JP5759288B2 - Polarization modulator and image projection apparatus - Google Patents

Description

The present invention relates to a polarization modulator used in an image projection apparatus such as a liquid crystal projector.

  Some image projection apparatuses as described above have a liquid crystal element that is driven in synchronization with image output on the screen side, which is a projection surface, with respect to a projection lens (projection optical system). Patent Document 1 discloses an image projection apparatus that displays a 3D image by alternately projecting a right-eye image and a left-eye image for each field using a liquid crystal element. Patent Document 2 discloses a video display device that improves video characteristics, such as reducing the afterimage feeling of a video by inserting a black image into the video using a liquid crystal element.

Japanese Patent Laid-Open No. 10-28275 JP 2001-42282 A

  The liquid crystal elements used in the devices disclosed in Patent Documents 1 and 2 are required to have high-speed response. For example, an optically compensated bend (OCB) type liquid crystal element is known as a liquid crystal element excellent in high-speed response. However, since the liquid crystal molecules of the OCB type liquid crystal element are bend-aligned and the liquid crystal element has self-compensation property in the rubbing direction, the incident angle characteristic in the rubbing direction is incident in the direction orthogonal to the rubbing direction. Angular characteristics are degraded.

  When high-speed modulation is performed by arranging a liquid crystal element on the screen side of the projection lens, the incident angle of light to the liquid crystal element is determined by the angle of view of the projection lens. However, particularly when a wide-angle projection lens is used, color unevenness occurs in the projected image.

  In an image projection apparatus using polarized light, light from a light source is converted into linearly polarized light of P-polarized light or S-polarized light, and then color separation and color composition are performed on a plurality of light modulation elements (liquid crystal display elements). For this reason, unless a phase difference plate is arranged on the exit side, the exit polarized light that forms the projected image is linearly polarized light having a polarization direction of 0 degrees or 90 degrees with respect to the horizontal direction.

  When the light emitted from the projection lens is projected as it is onto the screen as in the image projection apparatus disclosed in Patent Document 1, the emission polarization has a polarization direction that makes 0 degree or 90 degrees with respect to the horizontal, and the liquid crystal The element has a rubbing direction of 45 degrees with respect to the horizontal direction. For this reason, the diagonal direction of the projected image is a direction with a low incident angle characteristic, and when the angle of view of the projection lens to be used is increased, the color unevenness becomes conspicuous.

  In addition, if the rubbing direction of the liquid crystal element is a horizontal direction, it does not hold as it is, so a 45-degree polarizing plate must be inserted as an analyzer, and as a result, the amount of light to be projected (that is, the brightness of the projected image) Is halved.

  Furthermore, Patent Document 2 does not take into consideration any color unevenness in the screen or reduction in the amount of transmitted light that occurs when the backlight light source has a wide angle of view as in the image projection apparatus.

  The present invention provides a polarization modulation device capable of projecting a bright image with little color unevenness and an image projection device using the same.

A polarization modulation device according to one aspect of the present invention is a projection optical system that projects a plurality of color lights modulated by a light modulation element and having different wavelength bands onto a projection surface, and is disposed closer to the light modulation element than the projection optical system A wavelength-selective phase difference plate that matches the polarization direction of the specific color light among the plurality of color lights with the polarization direction of the other color light, and is disposed closer to the projection surface than the projection optical system, and is 45 degrees with respect to the horizontal direction. An incident polarizing plate having an inclined polarization transmission axis, and a half position that emits polarized light having a polarization direction of 45 degrees with respect to the horizontal direction, disposed between the wavelength selective phase difference plate and the incident polarizing plate. It has a phase difference plate and an optically compensated bend type liquid crystal cell which is disposed closer to the projection surface side than the incident polarizing plate and whose rubbing direction is inclined by 45 degrees with respect to the polarization transmission axis of the incident polarizing plate.

  Note that an image projection apparatus that includes at least a light modulation element that modulates light from a light source and in which the polarization modulation device is integrally provided or detachably mounted also constitutes another aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, even when the light incident angle to a liquid crystal cell is large, the polarization modulation apparatus which can display a projection image with little color unevenness can be provided.

1 is a diagram illustrating a configuration of an image projection apparatus having a polarization modulation device that is Embodiment 1 of the present invention. FIG. 1 is an exploded view of a polarization modulation device of Embodiment 1. FIG. The exploded view which shows the structure of an OCB system liquid crystal element. FIG. 6 is an exploded view of a polarization modulation device that is Embodiment 2 of the present invention. FIG. 6 is an exploded view of a polarization modulation device that is Embodiment 3 of the present invention.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows the configuration of a liquid crystal projector (image projection apparatus) provided with a polarization modulation device that is Embodiment 1 of the present invention. As an example, the polarization modulation apparatus of the present embodiment has a configuration suitable for improving video characteristics, such as inserting a black image in a video to reduce the afterimage feeling in the video.

  In FIG. 1, reference numeral 100 denotes a liquid crystal projector main body, which accommodates an illumination optical system, a color separation / synthesis optical system, and a liquid crystal panel. Reference numeral 1 denotes a light source such as a discharge lamp, and reference numeral 2 denotes an integrator that separates light from the light source 1 into a plurality of light fluxes and collects the light fluxes so as to overlap each other on a liquid crystal panel described later. The integrator 2 also includes a polarization conversion element that converts non-polarized light from the light source into linearly polarized light having a predetermined polarization direction.

  Reference numeral 3 denotes a dichroic mirror, which transmits light in the green wavelength band (green light: hereinafter referred to as G light), and transmits light in the red wavelength band (hereinafter referred to as R light) and in the blue wavelength band. Reflects light (blue light: hereinafter referred to as B light).

  Reference numeral 4 denotes an R wavelength selective phase difference plate that rotates only the polarization direction of the R light by 90 degrees. Reference numeral 5 denotes a reflection type liquid crystal display element (hereinafter referred to as a G liquid crystal panel) as a light modulation element for G light, and reference numeral 6 denotes a reflection type liquid crystal display element (hereinafter referred to as a B liquid crystal panel) as a light modulation element for B light. ). Reference numeral 7 denotes a reflective liquid crystal display element (hereinafter referred to as an R liquid crystal panel) as a light modulation element for R light.

  8a is a first polarization beam splitter, and 8b is a second polarization beam splitter. These first and second polarization beam splitters 8a and 8b transmit P-polarized light and reflect S-polarized light. A dichroic prism 9 transmits R light and B light and reflects G light.

  When the light converted by the polarization conversion element and emitted from the integrator 2 is S-polarized light, the G light as S-polarized light that has passed through the dichroic mirror 3 is reflected by the first polarization beam splitter 8a to be G Incident on the liquid crystal panel 5. The G light modulated and reflected by the G liquid crystal panel 5 becomes P-polarized light, passes through the first polarization beam splitter 8a, and enters the dichroic prism 9.

  On the other hand, the R light as S-polarized light reflected by the dichroic mirror 3 is rotated in the polarization direction by the R-wavelength selective phase difference plate 4 to become P-polarized light and enters the second polarizing beam splitter 8b. The R light passes through the second polarization beam splitter 8 b and enters the R liquid crystal panel 7. The R light modulated and reflected by the R liquid crystal panel 7 becomes S-polarized light, is reflected by the second polarization beam splitter 8b, and enters the dichroic prism 9.

  Further, the B light as S-polarized light reflected by the dichroic mirror 3 passes through the R-wavelength selective retardation plate 4 as it is and enters the second polarizing beam splitter 8b, and the second polarizing beam splitter 8b The light is reflected and enters the B liquid crystal panel 6. The B light modulated and reflected by the B liquid crystal panel 6 becomes P-polarized light, passes through the second polarization beam splitter 8b, and enters the dichroic prism 9.

  In the dichroic prism 9, the G light is reflected and the R light and the B light are transmitted. Thereby, the R light, the G light, and the B light are combined and enter the polarization modulator 200. The G light and B light emitted from the dichroic prism 9 are P-polarized light, and the R light is S-polarized light. That is, the polarization direction of the R light that is one specific color light among the plurality (three) of color lights is different from the polarization direction of the G light and B light that are the other color lights.

  In the polarization modulator 200, reference numeral 10 denotes an R wavelength selective phase difference plate that rotates only the polarization direction of the R light by 90 degrees, and matches the polarization direction of the R light with the polarization directions of the G light and the B light. As a result, the R light, G light, and B light emitted from the R wavelength selective phase difference plate 10 are all S-polarized light. Reference numeral 11 denotes a projection lens as a projection optical system.

  The R wavelength selective phase difference plate 10 is disposed between the projection lens 11 and the color separation / synthesis optical system, in other words, closer to the liquid crystal panel (5 to 7) side than the projection lens 11, that is, the light modulation element side. When the R wavelength selective phase difference plate 10 is arranged on the screen (17) side, that is, the projection surface side with respect to the projection lens 11, the R wavelength selective phase difference plate 10 is obtained when the projection lens 11 has a wide angle of view. Depending on the incident angle characteristics, the four corners of the projected image may be colored. On the other hand, since the projection lens 11 and the color separation / synthesis optical system are telecentric, such a problem does not occur.

  Reference numeral 12 denotes a ½ retardation plate (λ / 2 plate) that rotates the polarization direction of the incident polarized light by 45 degrees, and is disposed between the R wavelength selective retardation plate 10 and an incident polarizing plate 13 described later. ing.

  Reference numeral 13 denotes an incident polarizing plate, which is disposed on the screen (17) side, that is, on the projection surface side of the projection lens 11. The three color lights are analyzed by the first and second polarization beam splitters 8 a and 8 b, but the polarization state may be disturbed by the dichroic prism 9, the R wavelength selective phase difference plate 10 and the projection lens 11. For this reason, the incident polarizing plate 13 is disposed on the screen side of the projection lens 11 to cut unnecessary light.

  Reference numeral 14 denotes a liquid crystal cell as a liquid crystal layer that modulates incident polarized light at high speed, and is disposed on the screen side of the incident polarizing plate 13.

  Reference numeral 15 denotes a phase compensation plate, which is disposed on the screen side of the liquid crystal cell 14. Reference numeral 16 denotes an exit polarizing plate, which is disposed on the screen side of the phase compensation plate 15. The screen 17 projects the light emitted from the polarization modulator 200 and displays an image. Instead of the screen 17, an image may be projected and displayed on a projection surface other than the projector-dedicated screen, such as a wall of a room.

  The liquid crystal cell 14 used in the polarization modulator 200 of this embodiment is an optically compensated bend (OCB) type liquid crystal cell, and as shown in FIG. 3, the liquid crystal molecules are bowed along the rubbing direction. (Bend orientation). For this reason, it has the characteristic that the incident angle characteristic of a rubbing direction is high. However, the incident angle characteristic is lower in the direction orthogonal to the rubbing direction than in the rubbing direction.

  When the liquid crystal cell 14 is arranged on the screen side with respect to the projection lens 11 to perform high-speed modulation of incident light, the projection lens 11 has a wide angle of view (for example, the half angle of view of the projection lens 11 is 35 degrees or more). ) Color unevenness occurs in the projected image in a direction orthogonal to the rubbing direction. Since the projected image is a rectangular image, and the diagonal direction of the rectangle has the largest angle of view, the rubbing direction of the OCB type liquid crystal cell is preferably a vertical direction or a horizontal direction with respect to the image plane.

  However, the polarization direction of the polarized light emitted from the projector main body 100 is 0 or 90 degrees. For this reason, when the OCB type liquid crystal cell is arranged as it is, the rubbing direction becomes 45 degrees, and color unevenness is conspicuous only in the direction orthogonal to the rubbing direction in the diagonal direction of the projected image. On the other hand, if the OCB type liquid crystal cell is arranged so that the rubbing direction is the horizontal direction or the vertical direction in order to reduce color unevenness, the amount of light incident on the incident polarizing plate 13 is halved.

  In the polarization modulation device 200 of the present embodiment, as shown in FIG. 2, a ½ phase difference is provided on the liquid crystal panel side (between the R wavelength selective phase difference plate 10 and the incident polarizing plate 13) with respect to the incident polarizing plate 13. A plate 12 is arranged. And it adjusts so that the emitted polarized light from the 1/2 phase difference plate 12 may have a polarization direction of 45 degrees with respect to the horizontal direction or the vertical direction.

  A birefringent material having uniaxial birefringence in the plane is used for the half retardation plate 12. A uniaxial birefringent material has a fast axis and a slow axis perpendicular to the fast axis, the phase of the polarization component along the fast axis advances, and the phase of the polarization component along the slow axis is delayed. Has characteristics. When the phase difference between the fast axis and the slow axis is set to ½ of the wavelength, a 1/2 phase difference plate is used, and when the angle between the slow axis and the incident linearly polarized light is θ, 2θ Only has the function of rotating the polarization direction.

  In the present embodiment, the polarization direction of the polarized light incident on the half phase plate 12 is the horizontal direction (specific direction). In this case, when the slow axis of the 1/2 phase difference plate 12 is arranged at 22.5 degrees, the polarization direction of the polarized light emitted from the 1/2 phase difference plate 12 is 45 degrees with respect to the horizontal direction. . For this reason, the polarization transmission axis of the incident polarizing plate 13 is inclined 45 degrees with respect to the horizontal direction, and the rubbing direction of the liquid crystal cell 14 is changed to the horizontal direction (specific direction) inclined 45 degrees with respect to the polarization transmission axis of the incident polarizing plate 13. In the same direction). Therefore, it is possible to arrange a direction in which the incident angle characteristic of the liquid crystal cell 14 is good with respect to the diagonal direction where the angle of view is large, thereby reducing color unevenness of the projected image. Note that the ½ phase difference plate 12 may be disposed between the R wavelength selective phase difference plate 10 and the projection lens 11.

  The phase compensation plate 15 compensates the incident angle characteristic of the liquid crystal cell 14. The phase compensation plate 15 is preferably arranged before and after the liquid crystal cell 14 so as to sandwich the liquid crystal cell 14. However, as shown in FIGS. 1 and 2, the color unevenness can be further reduced by disposing at least the liquid crystal cell on the screen side.

  The exit polarizing plate 16 cuts unnecessary light out of the light modulated by the liquid crystal cell 14. The exit polarizing plate 16 is arranged in a crossed nicols state with respect to the incident polarizing plate 13. That is, the exit polarizing plate 16 has a polarization transmission axis orthogonal to the polarization transmission axis of the incident polarization plate 13.

  In this embodiment, a reflective liquid crystal display element is used as a light modulation element in the projector main body 100, but a transmissive liquid crystal display element or a micromirror device (DMD) may be used. In this embodiment, the outgoing polarized light from the R wavelength selective phase difference plate 10 is S-polarized light, but it may be P-polarized light.

  Further, in this embodiment, the wavelength-selective retardation plate 10 that rotates only the polarization direction of the R light is used. However, the wavelength-selective retardation plate that rotates the polarization direction of the G light and B light. It is good. Further, a wavelength-selective phase plate that rotates the polarization direction of the G light may be used in accordance with the change in the optical configuration of the projector main body 100. Further, in combination with the 1/2 phase difference plate, the polarization direction of the R light is rotated 45 degrees, the polarization direction of the G light and the B light is rotated by −45 degrees, and the polarization direction of the R light is changed to the G light and It is good also as an element matched with the polarization direction of B light.

  In this embodiment, the rubbing direction of the liquid crystal cell 14 is a horizontal direction, but the rubbing direction may be a vertical direction (a direction orthogonal to a specific direction) inclined by 45 degrees with respect to the polarization transmission axis of the incident polarizing plate 13. . Many projectors have a so-called lens shift function for shifting the projection lens in a direction perpendicular to the optical axis. However, if the lens shift amount in the vertical direction is increased, the angle of view may be larger in the vertical direction than in the horizontal direction. Therefore, it is advantageous to take the rubbing direction perpendicular to color unevenness.

  In this embodiment, the half retardation plate 12, the incident polarizing plate 13, the liquid crystal cell 14, the phase compensation plate 15 and the exit polarizing plate 16 are arranged in this order on the screen side from the projection lens 11. Yes. On the other hand, the half retardation plate 12, the incident polarizing plate 13, the liquid crystal cell 14, the phase compensation plate 15, and the exit polarizing plate 16 can be disposed between the dichroic prism 9 and the projection lens 11. In this case, however, the incident angle characteristic of the liquid crystal cell 14 is improved, but the back focus of the projection lens 11 is increased, and the size of the projection lens 11 is significantly increased.

  FIG. 4 shows the configuration of a polarization modulation device that is Embodiment 2 of the present invention. The polarization modulation apparatus of the present embodiment has a configuration suitable for displaying 3D video.

  The present embodiment has a configuration in which the exit polarizing plate 16 is removed from the configuration of the polarization modulator 200 of the first embodiment. In this configuration, polarized light having a polarization direction of 45 degrees and −45 degrees with respect to the horizontal direction is projected alternately according to the modulation of the liquid crystal cell 14. And by projecting the image for the right eye and the image for the left eye in synchronization with this, the user is provided with a polarizing plate having a polarization transmission axis of 45 degrees for the right eye, and the polarization transmission axis is − A 3D image can be observed through polarizing glasses having a 45-degree polarizing plate.

  FIG. 5 shows the configuration of a polarization modulation device that is Embodiment 3 of the present invention. The polarization modulation device of the present embodiment also has a configuration suitable for displaying 3D video.

  The present embodiment has a configuration in which a quarter retardation plate 18 is used instead of the exit polarizing plate 16 used in the polarization modulator 200 of the first embodiment. Viewing angle characteristics from the user can be improved by providing a ¼ phase difference plate for one of the right eye and the left eye of the polarizing glasses used by the user and a polarizing plate for the other.

  By using the polarization modulation device of each embodiment described above integrally provided in the projector main body or detachably mounted, it is possible to easily project an image that is brighter and less uneven in color than conventional projectors. .

  Each embodiment described above is only a representative example, and various modifications and changes can be made to each embodiment in carrying out the present invention.

  It is possible to provide a polarization modulation device and an image projection device capable of projecting a bright image with little color unevenness.

DESCRIPTION OF SYMBOLS 100 Liquid crystal projector main body 200 Polarization modulator 5, 6, 7 Reflection type liquid crystal display element 10 R wavelength selective phase difference plate 11 Projection lens 12 1/2 phase difference plate 13 Incident polarizing plate 14 Liquid crystal cell 15 Phase compensation plate 17 Screen

Claims (9)

A projection optical system that projects a plurality of color lights having different wavelength bands modulated by the light modulation element onto a projection surface;
A wavelength-selective phase difference plate that is disposed on the light modulation element side of the projection optical system and matches the polarization direction of specific color light among the plurality of color lights with the polarization direction of other color light;
An incident polarizing plate disposed on the projection surface side of the projection optical system and having a polarization transmission axis inclined by 45 degrees with respect to the horizontal direction;
A half-phase plate that is disposed between the wavelength-selective phase plate and the incident polarizing plate and emits polarized light having a polarization direction of 45 degrees with respect to the horizontal direction;
A polarization modulation comprising: an optically compensated bend type liquid crystal cell disposed on the projection surface side of the incident polarizing plate and having a rubbing direction inclined by 45 degrees with respect to the polarization transmission axis of the incident polarizing plate. apparatus. The polarization modulation device according to claim 1, further comprising a phase compensation plate disposed closer to the projection surface than the optical compensation bend type liquid crystal cell. The polarization modulation device according to claim 1, wherein the rubbing direction is the same direction as the horizontal direction. Polarization modulation apparatus according to claim 1 or 2, characterized in that the rubbing direction is the direction perpendicular to the horizontal direction. 2. The liquid crystal cell according to claim 1, further comprising an exit polarizing plate that is disposed closer to the projection surface than the optical compensation bend type liquid crystal cell and has a polarization transmission axis perpendicular to the polarization transmission axis of the incident polarization plate. 5. The polarization modulation device according to any one of items 1 to 4. Polarization modulation device according to any one of claims 1 to 5 in which the half angle of the projection optical system is characterized in that at least 35 degrees. Said wavelength-selective phase plate, the polarization modulator according to any one of claims 1 to 6, wherein a retardation plate for rotating 90 ° the polarization direction of the red light is a specific color light . The light modulation element is a reflective liquid crystal display polarization modulating device according to any one of claims 1 to 7, characterized in that the element. Including a light modulation element for modulating light from the light source;
Image projection apparatus a polarization modulator according to any one of claims 1 8, characterized in that it is mounted so as to be or removably provided integrally.