it 90 degrees, and spatially combines the two again. It can be obtained with In this case, by arranging a plurality of units of the birefringent lens and the optical rotation layer, a compact system with good uniformity can be obtained.

[Operation] Figure 1 is a principle diagram for explaining the present invention in detail. X
Natural light 102 incident in the Y direction on a birefringent lens 101, which is uniaxially oriented in the direction and has a curvature in a plane perpendicular to its principal optical axis, is isometrically polarized in the X and Z directions as a plane wave Px (
solid line) and Pz (broken wA). In the above-mentioned birefringent lens, different refractive indexes Nx and N
z exists and undergoes different refraction due to the interface 103. When the birefringent lens is a convex lens, the medium outside the lens has a smaller refractive index than the lens medium such as air, and N
, x>Nz, Px will undergo greater refraction. In general, the image-side effective focal length of a lens: f゛ is
Optronics 1983. No.

10, P2O, for example, in the case of a plano-convex lens placed in air, it is given by the following equation.

f”=r2/(1-n) (1) (However, r2
is the radius of curvature of the convex surface, and n is the refractive index of the lens. ) Near the focal point Fx of Px, an optical rotation layer 105 made of a 1/2 wavelength plate has its optical principal axis aligned with X (or Z) in the X7 plane.
It is installed at an angle of 45 degrees from the axis with a diameter larger than the focal spot diameter. Therefore, the Pz acid component receives a phase difference of 1/2 wavelength, and its polarization plane is converted into a Px acid component by rotating by 90 degrees. On the other hand, most of the Pz component, except for a small amount of the component that passes through the 1/2 wavelength plate layer, is transmitted without undergoing rotation of the plane of polarization, so that the majority of the incident light as a whole can align its plane of polarization with Pz polarization. It becomes possible. When the lens shape is cylindrical, if the lens diameter is 2d and the width of the optical rotation layer is 2a, then the optical rotation layer 1
Intensity ratio QXI of Px and P22 components behind 05
QZ is given by the following formula.

Qx=50* (a/d) (2) Qz
=50* (2-a/d) (3) For example,
When a/d=0.1, Qz takes a large value of 95%.

On the other hand, FIG. 2 shows the lens 101 and optical rotation layer 10 shown in FIG.
The overall configuration is shown when a large number of units of 5 are arranged in an array. The luminous flux from each unit overlaps and almost -like Pz
Deflection is obtained. In order to increase the degree of polarization, it is effective to install a normal polarizing plate or polarizing element 201 that transmits Pz polarized light at the rear. The polarizing element of the present invention will be described below based on Examples.

[Example] Example 1 Figure 3 is a perspective view of a structure in which a nematic liquid crystal layer cell is used as a birefringent lens according to an example of the present invention. Transparent substrate 301 and cylindrical concave array 30
Nematic liquid crystal 304 between transparent substrates 303 having 2
A birefringent lens array sandwiching a birefringent lens array uniaxially aligned in the It consists of an optically active layer arranged in stripes. The maximum thickness of the liquid crystal layer was approximately 19 μm, and a cyanobiphenyl mixture with high birefringence was used as the liquid crystal. The pitch of the concave array is 0.5 mm, and the radius of curvature of the concave surface is approximately 14.3 mm. Acrylic, which has good processability and a low refractive index, was used for the substrate of the cylindrical array.

FIG. 4 shows the trajectory of a typical light ray when plane waves Px and Pz polarized in the X and Z directions are perpendicularly incident on one unit of the above structure. A solid line 106 indicates Px, and a broken line 107 indicates Pz. Px incident on the liquid crystal layer.

Pz is the refractive index N of the ordinary light and extraordinary light of the nematic liquid crystal layer, respectively.
I feel x, Nz. At the concave interface 302, the incident angle θ
i and the output angle θ0 are related to each other according to the 5nell's law. Output angle θOX, θo with respect to Px, Pz
z is given by the following formula.

sinθox=Nx/No*sinθj (4) si
nθOZ:N7/Nc)ksinθi (5) (However, NO is the refractive index of the second transparent substrate.) On the other hand, θi is given by the following equation, assuming that the radius of curvature of the concave surface is r2 and the aperture of the lens is 2d.

sin θi=d/r2 (6) For cyanobiphenyl liquid crystals, Nx>Nz (4), (
From equation 5), θoz>θoz, and Px and Pz are spatially separated in the plane where Px 106 is focused in the front and the optical rotation layer 105 is placed. Although the position of the optical rotation layer may be on the focal line plane of Pz, it is preferable to align it with the front Px in view of the thickness of the element.

The optical rotation layer 105 was formed by adhering or pressing PC to a glass substrate, and then removing it by heating or selectively eluating it into stripes having a width of 50 μm. As a result, the rear 401 of the linear polarizing plate 201
When the transmittance of Px and Py was measured at
%, 70%.

100m by skillfully controlling the thickness of the liquid crystal layer.
It was possible to make a m-sized one relatively easily.

Table 1 shows the refractive index values at 589 nm of the materials used in this example.

Table 1゜Example 2 PC or polyvinyl alcohol (P
A polymer obtained by dispersing or otherwise dispersing molecules with large electronic polarization that does not absorb in the visible region in VA) was molded into a lenticular shape by injection or the like, and then uniaxially stretched. The structure is the same as in Figure 1. In this case, the birefringence value was as small as 0.001 for PC and about 0.1 for PVA, and the degree of separation of light beams was poor, but the same effect as in Example 1 was observed for Pz.

In the above embodiments, nematic liquid crystal, PC, and PVA were used as optically uniaxial materials, but it is obvious that liquid crystal polymers and the like are also useful as materials with high orientation.

[Effects of the Invention] As is clear from the above embodiments, the present invention provides a birefringent lens in which the surface of an optically uniaxial material has a curvature in a plane perpendicular to its optical principal axis, and By arranging a plurality of units consisting of an optical rotation layer selectively provided near one focal line of a refractive lens in the same plane, the same brightness can be obtained with a light source with approximately 1/2 the amount of light of a conventional one, and It is possible to provide a polarizing element that is compact, generates little heat due to absorption, and has a large area. We are confident that this will greatly contribute to the development of liquid crystal displays, which were previously dark and difficult to see, and array-shaped polarization detectors, which had sensitivity issues.

[Brief explanation of the drawing]

FIG. 1 is a principle diagram explaining the operation of the polarizing element of the present invention. FIG. 2 is an overall view of the polarizing element of the present invention. FIG. 3 is a perspective view of a configuration using the liquid crystal of the present invention. FIG. 4 is a trajectory diagram of typical light rays in the polarizing element of the present invention. 101 Birefringent lens 1/2 wavelength plate Linear polarizing plate Cylindrical anematic liquid crystal transparent support substrate Ray substrate Applicant Seiko Epson Corporation agent Patent attorney Masayoshi Kamiyanagi and 1 other person

Claims (1)

[Claims] A unit consisting of a birefringent lens in which the surface of an optically uniaxial material has a curvature in a plane perpendicular to its principal optical axis, and an optical rotation layer selectively provided near one focal line of the birefringent lens. A polarizing element characterized in that a plurality of are arranged in the same plane.