JP2008009118A - Polarization conversion unit, illumination device using the same and projection type image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the polarization conversion efficiency of a polarization conversion unit used for an image display device. <P>SOLUTION: An illumination device for the image display device to lighten a liquid crystal panel 6 with uniformly distributed light is provided with a light source 1, a first rod integrator 2, a polarized beam splitter (PBS) array 3, a second rod integrator 4 and a 1/2 wave length plate 5. The PBS array 3 comprises 4 PBSs 3a-d. A P-polarized component transmitting the PBS array 3 (PBS 3b-3c) is converted to S-polarized light by the 1/2 wave length plate 5 pasted to an incident surface side of the second rod integrator 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarization conversion unit that converts incident random polarized light into unidirectional polarized light and emits it, an illumination device using the same, and an illumination device using the same.

  The vibration direction (polarization direction) of light emitted from the light source from the liquid crystal projector is various (random). On the other hand, linearly polarized light in a specific direction needs to be incident on a liquid crystal panel that generates image light by modulating light from the light source. For this purpose, a polarizing plate that transmits only linearly polarized light in one direction out of random polarized light is provided on the incident side of the liquid crystal panel. This incident side polarizing plate transmits polarized light in one direction and absorbs polarized light orthogonal thereto. If it does so, about half of the light was lost in the incident side polarizing plate, and there also existed a problem that the incident side polarizing plate heated up for absorption.

  Therefore, there is a liquid crystal projector that solves the above problem by disposing a polarization conversion unit using a PBS (Polarized Beam Splitter) array in front of the incident side polarizing plate (for example, Patent Document 1, Non-patent document 1). This polarization conversion unit has a structure in which a half-wave plate is attached to the PBS light exit surface of a part of the PBS array, and has a function of aligning polarized light in one direction. Thereby, since the polarized light incident on the incident side polarizing plate is aligned in one direction, the loss of light in the incident side polarizing plate can be reduced.

An example of said polarization conversion unit is shown. As shown in FIG. 3, the polarization conversion unit includes polarization beam splitters 63a, 63b, 63c, and 63d, and half-wave plates 63e and 63f. The polarization beam splitters 63b and 63c transmit the P-polarized light among the incident random polarized light and change the optical path of the S-polarized light by 90 °. p-polarized light refers to polarized light whose electric field vector oscillation plane is parallel to the plane on which the incident and outgoing light rays are formed, whereas s-polarized light refers to the plane of electric field vector oscillation on the plane on which the incoming and outgoing light rays are formed. Vertical polarization. The polarization beam splitters 63a and 63d change the optical path of the S-polarized light separated by the polarization beam splitters 63b and 63c by 90 ° and guide it in the same direction as the traveling direction of the P-polarized light transmitted through the polarization beam splitters 63b and 63c. The half-wave plates 63e and 63f convert the P-polarized light transmitted through the polarization beam splitters 63b and 63c into S-polarized light. As described above, the polarization conversion unit has a function of converting incident random polarized light into linearly polarized light in a specific direction.
JP-A-11-72707 Information Display Research Committee Report (March 1998)

  However, when a PBS array in which a plurality of polarizing beam splitters are bonded as described above is formed, a step may be generated between the polarizing beam splitters due to manufacturing tolerances (FIG. 4A). In addition to the displacement at the time of pasting, a step occurs due to the variation in the size of the polarizing beam splitter.

  When the half-wave plates 63e and f are to be attached to the entire exit surface of the polarizing beam splitter in which such a level difference has occurred, a portion where air has intervened is provided in the vicinity 63g of the polarizing beam splitters 63b and 63c. As a result, peeling easily occurs (FIG. 4B). In particular, since a high temperature is applied when an antireflection film (AR coating) is applied to the exit surface side of the PBS array, the half-wave plate is more easily peeled off. When such peeling occurs, there is a problem that the polarization plane of the light converted into the polarized light in the specific direction is disturbed or the dispersion angle reduced by the first rod integrator 2 becomes large again.

  In order to eliminate this inconvenience, a half-wave plate slightly smaller than the exit surfaces of the polarization beam splitters 63b and 63c may be attached to the exit side of the polarization beam splitter of the PBS array (FIG. 4). (C)).

  However, in the polarization conversion unit of FIG. 4C, the half-wave plates 63e and 63f are slightly smaller than the exit surfaces of the polarization beam splitters 63b and 63c. As a result, among the P-polarized light that has passed through the polarizing beam splitters 63b and 63c, one that is not converted to S-polarized light is generated. Light that is not converted to S-polarized light cannot be transmitted through the above-described incident-side polarizing plate, and therefore cannot be used for light modulation in the liquid crystal panel, which causes a reduction in light use efficiency. Therefore, the configuration as shown in FIG. 4C is not preferable.

  Accordingly, an object of the present invention is to improve the polarization conversion efficiency of a polarization conversion unit employed in an image display device or the like.

  The polarization conversion unit according to the present invention is a polarization conversion unit that converts random polarized light into unidirectional polarized light, and separates the random polarized light into a first polarized light and a second polarized light orthogonal to the first polarized light. First and second polarizing beam splitters, and first and second reflecting means for reflecting the first polarized light separated by the first and second polarizing beam splitters and guiding them in the same direction as the second polarized light, respectively An optical member having an incident surface larger than the combined size of the exit surfaces of the first and second polarizing beam splitters on at least the exit side of the first and second polarizing beam splitters; A half-wave plate for converting the second polarized light separated by the polarizing beam splitter into the first polarized light is attached to the incident surface of the optical member.

  In the polarization conversion unit, a half-wave plate that receives P-polarized light emitted from the first and second polarization beam splitters and converts it to S-polarized light is attached to the incident surface of the optical member. Since there is no step formed at the boundary between the first and second polarizing beam splitters on this incident surface, there is no possibility that the half-wave plate will be peeled off.

  Preferably, the optical member is a rod integrator that makes light distribution uniform.

  Since this rod integrator serves both as a holder for holding the half-wave plate and a function for making the light distribution uniform, it can contribute to a reduction in the number of parts of the illumination device.

  An illuminating device of the present invention is an illuminating device including the above-described polarization conversion unit, a light source that emits randomly polarized light, and a taper that is incident on the polarization conversion unit by reducing a dispersion angle of light from the light source. Features a type rod integrator.

  According to the configuration described above, the polarization conversion unit not only has a function of converting random polarization into polarization in a specific direction, but also allows the outgoing light from the taper-type rod integrator to be enlarged and incident on the rod integrator. The size of the rod integrator is determined according to the size of the liquid crystal panel. Therefore, according to the illumination device having the above-described configuration, it is possible to reduce the size of the tapered rod integrator that reduces the light dispersion angle.

  A projection display apparatus according to the present invention includes the illumination device, a display element that modulates light from the illumination device and displays an image, and a projection optical system that enlarges and projects an image of the display element. It is characterized by.

  According to the present invention, it is possible to improve the polarization conversion efficiency of a polarization conversion unit (unit) employed in an image display device or the like.

  Hereinafter, embodiments of the polarization conversion unit and the illumination device of the present invention will be described.

  1 and 2 are diagrams showing the configuration of the illumination device of the present invention. 1 is a front view, and FIG. 2 is a perspective view. The illumination device includes a light source 1, a first rod integrator 2, a PBS array 3, a second rod integrator 4, and a half-wave plate 5. This illumination device illuminates the liquid crystal panel 6 with light having a uniform illuminance distribution by the action of the first and second rod integrators.

  The light source 1 is, for example, an LED light source. The first rod integrator 2 has a tapered shape in which the exit surface is larger than the entrance surface. The light beam incident on the first rod integrator 2 is repeatedly reflected on the side surface of the first rod integrator 2 to reduce the light dispersion angle.

  The PBS array 3 includes four polarizing beam splitters (PBS) 3a to d. This PBS array is arranged such that the incident surfaces of the polarization beam splitters 3 b and 3 c are opposite to the exit surface of the first rod integrator 2. Further, the exit surface of the first rod integrator 2 has substantially the same size as the sum of the entrance surfaces of the polarization beam splitters 3b and 3c. Therefore, almost all of the outgoing light from the first rod integrator 2 enters the polarization beam splitter 3b or 3c. Then, light (random polarization) from the first rod integrator 2 is separated into P-polarized light and S-polarized light by the polarization beam splitters 3b and 3c. The separated P-polarized light passes through the polarization beam splitters 3b and 3c.

  On the other hand, the S-polarized light separated by the polarization beam splitter 3b is reflected by the polarization separation film of the polarization beam splitter 3b and travels toward the polarization beam splitter 3a. Then, the light is reflected by the polarization beam splitter 3 a and travels toward the second rod integrator 4. The S-polarized light separated by the polarization beam splitter 3c is reflected by the polarization separation film of the polarization beam splitter 3c and travels toward the polarization beam splitter 3d. Then, the light is reflected by the polarization beam splitter 3 d and travels toward the second rod integrator 4.

  The half-wave plate 5 is attached to the incident surface side of the second rod integrator 4 and converts the incident P-polarized light into S-polarized light and emits it. The half-wave plate 5 is affixed to the second rod integrator 4 at a position in front of the exit surfaces of the polarization beam splitters 3b and 3c. The size of the incident surface of the second rod integrator 4 is substantially the same as the sum of the exit surfaces of the polarization beam splitters 3b and 3c. Therefore, almost all of the P-polarized light emitted from the polarization beam splitters 3b and 3c is incident on the half-wave plate 5 and converted to S-polarized light.

  On the other hand, the S-polarized light emitted from the polarization beam splitters 3 a and 3 d enters the second rod integrator 4 as it is. Therefore, all the emitted light from the polarization beam splitters 3a, 3b, 3c, and 3d becomes S-polarized light and enters the second rod integrator 4.

  The second rod integrator 4 makes the illuminance distribution of the incident light uniform. The light beam incident on the second rod integrator 4 is emitted as a uniform surface light source while repeatedly reflecting on the side surface of the second rod integrator 4.

  Then, the light emitted from the second rod integrator 4 is modulated by the liquid crystal panel 6 and output as video light. In this way, the illuminating device of this embodiment makes light of uniform distribution and linearly polarized light incident on the liquid crystal panel.

  The polarizing beam splitters 3b and 3c correspond to examples of the first and second polarizing beam splitters in the claims of the present application, respectively. The polarization beam splitters 3a and 3d correspond to examples of the first and second reflecting means in the claims of the present application, respectively. The 2nd rod integrator 4 is equivalent to an example of the optical member of a claim of this application.

  In addition, an example of the polarization conversion unit of the present invention includes the polarization beam splitters 3a to 3d, the second rod integrator 4, and the half-wave plate 5.

(Modification)
In FIG. 2, the liquid crystal panel 6 is arranged so that the y direction in the figure becomes a long side, but may be arranged so that the x direction in the figure becomes a long side. Needless to say, the sizes of the first rod integrator 2, the PBS array 3, and the second rod integrator 4 should be appropriately determined according to the arrangement direction of the liquid crystal panel 6.

  Further, instead of the polarization beam splitters 3a and 3d that reflect S-polarized light and guide it toward the second rod integrator 4, a prism having a reflecting surface or a reflecting mirror may be used.

  Further, by using three illumination devices as shown in FIG. 1 (FIG. 2), a three-plate (3LCD system) video display device can be realized. That is, the illumination device and the red liquid crystal panel using the red LED as the light source 1, the illumination device and the green liquid crystal panel using the green LED, the illumination device and the blue liquid crystal using the blue LED. A three-panel image display device can be realized by providing a panel and color combining means (for example, using a dichroic cube) that combines light from the three lighting devices.

  Further, a projection type image display device (a liquid crystal projector, a rear projection television, etc.) may be realized by providing a projection lens after the color synthesizing means.

  Alternatively, if a single-panel image display device using only one illumination device is realized, a white LED is used as the light source (light source 1), or LEDs of three colors of red, green, and blue are used. What is mounted on one board | substrate is used.

  In the above example, there are four polarizing beam splitters (polarizing beam splitters 3b and 3c as "first and second polarizing beam splitters" and polarizing beam splitters 3a and 3d as "first and second reflecting means". However, it may be a configuration provided with four or more polarization beam splitters.

  Moreover, in the said Example, although the half-wave plate 5 is affixed on the light-incidence surface of the 2nd rod integrator 4, it is a transparent plate-like member (glass plate) on the light-incidence surface side of the 2nd rod integrator 4. And a half-wave plate may be attached to the plate member. In this case, the transparent plate-like member corresponds to the “optical member” in the claims of the present application.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

It is a front view of the illuminating device of this invention. It is a perspective view of the illuminating device of this invention. It is a figure which shows an example of the polarization conversion unit known conventionally. (A) It is a figure which shows the polarization | polarized-light conversion unit pasted together in the state from which the polarization beam splitter shifted | deviated. (B) It is a figure which shows the polarization conversion unit comprised by sticking a 1/2 wavelength plate to the polarizing beam splitter of (a). (C) It is a figure which shows the polarization conversion unit which improved (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 1st rod integrator 3 PBS array 4 2nd rod integrator 5 1/2 wavelength plate 6 Liquid crystal panel

Claims (4)

A polarization conversion unit that converts random polarized light into polarized light in one direction,
First and second polarization beam splitters that separate random polarization from the light source into first polarization and second polarization orthogonal to the first polarization;
First and second reflecting means for respectively reflecting the first polarized light separated by the first and second polarizing beam splitters and guiding them in the same direction as the second polarized light;
An optical member having an incident surface larger than the combined size of the exit surfaces of the first and second polarizing beam splitters on at least the exit sides of the first and second polarizing beam splitters;
A half-wave plate for converting the second polarized light separated by the first and second polarizing beam splitters into the first polarized light is attached to the incident surface of the optical member. , Polarization conversion unit.
The polarization conversion unit according to claim 1, wherein the optical member is a rod integrator that makes light distribution uniform.
An illumination device comprising the polarization conversion unit according to claim 1,
A light source that emits randomly polarized light;
An illuminating device comprising a tapered rod integrator that reduces a dispersion angle of light from the light source and causes the light to enter the polarization conversion unit.
A lighting device according to claim 3;
A display element for displaying light by modulating light from the lighting device;
A projection-type image display apparatus comprising a projection optical system for enlarging and projecting an image of the display element.

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