JP3659637B2 - Projection-type image display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a projection type image display apparatus such as a liquid crystal projector, which modulates light from a light source by an image display element and enlarges and projects it onto a screen by a projection lens.
[0002]
[Prior art]
As a projection type image display apparatus having an optical system that performs polarization separation or synthesis on light from a light source, for example, there are those disclosed in Japanese Patent Laid-Open Nos. 63-39294 and 8-160374.
[0003]
First, a projection type display device disclosed in Japanese Patent Laid-Open No. 63-39294 will be described.
[0004]
A schematic configuration diagram of the apparatus is shown in FIG.
[0005]
The light emitted from the light source 12 passes through the collimating lens 13 and is separated into linearly polarized light components in two directions orthogonal to each other by a regular quadrangular prism-shaped polarizing beam splitter (hereinafter referred to as PBS) 14. Of the separated light, the light reflected by the PBS 14 enters the color separation prism 15. The color separation prism includes a first prism 15A, a second prism 15B, and a third prism 15C. A dichroic interference thin film that reflects blue and transmits a longer wavelength region is deposited on the second surface 15e of the first prism 15A. Has been. A gap is provided between the first prism 15A and the second prism 15B, and a dichroic interference thin film of red reflection and green transmission is deposited on the surface 15f between the second prism 15B and the third prism 15C. . Therefore, when white light is incident on the incident surface 15a, the blue light is reflected by the surface 15e, is totally reflected by the surface 15a, travels to the exit surface 15b, and the green light transmitted through the surface 15f travels to the exit surface 15d. Head. Reference numerals 16, 17 and 18 denote liquid crystal elements that sequentially display a blue component image, a red component image, and a green component image. Reference numerals 19, 20, and 21 are dielectric reflectors provided on the back surfaces of the liquid crystal display elements 16, 17, and 18. The light separated by the respective prisms is transmitted through the liquid crystal element, reflected by the reflecting mirrors 19, 20, and 21, and again transmitted through the liquid crystal element. The reflected light from each liquid crystal element is synthesized by the color separation prism and again enters the PBS 14. At this time, the light whose polarization direction is modulated by the liquid crystal element according to the image signal is transmitted through the PBS 14 and projected onto the screen by the projection lens.
[0006]
Next, a projection type image display device disclosed in JP-A-8-160374 will be described.
[0007]
A schematic configuration diagram of the apparatus is shown in FIG.
[0008]
Reference numeral 22 denotes a projection light source composed of a light source and a reflecting mirror for collecting the emitted light. The emitted light passes through the IR and UV cut filters that block unnecessary infrared rays and ultraviolet rays and enters the PBS 23. The light is separated into P-polarized light and S-polarized light orthogonal to each other by the polarization separation surface 23-1.
[0009]
The reflected S-polarized light is separated into red, green, and blue by the dichroic mirrors 24, 25, and 26, and is incident on the red liquid crystal panel 27, the green liquid crystal panel 28, and the blue liquid crystal panel 29, respectively. In the liquid crystal panel, the polarization direction is rotated in accordance with the image signal, enters the dichroic mirrors 30, 31, and 32, and enters the other PBS 33. Therefore, the P-polarized light is transmitted through the PBS and enlarged and projected on the screen by the projection lens 34. Further, the P-polarized light transmitted through the PBS 23 enters the liquid crystal panel 35. The light whose polarization direction is modulated by the liquid crystal panel is reflected by the PBS 33, passes through the projection lens 34, and is enlarged and projected on the screen as the luminance signal light of the image.
[0010]
[Problems to be solved by the invention]
The projection type image display device as described above has the following drawbacks.
[0011]
The image display element disclosed above uses a regular quadrangular prism-like PBS as a polarization selective reflection element having a function of reflecting or transmitting light according to its polarization direction.
[0012]
Such PBS is usually produced by depositing a dielectric multilayer film on the surface of a glass prism made of optical glass such as BK7 and bonding the two prisms. The glass prism is made, for example, by cooling a glass melted at a high temperature to form a large glass block, cutting out a small glass block therefrom, and further polishing the surface. When the glass is cooled and hardened, the strain is removed by annealing, but it is difficult to completely remove the glass. In addition, this distortion generally occurs nonuniformly in the prism. This distortion causes birefringence with respect to light in the prism. However, since the distortion is not uniform, the degree of birefringence and the direction of the main axis of birefringence exhibit a non-uniform distribution.
[0013]
When light is incident on a uniaxial birefringent material, the traveling speed of light differs between ordinary light and extraordinary light.For example, normal light is incident when obliquely polarized light is incident on the main axis of birefringence. There is a phase difference between the component and the extraordinary light component, which affects the polarization state of the incident light.
[0014]
In the projection type image display element, problems when birefringence remains in PBS will be described using a projection type image display device disclosed in Japanese Patent Laid-Open No. 63-39294.
[0015]
The light emitted from the light source enters the PBS, is separated into two linearly polarized lights whose polarization directions are orthogonal to each other on the film surface, and only the component orthogonal to the incident light whose polarization direction is rotated by a liquid crystal element according to image information. Is ideally transmitted through the PBS and enlarged and projected onto the screen by the projection lens.
[0016]
However, when birefringence remains in the prism constituting the PBS, a component perpendicular to the polarization direction of the incident light is generated while traveling through the glass prism constituting the PBS. The light whose polarization direction is not modulated by the liquid crystal element reaches the screen. That is, even in a black display state, light leaks and the contrast is lowered. The phenomenon described above reduces not only the contrast of the image projected on the screen but also the brightness. In addition, since the distortion in the prism is not uniform, there is a significant problem in performance such as uneven brightness in the image on the screen.
[0017]
Next, problems in the case where PBS having a polarization separation function using a derivative multilayer film is used in a projection type image display apparatus will be described with reference to FIG.
[0018]
A PBS composed of a dielectric multilayer film transmits a component (P-polarized light) having a polarization direction parallel to an incident surface (a surface including incident light and reflected light), and a component (S-polarized light) having a polarization direction perpendicular to the incident surface. It has the property of reflecting. Accordingly, when the incident direction of light is different, the polarization direction of light that is transmitted (P-polarized light) and reflected (S-polarized light) is also different.
[0019]
In a projection type image display apparatus, the illumination light is generally not a perfect parallel light but a light having a certain spread angle. When these illumination lights are incident on the PBS, the incident direction with respect to the film surface of the PBS differs depending on the spread angle of the light. Therefore, the light transmitted and reflected by the PBS is not completely linearly polarized in one direction. Therefore, the use of liquid crystal birefringence as disclosed in JP-A-63-39294 or the like causes a reduction in contrast. In addition, in PBS, the polarization direction of reflected and transmitted light cannot be set to an arbitrary angle. When a display element having a fixed polarization direction of incident light, such as a liquid crystal panel, is used, a wavelength plate or the like is used. , It may be necessary to change the polarization direction of the light from the PBS.
[0020]
These problems also occur in a projection type image display apparatus using a transmission type image display element as disclosed in Japanese Patent Laid-Open No. 8-160374.
[0021]
Further, since the size of PBS usually needs to be about several tens of millimeters according to the size of the liquid crystal panel, those made of glass prism are expensive, leading to an increase in cost and weight of the apparatus.
[0022]
The present invention has been made in order to solve the above-described problems, and an object of the present invention is to provide a low-cost projection-type image display apparatus having an optical system that performs polarization separation or synthesis on light from a light source, and It is lightweight, and it is intended to reduce the decrease in screen illuminance and the decrease in contrast due to birefringence, and suppress the occurrence of uneven brightness.
[0023]
[Means for Solving the Problems]
  The projection type image display apparatus of the present invention includes a light source,A polarization selective reflection unit having a function of reflecting or transmitting light from the light source according to a polarization direction; a reflection type image display element that modulates a polarization plane of light from the polarization selective reflection unit according to an image signal; The polarization selective reflection means transmits a linearly polarized light component in one direction regardless of an incident direction of light to the polarized light selective reflection means, and the linearly polarized light in one direction. A polarization selective reflection sheet having an optical transmission axis and a reflection axis for reflecting a linearly polarized light component orthogonal to the component, and a first polarizing filter means for transmitting only the linearly polarized light component in one direction of the light, the reflective image display Laminated in order from the side close to the element, provided on the glass substrate, and disposed such that the polarization direction of the light incident on the pixel display element coincides with the transmission axis or the reflection axis. Said bias The optical path between the selective reflection means is further provided with a second polarizing filter means having a transmission axis arranged so as to be in a crossed Nicol state with respect to the transmission axis of the first polarizing filter means. .
[0024]
  MaThe projection type image display apparatus of the present invention includes a light source, color separation means for separating light from the light source into a plurality of lights having different wavelength ranges, and the plurality of lights separated by the color separation means, respectively. A plurality of polarization selective reflection means for reflecting or transmitting according to the polarization direction, a plurality of reflective image display elements for modulating the polarization planes of the respective lights from the respective polarization selective reflection means in accordance with an image signal, A combining unit configured to combine the light beams reflected by the reflection type image display element; and a projection lens configured to project the light combined by the combining unit onto a screen. Are provided between the light source and each polarization selective reflection means so as to form an optical path of each light in a predetermined wavelength range, respectively, and the color synthesizing means includes the each polarization selective reflection means and the above Between the projection lens Each of the polarization selective reflection means arranged in the optical path transmits a linear polarization component in one direction regardless of the incident direction of the light to each polarization selective reflection means, and the linear polarization component in one direction. A reflection-selective reflection sheet having an optical transmission axis and a reflection axis for reflecting a linearly polarized light component orthogonal to the first polarization filter means for transmitting only a linearly polarized light component in one direction of light, and the reflective image display element Are provided in order on the glass substrate, and the polarization direction of the light incident on each reflective image display element coincides with the transmission axis or the reflection axis of each polarization selective reflection sheet. It is characterized by being arranged respectively.
[0025]
  Each transmission axis of each light separated by the color separation means is arranged in a crossed Nicols state with respect to the transmission axis of each first polarization filter means in each optical path to each polarization selective reflection means. It is preferable that a second polarizing filter means is further provided.
[0028]
The operation of the present invention will be described below.
[0029]
Glass having birefringence in the optical path from the polarization selective reflection means to the image display element and in the optical path from the image display element to the polarization selective reflection means by using a plate-shaped or sheet-like one as the polarization selective reflection means The amount of can be greatly reduced. For this reason, the fall of the contrast on the screen by the influence of the birefringence of glass and the fall of illumination intensity can be improved. In addition, since a large glass prism is not used, the cost is low and the weight of the apparatus can be reduced.
[0030]
In addition, since the polarization selective reflection means has a transmission axis and a reflection axis that transmit a linearly polarized light component that is unique within the plane and reflects the linearly polarized light component orthogonal thereto, even if the illumination light has a spread angle, The light transmitted and reflected by the polarization selective reflection means is linearly polarized light in one direction. As a result, contrast can be improved. Further, by adjusting the transmission axis and the reflection axis, it is possible to reflect or transmit light having an arbitrary polarization direction. Therefore, even if the polarization direction of light to be incident on the liquid crystal panel is inclined with respect to the P-polarized light and the S-polarized light, it is not necessary to change the polarization by the waveplate, so that the cost is low and the light passes through the waveplate. It is possible to prevent the loss of light during the process.
[0031]
When a PBS array in which a plurality of small PBSs are arranged in a plate shape is used as the polarization selective reflection means, the optical path through which light passes through the glass is shortened. For this reason, the influence by the birefringence of the glass which forms PBS can be reduced.
[0032]
When the polarization filter means is provided between the light source and the polarization selective reflection means, the polarization direction of the light incident on the polarization selective reflection means can be limited to only one direction. Regardless of the extinction ratio, only light in one polarization direction can be guided to the image display element. Further, when a polarization filter means is provided between the polarization selective reflection means and the projection lens, only light in one polarization direction is guided to the screen regardless of the polarization characteristics (extinction ratio) of the polarization selective reflection means. Is possible. As a result, an apparatus with higher contrast can be realized by these effects.
[0033]
When a polarizing filter means disposed between the polarized light selective reflecting means and the projection lens is provided, the polarizing filter means and the polarized light selective reflecting means are stacked, and the polarized light selective reflecting means is directed to the reflective image display element side. Thus, a device with higher contrast can be realized. This is because there is no element having birefringence in the optical path between the polarization selective reflection means and the polarizing filter.
[0034]
In addition, when no means for separating or synthesizing light is disposed in the optical path between the polarization selective reflection means and the reflective image display element, birefringence is applied to the optical component used as the light separating and synthesizing means. Even if there is, it is possible to suppress the decrease in contrast and the occurrence of uneven brightness.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 is a schematic view of a projection type color image display apparatus of the present invention. In this embodiment, a metal halide lamp having a power of 250 W and an arc length of 3 mm is used as the light source 1. In addition to this, a halogen lamp or a xenon lamp can be used as the light source. A parabolic mirror 2 for emitting light from the light source as substantially parallel light is disposed on the back surface of the light source 1. A polarization selective reflection plate 3 is positioned in front of the light source 1. The polarization selective reflection plate 3 is formed of a PBS array 3 (a) in which a plurality of small polarization beam splitters (hereinafter referred to as PBS) as shown in FIG. 2 are arranged in a plate shape. Separated into polarized light and S polarized light. S-polarized light reflected by the PBS array 3 (a) enters the dichroic mirrors 4-R and 4-B, and is separated into red, green, and blue (hereinafter referred to as R, G, and B) light. Thereafter, these lights are respectively incident on the corresponding reflective liquid crystal display panels 5-R, 5-G, and 5-B, and the polarization state is modulated in accordance with the image signal and reflected. The reflective liquid crystal display panel 5 is a 1.3-type S-VGA (pixel pitch is 33 μm × 33 μm), the display mode utilizes the birefringence of the liquid crystal, the polarization direction of incident light is controlled, and an image is displayed. A birefringent type was used.
[0036]
The light reflected by the panel is synthesized again by the dichroic mirrors 4-R and 4-B, and the polarized light is rotated by the reflective liquid crystal display panel, and only the light that becomes the P-polarized light component passes through the PBS array 3 (a). Then, the light is projected onto the screen 7 through the projection lens 6. The S-polarized component is reflected by the PBS array 3 (a) and returns to the light source 1.
[0037]
In the present embodiment, the polarizing filter 8 is provided between the light source 1 and the PBS array 3 (a), and the polarizing filter 9 is provided between the PBS array 3 (a) and the projection lens 6. Further, the transmission axes of these polarizing filters 8 and 9 are arranged so as to be in a crossed Nicols state with respect to the optical path. In the apparatus shown in FIG. 1, the transmission axis of the polarizing filter 8 on the incident side is set in a direction perpendicular to the paper surface. In this way, the polarizing filters 8 and 9 are arranged in the crossed Nicols state between the light source 1 and the PBS array 3 (a), and between the PBS array 3 (a) and the projection lens 6, so that the light enters the PBS array 3 (a). The light becomes S-polarized light, and most of the light incident on the reflective liquid crystal display panel becomes S-polarized light even if the extinction ratio of the PBS array 3 (a) is poor. Further, the light reflected as S-polarized light by the reflective liquid crystal display panel 5 is reflected again by the PBS array 3 (a), and most of it returns to the light source 1. Part of the S-polarized light passes through the PBS array 3 (a). When this light is projected onto the screen by the projection lens, it causes a decrease in contrast, but the polarization axis of the polarization filter 9 inserted between the PBS array 3 (a) and the projection lens 6 cuts the S-polarized component. Therefore, it is possible to greatly suppress the decrease in the contrast ratio. In the present embodiment, the polarizing plates are arranged before and after the PBS array 3 (a). However, the effect can be obtained even if the polarizing plates are arranged only in one of them.
[0038]
Here, a comparative example is shown in order to explain the effect of this embodiment. In this comparative example, the polarization selective reflection plate 3 is not an array of a plurality of small PBSs, but a single PBS as shown in FIG.
[0039]
In the comparative example, in order to cover the display area of the 1.3-inch panel, a PBS having a width of about 40 mm or more is required in consideration of the light spread angle. Further, when used in a reflective optical system as in the present embodiment, the light travels back and forth through the PBS, and thus passes through twice as much glass as 80 mm. FIG. 4 shows the relationship between the birefringence (phase difference) of glass and the contrast ratio. Usually, birefringence in glass is 2 to 5 nm / cm even if it has a good quality. Therefore, according to FIG. 4, when this PBS is used, a phase difference of about 16 to 40 nm exists. For this reason, it can be seen that in an apparatus using one PBS, the contrast is extremely lowered.
[0040]
On the other hand, the size of each PBS constituting the polarization selective reflection plate 3 used in this embodiment is as thin as 5 mm, so that light passes through the glass even if a reflective optical system is used. The distance to do is 10 mm. This is 1/8 of the case where one PBS is used. Therefore, the phase difference is also reduced to 2 to 5 nm, and a sufficient contrast can be obtained. In practice, birefringence also occurs when distortion occurs due to temperature unevenness in the glass. However, in the PBS array 3 (a), the width of each PBS is thin, so temperature unevenness occurs. In addition to being difficult, even if birefringence occurs, it is difficult to be affected by it, so the decrease in contrast due to temperature rise is very small.
[0041]
When the configuration shown in FIG. 3 was used, a place where the contrast ratio was less than 50: 1 occurred in the screen. On the other hand, as described in the present embodiment, when the projection is configured using the PBS array 3 (a), there is no unevenness in contrast while maintaining the brightness (contrast ratio of 100: 1 or more over the entire screen), and A lightweight and inexpensive image display device could be realized.
[0042]
In this embodiment, the R reflection and B reflection dichroic mirrors are used as the color separation / combination means, but any one having a color separation / combination function may be used, as shown in FIGS. 5 (a) and 5 (b). It is also possible to use a so-called Phillips type prism composed of three dichroic prisms or three prisms.
[0043]
However, in this case, as described above, since the contrast is lowered due to the birefringence in these prisms, it is disclosed in Japanese Patent Laid-Open Nos. 5-341254 and 8-21357. It is preferable to use a prism in which the inside of the prism is filled with a liquid to reduce birefringence.
[0044]
(Embodiment 2)
FIG. 6 is a schematic diagram of a projection type color image display apparatus according to the second embodiment of the present invention. In this embodiment, the same optical components as those in Embodiment 1 are denoted by the same numbers.
[0045]
After the light from the light source 1 is divided into RGB light by the dichroic mirrors 4-C and 4-G, the respective light passes through the PBS array 3 (a) and the corresponding reflective liquid crystal display panels 5-R, 5- G, 5-B. The PBS array 3 (a) is configured to be disposed on all the liquid crystal panels. The light reflected from the reflective liquid crystal display panels 5-R, 5-G, and 5-B is incident on the corresponding PBS array 3 (a) again. Of the incident light, only the light whose polarization direction has been changed by the reflective liquid crystal display panel is transmitted through the PBS array 3 (a), synthesized by the cross dichroic prism 10, and then projected onto the screen 7 by the projection lens 6. The
[0046]
In the present embodiment, a polarizing filter 8 is inserted on the light source side of each PBS array 3 (a). Further, a polarizing filter 9 is inserted between each PBS array 3 (a) and the cross dichroic prism 10. The same effects as those of the first embodiment are obtained by the polarizing filters 8 and 9.
[0047]
In the first embodiment, the unevenness in contrast can be reduced to a practical level or more, but white light is separated into RGB light and combined between the PBS array 3 (a) and the reflective liquid crystal display panel 5. Therefore, the following problems occur in the color separation / synthesis optical system.
[0048]
In other words, the color separation / combination system using these prisms has a large polarization dependency of its spectral characteristics, so that when light having a different incident direction (illumination light having a spread angle) is incident as in the case of PBS, Even if the incident light has only one direction of linearly polarized light, the transmitted and reflected light is not unidirectional linearly polarized light but has light of a component orthogonal thereto. In addition, when a glass prism is used, birefringence occurs, which causes the contrast to decrease.
[0049]
On the other hand, in this configuration, before entering the PBS array 3 (a), the light is divided into RGB lights and synthesized by the cross dichroic prism after exiting the PBS array 3 (a). That is, an optical component that performs color separation and synthesis that affects the contrast ratio is disposed outside the PBS array 3 (a) and the reflective liquid crystal display panel 5. For this reason, there is no reduction in contrast.
[0050]
When the projection is configured as described above, it is possible to realize an image display device having a contrast ratio of 200: 1 or more over the entire screen while maintaining the same brightness as in the first embodiment even when a glass prism is used. It was.
[0051]
In this embodiment, a dichroic mirror is used for color separation and a cross dichroic prism is used for color composition. In addition, a cross dichroic prism may be used for color separation, a dichroic mirror may be used for color composition, and a Philips type prism as shown in FIG. 5B. FIG. 7 shows an example of a projection type color image display device that performs color separation using a cross dichroic mirror 37 and performs color composition using a cross dichroic prism 41.
[0052]
In the configuration shown in FIG. 7, light from the light source is reflected by the total reflection mirror 36, enters the upper cross dichroic mirror 37, and is separated into R, G, and B light. Thereafter, the light is reflected by total reflection mirrors 38, 39 and 40 in the direction of the corresponding three polarization selective reflection plates 3. The linearly polarized light that has passed through the respective polarization selective reflection plates 3 enters the reflective liquid crystal panels 5-R, 5-G, and 5-B. The light whose polarization plane is modulated by the liquid crystal panel is reflected by the polarization selective reflection plate 3, enters the lower cross dichroic prism 41, is synthesized, and then projected onto the screen by the projection lens 6.
[0053]
In the configuration shown in FIG. 7, all three optical paths between the light source and the reflective liquid crystal panels 5-R, 5-G, 5-B corresponding to the R, G, and B lights are the same. . For this reason, the white balance is not lost and a good image is obtained.
[0054]
The same effect can be obtained even if the cross dichroic mirror 37 in the apparatus of FIG. 7 is replaced with a cross dichroic prism.
[0055]
(Embodiment 3)
FIGS. 8A and 8B are schematic views of a projection color image display apparatus according to the third embodiment of the present invention.
[0056]
In this embodiment, instead of the PBS array 3 (a) used as the polarization selective reflection plate 3 in Embodiments 1 and 2, a linearly polarized light component in one direction is transmitted regardless of the incident direction of light, and is orthogonal thereto. The polarization selective reflection film 3 (b) having an optical transmission axis and a reflection axis for reflecting the linearly polarized light of the component to be used was used.
[0057]
As the polarization selective reflection film 3 (b), for example, a film 900 disclosed in Japanese Patent Laid-Open No. 57-158801 as shown in FIG. 15 can be used. In this film 900, the birefringent material 904 and the isotropic material 906 are alternately superposed so that the refractive index of the isotropic material and the refractive index in the direction of one optical axis of the birefringent material. Are almost the same. The film 900 is a polarizer that transmits light having a polarization plane in the direction of the optical axis and reflects light having a component orthogonal thereto. Also, an Optical Film D-BEF manufactured by Sumitomo 3M which has the same function as the film 900 can be used.
[0058]
Since this polarization selective reflection film 3 (b) itself has a transmission axis and a reflection axis, as shown in FIG. The linearly polarized light is parallel to each of the transmission axis and the reflection axis in (b). In addition, the polarization selective reflection film 3 (b) is not affected by birefringence because the film thickness is very thin. Therefore, as described above, the contrast can be further improved as compared with the case where the PBS in which the polarization direction of the reflected and transmitted light is different depending on the incident direction (divergence angle) of the light is used.
[0059]
In the apparatus shown in FIGS. 8A and 8B, the polarization direction of the incident light with respect to the reflective liquid crystal panel 5 is set to be perpendicular to the paper surface. For this reason, the polarization selective reflection film 3 (b) is arranged so that the reflection axis (FIG. 9) is also perpendicular to the paper surface.
[0060]
When a projection was configured with the configuration of FIG. 8A, a contrast ratio of 200: 1 or more could be realized over the entire screen while maintaining the same brightness as in the first and second embodiments. Similarly, with the configuration of FIG. 8B, a contrast ratio of 300: 1 or more could be realized.
[0061]
In the present embodiment, the reflection axis of the polarization selective reflection film 3 (b) is arranged so as to be perpendicular to the paper surface, but the direction of the axis is not limited to this. The direction of the reflection axis may be any direction such as a horizontal direction or a 45 ° direction in accordance with the characteristics of the liquid crystal panel.
[0062]
In the first, second, and third embodiments, the plate-like PBS array 3 (a) and the polarization-selective reflection film 3 (b) in which a plurality of small PBSs are arranged are used as the polarization selective reflection plate 3. Any material may be used as long as it has an effect, and a combination of a cholesteric polarizer and a quarter-wave plate disclosed in JP-A-6-281814 may be used. According to Japanese Patent Laid-Open No. 6-281814, a cholesteric polarizer has an optically active layer of a cholesteric (chiral nematic) material. The remaining components are transmitted. The transmitted or reflected circularly polarized light component can be converted into linearly polarized light by the quarter wavelength plate.
[0063]
The contrast in the first, second, and third embodiments is determined by the optical path between the polarizing plates arranged before and after the polarization selective reflection plate 3.
[0064]
In order to give strength to the sheet-like polarization selective reflection plate 3 such as the polarization selective reflection film 3 (b) or the cholesteric polarizer as described above, it may be used by being bonded to a transparent substrate such as glass. In this case, since the polarization selective reflection plate 3 is directed to the reflective liquid crystal display panel side 5, the distance through which light passes through the transparent substrate can be reduced (reduced by one transparent substrate), thereby reducing the influence of birefringence. .
[0065]
Further, when the sheet-like polarization selective reflection plate 3 is used as shown in FIG. 10, the polarizing filter 9 provided on the projection lens side of the polarization selective reflection plate 3 is sandwiched between the polarization selective reflection plate and the glass substrate 51. As a result, since the light passes through the polarizing plate and then passes through the transparent substrate, the influence of the birefringence of the substrate can be completely prevented, and the contrast can be further improved.
[0066]
(Embodiment 4)
FIG. 11 is a schematic diagram of a projection type color image display apparatus according to the fourth embodiment of the present invention.
[0067]
In the apparatus of FIG. 11, the light emitted from the light source 1 is guided to the cross dichroic prism 10a. The cross dichroic prism 10a splits light into R component (or B component) light and G component and B component (or R component) light. The R component (or B component) light is reflected by the total reflection mirror 36a and is incident on the corresponding polarization selective reflection film 3 (b). The light including the G component and the B component (or R component) is reflected by the total reflection mirror 36 b and enters the dichroic mirror 4. The dichroic mirror 4 splits this light into G component light and B component light (or R component). Then, the divided G component light and B component (or R component) light are incident on the corresponding polarization selective reflection films 3 (b). Of the light incident on the polarization selective reflection film 3 (b), linearly polarized light that vibrates in a direction parallel to the reflection axis of the polarization selective reflection film 3 (b) is reflected, and the corresponding reflective liquid crystal display panel 5-R, Incident to 5-G and 5-B. The polarization selective reflection film 3 (b) is arranged on all the liquid crystal panels. The light reflected from the reflective liquid crystal display panels 5-R, 5-G, and 5-B is incident on the polarization selective reflection film 3 (b) again. Of the incident light, only the light whose polarization direction is changed by the reflective liquid crystal display panels 5-R, 5-G, and 5-B is transmitted through the polarization selective reflection film 3 (b) and synthesized by the cross dichroic prism 10. Then, the image is projected onto the screen 7 by the projection lens 6.
[0068]
In this embodiment, the polarizing filter 8 is inserted on the light source side of each polarization selective reflection film 3 (b). A polarizing filter 9 is also inserted between each polarization selective reflection film 3 (b) and the cross dichroic prism 10. The same effects as those of the first embodiment are obtained by the polarizing filters 8 and 9.
[0069]
In the structure described in the fourth embodiment, unlike the structure described in the third embodiment, the lengths of the three optical paths from the light source to the projection lens through which light of each color of R, G, B passes are the same. For this reason, the white balance of the image does not shift. Therefore, it is not necessary to use a relay lens that has been conventionally required to prevent a white balance shift, and the apparatus can be reduced in size and cost.
[0070]
When the projection is configured as described above, it is possible to realize an image display device having a contrast ratio of 300: 1 or more over the entire screen while maintaining the same brightness as that of the first embodiment even when a glass prism is used. It was.
[0071]
(Embodiment 5)
A projection type color image display apparatus according to Embodiment 5 will be described.
[0072]
In the apparatus shown in FIG. 16, two polarization selective reflection films 3 (b) 1 and 3 (b) 2 are used. In addition, transmissive liquid crystal panels 5′-R, 5′-G, and 5′-B are located between the optical paths connecting these polarization selective reflection films 3 (b) 1 and 3 (b) 2. The direction of the transmission axis and the direction of the reflection axis of the polarization selective reflection film 3 (b) 1 are the same as the direction of the transmission axis and the direction of the reflection axis of the polarization selective reflection film 3 (b) 2, respectively.
[0073]
The light from the light source 1 reflected by the reflecting mirror 2 passes through an IR and UV cut filter that blocks unnecessary infrared and ultraviolet rays, and enters the polarization selective reflection film 3 (b) 1. Of the incident light, linearly polarized light having a polarization plane parallel to the direction of the reflection axis of the polarization selective reflection film 3 (b) 1 is reflected, while light having a polarization plane parallel to the direction of the transmission axis is polarized. The selective reflection film 3 (b) 1 is transmitted.
[0074]
The light reflected by the polarization selective reflection film 3 (b) 1 enters the dichroic mirror 4-B that reflects blue light. The reflected blue light is reflected by the total reflection mirror 36 and then enters the blue liquid crystal panel 5′-B.
[0075]
On the other hand, red and green light are transmitted through the dichroic mirror 4-B and are incident on the dichroic mirror 4-R that reflects red light. The reflected red light is incident on the red liquid crystal panel 5′-R. The green light passes through the dichroic mirror 4-R and enters the green liquid crystal panel 5′-G.
[0076]
Each of the liquid crystal panels 5′-R, 5′-G, and 5′-B rotates the polarization direction of light according to the image signal.
[0077]
The light of each color transmitted through the liquid crystal panels 5′-B and 5′-R is combined with each other by the dichroic mirror 4′-R. Thereafter, the combined light of blue and red is incident on the dichroic mirror 4′-G. On the other hand, the light transmitted through the liquid crystal panel 5′-G is reflected by the total reflection mirror 36 and then enters the dichroic mirror 4′-G. As a result, the RGB lights are combined with each other by the dichroic mirror 4'-G.
[0078]
Thereafter, the combined RGB light is incident on another polarization selective reflection film 3 (b) 2. Of the incident linearly polarized light, only the linearly polarized light whose plane of polarization is rotated by 90 ° by the liquid crystal panels 5′-R, 5′-G, 5′-B is transmitted through the polarization selective reflection film 3 (b) 2; As a result, the projection lens 6 enlarges and projects the image onto the screen.
[0079]
On the other hand, the linearly polarized light transmitted through the polarization selective reflection film 3 (b) 1 is reflected by the two total reflection mirrors 36 and then enters the liquid crystal panel 35. The linearly polarized light transmitted through the liquid crystal panel 35 is further incident on the polarization selective reflection film 3 (b) 2. Of the incident linearly polarized light, the light whose polarization plane of polarization is modulated by the liquid crystal panel 35 in a direction different from the polarization plane upon incidence by 90 ° is reflected by the polarization selective reflection film 3 (b) 2, and as a result, The image passes through the projection lens 6 and is projected on the screen as a luminance signal light of the image.
[0080]
Since the polarization selective reflection films 3 (b) 1 and 3 (b) 2 have a transmission axis and a reflection axis in the plane of the film that transmit a specific linearly polarized light component and reflect a linearly polarized light component orthogonal thereto, Even if the illumination light has a divergence angle, the light transmitted and reflected by the polarization selective reflection film is linearly polarized light having a polarization plane in one direction. For this reason, the contrast of the displayed image is improved.
[0081]
Moreover, since the directions of the transmission axis and the reflection axis of the polarization selective reflection films 3 (b) 1 and 3 (b) 2 can be arbitrarily set, the directions of the polarization vectors of the transmitted light and the reflected light can be controlled. For this reason, the polarization direction of the incident light is adjusted to the preferred polarization direction of the light with respect to the liquid crystal panels 5′-R, 5′-G, 5′-B without using an optical element such as a quarter-wave plate. Can do.
[0082]
【The invention's effect】
As described above, according to the present invention, contrast unevenness can be eliminated by using a plate-like or sheet-like polarization selective reflection element with low birefringence in the projection type image display device. A uniform image can be realized.
[0083]
In addition, illumination is provided by including a polarization selective reflection element having an optical transmission axis and a reflection axis that transmits a linearly polarized light component in one direction regardless of the incident angle of light and reflects light of a component orthogonal thereto. Even if the light has a spread angle, the transmitted light and the reflected light are linearly polarized light parallel to the transmission axis and the reflection axis, so that the contrast can be further improved.
[0084]
Further, by performing color separation / combination in an optical path other than between the polarization separation element and the reflective liquid crystal display element, it is possible to eliminate a decrease in contrast due to the color separation / synthesis optical system.
[0085]
Furthermore, when the sheet-like polarization selective reflection plate is used by bonding to a transparent substrate such as glass, the light passes through the polarization plate by sandwiching the polarization plate between the polarization selective reflection plate and the glass, Since it passes through the transparent substrate, the influence of the birefringence of the transparent substrate can be completely prevented. For this reason, contrast can be further improved.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a projection color image display apparatus according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram of a polarization selective reflection plate used in the first embodiment.
FIG. 3 is a schematic diagram of a conventional reflective image display device.
FIG. 4 is a graph showing the relationship between birefringence (phase difference) and contrast ratio of glass.
FIG. 5 is an explanatory diagram of another color separation / synthesis system.
FIG. 6 is a schematic diagram of a projection color image display apparatus according to a second embodiment.
FIG. 7 is a perspective view of a projection color image display apparatus according to a second embodiment.
8A and 8B are schematic views of a projection type color image display apparatus according to a third embodiment.
FIG. 9 is an explanatory view of a polarization selective reflection film of Embodiment 3.
FIG. 10 is a layout view of a sheet-like polarization selective reflection plate.
FIG. 11 is a schematic diagram of a projection color image display apparatus according to a fourth embodiment.
FIG. 12 is a schematic diagram of a conventional projection type image display apparatus.
FIG. 13 is a schematic diagram of a conventional projection type image display apparatus.
FIG. 14 is a diagram illustrating the principle of PBS.
FIG. 15 is a diagram showing a configuration of a polarization selective reflection film.
FIG. 16 is a schematic diagram of a projection color image display apparatus according to a fifth embodiment.
[Explanation of symbols]
1: Metal halide lamp
2: Parabolic mirror
3 (a): PBS array
3 (b): Polarization selective reflection film
4: Dichroic mirror
5-R, 5-G, 5-B: reflective liquid crystal panel
6: Projection lens
7: Screen
8: Polarizing filter
9: Polarizing filter
37: Cross dichroic mirror
10, 41: Cross dichroic prism

Claims (3)

A light source;
Polarization selective reflection means having a function of reflecting or transmitting light from the light source according to the polarization direction;
A projection-type image display device comprising: a reflection-type image display element that modulates a polarization plane of light from the polarization selective reflection means according to an image signal ,
The polarization selective reflection means, regardless of the incident direction of the light to the polarizing selective reflecting means, passes through the one-way linear polarization component, an optical reflecting a linearly polarized light component perpendicular to the linearly polarized light component of the one-way A polarizing selective reflection sheet having a transparent transmission axis and a reflection axis, and first polarizing filter means for transmitting only a linearly polarized light component in one direction of light are laminated in order from the side closer to the reflective image display element, and a glass substrate. And is arranged so that the polarization direction of light incident on the pixel display element coincides with the transmission axis or the reflection axis ,
In the optical path between the light source and the polarization selective reflection means, there is further provided a second polarization filter means having a transmission axis arranged so as to be in a crossed Nicols state with respect to the transmission axis of the first polarization filter means. A projection-type image display device characterized by that. A light source;
Color separation means for separating light from the light source into a plurality of lights having different wavelength ranges;
A plurality of polarization selective reflection means for reflecting or transmitting in accordance with the separated plurality of light into respective polarization directions in the color separation means,
A plurality of reflective image display elements that modulate the polarization plane of each light from each of the polarization selective reflection means in accordance with an image signal ;
And combining means for combining said respective light reflected by the reflection type image display device,
A projection lens that projects the light combined by the combining means onto a screen ,
The color separation means is provided between the light source and each polarization selective reflection means so as to form an optical path of each light in a predetermined wavelength range with respect to each polarization selective reflection means ,
The color synthesizing means, wherein arranged in the optical path between the projection lens and the polarized-light selective reflection means,
Wherein each of the polarized-light selective reflection means, wherein regardless of the respective direction of incidence of light to the polarizing selective reflecting means, passes through the one-way linear polarization component, the linearly polarized light orthogonal to the linearly polarized light component of the one-way A polarizing selective reflection sheet having an optical transmission axis and a reflection axis for reflecting the components, and a first polarizing filter means for transmitting only the linearly polarized light component in one direction of light, in order from the side closer to the reflective image display element are stacked, together provided on a glass substrate, the polarization direction of light incident respectively to the each reflection type image display element, it is arranged so as to coincide the said transmission axis or the reflection axis of the polarization selective reflection sheet A projection-type image display device. Respective transmission axes are arranged in the respective optical paths of the respective lights separated by the color separation means with respect to the respective polarization selective reflection means so as to be in a crossed Nicols state with respect to the transmission axes of the respective first polarization filter means. 3. The projection type image display device according to claim 2, further comprising a second polarizing filter means.

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