JP2005242106A - Projection display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection display device which realizes a tight and uniform black screen and a bright and uniform white screen and is high in contrast ratio. <P>SOLUTION: Quarter-wavelength plates 10R, 10G and 10B are arranged among respective spatial optical modulators 61, 62, 63 of R, G and B and PBSs 3 and 4. S polarized light which is reflected light of the PBS 4 is made incident on the wavelength plate 10B for B. The slow axis of the wavelength plate 10B for B is arranged by being set perpendicularly to the polarization direction of the S polarized light. P polarized light which is the transmitted light of the PBS 4 is made incident on the wavelength plate 10R for R. The slow axis of the wavelength plate 10R for R is arranged by being set perpendicularly to the polarization direction of the P polarized light. P polarized light which is the transmitted light of the PBS 3 is made incident on the wavelength plate 10G for G. The slow axis of the wavelength plate 10G for G is arranged by being set perpendicularly to the polarization direction of the P polarized light. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a projection display device using a reflective light modulation element and a wave plate, and relates to increasing the contrast of the projected image.

  Projection-type display devices using reflective light modulation elements are characterized by their high resolution and high contrast ratio, and various configurations have been developed and commercialized. Most of them are three-plate type color projectors that use three reflection type light modulation elements, which separates the white light obtained from a powerful light source such as a metal halide lamp into three primary colors, and converts the color-separated light into corresponding colors. A method is adopted in which the light is guided to a spatial light modulator such as a liquid crystal panel driven by such a video signal, modulated, and the modulated light is combined and projected (see, for example, Patent Document 1).

  FIG. 10 shows a configuration example of a projection display device according to Patent Document 1. This optical system has a hierarchical structure up and down, and in the upper layer, the light source 11, the collimating lens 20, the integrator 21, the cold mirror 22, the infrared cut filter 23, the three-color separation cross dichroic prism 24, and the decomposed Polarizing beam splitter prisms 12r, 12g, and 12b that polarize each color and reflect it downward are arranged. Convex lenses 13r, 13g, 13b and polarizers 14r, 14g, 14b are arranged in the middle layer. Further, in the lower layer, the polarization beam splitter prisms 15r, 15g, and 15b, the wave plates 16r, 16g, and 16b, the reflective display elements 17r, 17g, and 17b, the three-color composition cross dichroic prism 25, and the projection lens 18 for each color light. Is arranged.

  The polarized light beam splitter prism 12 and the polarizer 14 in the upper layer portion make S-polarized linearly polarized light, and the S polarized light is reflected in the polarized beam splitter prism 15 in the lower layer portion and supplied to the reflective display element 17 for display. The light modulated by the liquid crystal of the element is reflected and returned to the polarization beam splitter prism 15 again, and the P-polarized light as the modulated component is transmitted and guided to the three-color synthesis dichroic prism 25.

  At this time, the wave plate 16 is disposed between the reflective display element 17 and the polarization beam splitter prism 15. When the oblique light component is incident on the polarization beam splitter film, it shifts from the linearly polarized light, so that the phase characteristic is corrected by the wave plate and returned to the straight line. In addition, the pretilt correction of the liquid crystal is also performed at the same time. The light beam synthesized in this way is projected onto the screen by the projection lens 18.

The necessity and correction effect of the above-described wave plate are described in detail in, for example, Patent Document 2. Further, a reflection type spatial light modulation element structure incorporating a wave plate and a structure of a liquid crystal projector device are described in Patent Document 3, for example.
JP 10-197949 A Japanese National Patent Publication No. 9-508709 JP-A-11-305574

  By the way, in recent years, projection-type display devices have come to have very high demands for high brightness and high contrast. In order to realize a high contrast ratio, a wave plate is disposed between the reflective display element and the polarizing beam splitter prism, thereby correcting oblique light components on the prism polarization separation surface of the polarizing beam splitter, and liquid crystal The pretilt is corrected. Therefore, in actual wave plate mounting, in order to obtain the maximum contrast ratio, as described in Patent Document 3, the circular wave plate having a circular outer shape is rotated and adjusted. However, by adjusting the wave plate, There is a problem that the contrast ratio varies greatly.

  In addition, since the wave plate is adjusted by rotating the wave plate, the wave plate must be attached in a circular movable structure, resulting in a complicated mechanism around the wave plate.

  Furthermore, since the circular movable structure portion is fixed after adjusting the wave plate, there is a problem that the adjustment position is shifted due to vibration or the like.

  The present invention has been made in view of the above points, and by arranging the wavelength plate in the optimum direction along the slow axis with respect to the pixel display region of the spatial light modulator, the tightened uniform black An object of the present invention is to provide a high-contrast-ratio projection display device that realizes a bright, uniform white screen.

In order to solve the above-mentioned problems, the present invention comprises means described in the following 1) to 3).
That is,
1) A projection display device using a light source, an illumination optical system, polarization selective conversion means, at least two sets of spatial light modulators and a wavelength plate corresponding to the spatial light modulators,
After the light emitted from the light source is made into substantially uniform parallel light by the illumination optical system, it is selected by the polarization selective conversion means as colored light according to the number of sets of the spatial light modulation elements, and the polarization direction is aligned. While being sequentially supplied to the wave plate and the spatial light modulator,
The slow axis of at least one set of the wave plates among the wave plates is made to substantially coincide with the long side direction of the aspect of the image display area of the corresponding reflection type light modulation element, and the slow axis of another set of wave plates Is configured to substantially coincide with the corresponding short side direction of the aspect.

2) Projection-type display device using a light source, an illumination optical system, polarization selective conversion means, three sets of spatial light modulation elements corresponding to three primary colors among the light sources, and a wavelength plate corresponding to the spatial light modulation element Because
After the light emitted from the light source is converted into uniform parallel light by the illumination optical system, it is selected by the polarization selective conversion means as color light according to the three sets of the spatial light modulation elements, and the polarization direction is aligned. Sequentially supplied to the plate and the spatial light modulator,
Of the three sets of wave plates, the slow axes of the two sets of wave plates are made to substantially coincide with the long side direction of the aspect of the image display area of the corresponding reflection type light modulation element, and the remaining one set of wave plates is delayed. A projection display device characterized in that the phase axis substantially coincides with the corresponding short side direction of the aspect.

  3) The projection display device according to 1) or 2), wherein the phase difference of the wave plate has a phase difference of approximately ¼ wavelength at the center wavelength of the color light.

  According to the “projection type display device” of the present invention, the aspect of the reflection type light modulation element using the reflection type light modulation element and two or more sets of wave plates and corresponding to the slow axis of at least one set of wave plates. A projection type capable of obtaining a high contrast ratio by substantially matching the long-side direction of the light source and substantially matching one or more pairs of wave plate slow axes with the short-side direction of the aspect of the corresponding reflective light modulation element A display device can be provided.

  In addition, since the wavelength plate is formed in a rectangular shape and finely adjusted and fixed to the pixel display region of the spatial light modulator, a mechanism for rotating and fixing the conventional disk-shaped wavelength plate after adjustment is provided. Since it does not have to be used, performance can be maintained after obtaining a high contrast ratio, and a projection display device with high reliability can be provided.

  The best mode for carrying out the invention of the projection type display apparatus according to the present invention will be described below with reference to preferred embodiments.

  FIG. 1 is a schematic plan view showing the configuration of a projection display device applied to this embodiment. As shown in the figure, a light source 11 that emits light including visible light from the left, an illumination optical system 19 that irradiates light emitted from the light source 11 toward the color separation / synthesis optical system 1 as uniform parallel light, and illumination light. Color separation / combination optical system 1 that separates the light into three primary colors, guides it to three spatial light modulators 61, 62, 63, and color-combines each light beam modulated according to the image signal, and projects image light onto a screen (not shown) The projection lens 18 is made up of. The color separation / synthesis part is composed of four polarization beam splitters (hereinafter referred to as PBS) and four wavelength selective phase plates.

  That is, the four first, second, third, and fourth PBSs 2, 3, 4, and 5 having a cubic or prism shape, and the polarization separating surfaces 21, 31, 41, and 51 of each PBS are substantially X-shaped. It is arranged to intersect. In this case, the first PBS 2 is the incident side PBS, and the fourth PBS 5 arranged at the diagonal position is the outgoing side PBS.

  Note that it is free to select the incident side PBS, but in any case, the PBS located diagonally with respect to the incident side PBS is always in the relationship with the outgoing side PBS.

  The front side of one light-transmitting surface 2a (incident side surface) selected from the four light-transmitting surfaces 2a, 2b, 2c, and 2d of the first PBS 2 (incident side PBS) and the fourth PBS 5 (outgoing side PBS) The first wavelength-selective polarization conversion that rotates the polarization plane of the G light by 90 ° behind one of the four translucent surfaces 5a, 5b, 5c, and 5d. Means (hereinafter referred to as G phase plate) 6 and 7 are arranged.

  Further, between the first PBS 2 and the third PBS 4 and between the third PBS 4 and the fourth PBS 5, the second wavelength selective polarization conversion that rotates the polarization plane of the R light by 90 °. Means (hereinafter referred to as R phase plate) 8 and 9 are provided.

  In this case, the spatial light modulation element 61 corresponding to the G light is disposed on the side surface of the light transmission surface 3c of the second PBS 3, and the spatial light modulation element 62 corresponding to the R light is the light transmission surface 4b of the third PBS 4. In addition, the spatial light modulation element 63 corresponding to the B light is arranged on the side surface of the light transmitting surface 4 a of the third PBS 4.

  The color separation photosynthesis system 1 performs the function of color-separating R, G, B light from white light and further synthesizing it as follows.

  First, S-polarized light of white light is given to the G phase plate 6. In this case, since the G phase plate 6 has a function of rotating the plane of polarization of only the G light by 90 °, only the G light out of the white light transmitted through the G phase plate 6 is subjected to polarization conversion to be S-polarized light. To P-polarized light. On the other hand, the R light and B light remain S-polarized light.

  Hereinafter, the transition of the optical path and the plane of polarization of each color light will be described individually.

  First, the G light transmitted through the G phase plate 6 will be described.

  The G light is converted to P-polarized light as described above. The G light travels straight through the polarization separation surfaces 21 and 31 of the first and second PBSs 2 and 3, exits from the light transmission surface 3 c of the second PBS 3, and enters the G-type reflective spatial light modulator 61. Incident. Then, the reflection type spatial light modulation element 61 receives light modulation according to the video signal corresponding to G and reflects the light.

  The S-polarized component of the G light generated by the light modulation is reflected by the polarization separation surface 31 of the second PBS 3 and enters the fourth PBS 5. Then, the light is reflected by the polarization separation surface 51 of the fourth PBS 5, is emitted from the light-transmitting surface 5 c of the fourth PBS 5, and is incident on the G phase plate 7 disposed in the subsequent stage.

  Since the G phase plate 7 has a function of rotating the polarization plane of the G light by 90 ° as described above, the S polarized light of the G light is converted into P polarized light and emitted.

  Next, the R light will be described.

  The S-polarized R light transmitted through the G phase plate 6 is reflected by the polarization separation surface 21 of the first PBS 2 and enters the R phase plate 8. Here, since the R phase plate 8 has a function of rotating the polarization plane of the R light by 90 °, the R light is converted from S-polarized light to P-polarized light, and is emitted therefrom. Incident. Further, the P-polarized R light travels straight through the polarization separation surface 41 of the third PBS 4, exits from the light-transmitting surface 4 b, and enters the R-compatible reflective spatial light modulator 62. Then, the reflection type spatial light modulator 62 receives light modulation corresponding to the R-compatible video signal and reflects the light.

  The light-modulated S-polarized component of the R light is reflected by the polarization separation surface 41 of the third PBS 4 and enters the R phase plate 9. Since the R phase plate 9 has the function of converting the polarization plane of the R light as described above, the S polarization component of the R light is converted into P polarization and enters the fourth PBS 5. Then, the light travels straight through the polarization separation surface 51 of the fourth PBS 5, exits from the light transmission surface 5 c of the fourth PBS 5, and enters the G phase plate 7 disposed in the subsequent stage.

  As described above, the G phase plate 7 does not act on the R light, and the R light is emitted as P-polarized light.

  Next, the B light will be described. The S-polarized B light transmitted through the G phase plate 6 is reflected by the polarization separation surface 21 of the first PBS 2 and enters the R phase plate 8. Here, as described above, the R phase plate 8 does not act on the B light at all, and the B light is emitted as it is with S polarization without being subjected to polarization conversion, and is incident on the third PBS 4.

  The S-polarized B light is reflected by the polarization separation surface 41 of the third PBS 4, exits from the light transmitting surface 4 a, and enters the B-type reflective spatial light modulator 63. Then, the reflection type spatial light modulation element 63 receives the light modulation corresponding to the video signal corresponding to B and is reflected.

  The P-polarized component of the B light generated by the light modulation passes straight through the polarization separation surface 41 of the third PBS 4 and enters the R phase plate 9. The R phase plate 9 does not act on the B light as described above, and the B light exits from the P-polarized light and enters the fourth PBS 5. Then, the light travels straight through the polarization separation surface 51 of the fourth PBS 5, exits from the light transmission surface 5 c of the fourth PBS 5, and enters the G phase plate 7 disposed in the subsequent stage.

  As described above, the G phase plate 7 does not act on the B light, and the B light is emitted as it is P-polarized light.

  In this way, the white light is color-separated in the color separation / synthesis optical system 1 and then recombined, and the polarization planes of the R, G, and B light are all aligned with the P-polarized light and emitted from the color separation / synthesis optical system 1. To do. The light beam synthesized in this way is projected onto a screen (not shown) by the projection lens 18.

  Quarter-wave plates 10R, 10G, and 10B are arranged between each spatial light modulator and PBS, and oblique light correction with PBS and birefringence correction of liquid crystal are performed as in the conventional example. Yes. A black display level is input to such a color separation / combination optical system, a sensor is placed in the projection optical path, and a color filter for each color is sequentially installed in front of the sensor. When the contrast ratio was measured after rotating the lens, the results shown in Table 1 were obtained. The high contrast ratio for each color is obtained when the wavelength plate is aligned with the slow axis in the long side direction of the aspect ratio of the image area of the reflective light modulator and when the slow axis is aligned in the short side direction. There are two combinations, and there are a total of eight combinations of delay axes 1 to 8 in total. From the results, A, B, and C were ranked. A particularly good combination was the combination of the delay axes 2 and the next was the combination of the delay axes 4.

  The knowledge obtained from the measurement results in Table 1 will be described. It can be seen that the black level decreases and the contrast ratio increases when the polarization direction of the light beam incident on the reflection type light modulation element and the slow axis direction of the corresponding wave plate are substantially perpendicular. This phenomenon differs depending on the color, and there is a contrast difference of about twice in R, but it is small in B and G. Conventionally, since this relationship is unknown, adjustment is performed in a non-optimal direction among the adjustments that fall into black.

  The present embodiment is characterized in that the slow axis of the quarter-wave plate is arranged and finely adjusted in the direction as shown in FIG.

  S-polarized light, which is reflected light from PBS, enters the B wavelength plate. The slow axis of the B wavelength plate is set perpendicular to the polarization direction of S-polarized light (parallel to the paper surface). The R wave plate is incident with P-polarized light that is transmitted through PBS. At this time, the slow axis of the R wave plate is set perpendicular to the polarization direction of the P-polarized light (perpendicular to the paper surface). The G wave plate is incident with P-polarized light that is transmitted through PBS. At this time, the slow axis of the G wavelength plate is set perpendicular to the polarization direction of the P-polarized light (parallel to the paper surface). In order to obtain the maximum contrast ratio, fine adjustment of the liquid crystal birefringence correction is necessary, and a sensor is placed in the projection optical path, and the rotation is adjusted to display the black value and show the minimum value. It is rotated several degrees from the parallel angle with the described polarization direction. The reflection type light modulation elements are arranged so that the long sides thereof face in the direction perpendicular to the paper surface.

  At this time, the aspect ratio of the image area of the reflective light modulation element and the direction of the slow axis of the wave plate are shown in FIG.

  FIG. 3 shows the configuration of the combination delay axis 4 in Table 1. FIG. 4 shows the slow axis direction. Compared to FIG. 1, the slow axis of the G wave plate is different by 90 degrees. This configuration can also provide a good contrast ratio. In this combination, only the R element is parallel to the long side.

  As the wave plate, various materials such as birefringent crystals such as quartz or organic materials such as polycarbonate resin and polyolefin resin can be used. An organic material has a structure in which a resin film is bonded to one surface of a glass substrate or a structure in which a resin film is sandwiched between glass substrates.

  The phase difference of each ¼ wavelength plate is configured to have a ¼ wavelength phase difference at substantially the center wavelength of each color. The wavelength plate for R has a phase difference of about 155 nm, which is 1/4, with respect to the center wavelength of R of 620 nm. The wavelength plate for G has a phase difference of about 138 nm, which is 1/4 with respect to the center wavelength of G of 550 nm. The wavelength plate for B has a phase difference of about 115 nm at 1/4 of the center wavelength of B of 460 nm. It is difficult to maintain an ideal quarter over the entire wavelength range of each band, and the definition of the center wavelength changes depending on the desired performance of the display device to which the definition is applied. The configuration can be selected. Accordingly, in each wavelength region, there are wavelength regions in which the phase difference is ¼ or less at substantially the center wavelength of each color, and there are combinations of bands in which the phase difference is ¼ or more.

  Antireflection films are provided on both sides of the wave plate to reduce reflection loss at the air interface and to reduce unnecessary reflected light toward the screen.

  FIG. 5 shows in detail the configuration of a set of PBS prisms and a spatial light modulator for one color, and the structure will be described. In the present embodiment, the reflective spatial light modulator and the wave plate are integrated and packaged, and a sealing structure is used between the members so as to prevent dust and dust from entering.

  As described above, the wave plate 10 has a structure in which the retardation film 10d is sandwiched from both sides by the glass substrate 10c. The reflective spatial light modulator 65 includes a pixel substrate 65c in which pixels are arranged in a matrix and a transparent common electrode 65 on the opposite surface, and a liquid crystal layer 65b in which liquid crystal is sealed in the gap between the substrates. . Further, a heat sink 54 for cooling is provided on the back surface of the liquid crystal layer 65b of the pixel substrate 65c. A heat sink 54 and a wave plate 10 integrated with the reflective spatial light modulator 65 are housed in a package 53, and are hermetically fixed to the PBS 50 via a seal material 51. Since the wavelength plate 10 of the present embodiment is a rectangle having substantially the same area as the pixel substrate 65c for displaying an image, it is fixed to the package 53 by the wavelength plate fixing member 52. At this time, since it is not necessary to use a mechanism for rotating and fixing a conventional disc-shaped wave plate after adjustment, a simple fixing member may be used.

  FIG. 6 shows a configuration example of a display device in which two spatial light modulation elements are used and a two-plate type is used. The structure is composed of two plates of a first element 66 for BG and a second element 62 for R, and the R light is passed through the illumination light incident side of the PBS prism 6 as it is. In this case, a filter 60 for switching output light in a time division manner is arranged.

  FIG. 7 shows the slow axis direction of the wave plate. Two wave plates are arranged such that the axes when viewed from the front are in a substantially orthogonal relationship with each other.

  FIG. 8 shows another embodiment having a three-plate configuration. In this configuration, the dichroic mirror 12 replaces the configuration for color-separating incident light performed by the first PBS (incident side PBS). The incident direction of incident illumination light is also changed by 90 °. Other configurations are the same, and the second polarization PBS (main PBS) 32a, the third PBS (main PBS) 32b, the fourth PBS (exit side PBS) 32c, the spatial light modulation elements 52R, 52G, and 52B, It is comprised with the wave plate corresponding to them.

  At this time, the aspect ratio of the image area of the reflective light modulation element and the direction of the slow axis of the wave plate are shown in FIG.

  As described above, the projection type display device of the present invention realizes a tightened uniform black screen and a bright uniform white screen by arranging the wave plate with the slow axis in the optimum direction. A display device having a high contrast ratio is provided.

  The present invention can be applied not only to the color separation / synthesis optical system as shown in FIG. 1, but also to the configuration as shown in FIG. 10 as a conventional example.

  Further, as shown in FIG. 8, even if the configuration in which the color separation of the incident light is replaced with a dichroic mirror, it functions in exactly the same way. In addition, the same effect can be obtained not only in various three-plate configurations (a configuration using three spatial light modulation elements) but also in a two-plate configuration and a single-plate configuration.

  The present invention is a projection display device, a rear projection television which is a kind of projection display device, and the like, as a printer as an image output device using a spatial light modulation element, or as an image input device using a spatial light modulation element. There is a possibility that it can be applied to cameras and scanners.

It is a figure which shows schematic structure of the projection type display apparatus applied to a present Example. It is a figure which shows the relationship between the reflection type spatial light modulation element and wavelength plate in FIG. 1 is a diagram showing a schematic configuration in which the delay axis of the wave plate is changed in the projection display device. It is a figure which shows the relationship between the reflection type spatial light modulation element and wavelength plate in FIG. It is a figure which shows the detailed structural example of the reflection type spatial light modulation element and wavelength plate of a projection type display apparatus which are applied to a present Example. It is a figure which shows the structural example of the display apparatus made into the 2 plate type using two spatial light modulation elements. It is a figure which shows the relationship between the reflection type spatial light modulation element and wavelength plate in FIG. It is a figure which shows schematic structure of the projection type display apparatus applied to another Example. It is a figure which shows the relationship between the reflection type spatial light modulation element and wavelength plate in FIG. It is a figure which shows a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Color separation synthetic | combination optical system 2 ... 1st PBS (incident side PBS)
3 ... 2nd polarization PBS (main PBS)
4 ... Third PBS (main PBS)
5 ... Fourth PBS (Ejection side PBS)
6, 7, 16, 17... First wavelength selective polarization conversion means (G phase plate)
8, 9... Second wavelength selective polarization conversion means (R phase plate)
14, 15 ... third wavelength selective polarization conversion means (phase plate for B)
10 ... Joining member 12 ... Buffer member

Claims (3)

A projection display device using a light source, an illumination optical system, polarization selective conversion means, at least two sets of spatial light modulators and a wavelength plate corresponding to the spatial light modulators,
After the light emitted from the light source is made into substantially uniform parallel light by the illumination optical system, it is selected by the polarization selective conversion means as colored light according to the number of sets of the spatial light modulation elements, and the polarization direction is aligned. While being sequentially supplied to the wave plate and the spatial light modulator,
The slow axis of at least one set of the wave plates among the wave plates is made to substantially coincide with the long side direction of the aspect of the image display area of the corresponding reflection type light modulation element, and the slow axis of another set of wave plates Is configured to substantially coincide with the corresponding short side direction of the aspect. A projection display device using a light source, an illumination optical system, polarization selective conversion means, three sets of spatial light modulators corresponding to three primary colors of the light sources, and a wavelength plate corresponding to the spatial light modulator. And
After the light emitted from the light source is converted into uniform parallel light by the illumination optical system, it is selected by the polarization selective conversion means as color light according to the three sets of the spatial light modulation elements, and the polarization direction is aligned. Sequentially supplied to the plate and the spatial light modulator,
Of the three sets of wave plates, the slow axes of the two sets of wave plates are made to substantially coincide with the long-side direction of the aspect of the image display area of the corresponding reflection type light modulation element, and the remaining one set of wave plates is delayed. A projection display device characterized in that the phase axis substantially coincides with the corresponding short side direction of the aspect. 3. The projection display device according to claim 1, wherein the phase difference of the wave plate has a phase difference of approximately ¼ wavelength at a center wavelength of the color light.

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