JP2006145644A - Polarization splitter and projection display apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization splitter which uses a multilayer film polarized beam splitter (PBS) causing no color shift dependent on wavelength. <P>SOLUTION: The polarization splitter has two polarization splitting surfaces for reflecting an S-polarized beam in which two surfaces are arranged in parallel, wherein one surface performs transmission and reflection with respect to a first effective polarized beam and makes the beam incident to and outgoing from a reflection type image display element, and the other surface at least performs reflection with respect to a second effective polarized beam. According to such a constitution, optical path lengths of respective wavelengths of the S-polarized beam are equalized and image display without color shift dependent on wavelength can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polarization beam splitting device configured by a polarization beam splitter (hereinafter referred to as PBS) having a transmission or reflection action depending on the polarization state of P-polarized light or S-polarized light, and a projection display device using the same.

  The types of liquid crystal display elements used in liquid crystal projectors and projection televisions are roughly classified into a transmissive LCD panel (hereinafter referred to as “transmissive panel”) and a reflective LCOS panel (hereinafter referred to as “reflective type”). Panel)). In the transmissive panel, when downsizing or high resolution is performed, the aperture ratio of each pixel is reduced due to circuit wiring, and the black matrix around each pixel is conspicuous. On the other hand, in the case of a reflective panel, circuit wiring can be arranged on the back side of a pixel having a reflective surface, so that an image with an inconspicuous black matrix can be obtained. In the case of a reflective panel, since the light beam passes through the liquid crystal layer twice, the thickness of the liquid crystal layer can be reduced accordingly, and the response of the liquid crystal becomes faster. This means that the reflective panel is suitable for television applications that display moving images.

  By the way, in the case of a transmissive panel, transmission of ON light and shielding of OFF light can be realized by a shutter action of liquid crystal. On the other hand, in the case of a reflective panel, both ON light and OFF light are reflected. Therefore, it is necessary to transmit ON light and block OFF light by a combination of polarization state control and PBS.

  The operation will be described with reference to FIG. In FIG. 9, a light beam aligned with P-polarized light by an illumination optical system (not shown) passes through the PBS 10 disposed in front of the reflective panel 20 and is irradiated to the reflective panel 20. In the state where each pixel is ON, P-polarized light is converted to S-polarized light while reciprocating the liquid crystal layer, so that it is reflected by the PBS 10 and the optical path is bent toward the projection lens 30 side. When each pixel is in the OFF state, it remains P-polarized light even if it reciprocates through the liquid crystal layer. Therefore, it passes through the PBS 10 again and returns to the illumination optical system (not shown) side, and the light beam cannot reach the projection lens 30. .

  As shown in FIG. 10, the optical path layout is reflected light that is incident on the PBS 10 as S-polarized light, reflected S-polarized light is applied to the reflective panel 20, and is converted to P-polarized light when each pixel is ON. However, an optical path layout that passes through the PBS 10 may be used. In any case, the PBS 10 acts as a polarizer and an analyzer for the reflective panel 20.

  By the way, as the PBS, a PBS prism having a dielectric multilayer film provided on the PBS surface is widely known. However, this PBS prism is used for a light beam perpendicularly incident on the prism as shown in FIG. Although the extinction ratio (ratio of ON light to OFF light) is good, it has a characteristic that the extinction ratio to obliquely incident light is bad. The perpendicular incidence to the prism is 45 degrees with respect to the PBS surface, and this ray is usually the design center ray for the film design.

  On the other hand, there is a metal grid type PBS in which a metal grid called ProFlux (trade name) manufactured by MOXTEK is provided on the surface of a glass plate. This metal lattice type PBS has an extinction ratio with respect to a light beam incident on a glass plate at 45 degrees (light beam at the design center), which is worse than that of the PBS prism, but the deterioration of the extinction ratio with an oblique incident light beam deviated from 45 degrees. Therefore, a good extinction ratio can be obtained as a whole light beam having a small angular spread. However, in the configuration in which light rays pass through the glass plate obliquely, astigmatism occurs, so there are restrictions on the optical layout, and for the projection lens, an air layer is required. Increases the size of the projection lens.

  In response to these problems, Non-Patent Document 1 below discloses a PBS using a multilayer film prism. This multilayer prism PBS prism has an extinction ratio with respect to oblique incidence better than a PBS prism provided with a dielectric multilayer film.

  By the way, in this document, as an example of the multilayer film, the number of layers is 892 and the thickness is described as about 0.15 mm.

  In this document, a glass plate is disposed in order to prevent the generation of astigmatism due to the difference between the refractive index of the PBS prism and the refractive index of the multilayer film. The glass plate itself that can be confirmed in the figure in the non-patent document can be made unnecessary by selecting a glass material close to the refractive index of the film as the glass material of the prism.

SID03 DIGEST High-Performance LCoS Optical Engineering Using Cartesian Polarizer

  Problems when the multilayer film is used in the PBS of FIGS. 9 and 10 will be described with reference to FIGS. 11 and 12. FIG. In the first place, the layers in the multilayer film that act on the light beams of each wavelength included in the visible light are separate layers. In FIG. 9, the reflected light that is incident on the PBS 10 with P-polarized light and is transmitted to the reflective panel 20 is turned on, and the reflected light converted to S-polarized light is now PBS 10. I explained that it reflects. Since FIG. 11 has the same layout as FIG. 9, S-polarized reflected light from the reflective panel 20 is reflected by the PBS 10. In this case, the first wavelength ray 4 is reflected by the layer 1 of the multilayer film, the second wavelength ray 5 is reflected by the layer 2, and the third wavelength ray 6 is reflected by the layer 3. Accordingly, light beams of different wavelengths emitted from the same point on the reflective panel 20 are reflected by different layers of the multilayer film. That is, when reflecting the multilayer film which comprises the PBS surface of PBS10, the optical path length difference by the difference in wavelength arises. As a result, color deviation occurs in the projected white image. When the thickness of the multilayer film of about 0.15 mm is converted to the length on the reflective panel 20, it is multiplied by √2 to be about 0.2 mm. This amount is as large as 10 to 20 times the size of one pixel, indicating that it cannot be used in the projection system.

  Similarly, in FIG. 10, the reflected light that is incident on the PBS 10 as S-polarized light and is reflected on the reflective panel 20 is turned on, and the reflected light converted to P-polarized light is now turned on with each pixel of the reflective panel 20 turned on. Explained that it penetrates PBS10. Since FIG. 12 has the same layout as FIG. 10, the S-polarized light incident on the PBS 10 is reflected by the PBS surface and enters the reflective panel 20. In this case, the first wavelength ray 4 is reflected by the layer 1 of the multilayer film, the second wavelength ray 5 is reflected by the layer 2, and the third wavelength ray 6 is reflected by the layer 3. Therefore, when the S-polarized light beam from the illumination optical system (not shown) reflects the multilayer film constituting the PBS surface of the PBS 10, an optical path length difference due to the difference in wavelength occurs, and the wavelength on the reflective panel 20 is increased. It will be irradiated every time. If a deviation occurs in the effective range of the reflective panel, so-called color unevenness occurs in the peripheral portion. This deviation is an amount by which the light beam of the illumination optical system is displaced on the reflective panel 20, so that the reflective panel 20 is preliminarily formed. If you leave a large area to irradiate, there is no problem. However, although the uneven color can be prevented by increasing the irradiation range of the reflective panel 20 by, for example, about 0.2 mm as described above, it is not preferable because the light transmission rate is deteriorated accordingly. In the future, as the reflective panel 20 becomes smaller, the influence of about 0.2 mm will increase.

  Even if the light beam transmission rate is sacrificed, the layout of optical components as shown in FIG. 12 is essential, which is a constraint in terms of the layout of the optical system.

  The present invention has been made in view of the above-described problems, and the object thereof is an optical path length difference caused by a difference in wavelength at the time of PBS surface reflection, which occurs when a multilayer film PBS in which the PBS surface is formed of a multilayer film is used. It is an object of the present invention to provide a polarization separation device that can reduce color misregistration and color unevenness.

  In order to achieve the above-described object, the present invention is a polarization separation device that irradiates light from a light source onto a reflective image display element and emits reflected light from the reflective image display element toward the projection lens. Two planes are arranged in parallel and have two polarization separation planes for reflecting S-polarized light. One plane transmits and reflects the first effective polarized light, and is used for reflection type image display elements. The light enters and exits, and the other surface is configured to reflect at least the second effective polarized light. With this configuration, the optical path length of each wavelength of S-polarized light can be made equal.

  According to the present invention, it is possible to provide a polarized light separation device free from color shift and color unevenness even when a multilayer film PBS having an excellent extinction ratio is used.

  The specific configuration and operation of the present invention will be described below with reference to the drawings.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a polarization separation apparatus according to a first embodiment of the present invention, FIG. 2 is a diagram for explaining the principle of correcting the optical path length difference depending on the wavelength of the polarization separation apparatus according to the first embodiment, and FIG. FIGS. 4A and 4B are diagrams illustrating a modification of the example polarization separation device, and FIG. 4 is a configuration diagram of a main part in which the polarization separation device according to the first embodiment is applied to a three-plate reflection type panel. 1 to 4, elements having the same function are denoted by the same reference numerals.

  First, the configuration of the polarization beam splitting apparatus according to the first embodiment will be described with reference to FIG. In FIG. 1, the polarization separation device includes a first PBS 11 disposed on the incident optical path of the reflective panel 20, a reflection mirror 50 that reflects the transmitted light from the first PBS 11, and a reflected mirror 50 that transmits the transmitted light from the first PBS 11. A quarter-wave plate 40 that converts the polarization direction of the transmitted light into a perpendicular polarization direction while reciprocating between the PBS, a PBS surface 11a that is a polarization separation surface of the first PBS 11, and a PBS surface 12a that is the polarization separation surface. Are arranged so as to be parallel to each other. The reflection type panel 20, the quarter wavelength plate 40, and the reflection mirror 50 are arranged on the prism surfaces of the first PBS 11 and the second PBS 12 over which the PBS surface 11a and the PBS surface 12a can face each other.

  When a light beam 110p that has been previously aligned with P-polarized light as effective polarized light by an illumination optical system (not shown) is incident on the first PBS 11 as shown in FIG. 1, the P-polarized light is transmitted through the first PBS 11. The transmitted P-polarized light beam 110p passes through the quarter-wave plate 40, is reflected by the reflection mirror 50, and passes through the quarter-wave plate 40 again, thereby being converted into S-polarized light. Accordingly, the effective polarized light becomes S-polarized light, and the S-polarized light beam 110 s is reflected by the PBS surface 11 a of the first PBS 11 and the PBS surface 12 a of the second PBS 12 and is applied to the reflective panel 20. When the pixel of the reflective panel 20 is ON, the S-polarized light is converted to the P-polarized light and reflected, so that the P-polarized light becomes effective polarized light, and the P-polarized light beam 120p, which is effective polarized light, becomes the second PBS 12 , And enters the projection lens 30.

  Here, PBS in which a multilayer film is sandwiched between two prisms is used for the first PBS 11 and the second PBS 12, but in this embodiment, the PBS surface 12a of the second PBS 12 faces the PBS surface 11a of the first PBS 11 as shown in FIG. Are aligned.

  In FIG. 2, of the S-polarized light beam 110s, which is effective polarized light from the reflecting mirror 50, the light beam having the first wavelength is reflected by the layer 11a1 of the PBS surface 11a, and further reflected by the layer 12a1 of the PBS surface 12a. The light enters the reflective panel 20. The light beam having the third wavelength is reflected by the layer 11a3 on the PBS surface 11a, and further reflected by the layer 12a3 on the PBS surface 12a and enters the reflective panel 20. Accordingly, the optical path lengths of the respective wavelengths from the reflecting mirror 50 to the reflective panel 20 are equal, that is, the optical path length difference caused by the wavelength generated on the PBS surface 11a is canceled by the optical path length difference generated on the PBS surface 12a (that is, depending on the wavelength). The optical path length difference is corrected), and color unevenness due to the difference in wavelength can be prevented.

  FIG. 3 shows a configuration in which prisms facing each other between the first PBS 11 and the second PBS 12 are integrated. In FIG. 1, the first PBS 11 and the second PBS 12 are constituted by four triangular prisms, but in FIG. 3, two triangular prisms and one parallelogram-shaped quadrangular prism are used, and a multilayer film is formed at the interface between them. The PBS surfaces 13a and 13b, which are polarization separation surfaces of the configuration, are formed to constitute the integrated PBS 13. This is a configuration in which the half-wave plate is not disposed between the first PBS 11 and the second PBS 12 in FIG. 1, so that the facing prisms can be integrated.

  FIG. 4 shows an example in which the polarization separation device of FIG. 1 is used in a three-plate configuration. In FIG. 4, 60 is a dichroic prism, and 71 and 72 are half-wave plates. In FIG. 4, other components having the same functions as those in FIG. 1 are denoted by the same reference numerals.

  In FIG. 4, P-polarized white light is previously separated into three colors of red, green, and blue by a color separation means (not shown), and light beams of the respective colors are incident on the polarization separation device described with reference to FIG. The luminous flux reflected by each reflective panel 20 is color-combined by a dichroic prism 60 having a color-combining action and is incident on the projection lens 30. The two colors are incident on the cross dichroic prism 60 after the polarization state is converted from P-polarized light to S-polarized light by the half-wave plates 71 and 72 arranged in front of the dichroic prism 60 in two optical paths. Is done. The reason why the polarization states of the two colors (for example, red and blue) are converted by the half-wave plates 71 and 72 is that the S-polarized light is more efficient in reflection, and the same polarization state for all three colors. This is because it is more efficient to design the cross dichroic prism 60 with red and blue as S-polarized light and green as P-polarized light.

  Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a diagram for explaining a modification of the polarization separation device according to the second embodiment of the present invention, and FIG. 6 is a diagram for explaining a modification of the polarization separation device according to the second embodiment. 5 and 6, elements having the same functions in FIGS. 1 to 3 are denoted by the same reference numerals, and description thereof is omitted.

  As shown in FIG. 5, when a light beam preliminarily aligned with P-polarized light as effective polarized light by an illumination optical system (not shown) is incident on the first PBS 11, the P-polarized light is transmitted through the first PBS 11 and irradiated on the reflective panel 20. . When the pixel of the reflective panel 20 is ON, the P-polarized light is converted to S-polarized light and reflected, so that the S-polarized light becomes effective polarized light and the S-polarized light beam is reflected by the PBS surface 11a of the first PBS 11. . The reflected S-polarized light beam is reflected by the PBS surface 12 a of the second PBS 12 and enters the projection lens 30.

  Here, PBS in which a multilayer film is sandwiched between two prisms is used for the first PBS 11 and the second PBS 12, but the PBS surface 12a of the second PBS 12 is arranged so as to be parallel to the PBS surface 11a of the first PBS 11. Thus, for the same reason described in FIG. 2, the optical path length difference due to the wavelength difference can be reduced, and as a result, the color shift can be prevented.

  FIG. 6 shows a configuration in which prisms facing each other between the first PBS 11 and the second PBS 12 are integrated. In FIG. 5, the first PBS 11 and the second PBS 12 are configured by four triangular prisms, but in FIG. 6, two triangular prisms and one parallelogram-shaped quadrangular prism are used, and a multilayer film is formed at the interface between them. The PBS surfaces 13a and 13b, which are polarization separation surfaces of the configuration, are formed to constitute the integrated PBS 13. This is because the half-wave plate is not disposed between the first PBS 11 and the second PBS 12 in FIG. 5, so that the prisms facing each other can be integrated.

  Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 7 is a diagram illustrating a polarization separation apparatus according to a third embodiment of the present invention, and FIG. 8 is a diagram illustrating a modification of the polarization separation apparatus according to the third embodiment. 7 and 8, elements having the same functions in FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted.

  As shown in FIG. 7, when a light beam that has been previously aligned with S-polarized light as effective polarized light by an illumination optical system (not shown) is incident on the first PBS 11, the S-polarized light is reflected by the PBS surface 11 a of the first PBS 11. The reflected S-polarized light beam is reflected by the PBS surface 12 a of the second PBS 12 and is applied to the reflective panel 20. When the pixel of the reflection type panel 20 is ON, the S-polarized light is converted to the P-polarized light and reflected, so that the P-polarized light becomes effective polarized light, and the P-polarized light beam passes through the second PBS 12 and is projected. 30 is incident.

  Here, PBS in which a multilayer film is sandwiched between two prisms is used for the first PBS 11 and the second PBS 12, but the PBS surface 12a of the second PBS 12 is arranged so as to be parallel to the PBS surface 11a of the first PBS 11. Thus, for the same reason described in FIG. 2, the optical path length difference due to the difference in wavelength can be reduced, and as a result, uneven color can be prevented.

  FIG. 8 shows a configuration in which prisms facing each other between the first PBS 11 and the second PBS 12 are integrated. In FIG. 7, the first PBS 11 and the second PBS 12 are configured by four triangular prisms, but in FIG. 7, two triangular prisms and one parallelogram-shaped quadrangular prism are used, and a multilayer film is formed at the interface between them. The PBS surfaces 13a and 13b, which are polarization separation surfaces of the configuration, are formed to constitute the integrated PBS 13. This is because the half-wave plate is not arranged between the first PBS 11 and the second PBS 12 in FIG. 7, and the prisms facing each other can be integrated.

In the embodiments described above, the reflective panel is an LCOS panel. However, the present invention is not limited to this, and it is needless to say that any reflective light valve that modulates light intensity using optical rotation may be used. Absent.
FIG. 13 is a block diagram showing the configuration of a projection display device to which the polarization separation device of the present invention is applied.

  In FIG. 13, reference numeral 1 denotes a light source, which is a white lamp such as an ultra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, a mercury xenon lamp, or a halogen lamp. The light emitted from the light bulb of the light source 1 is reflected by, for example, the parabolic reflecting mirror 2, becomes parallel to the optical axis, and enters the first array lens 3. The first array lens 3 divides incident light into a plurality of lights by a plurality of lens cells arranged in a matrix, and efficiently guides the light to pass through the second array lens 4 and the polarization conversion element 5. That is, the first array lens 3 is designed so that the light source 1 and each lens cell of the second array lens 4 have an object-image relationship (conjugate relationship) with each other. Similar to the first array lens 3, the second array lens 4 having a plurality of lens cells arranged in a matrix form reflects the shape of the lens cell of the first array lens 3 corresponding to each of the constituting lens cells. Project to the panel 20. At this time, the light from the second array lens 4 in the polarization conversion element 5 is aligned with a predetermined polarization direction, that is, S-polarized light in this embodiment. The light beam divided into a plurality by the first array lens 3 is projected onto the reflective panel 20 by the second array lens 4 and a condensing lens (not shown), and has a level of uniformity with no practical problem. Illumination with a high illuminance distribution is possible.

  The light beam aligned with the S-polarized light as the effective polarized light by the polarization conversion element 5 is incident on the first PBS 11 and reflected by the PBS surface. The reflected S-polarized light beam, which is effective polarized light, is reflected by the PBS surface of the second PBS 12 and applied to the reflective panel 20. When the pixel of the reflective panel 20 is ON, the S-polarized light is converted to the P-polarized light and reflected, so that the P-polarized light becomes effective polarized light, and the P-polarized light passes through the second PBS 12 and is projected. Incident to

  Although the case where the polarization separation device in the third embodiment is applied as the polarization separation device in the present embodiment has been described, the polarization separation device in the first or second embodiment is also applicable. Not too long.

BRIEF DESCRIPTION OF THE DRAWINGS The figure explaining the polarization splitting device of the 1st Example of this invention. The figure explaining the correction principle of the optical path length difference by a wavelength. The figure explaining the modification of the polarization beam splitter of the 1st Example of this invention. The principal part block diagram which applied the polarized light separation apparatus of the 1st Example of this invention to the 3 plate-type reflection type panel. The figure explaining the polarization splitting device of the 2nd Example of this invention. The figure explaining the modification of the polarization beam splitter of the 2nd Example of this invention. The figure explaining the polarization splitting device of the 3rd Example of this invention The figure explaining the modification of the polarization splitting device of the 3rd Example of this invention. The figure explaining the layout in which the ON light beam reflected by the reflective panel is reflected by PBS. The figure explaining the layout which ON luminous flux reflected by the reflection type panel permeate | transmits PBS. The figure explaining the effect | action of the multilayer film PBS in the layout in which the ON light beam reflected by the reflective panel reflects in PBS. The figure explaining the effect | action of the multilayer film PBS in the layout which the ON light beam reflected by the reflection type panel permeate | transmits PBS. It is a block diagram which shows the structure of the projection type display apparatus to which the polarized light separation apparatus of this invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Reflecting mirror, 3 ... 1st array lens, 4 ... 2nd array lens, 5 ... Polarization conversion element, 10 ... PBS, 11 ... 1st PBS, 12 ... 2nd PBS, 13 ... Integrated PBS, 20 ... reflective panel, 30 ... projection lens, 40 ... 1/4 wavelength plate, 50 ... reflective mirror, 60 ... cross dichroic prism, 71, 72 ... 1/2 wavelength plate.

Claims (8)

A polarization separation device that irradiates light from a light source onto a reflective video display element and emits reflected light from the reflective video display element toward a projection lens,
The two surfaces are arranged in parallel and have two polarization separation surfaces that reflect S-polarized light,
One surface transmits and reflects the first effective polarized light, and enters and outputs the light to and from the reflective image surface element.
The other surface is configured to reflect at least the second effective polarized light,
A polarization beam splitting device, characterized in that the optical path length of each wavelength of the S-polarized light is equal.   The polarization separation device according to claim 1, wherein a retardation plate is not disposed between the two polarization separation surfaces.   3. The polarization separation device according to claim 1, wherein the two polarization separation surfaces are film surfaces of a multilayer film prism in which a multilayer film is sandwiched between two prisms. 4. . The first effective polarized light is S-polarized light when the light is incident on the reflective image display element, and P-polarized light when emitted.
4. The polarization separation device according to claim 1, wherein the second effective polarized light is S-polarized light. 5. The first effective polarized light is P-polarized light when the light is incident on the reflective image display element, and S-polarized light when emitted.
4. The polarization separation device according to claim 1, wherein the second effective polarized light is S-polarized light. 5.   It has four triangular prisms, each of the two polarization separation surfaces is sandwiched between two triangular prisms, and two sets of the sandwiched two triangular prisms are integrated. The polarization beam splitting device according to any one of claims 1 to 5.   Two triangular prisms and one parallelogram-shaped quadrangular prism, and the two polarization separation surfaces are configured to be sandwiched between the triangular prism and the rectangular prism, respectively. The polarization separation device according to claim 1, wherein the polarization separation device is provided. A light source;
A polarization conversion element that aligns the luminous flux from the light source with predetermined polarized light;
The polarization separation device according to any one of claims 1 to 7,
A reflective video display element that forms an optical image based on a video signal;
A projection lens for enlarging and projecting an optical image from the image display element,
A projection-type display device, wherein a light beam enters and exits the image display element through the polarization separation device.

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