JPH035706A - Polarizing element - Google Patents

Abstract

PURPOSE:To separate a linear polarized component from random polarized light by using a liquid crystal material which is birefringent as a means which converges polarized components. CONSTITUTION:The liquid crystal material which is birefringent is sandwiched in an oriented state between isotropic parts (12 and 14) formed of two optically isotropic transparent materials (with a refractive index ni). An anomalous light component (17) shown by a broken line is refracted by the border surface (15) between a liquid crystal layer (13) and the isotropic layer (12) because there is a difference ne>ni in refractive index between both the layers and then focused according to the lens shape formed of the border surface between the isotropic layer and liquid crystal layer. Then the polarizing direction of the anomalous light component is rotated by 90 deg. by using a phase difference plate (18) such as a lambda/2 plate to the polarization direction of an ordinary light component and then the incident light beam is hardly absorbed and projection light (2) having a uniform polarization direction is obtained. Consequently, the compact, inexpensive polarizing element which has small light absorption, nemely, has high efficiency of conversion to unidirectionally polarized light is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] A typical example of the conventional optical element is a polarizing plate. This method selectively absorbs only one linearly polarized light component of the incident light that has polarization components orthogonal to each other, and transmits only the other linearly polarized light component, resulting in output light that has only one polarized light component. It is converted into . However, since conventional polarizing plates utilize dichroism of light absorption, the light utilization efficiency is low at about 45% at maximum, and there is also a risk that the polarizing plate itself may be thermally destroyed due to the heat generation effect associated with light absorption. had sex. Therefore, the development of a polarizing element that has high efficiency in converting light into unidirectionally polarized light and has low light absorption has been awaited. Under such circumstances, an optical element (polarizing element) disclosed in Japanese Patent Application Laid-Open No. 57-158801 has been proposed to meet the above requirements.

[Industrial application field]

The present invention relates to a polarizing element that changes the polarization characteristics of random light into unidirectional linearly polarized light.

[Problem to be solved by the invention]

However, in the optical element (polarizing element) shown in JP-A-57-158801, an amide polymer is used as a material exhibiting -axial birefringence, but this type of organic polymer Although the combination exhibits large birefringence, it has problems with molecular orientation and extremely difficult polymer molding methods.

Therefore, the present invention is intended to solve the above-mentioned problems.The purpose of the present invention is to use a birefringent material with excellent molecular orientation and moldability to reduce light absorption, that is, to reduce light absorption in one direction. An object of the present invention is to provide a compact and inexpensive polarizing element that has high conversion efficiency into polarized light.

[Means to solve the problem]

In order to solve the above problem, the polarizing element of the present invention is a polarizing element that converts incident light having mutually orthogonal polarized light components into output light having only one polarized light component, and a means for condensing the polarized light components. It is characterized by using a liquid crystal material that exhibits birefringence.

Further, the present invention is characterized in that a plurality of the polarizing elements are arranged in an array in a plane perpendicular to the incident light beam.

[Effect]

In the liquid crystal state, optical anisotropic axes are formed by regularly arranging polar polymers. When light enters here, it is separated into two beams (ordinary light and extraordinary light) having vibration planes corresponding to the optical anisotropic axis in the medium. This phenomenon occurs because the refractive power of the medium differs between the two optical axes,
-A liquid crystal material that is an axial birefringent material has two refractive indices: no for the ordinary light component and ne for the extraordinary light component.

FIG. 1 is a cross-sectional view of the structure of a polarizing element of the present invention, and the present invention will be explained in detail based on this FIG.

Between isotropic layers (12, 14) formed of two optically isotropic transparent materials (refractive index ni), liquid crystal material exhibiting birefringence (ordinary refractive index no, extraordinary refractive index ne ,
(ne>no) are sandwiched while maintaining their orientation. Here, a lens pattern (15) having a concave cross-sectional shape is formed on the side of the isotropic layer (12) facing the liquid crystal M (13). The concave lens pattern (15) formed in the isotropic layer (12) has a relationship between the refractive index ni of the isotropic layer and the extraordinary refractive index ne of the liquid crystal material n e> n
This is because it is assumed that ni>ne, and conversely, if it is assumed that ni>ne, a convex lens shape must be formed in the isotropic layer (12).

Now, if you pay attention to the ordinary light component (16) shown by the solid line in the incident light beam, you will see that it is a liquid crystal! (13), isotropic! Since there is no difference in refractive index between (12), the two layers can be regarded as an optically homogeneous integral layer with respect to the ordinary light component (16). In other words, the ordinary light component is not subjected to any refractive effect. On the other hand, focusing on the extraordinary light component (17) shown by the broken line, between the liquid crystal layer (13) and the isotropic layer (12), n
Since there is a refractive index difference e> n i, the light is refracted at the interface (15) between the two layers, and the focus is determined according to the lens shape formed by the interface between the isotropic layer and the liquid crystal layer. form.

Next, if the polarization direction of the extraordinary light component is rotated by 90'' using a retardation plate (18) such as a λ/2 plate to match the polarization direction of the ordinary light component, almost no incident light will be absorbed. , it is possible to obtain output light (20) with well-aligned polarization directions.

〔Example〕

Hereinafter, the present invention will be explained in detail based on Examples.

However, the present invention is not limited to the following examples.

[Example 1] An example of the present invention will be described in detail based on FIG. An optically isotropic layer having a concave lens pattern on one side and showing no birefringence, 1ffl ((12), hereinafter referred to as substrate 1), and an isotropic layer having a flat plate shape on both sides ((14) , hereinafter referred to as substrate 2) was formed from a highly heat-resistant acrylic resin material (refractive index n=1.49). Note that the thicknesses of substrate 1 and substrate 2 were 1 mra and 1.32 mra, respectively.

As shown in Figure 2, the lens pattern is an array of unidirectional light-concentrating linear lenticular patterns with a concave cross-sectional shape, each with a lens width of 0°1 mm and a radius of curvature. It is 0.2n+m. A cell having a gap of about 10 μm was fabricated by laminating the substrates 1 and 2 together according to the method of assembling a normal liquid crystal cell. After that, approximately 10 μm was obtained using the reduced pressure encapsulation method.
Liquid crystal material (nematic liquid crystal, ordinary refractive index no =
1.49, extraordinary refractive index ne=1. .

71) was injected and sealed to form a three-layer structure consisting of an isotropic layer, a birefringent layer, and an isotropic layer. In this case, the substrate 1
An alignment material made of polyimide was applied in advance to the areas of the substrate 2 that were in contact with the liquid crystal material, so that the liquid crystal material could be easily aligned. In addition, on the surface of the substrate 2 not in contact with the liquid crystal material, there is a striped retardation plate (18) with a width of 20 μm that provides a phase difference of λ/2 in accordance with the lens pitch.
was formed in advance.

Now, in Figure 1, if we show the ordinary light component (polarization direction parallel to the page) as a solid line and the extraordinary light component (polarization direction perpendicular to the page) as a broken line, we can see that it is isotropic! (12) refractive index ni and liquid crystal layer (
13) Since the ordinary light refractive index no is the same, the ordinary light component of the light incident on the polarizing element is isotropic! At the interface between (12) and the liquid crystal layer (13), the light travels straight without being subjected to the same refraction effect, whereas the extraordinary light component is subject to the refraction effect due to the change in the refractive index at the interface. is focused on a retardation plate (18) that provides a phase difference of λ/2. Since the polarization direction is rotated 900 times by passing through this retardation plate, the polarization direction of the extraordinary light component is the same as the polarization direction of the ordinary light component. Note that the ordinary light component incident on the retardation plate is also subject to the rotation of the polarization direction, but if the ratio of the area occupied by the retardation plate to the total light transmission area is small, output light with sufficiently uniform polarization directions can be obtained. Is possible. Incidentally, in the case of this example, the area ratio of the retardation plate to the total light transmission area is 20%, so the ratio of light with the same polarization direction to all emitted light is approximately 90%, which is extremely large. expensive.

Conventional polarizing plates take advantage of the dichroism of light absorption to extract only a specific polarized component, so there is a risk of thermal destruction from strong light due to the heat generation effect that accompanies light absorption. . On the other hand, the polarizing element of the present invention hardly causes any light absorption effect, so it can convert the polarization direction with high efficiency without causing thermal damage even when strong light is incident. It is.

While the conventional method using a polarizing plate has a maximum light transmittance of about 45%, the method using the polarizing element of the present invention provides a light transmittance close to 100%. The light that passes through the focal point spreads out at the same angle as when it was focused, but the above configuration can be modified to a somewhat smaller size (in this example, the width of the focusing lens is 1
00 μm), and if the focal length is set to a certain length (that is, the spread angle of light is small), the divergence of light rays will hardly be a problem, and almost all of the incident light will be absorbed without light absorption. can be converted into emitted light with uniform polarization direction.

However, as shown in Figure 2, a conventional polarizing plate (( 21),
Only light whose polarization direction is parallel to the paper surface can be transmitted), it is possible to obtain output light with extremely uniform polarization directions. A polarizing plate that utilizes the dichroism of light absorption exhibits a heat-generating effect as it absorbs light, but when used in combination with the polarizing element of the present invention, the proportion of light absorbed is 1/10 of the amount of incident light.
Therefore, even when strong light is incident, thermal destruction hardly occurs. When introducing the polarizing element of the present invention into a liquid crystal display element, a lighting device, an optical measuring instrument, etc., it is ideal to have the above configuration.

[Example 2] Figure 2 shows an application example of the polarizing element of the present invention, and is a cross section showing a polarizing element constructed by combining a polarizing element and a conventional polarizing plate that utilizes dichroism of light absorption. It is a diagram. Using the Polarizing Element of the Invention Alone In the above embodiments, a linear lenticular lens array with unidirectional light condensing properties was used as the condensing lens body, but of course other general circular or elliptical lenses may also be used. However, in order to increase the conversion efficiency of light into unidirectionally polarized light, it is important to close-pack the lens body two-dimensionally and to prevent the formation of non-lens parts (that is, parts that do not participate in light collection). Considering this, it can be said that the most ideal lens shape is a linear lenticular shape. Note that other liquid crystal materials that can be used include smectic and cholesteric materials.

〔Effect of the invention〕

As explained above, the polarizing element of the present invention converts incident light having polarization components orthogonal to each other into output light having only one polarization component, and uses birefringence as a means for focusing the polarization components. By using a liquid crystal material that exhibits properties, it is possible to easily construct a birefringent lens that separates linearly polarized light components from random polarized light. Furthermore, since manufacturing technology for liquid crystal display elements can be applied, manufacturing costs can be kept low. Since the configuration of the present invention does not require moving liquid crystal molecules, it is possible to use a wide variety of liquid crystal materials without being limited by the viscosity characteristics of liquid crystal, for example. By adopting the configuration of the present invention, it is possible to convert almost all of the incident light into output light with a uniform plane of polarization with high efficiency.

Unlike conventional polarizing plates used for similar purposes, the polarizing element of the present invention has essentially no light absorption, so even when strong light is incident, it remains stable without self-destruction due to heat generation. functions.

The polarizing element of the present invention takes advantage of the above characteristics to be used in various display elements that require polarized light, particularly liquid crystal display elements, optical isolators, optical switches, optical filters, and various optical measurement instruments that use these as constituent elements. , a wide range of applications are possible.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the structure of the polarizing element of the present invention for explaining its basic structure. Figure 2 is an external view of base plate 1. FIG. 3 is a cross-sectional view of a polarizing element constructed by combining the polarizing element of the present invention with a conventional polarizing plate. 1 2 3 4 5 6 7 8 9 0 Incident light isotropic layer Liquid crystal layer (birefringent layer) Isotropic layer lens pattern (boundary surface) Ordinary ray Extraordinary ray Retardation plate Ordinary ray (after conversion) Output light 21 ・・Polarizing plate The same numbers are used for common parts in FIGS. 1 and 3. Figure 3 above

Claims (2)

[Claims] (1) In a polarizing element that converts incident light having polarization components orthogonal to each other into outgoing light having polarization components in only one direction, a liquid crystal material exhibiting birefringence is used as a means for focusing the polarization components. A polarizing element characterized by: (2) The polarizing element according to claim 1, wherein a plurality of the polarizing elements are arranged in an array in a plane perpendicular to the incident light beam.