JPH032732A - Polarizing element - Google Patents

Abstract

PURPOSE:To improve the efficiency of conversion to light polarized in one direction to make a polarizing element compact and low-cost by constituting the element of a means, which condenses only one of two linearly polarized components whose planes of polarization are orthogonal to each other, and a polarization plane rotating means where twisted nematic liquid crystal to rotate the plane of polarization at 90 deg. is arranged. CONSTITUTION:Ordinary ray components of light 101 made incident on the polarizing element go straightly as shown by an arrow 104 without refraction on the boundary surface between a double reflection layer 102 and an isotropic layer 103, but extraordinary ray components are refracted in accordance with the change of the refractive index on the boundary surface and are spatially collected and are focused on TN type liquid crystal elements 107 and 108 which give a phase difference. Since the direction of polarization of extraordinary ray components is rotated at 90 deg. when they are transmitted through the liquid crystal element part 107 to which an electric field is applied, this direction of polarization is equalized to that of ordinary ray components. Consequently, incident rays are scarcely absorbed, and exit light 110 whose direction of polarization is satisfactorily equalized is obtained. Thus, the compact and inexpensive polarizing element is obtained which efficiently converts light to light polarized in one direction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polarizing element that changes the polarization characteristics of random light into unidirectional linearly polarized light.

[Conventional technology]

Conventionally, to obtain linearly polarized light from natural light emitted by a normal light source, birefringent prisms such as Wollaston-type and lotion-type prisms, or unidirectionally stretched oriented films that utilize the dichroism of light absorption have been used. .

(Problem to be solved by the invention) However, when a normal birefringent prism is used, the optical axes of the two light beams separated by the prism do not overlap,
Since the light beam is separated at a certain angle with respect to the incident light, the subsequent processing of the light beam becomes complicated and the overall size becomes large. On the other hand, stretched oriented films are made of organic polymer materials, making them easy to mass produce and being inexpensive. However, since they utilize dichroism in light absorption, the film itself absorbs a portion of the incident light. As a result, the light transmittance is low. Furthermore, there is a problem in that the film itself may self-destruct in response to strong light due to the heat generation effect associated with light absorption.

Therefore, the present invention is intended to solve the above-mentioned problems, and its purpose is to reduce light absorption, that is, to
An object of the present invention is to provide a compact and inexpensive polarizing element that has high efficiency in converting light into unidirectionally polarized light.

[Means to solve the problem]

In order to solve the above problems, the polarizing element of the present invention has a means for condensing only one polarized light component out of two linearly polarized light components whose polarization planes are orthogonal to each other, and It is characterized by comprising a polarization plane rotating means arranged with a twisted nematic liquid crystal that rotates the polarization plane by 90 degrees, which is a means for converting the plane of polarization to be the same as the plane of polarization of the other polarization component. 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]

When natural light emitted from a normal light source is incident on an optically anisotropic medium such as calcite or a uniaxially oriented polymer, two light beams (
It is separated into ordinary light and extraordinary light). This phenomenon occurs because the refractive power of the medium is different between the two beam axes. In other words, -
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.

One side of the birefringent layer (102) formed of an optically anisotropic material exhibiting birefringence is processed into a flat plate shape, and the opposing side is processed into a lens shape, and further, the birefringent layer (102) is formed in close contact with the birefringent layer without any gaps. , an isotropic layer (103) made of an isotropic material
is formed. Here, the refractive index ni of the isotropic layer is the same value as the smaller of the two refractive indices (no, ne) of the birefringent layer. In Figure 1, no<
Assuming ne (therefore n i=no)
shows.

Now, focusing on the ordinary light component (104) in the incident light beam, there is no difference in refractive index between the birefringent layer (102) and the isotropic layer (103), so the two layers are optically different for the ordinary light component. It can be regarded as a homogeneous monolithic layer.

In other words, the ordinary light component is not affected by the refraction effect.

On the other hand, if we pay attention to the extraordinary light component (105), we can see that the birefringent layer (
102), there is a refractive index difference of ne>ni between the isotropic layers (103), so light is refracted at the interface between the two layers, and depending on the lens shape of the birefringent layer (102), Form a focal point.

Next, by using a twisted nematic liquid crystal to rotate the polarization plane of one polarization component by 90 degrees and aligning it with the polarization plane of the other polarization component, the incident light is hardly absorbed and the polarization is Emitted light (110) whose directions are well aligned can be obtained.

〔Example〕

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

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

[Example 1] Polyimide compound (poly[2,2'
-Bis(trifluoromethyl)-4,4-biphenylene]-2",2"-dimethoxy-4,4"-biphenylenedicarboxamide, no=1.5, ne=2.0
) was stretched in one direction and then press-molded to form a birefringent layer (102) having a lens shape on one surface.

This lens body is a hollow-shaped lenticular lens, and is capable of condensing light in only one direction. The outline of the lens body is that the lens width and lens pitch are both 150 μm, and the radius of curvature of the lens is 0.5 μm. It was designed so that the focal length (back focus distance) of the lens would be 1.41a++ when the refractive index difference at the interface was 0.5. next,
After forming an acrylic plastic layer (isotropic layer (103), no=1.5) on the side of the birefringent layer where the lens is formed by casting, a glass plate with a thickness of 1°41° ( It was closely bonded to a liquid crystal element substrate (106), and only one polarized light component was focused on the back surface of the glass plate using the previous lens. Gap thickness in this part: 7μm1 Width: 30
A μm striped liquid crystal (twisted nematic liquid crystal) element was constructed. Of the striped liquid crystal elements, an electric field is applied only to the liquid crystal element part (107) at the focus position by the lens, and only the light transmitted through this liquid crystal element is configured to have its polarization direction rotated by 90''. .

Now, in Figure 1, if the ordinary light component (polarization direction is parallel to the page) is shown by a solid line and the extraordinary light component (polarization direction is perpendicular to the page) is shown by a broken line, by adopting the above configuration, the light incident on the polarizing element Of these, the ordinary light component is not affected by the refraction effect and travels straight (104) at the interface between the birefringent layer (102) and the isotropic layer (103), whereas the extraordinary light component is caused by a change in refractive index at the interface. TN-type liquid crystal elements (107, 108
) Focus on the top.

The polarization direction of the extraordinary light component is rotated by 90 degrees by passing through the liquid crystal element portion (107, hereinafter referred to as a phase difference shoulder) to which an electric field is applied, so that it becomes the same as the polarization direction of the ordinary light component. Note that the ordinary light component incident on the retardation shoulder is also subject to the rotation of the polarization direction, but the total light transmission area (i.e., the portion of the liquid crystal element to which no electric field is applied (ioa, hereinafter referred to as transparent aperture)) If the ratio of the phase difference shoulder to the sum of the phase difference shoulders (107) is small, it is possible to obtain emitted light with sufficiently uniform polarization directions. By the way, in this example, the area ratio of the transparent opening and the phase difference shoulder is 4:1.
Therefore, the proportion of light with the same polarization direction among all the emitted light is very high, about 90%.

Conventional polarizing plates utilize dichroism of light absorption to extract only specific polarized light components, 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 resulted in 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 made to a fairly small size (in this example, the diameter of the condensing lens is 150 μm), and the focal length is relatively long (i.e., If the configuration is such that the divergence angle of the light is small), the divergence of the light rays will not be much of a problem, and almost all of the incident light will be output light with the same polarization direction without any light absorption. is possible.

[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. Even if the polarizing element of the present invention is used alone, it is possible to obtain a luminous flux with fairly uniform polarization directions, but as shown in FIG. If a conventional polarizing plate (201, which can only transmit light whose polarization direction is parallel to the plane of the paper) is placed behind the section (107) in alignment with the polarization direction of the transmitted light, the polarization direction can be extremely aligned. Output light can be obtained. A polarizing plate that utilizes 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 about 1710 of the amount of incident light, so strong light There is almost no thermal damage even when it is incident. When the polarizing element of the present invention is incorporated into a liquid crystal display element, a lighting device, an optical measuring instrument, etc., it is ideal to have the above structure.

In the above embodiments, a linear lenticular lens array with unidirectional light condensing properties is used as the condensing lens body, but other general circular or elliptical lenses may of course be used. However, in order to increase the efficiency of converting light into unidirectionally polarized light, it is important to close-pack the lens body two-dimensionally so that there are no 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. In addition, when the shape of the condensing lens is circular, it goes without saying that it is desirable that the shape of one pixel of the liquid crystal element be close to the condensed spot shape, for example, square, in consideration of the condensed spot shape by the lens. stomach. Furthermore, although twisted nematic liquid crystal was used as the liquid crystal, other types such as chiral smectic liquid crystal can also be used.

〔Effect of the invention〕

As explained above, the polarizing element of the present invention includes a means for condensing only one polarized light component out of two linearly polarized light components whose polarization planes are orthogonal to each other, and a polarization of the condensed linearly polarized light component. By comprising means for rotating the surface, it is possible to convert almost all of the incident light into output light with a uniform plane of polarization with high efficiency.

In particular, since a TN type liquid crystal element is used as a means for rotating the polarization direction, for example, by dividing the minimum drive unit of the liquid crystal element into smaller dimensions, it is possible to It is possible to cope with this problem without reducing the conversion efficiency of light into unidirectionally polarized light. In other words, when light is incident at a large angle to the optical axis, the focusing position by the lens changes greatly, but even in that case, by simply changing the position of the electric field applying part of the liquid crystal element, the area of the retardation layer part can be changed. It can be seen that the retardation layer portion can be optimally placed at the in-focus position without changing the angle.

In other words, without increasing the ratio of the retardation layer to the total light transmission area (increasing this ratio means lowering the conversion efficiency of light into unidirectionally polarized light), It is clear that you can respond flexibly.

Unlike conventional polarizing plates used for similar purposes, the polarizing element of the present invention essentially has 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 for various displays that require polarized light, especially liquid crystal displays, optical isolators, etc.
A wide range of applications are possible, including optical switches, optical filters, and various optical measuring instruments that use them as components.

108...Liquid crystal element (non-electric field application part, transparent opening) 109...Transparent electrode 110...Outgoing light flux

[Brief explanation of the drawing]

201...Polarizing plate FIG. 1 is a structural sectional view for explaining the principle structure of the polarizing element of the present invention. FIG. 2 is a cross-sectional view of a polarizing element constructed by combining the polarizing element of the present invention with a conventional polarizing plate. Incident light beam birefringent layer Isotropic layer Ordinary rays Extraordinary rays Liquid crystal element substrate Liquid crystal element (electric field applying part, retardation layer part) The same numbers are used for common parts in FIGS. 1 and 2. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kisanbe Meiki (and 1 other person) Figure 2

Claims (2)

[Claims] (1) A means for focusing only one of two linearly polarized light components whose polarization planes are orthogonal to each other, and the polarization plane of one polarization component is the same as the polarization plane of the other polarization component. 1. A polarizing element comprising a polarizing plane rotating means in which a twisted nematic liquid crystal for rotating a polarizing plane by 90° is arranged. (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.