JP2007093964A - Polarization conversion element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization conversion element having a low production cost. <P>SOLUTION: The polarization conversion element 5 comprises a birefringent plate 6 and is provided with a 1/2 wavelength plate 7 on a prescribed position of the birefringent plate 6. When randomly polarized light L1 is made incident to the polarization conversion element 5, a component of linear polarization in the direction orthogonal to the light axis of the birefringent plate 6 becomes a normal light ray, advances on an optical path of incident light L1 as it is, becomes linearly polarized light L2 and is emitted from a second path, in a birefringent plate 6. Also, a component of linear polarization in the direction parallel to the light axis of the birefringent plate 6 becomes an abnormal light ray, refracts in the birefringent plate 6, becomes a linearly polarized light ray L3 and is separated. Further on an emission surface of the linearly polarized light L3 becoming an abnormal light ray, the 1/2 wavelength plate 7 is disposed; a polarization surface of linearly polarized light is rotated by 90° and the abnormal light ray is converted into a linearly polarized light L3' in the polarization direction equal to the linearly polarized light L2 of a normal light ray and is emitted from the first path. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polarization conversion element, and more particularly to a low-cost polarization conversion element that exhibits a predetermined function with a simple structure as compared to a polarization conversion element that uses a prism array having a complicated structure.

Liquid crystal projectors that can directly project a screen displayed by a personal computer or the like onto a screen are becoming widespread for the purpose of presentations, etc., and have been downsized, improved resolution, and improved light utilization efficiency. It is illustrated.
Therefore, a polarized light conversion element is built in the liquid crystal projector, and a predetermined light beam output from a light source using a halogen lamp or the like is subjected to polarization conversion so that the polarization direction of the light beam incident on the liquid crystal panel is aligned and efficient use of light energy is achieved. Has been made.

  FIG. 2 shows a configuration example of a conventional polarization conversion element. The polarization conversion element 1 has a structure including a half-wave plate 4 made of a film at a predetermined position of a prism array 3 in which an optical thin film 2 is formed on the slope of a prism made of white glass. Further, although not shown, a reflection film is applied to the incident / exit surface of the prism array 3 and the exit surface of the half-wave plate 4.

  Hereinafter, the function of the polarization conversion element shown in FIG. 2 will be described. First, a light beam emitted from a light source such as a halogen lamp includes an S-polarized component and a P-polarized component, and is input to the prism array 3 as incident light of the polarization conversion element 1. Here, since the light beam necessary for the projection of the screen using the liquid crystal panel is only the polarization component of either S-polarized light or P-polarized light, the polarization direction of the emitted light is set to one direction using the polarization conversion element 1. In order to use light energy efficiently in liquid crystal projectors.

Hereinafter, the principle of aligning the polarization direction of outgoing light in one direction will be described.
First, the P-polarized component of incident light input to the prism array 3 is reflected by the optical thin film 2 and input to the half-wave plate 4. The optical thin film 2 functions to reflect the P-polarized component of incident light and transmit the S-polarized component. Here, the P-polarized component of the incident light is emitted as S-polarized light from the first path by rotating the polarization plane by 90 ° when passing through the half-wave plate. On the other hand, the S-polarized light component contained in the incident light input to the prism array 3 is transmitted through the optical thin film 2 and emitted as S-polarized light from the second path. Therefore, the outgoing light output from the polarization conversion element 1 is aligned with the S-polarized light, and efficient use of light energy is achieved in the liquid crystal projector.
JP 2005-91750 A

However, the conventional polarization conversion element has a complicated manufacturing process because a half-wave plate is bonded and fixed at a predetermined position after a prism array in which an optical thin film is formed on the slope of a prism made of white glass is manufactured. As a result, the manufacturing cost has increased and has been a problem.
The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a polarization conversion element having a low manufacturing cost.

In order to achieve the above object, a polarization conversion element according to the present invention has the following configuration.
The polarization conversion element according to claim 1 is a polarization conversion element constituted by a birefringent plate processed to a predetermined plate thickness and a half-wave plate, and the optical axis of the birefringent plate incident on the birefringent plate. The component of linearly polarized light in the direction perpendicular to the straight line travels straight through the optical path of incident light as an ordinary ray, while the component of linearly polarized light in the direction parallel to the optical axis of the birefringent plate is abnormal. The light beam is refracted as a light beam by a birefringent plate, separated from the optical path of the incident light by a predetermined distance and emitted, and the extraordinary light beam emitted from the birefringent plate is polarized using the half-wave plate. The extraordinary ray is rotated by 90 deg so as to be emitted as linearly polarized light having the same polarization direction as that of the ordinary ray.

  The polarization conversion element according to claim 2 is configured to use quartz as a substrate material of the birefringent plate.

  The change conversion element according to claim 3 is configured to use rutile or lithium niobate as a substrate material of the birefringent plate.

  Since the invention according to any one of claims 1 to 3 is different from a polarization conversion element using a prism array having a complicated structure that has been conventionally used, the polarization conversion element is configured using a single birefringent plate. Since the structure is simple, it is easy to manufacture and exhibits a great effect in providing a low-cost polarization conversion element.

Hereinafter, the present invention will be described in detail based on illustrated embodiments.
In the present invention, a prism array having a complicated structure is not required, and a polarization conversion element is configured using a single-plate birefringent plate. As is well known, the birefringent plate is made of a birefringent crystal or the like, and separates incident light rays into ordinary rays and extraordinary rays having polarization directions orthogonal to each other. Therefore, the separated extraordinary ray is rotated by 90 ° using a half-wave plate to obtain a linearly polarized light having the same polarization direction as the ordinary ray, and the polarization direction of the outgoing light emitted from the polarization conversion element is changed to the ordinary ray. By aligning them, the liquid crystal projector functions so as to use light energy efficiently.

  FIG. 1 is a structural diagram showing an embodiment of a polarization conversion element according to the present invention. The polarization conversion element 5 includes a birefringent plate 6, and includes a half-wave plate 7 at a predetermined position of the birefringent plate 6. Therefore, when the randomly polarized light L1 emitted from a light source such as a halogen lamp is incident on the polarization conversion element 5, the component of linearly polarized light in the direction orthogonal to the optical axis of the birefringent plate 6 in the birefringent plate 6 is Then, it becomes an ordinary ray, goes straight through the optical path of the incident light L1, and is emitted from the second path as linearly polarized light L2. On the other hand, the linearly polarized light component in the direction parallel to the optical axis of the birefringent plate 6 becomes an extraordinary ray and is refracted by the birefringent plate 6 to be separated into the linearly polarized light L3.

  On the other hand, a half-wave plate 7 is provided on the exit surface of the linearly polarized light L3 that has become an extraordinary ray, and the polarization plane of the linearly polarized light is rotated by 90 ° so that the extraordinary ray is the same as the ordinary linearly polarized light L2. Is converted into linearly polarized light L3 ′ having a proper polarization direction and emitted from the first path. Therefore, the linearly polarized light emitted from the polarization conversion element 5 is aligned with the polarization direction of ordinary light.

  Next, the separation distance between the ordinary ray L2 and the extraordinary ray L3 that are separated when the randomly polarized light L1 enters the birefringent plate 6 will be described. The polarization conversion element 5 uses a birefringent plate 6 made of a birefringent crystal or the like processed to a predetermined plate thickness, and the incident random polarized light L1 is converted into ordinary linearly polarized light L2 and extraordinary linearly polarized light L3. The separation distance d between the ordinary ray and the extraordinary ray increases as the difference between the ordinary ray refractive index n0 and the extraordinary ray refractive index ne increases, and the thickness of the substrate material increases. If the thickness of the birefringent plate 6 is t, the separation distance d can be expressed by the following equation.

d = t · | ((n 0 ² −ne ² ) · tan θ) / (n 0 ² · tan θ + ne ² ) | (1)
However, θ is an angle formed by the principal surface normal of the birefringent plate and the optical axis, and when quartz is used as the birefringent plate, it is usually desirable to set it at 45 °.

  The separation distance d is related to the transmission efficiency between the incident light and the outgoing light, and the transmission efficiency increases as the separation distance d is reduced and the pitch for attaching the half-wave plate is reduced. However, there is a tradeoff with cost. The thickness t of the birefringent plate is appropriately determined so as to obtain optimum optical characteristics.

  As a substrate material for the birefringent plate, quartz is often used from the viewpoint of ease of use and cost, but it is also possible to use a crystal such as lithium niobate or rutile having birefringence.

It is a structural diagram showing an example of a polarization conversion element according to the present invention. The structural example of the conventional polarization conversion element is shown.

Explanation of symbols

1. Polarization conversion element,
2. Optical thin film,
3. Prism array,
4. 1/2 wave plate,
5. ・ Polarization conversion element,
6. Birefringent plate,
7 ・ ・ 1/2 wave plate

Claims (3)

In a polarization conversion element including a birefringent plate and a half-wave plate processed to a predetermined plate thickness,
The component orthogonal to the optical axis direction of the linearly polarized birefringent plate obtained by being incident on the birefringent plate is emitted as an ordinary ray by traveling straight through the optical path of the incident light and incident on the birefringent plate. A component parallel to the optical axis direction of the obtained linearly polarized birefringent plate is refracted as an extraordinary ray in the birefringent plate, and separated into an optical path separated by a predetermined distance from the optical path of the incident light and emitted. The extraordinary ray emitted from the birefringent plate is rotated by 90 ° in the polarization direction using the half-wave plate, and the extraordinary ray is linearly polarized in the same polarization direction as the ordinary ray. A polarization conversion element that is emitted as The polarization conversion element according to claim 1, wherein quartz is used as a substrate material of the birefringent plate. The polarization conversion element according to claim 1, wherein rutile or lithium niobate is used as a substrate material of the birefringent plate.

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