JPH03278020A - Polarizer - Google Patents

Abstract

PURPOSE:To allow the conversion from random polarized light to specific linearly polarized light with high efficiency by spacially separating the randomly polarized light from a light source to two linearly polarized light rays which intersect orthogonally with each other in polarization directions and then synthesizing the polarized light rays by using two TN liquid crystal elements and one reflecting mirror in such a manner that the polarization directions are equaled. CONSTITUTION:This element has the means for spacially separating the randomly polarized light 15 from the light source 21 mainly to the two linearly polarized light components (P polarized light 24 and S polarized light 23) having the planes of polarization intersecting orthogonally with each other and the two twisted nematic liquid crystal elements which are the means for rotating the planes of polarization of the two linearly polarized light components 23, 24. The element is constituted by having also the reflecting mirror which is the means for symmetrically inverting the plane of polarization of either of the two linearly polarized light components 23, 24. The randomly polarized light is converted to the unidirectionally polarized light with the high efficiency in this way with substantially no losses by light absorption and reflection.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a polarizing element that converts randomly polarized light into linearly polarized light having a plane of polarization in one direction.

[Conventional technology]

Conventionally, to obtain unidirectionally polarized light from random polarized light,
A common method has been to use a polarizer or birefringent crystal to selectively extract only linearly polarized light having a specific plane of polarization. A typical example is a polarizing plate. This is by selectively absorbing only one linearly polarized component of the incident light, which is randomly polarized light with polarization components orthogonal to each other, and transmitting only the other linearly polarized component. This converts the output light into output light having the following values. Other examples of prisms using birefringent crystals include Rochon prisms and Nicol prisms. Furthermore, there is a polarizing beam splitter in which a multilayer deposited film is sandwiched between glasses, and the incident light is extracted as two linearly polarized lights whose polarization planes are orthogonal to each other.

[Problem to be solved by the invention]

However, since conventional polarizing plates utilize dichroism of light absorption, the conversion efficiency to unidirectionally polarized light is low at about 45% at maximum, and the polarizing plate itself is destroyed by heat due to the heat generation effect caused by light absorption. There was a risk that this would occur. In addition, with devices using birefringent crystals, unnecessary polarized light components with different polarization directions are removed by means such as reflection, so even with this method, the exchange efficiency for unidirectional polarized light is up to 50%.
The problem is that it is as low as below.

Therefore, the present invention aims to solve the above problems, and its purpose is to convert randomly polarized light into unidirectionally polarized light with high efficiency, with almost no loss due to light absorption or reflection. The object of the present invention is to provide a conomact polarizing element.

[Means for Solving the Problems] In order to solve the above problems, the polarizing element of the present invention converts randomly polarized light from a light source into mainly two linearly polarized light components (P polarized light and S polarized light) whose polarization planes are orthogonal to each other. two twisted nematic liquid crystal elements serving as a means for spatial separation, a means for rotating the plane of polarization of the two linearly polarized light components, and a plane of polarization of one of the two linearly polarized light components; It is characterized by comprising a reflecting mirror, which is a means for symmetrically inverting. In addition, the above 2
The polarization plane rotation angle of the linearly polarized light component by the two twisted nematic liquid crystal elements is θ for P polarized light and 90°-θ for S polarized light. Furthermore, the device is characterized in that the means for spatially separating the randomly polarized light from the light source into mainly two linearly polarized light components (P-polarized light and S-polarized light) whose polarization planes are orthogonal to each other is a polarizing beam splitter.

[Function] The present invention will be explained in detail using FIG. 2 and FIGS. 3(a) to 3(c). Randomly polarized light 15 from the light source 21 is polarized by the polarizing beam splitter 11 so that the polarized light 15 has equal intensity P.
The light is separated into polarized light 24 and S-polarized light 23 (at this time, the S-polarized light is totally reflected at the birefringent layer interface 22 of the polarizing beam splitter). While the separated S-polarized light passes through the second twisted nematic liquid crystal element (hereinafter abbreviated as TN liquid crystal element) 12, it becomes 03 polarized light clockwise (or counterclockwise) when viewed from the side facing the emitted light. undergoes plane rotation. however,
The second TN liquid crystal element 12 is installed parallel to the exit surface on the S-polarization side of the polarization beam splitter. The polarization direction of the emitted light in this case is shown in FIG. 3(C). Similarly, while the P-polarized light passes through the first TN liquid crystal element 13,
The polarization plane is rotated, and the polarization direction is further symmetrically reversed by the reflecting mirror 14 (symmetrical angle θ2, θ2 = 90° - θ1).
be done. However, the first TN liquid crystal element 13 is arranged parallel to the exit surface on the P polarization side of the polarization beam splitter, and
The reflecting mirror 14 is installed so that the normal line of the mirror and the first TN liquid crystal element form an angle of 45°. The polarization directions of the light emitted from the first TN liquid crystal element 13 and the reflection mirror 14 in this case are shown in FIGS. 3(a) and 3(b), respectively.

Here, the above two TN liquid crystal elements are homogeneously aligned, and the director of the liquid crystal molecules located on the light incident side is
is configured so that the direction of the polarized light coincides with the polarization direction of the polarized light incident on the TN liquid crystal element.

As a result, the two emitted lights 17 and 18 are combined into polarized light having the same polarization direction.

Here, the rotation directions of the planes of polarization by the first and second TN liquid crystal elements do not necessarily have to be the same direction, but in FIGS. 3(a) and 3(C), θ1=90°−θ
It is necessary that there be three relationships.

As described above, in the present invention, after spatially separating randomly polarized light from a light source into two linearly polarized lights whose polarization directions are orthogonal to each other, two TN liquid crystal elements and at least one reflective mirror are used to separate the two linearly polarized lights. By combining the linearly polarized lights so that their polarization directions are the same, it is possible to exchange random polarized light with specific linearly polarized light with high efficiency.

〔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] Fig. 1 (perspective view) shows one embodiment of the polarizing element of the present invention.
Shown below. Please also refer to FIG. 2.

The main components will be explained below. The polarizing beam splitter 11 is a Ma (Nielle type) visible broadband type, and the light incident side is coated with an antireflection film (average reflectance at the time of incidence is 0.7% or less). A polarizing beam splitter is made by forming a multilayer film on the oblique sides of two right-angled prisms and joining the oblique sides together, and has excellent polarization separation properties.

Other polarizing beam splitters, such as plate-shaped ones, can also be used depending on the wavelength range of the light. The first and second liquid crystal elements 13.12 had the same specifications, used nematic liquid crystal with Δn = 0.264 (20''C), gap length = 7.0 μm, and Tonist angle = 45°. The liquid crystal element and the polarizing beam splitter were made using the same glass material (BK7), and the zero-reflection mirror 14 in optical contact was made by vapor-depositing aluminum on a glass plate (BK7) (approximately 90% in the visible range). As the zero-reflection mirror (having a reflectance of may also be
A 200W xenon lamp was used as a light source.

In a polarizing element using the above components, randomly polarized light 15 from a light source is separated by a polarizing beam splitter 11 into two linearly polarized lights (P polarized light 24 and S polarized light 23) with equal intensity and orthogonal polarization directions. be done. While the separated S-polarized light passes through the second TN liquid crystal element 12, it rotates clockwise by 45° (
The polarization plane is rotated by θ3=45°). However, the second liquid crystal element 12 is installed parallel to the exit surface of the polarization beam splitter on the S-polarization side. Similarly, the P-polarized light passes through the first TN liquid crystal element 13 at 45° (θ
1-45°), and further, the polarization direction is symmetrically reversed (symmetrical angle of 45°, that is, rotated 90° clockwise) by the reflecting mirror 14 (θ2 = 45°).
. However, the first liquid crystal element 13 is arranged parallel to the exit plane on the P polarization side of the polarizing beam splitter, and the reflection mirror 14 is arranged so that the normal line of the mirror and the first liquid crystal element form an angle of 45°. is set up. As a result, two outgoing lights 1
7.18 is polarized light having the same polarization direction (θ2=03) and traveling in the same direction. Therefore, by combining these two lights, it was possible to convert random polarized light from a light source into specific linearly polarized light with high efficiency without causing any loss of light.

FIG. 4 shows the relative light intensity distribution of the emitted light with respect to the incident light. It can be seen that a conversion efficiency of about 80% or more is obtained in the visible region, and that the wavelength dependence of the conversion efficiency is very small. Note that the wavelength dependence can be changed by changing the parameters of the liquid crystal element.

In addition, with this polarizing element, the width of the output beam increases relative to the input beam, but it is possible to reduce the width of the output beam to less than that of the input beam by combining the two beams using mirrors, lenses, etc. It should be noted that this is obvious and that the broadening of the width of the emitted light beam is not a drawback at all. Furthermore, the angle between the normal line of the reflecting mirror 14 and the first liquid crystal element is 45
It is possible to combine the two light beams without using the mirrors or lenses mentioned above by setting the value slightly larger than °, but it is possible to avoid widening the light beam width at the time of synthesis, but in that case, The synthesis distance becomes very long, and the conversion efficiency to specific polarized light deteriorates to some extent.

[Example 2] A polarizing element similar to that in Example 1 was produced. However, the twist angle of the first liquid crystal element is 30 degrees counterclockwise when viewed from the side facing the output light, and the twist angle of the second liquid crystal element is 30 degrees clockwise when viewed from the side facing the output light. °. This polarizing element also has approximately 8
It was confirmed that a conversion efficiency of 0% or more (conversion efficiency of specific linearly polarized light to random polarized light) could be obtained.

〔Effect of the invention〕

As explained above, in the polarizing element of the present invention, after spatially separating randomly polarized light from a light source into two linearly polarized lights whose polarization directions are orthogonal to each other, the polarizing element uses two TN liquid crystal elements and at least one reflective mirror to , by combining two linearly polarized lights so that their polarization directions are equal, it is possible to convert random polarized light into specific linearly polarized light with high efficiency (that is, excellent light utilization efficiency). This means that more specific linearly polarized light can be obtained from a given light source than before, and in other words, it means that a smaller light source can be used to obtain the same intensity of specific polarized light. There is. In addition, by appropriately selecting the twist angle, twist direction, and liquid crystal material used in the two TN liquid crystal elements that rotate the plane of polarization, the wavelength dependence of the output light intensity can be controlled. It is possible to freely control the optical characteristics (spectrum, distribution of luminous flux, etc.) during synthesis, and this is particularly effective when it is necessary to increase the cross-sectional area of the emitted luminous flux. Therefore, the polarizing element of the present invention is most effectively applied to a light source section of a liquid crystal display element, a light source section of a liquid crystal printer, etc. that require specific linearly polarized light.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing one configuration of a polarizing element of the present invention. FIG. 2 is a diagram for explaining the function of the polarizing element of the present invention. FIG. 3(a) is a diagram showing the polarization direction of polarized light emitted from the first TN liquid crystal element. FIG. 3(b) is a diagram showing the polarization direction of polarized light emitted from the reflection mirror. FIG. 3(C) is a diagram showing the polarization direction of polarized light emitted from the second TN liquid crystal element. FIG. 4 is a diagram showing the intensity spectrum of emitted light obtained by the polarizing element of the present invention shown in Examples. 11...Polarizing beam splitter 12...Second TN liquid crystal element 13...First TN liquid crystal element 14...Reflection mirror 15...Random polarized light 16...From the first TN liquid crystal element Polarization direction of polarized light emitted from the reflective mirror Polarization direction of polarized light emitted from the reflecting mirror Polarization direction of polarized light emitted from the second TN liquid crystal element 21 Light source 22 Birefringent layer interface 23...S polarized light component 24...P polarized light component or more

Claims (3)

[Claims] (1) A means for spatially separating randomly polarized light from a light source into mainly two linearly polarized light components (P polarized light and S polarized light) whose polarization planes are orthogonal to each other, and It is characterized by being composed of two twisted nematic liquid crystal elements, which are means for rotating, and a reflecting mirror, which is a means for symmetrically inverting the plane of polarization of one of the two linearly polarized light components. polarizing element. (2) The polarization plane rotation angle of the linearly polarized light component by the two twisted nematic liquid crystal elements is θ with respect to the P polarized light.
, 90°-θ with respect to S-polarized light. (3) The means for spatially separating the randomly polarized light from the light source into mainly two linearly polarized light components (P polarized light and S polarized light) whose polarization planes are orthogonal to each other is a polarizing beam splitter. The polarizing element according to claim 1.