Patent Publication Number: US-6702443-B2

Title: Projector

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a projector for projecting and displaying an image. 
     2. Description of Related Art 
     In projectors, light emitted from an illuminating optical system is modulated according to image information (image signals) with the use of a liquid crystal light valve or the like, and the modulated light is projected onto a screen, thereby achieving image display. 
     The liquid crystal light valve commonly includes a liquid crystal panel and a polarizer formed on the side of a light incidence surface or on the side of a light emission surface. The polarizer transmits only a light component in a direction of a polarization axis and intercepts other light components. This will modulate the light incident on the liquid crystal light valve according to image information. 
     The polarizer commonly generates heat when it intercepts light other than a light component in the direction of the polarization axis. When the temperature of the polarizer is raised by the generation of heat, the polarizer is strained or deteriorated, and the polarizer transmits light that should not be transmitted or intercepts light that should not be intercepted. In order to reduce the temperature rise, the polarizer has been provided on a single-crystal sapphire substrate having high heat conductivity. 
     FIG. 10 is an illustration showing a conventionally used single-crystal sapphire substrate  908 . A polarizer  902  is bonded on a single-crystal sapphire substrate  908  as shown by broken lines in the figure. The single-crystal sapphire substrate  908  and the polarizer  902  are formed according to an effective display area of a liquid crystal panel having nearly a rectangular shape, so that the single-crystal sapphire substrate  908  and the polarizer  902  have nearly a rectangular shape. 
     The single-crystal sapphire substrate  908  includes a c-axis substantially parallel to the surface of the substrate. In addition, the c-axis is substantially parallel to a first side s 1  selected from perpendicularly intersecting two sides s 1  and s 2  of the nearly rectangular shape. Specifically, the single-crystal sapphire substrate  908  is accurately formed so that an inclination angle θ of the c-axis with respect to the reference side s 1  of the substrate falls within about 1°. 
     Such a single-crystal sapphire substrate having high c-axis accuracy is used in the conventional projector in order not to change too much the polarization state of light passing through the single-crystal sapphire substrate. The use of such a single sapphire substrate can provide excellent maintenance of optical characteristics of the projector. 
     However, much labor is required to manufacture such a single-crystal sapphire substrate  908  having high c-axis accuracy and, consequently, much labor is required to manufacture a projector using the single-crystal sapphire substrate  908  having high c-axis accuracy. This is because, in order to obtain a single-crystal sapphire substrate having high c-axis accuracy, an adjusting procedure should be repeatedly performed such that the inclination angle θ of the c-axis is measured by X-ray diffraction or the like after producing a single-crystal sapphire substrate having relatively low c-axis accuracy and further, the sapphire glass substrate is polished. 
     This invention is made to solve the above-described problems in the conventional art. One object of the various embodiments of the invention is to provide a technique capable of easily manufacturing a projector without deteriorating too much the optical characteristics of the projector. 
     SUMMARY OF THE INVENTION 
     In order to solve at least a part of the above-described problems, according to a first embodiment of the present invention, there is provided a projector including: 
     an illuminating optical system that emits illumination light; 
     an electro-optical device that modulates light from the illuminating optical system according to image information; and 
     a projection optical system that projects a modulated light beam flux obtained by the electro-optical device; 
     wherein the electro-optical device includes a single-crystal sapphire substrate having a substantially rectangular shape disposed on at least one side of a light incidence surface and a light emission surface; and 
     a polarizer provided on the single-crystal sapphire substrate; 
     the single-crystal sapphire substrate includes a c-axis substantially parallel to the surface of the substrate; and 
     the c-axis has an inclination of about 3° to about 7° with respect to one reference side selected from perpendicularly intersecting two sides of the nearly rectangular shape. 
     In the projector of the present invention, the polarizer is provided on the single-crystal sapphire substrate having the c-axis inclined about 3° to about 7° with respect to the reference side of the nearly rectangular shape. The use of such a single-crystal sapphire substrate makes it possible to easily manufacture the projector without deteriorating too much the optical characteristics of the projector. 
     In the above device, the polarizer may be provided on the single-crystal sapphire substrate so that the polarization axis thereof is substantially parallel to or perpendicular to the reference side. 
     If the polarizer is provided on the single-crystal sapphire substrate in this way, the relationship between the c-axis of the substrate and the polarization axis of the polarizer can be set to be substantially parallel to or perpendicular to each other. This makes it possible to reduce the change in the polarization state of light due to the passage through the single-crystal sapphire substrate. 
     In the above device, the polarizer formed on the single-crystal sapphire substrate may be provided on the side of the light emission surface of the electro-optical device, and 
     the single-crystal sapphire substrate and the polarizer may be disposed so that light emitted from the polarizer enters the single-crystal sapphire substrate. 
     In addition, in the above device, the polarizer formed on the single-crystal sapphire substrate may be provided on the side of the light incidence surface of the electro-optical device, and 
     the single-crystal sapphire substrate and the polarizer may be disposed so that light emitted from the single-crystal sapphire substrate enters the polarizer. 
     If the single-crystal sapphire substrate and the polarizer are disposed in this order, the polarization state of light is changed by passing through the single-crystal sapphire substrate, but lowering of contrast of an image light (modulated light) is avoided. 
     According to a second embodiment of the present invention, there is provided a projector that projects and displays a color image, including: 
     an illuminating optical system that emits illumination light; 
     a color light separation optical system that separates the illumination light emitted from the illuminating optical system into first to third color lights having three color components; 
     first to third electro-optical devices that modulate the first to third color lights separated by the color light separation optical system according to image information to produce first to third modulated light beam fluxes; 
     a color synthesizing section that synthesizes the first to third modulated light beam fluxes; and 
     a projection optical system that projects synthesized light emitted from the color synthesizing section; 
     wherein each of the first to third electro-optical devices includes a single-crystal sapphire substrate having a substantially rectangular shape disposed on at least one side of a light incidence surface and a light emission surface; and 
     a polarizer provided on the single-crystal sapphire substrate; 
     the single-crystal sapphire substrate includes a c-axis substantially parallel to the surface of the substrate; and 
     the c-axis has an inclination of about 3° to about 7° with respect to one reference side selected from perpendicularly intersecting two sides of the nearly rectangular shape. 
     In this projector, the polarizer is also provided on the single-crystal sapphire substrate having the c-axis inclined about 3° to about 7° with respect to the reference side of the nearly rectangular shape, so that it is possible to easily manufacture the projector without deteriorating too much the optical characteristics of the projector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a first embodiment of a projector to which the present invention is applied. 
     FIG. 2 illustrates a principal part of a projector  1000  in FIG.  1 . 
     FIG. 3 illustrates a single-crystal sapphire substrate  308 . 
     FIG. 4 illustrates the crystalline structure of the single-crystal sapphire. 
     FIG. 5 illustrates a crystal-growing device using an EFG method. 
     FIG. 6 illustrates the relationship between a c-axis of a single-crystal sapphire substrate and a polarization axis of a polarizer. 
     FIG. 7 illustrates an experimental system for measuring angle dependency of the c-axis of the single-crystal sapphire substrate. 
     FIG. 8 is a graph showing transmittance characteristics of the single-crystal sapphire substrate obtained by the experimental system in FIG.  7 . 
     FIG. 9 illustrates a principal part of a second embodiment of a projector to which the present invention is applied. 
     FIG. 10 illustrates a conventional single-crystal sapphire substrate  908 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A mode for carrying out the present invention will now be described based on an embodiment. FIG. 1 illustrates a first embodiment of a projector to which the present invention is applied. A projector  1000  includes an illuminating optical system  100 , a color light separation optical system  200 , a relay optical system  220 , three liquid crystal light valves  300 R,  300 G, and  300 B, a crossed dichroic prism  520 , and a projection optical system  540 . 
     The illuminating optical system  100  includes a polarized-light generating optical system  160  that converts light emitted from a light source device  120  into one type of linear polarized light beam polarized in the same direction, and emits the light. Light emitted from the illuminating optical system  100  is separated by the color light separation optical system  200  into light of the three colors red (R), green (G), and blue (B). Each separated color light is modulated by the liquid crystal light valves  300 R,  300 G, and  300 B according to image information (image signals). Modulated light beam fluxes of the three colors modulated by the liquid crystal light valves  300 R,  300 G, and  300 B are synthesized by the crossed dichroic prism  520  to be projected onto a screen SC by the projection optical system  540 . This allows a color image to be displayed on the screen SC. Since configurations and functions of components in the projector shown in FIG. 1 are described in detail in, for example, Japanese Unexamined Patent Publication Application No.10-325954 to the present applicant, a detailed description of the projector will be omitted in this specification. 
     FIG. 2 illustrates a principal part of the projector  1000  in FIG.  1 . FIG. 2 shows the three liquid crystal light valves  300 R,  300 G, and  300 B, and the crossed dichroic prism  520  in FIG.  1 . 
     The color lights R, G, and B enter the first to third liquid crystal light valves  300 R,  300 G, and  300 B, respectively. The modulated light beam flux of the color light R emitted from the first liquid crystal light valve  300 R is reflected by a red light-reflecting film  521  of the crossed dichroic prism  520 , and the modulated light beam flux of the color light B emitted from the third liquid crystal light valve  300 B is reflected by a blue light-reflecting film  522 . On the other hand, the modulated light beam flux of the color light G emitted from the second liquid crystal light valve  300 G is transmitted by the two reflecting films  521  and  522  of the crossed dichroic prism  520 . In this way, three modulated light beam fluxes are synthesized, and a color image is displayed on the screen SC by the projection optical system  540 . In FIG. 2, positions where the red light and the blue light are reflected are shown at positions shifted from the two reflecting films  521  and  522  for convenience of illustration. 
     The first liquid crystal light valve  300 R includes a liquid crystal panel  301 R and two polarizers  302 Ri and  302 Ro provided on the side of a light incidence surface and on the side of a light emission surface thereof. The first polarizer  302 Ri provided on the side of the light incidence surface is bonded to the liquid crystal panel  301 R. On the other hand, the second polarizer  302 Ro provided on the side of the light emission surface is bonded on a single-crystal sapphire substrate  308  at a position apart from the liquid crystal panel  301 R. Antireflection films (not shown) for preventing reflection of light on interfaces are formed on the light incidence surface of the first polarizer  302 Ri, the light incidence surface of the second polarizer  302 Ro, and the light emission surface of the single-crystal sapphire substrate  308 R to which the second polarizer  302 Ro is bonded. 
     The color light R incident on the first liquid crystal light valve  300 R is a linear polarized light beam since it is emitted from the illuminating optical system  100  (FIG. 1) including the polarized-light generating optical system  160 . The polarization axis of the first polarizer  302 Ri provided on the side of the light incidence surface of the liquid crystal light valve  300 R is set so as to coincide with the polarization direction of the incident linear polarized light beam. Therefore, almost all of the color light R incident on the first polarizer  302 Ri passes unchanged through the first polarizer  302 Ri. The polarized light beam emitted from the first polarizer  302 Ri is modulated by the liquid crystal panel  301 R. The second polarizer  302 Ro emits only a light component polarized in the same direction as the polarization axis in the light modulated by the liquid crystal panel  301 R. The modulated light beam flux emitted from the second polarizer  302 Ro passes through the single-crystal sapphire substrate  308  to enter the crossed dichroic prism  520 . 
     As described above, while the first polarizer  302 Ri transmits almost all of the incident linear polarized light beams, the second polarizer  302 Ro intercepts a part of the incident modulated light. 
     For this reason, the second polarizer  302 Ro produces a larger amount of heat than the first polarizer  302 Ri does. In this embodiment, in order to reduce the temperature rise of the second polarizer  302 Ro that produces a relatively large amount of heat, only the second polarizer  302 Ro is provided on the single-crystal sapphire substrate  308 R. 
     This also applies to the second and third liquid crystal light valves  300 G and  300 B. Second liquid crystal light valve  300 G includes a liquid crystal panel  301 G and two polarizers  302 Gi and  302 Go provided on the side of a light incidence surface and on a side of a light emission surface thereof Only the second polarizer  302 Go is provided on the signal-crystal sapphire substrate  308 G. Third liquid crystal light valve  300 B includes a liquid crystal panel  301 B and two polarizers  302 Bi and  302 Bo provided on the side of a light incidence surface and on a side of a light emission surface thereof. Only the second polarizer  302 Bo is provided on the single-crystal sapphire substrate  308 B. 
     FIG. 3 illustrates the single-crystal sapphire substrate  308 R in FIG.  2 . Although only the single-crystal sapphire substrate  308 R is discussed here, it should be appreciated that the structure of the single-crystal sapphire substrate  308 R is identical to the structure of the single-crystal sapphire substrates  308 G and  308 B. The single-crystal sapphire substrate  308 R has a substantially rectangular shape including perpendicularly intersecting two sides s 1  and s 2 . The single-crystal sapphire substrate  308 R in this embodiment has a thickness of about 700 μm. 
     The c-axis of the single-crystal sapphire substrate  308 R is set to be substantially parallel to the surface of the substrate, in other words, included in a plane of the substrate. The c-axis of the single-crystal sapphire substrate  308 R is set to be substantially parallel to the surface of the single-crystal sapphire substrate  308 R because the temperature distribution of the polarizer bonded on the substrate becomes more uniform as compared with a case where the c-axis of the single-crystal sapphire substrate is set to be substantially perpendicular to the surface of the single-crystal sapphire substrate  308 R. 
     In addition, while the c-axis of the single-sapphire substrate  308 R is substantially parallel to the reference side s 1  selected from the perpendicularly intersecting two sides s 1  and s 2  of the substantially rectangular shape, the c-axis is inclined by an angle of θ with respect to the reference side s 1 . The inclination angle θ of the c-axis with respect to the reference side s 1  is set to be in the range of about 3° to about 7°. 
     FIG. 4 illustrates the crystal structure of the single-crystal sapphire substrate  308 R. Although the single-crystal sapphire is the rhombohedral system to be accurate, it may be considered as the hexagonal system as shown in FIG.  4 . As shown in FIG. 4, the c-axis is parallel to the plane A. The single-crystal sapphire substrate  308 R in FIG. 3 is molded so that the plane A is the surface of the substrate. 
     The single-crystal sapphire substrate  308 R used in this embodiment can be formed by, for example, a known EFG method (Edge-defined Film-fed Growth Method). FIG. 5 illustrates a crystal-growing device using the EFG method. The device includes a crucible  710  for storing alumina melt MA, a heating coil  720  arranged so as to surround the crucible, and a crystal-growing die  730  including a slit  730   s  for determining the external shape of a grown crystal. 
     The crucible  710  is heated by the heating coil  720 . The alumina melt MA in the heated crucible  710  fills the slit  730   s  due to a capillary phenomenon, and is led to the upper end of the die  730 . If a seed crystal of a single-crystal sapphire is placed in the alumina melt led to the upper end of the mold  730  and the seed crystal is slowly pulled up, a plate-like single-crystal sapphire plate  740  can be obtained. The single-crystal sapphire substrate  308 R in this embodiment is, as shown in FIG. 5, obtained by cutting the single-crystal sapphire plate  740  grown in the form of plate to a predetermined size. 
     When growing the single-crystal sapphire plate with the use of this device, it is possible to produce a single-sapphire plate such that the surface of the plate is substantially parallel to the c-axis by suitably adjusting the positional relationship between the seed crystal and the die  730 . It is also possible to make one side of the single-crystal sapphire plate substantially parallel to the c-axis by suitably adjusting the positional relationship between the seed crystal and the die  730 . Actually, however, it is very difficult to produce a single-crystal sapphire plate in which the inclination angle θ of the c-axis with respect to one side of the plate is about 1° or less, and many single-crystal sapphire plates having relatively low c-axis accuracy are produced in which the inclination angle θ is about 3° to about 7°. 
     As previously described, single-crystal sapphire plates having high c-axis accuracy have been produced in which the inclination angle θ is about 1° or less by repeatedly performing an adjusting procedure such that the inclination angle θ of the c-axis of the thus-produced single-crystal sapphire substrate having relatively low c-axis accuracy is measured by X-ray diffraction or the like, and the single-crystal sapphire substrate is polished. 
     The single-crystal sapphire substrate  308 R of this embodiment, however, does not require the above adjusting procedure. The c-axis of the single-crystal sapphire substrates  308 R is inclined about 3° to about 7° with respect to the reference side s 1 , as shown in FIG.  3 . This makes it possible to easily manufacture the single-crystal sapphire substrate  308 R for bonding thereto the polarizer, and consequently, it is possible to easily manufacture the projector. 
     FIG. 6 illustrates the relationship between the c-axis of a single-crystal sapphire substrate and the polarization axis of a polarizer. In a single-crystal sapphire substrate  308 R shown in FIG.  6 (A), a reference side is set to be a first side s 1  which extends vertically in the figure, and the c-axis is inclined about 3° to about 7° with respect to the reference side s 1 . A polarizer  302 Ro is provided on the substrate  308 R so that the polarization axis p thereof is substantially parallel to the reference side s 1  of the single-crystal sapphire substrate  308 R. In this case, the c-axis of the substrate  308 R is substantially parallel to the polarization axis p of the polarizer  302 Ro. On the other hand, in a single-crystal sapphire substrate  308 R shown in FIG.  6 (B), a reference side is set to be the second side s 2  which extends horizontally in the figure, and the c-axis is inclined about 3° to about 7° with respect to the reference side s 2 . A polarizer  302 Ro is provided on the substrate  308 R so that the polarization axis p thereof is substantially perpendicular to the reference side s 2  of the single-crystal sapphire substrate  308 R. In this case, the c-axis of the substrate  308 R is substantially perpendicular to the polarization axis p of the polarizer  302 Ro. 
     As shown in FIGS.  6 (A) and  6 (B), the polarizer  302 Ro may be provided on the single-crystal sapphire substrate so that the polarization axis p thereof is substantially parallel to or perpendicular to one reference side selected from perpendicularly intersecting two sides of the single-crystal sapphire substrate  308 R. In other words, the c-axis of the substrate  308 R may be substantially parallel to or perpendicular to the polarization axis p of the polarizer  302 Ro. 
     The c-axis of the substrate  308 R is set to be substantially parallel to or perpendicular to the polarization axis p of the polarizer  302 Ro in order not to change the polarization state of light passing through the single-crystal sapphire substrate  308 R. That is, the single-crystal sapphire is, as shown in FIG. 4, a uniaxial crystal, and a refractive index in the c-axis direction differs from a refractive index in the direction perpendicular to the c-axis. For this reason, when light enters in the direction substantially perpendicular to the c-axis as in this embodiment, the polarization state is changed according to an angle formed between a plane of vibration of light and the c-axis of the crystal. In this embodiment, in order to reduce the change of the polarization state due to the passage through the single-crystal sapphire substrate as much as possible, the relationship between the c-axis of the substrate  308 R and the polarization axis p of the polarizer  302 Ro is set to be substantially parallel to or perpendicular to each other. 
     FIG. 7 is an illustration showing an experimental system for measuring angle dependency of the c-axis of the single-crystal sapphire substrate. The experimental system includes a light source  610 , a first polarizer  620 , a second polarizer  622 , and a light intensity-measuring device  630  for measuring the intensity of incident light. Polarization axes p of the first and second polarizers  620  and  622  are set to be parallel to each other. A single-crystal sapphire substrate TP to be tested is placed between the first polarizer  620  and the second polarizer  622 . The single-crystal sapphire substrate TP is rotatably provided about a direction of travel of light, and an angle φ which the c-axis of the crystal with the polarization axes p of the first and second polarizers  620  and  622  can be changed. 
     Light emitted from the light source  610  passes through the first polarizer  620 , whereby it is turned into a linear polarized light beam. A linear polarized light beam emitted from the first polarizer  620  passes through the single-crystal sapphire substrate TP to enter the second polarizer  622 . The second polarizer  622  transmits only a polarized light component that is the same as the linear polarized light beam emitted from the first polarizer  620 . Light emitted from the second polarizer  622  is measured by the light intensity-measuring device  630 . 
     FIG. 8 is a graph showing transmittance characteristics of the single-crystal sapphire substrate TP obtained by the experimental system in FIG.  7 . The horizontal axis of the graph represents the wavelength (nm) and the vertical axis represents the transmittance ratio. The transmittance ratio is based on the transmittance that is measured when the angle φ in FIG. 7 is about 0°. Since the curve C 1  shows the transmittance ratio when the angle φ is about 0°, the value of the transmittance ratio is always 1. The curves C 2  to C 4  show the transmittance ratios when the angle φ is about 3°, 5°, and 7°, respectively. When the angle φ shifts about 3°, 5°, and 7° in the direction opposite to the direction shown in FIG. 7, almost the same results as the curves C 2  to C 4  are obtained. 
     As will be understood from the graph in FIG. 8, when the angle φ is about 3° (curve C 2 ), a wavelength band can be found in which the transmittance ratio becomes smaller about 1% at the maximum, as compared to a case where the angle φ is about 0° (curve C 1 ). When the angle φ is about 5° (curve C 3 ), a wavelength band can be found in which the transmittance ratio becomes smaller about 3% at the maximum, as compared to a case where the angle φ is about 0°. 
     Similarly, when the angle φ is about 7° (curve C 4 ), a wavelength band can be found in which the transmittance ratio becomes smaller about 6% at the maximum, as compared to a case where the angle φ is about 0°. The transmittance ratio becomes smaller according to the angle φ in this way because the polarization state of light (linear polarized light beam) emitted from the first polarizer  620  in FIG. 7 is changed by passing through the single-crystal sapphire substrate TP. 
     The angle φ which the c-axis of the single-crystal sapphire substrate TP forms with the polarization axis p of the polarizer in FIG. 7 is equivalent to the angle θ which the c-axis of the single-crystal sapphire substrate  308 R forms with the reference side s 1  in FIG.  3 . That is, by conducting the above experiment, the transmittance of the linear polarized light beam according to the angle θ can be known. In addition, the above experimental results proves that, when the single-crystal sapphire substrate  308 R is used having an inclination angle θ set to be about 3° to about 7° with respect to the reference side s 1 , as shown in FIG. 3, the transmittance is almost the same as that obtained when a conventional single-crystal sapphire substrate is having an inclination angle θ set within about 1°. 
     From the foregoing, when the single-crystal sapphire substrate  308 R in which the inclination angle θ of the c-axis falls within the range of about 3° to about 7° as in this embodiment is applied to a projector, it is possible to easily manufacture the projector without deteriorating too much the optical characteristics of the projector. 
     While the single-crystal sapphire substrate  308 R in which the inclination angle θ of the c-axis is about 3° to 7° is used in this embodiment, the inclination angle θ of the c-axis may preferably be as small as possible. For example, if a single-crystal sapphire substrate is used in which the inclination angle θ of the c-axis is about 3° to 5°, it is possible to further inhibit the deterioration of the optical characteristics of the projector. 
     In this embodiment, as shown in FIG. 2, the polarizer  302 Ro provided on the single-crystal sapphire substrate  308 R is disposed on the side of the light emission surface of the liquid crystal panel  301 R so that light emitted from the polarizer  302 Ro enters the single-crystal sapphire substrate  308 R. If the single-crystal sapphire substrate  308 R and the polarizer  302 Ro are disposed so that light enters in this order, light whose polarization state is changed by passing through the single-crystal sapphire substrate  308 R will enter the polarizer  302 Ro. In this case, since a part of light that should be transmitted is intercepted by the polarizer  302 Ro, contrast of an image light (modulated light) emitted from the liquid crystal light valve  300 R is lowered. That is, the disposition as shown in FIG. 2 offers the advantage of not lowering contrast of the image light emitted from the liquid crystal light valve  300 R, even if the polarization state of light is changed by the single-crystal sapphire substrate  308 R. 
     As described above, according to the projector of this embodiment, the liquid crystal light valves  300 R,  300 G, and  300 B include the single-crystal sapphire substrates each having a substantially rectangular shape provided on the side of the light emission surfaces, and the polarizers provided on the substrates. The single-crystal sapphire substrate includes the c-axis that is substantially parallel to the surface of the substrate. In addition, the c-axis of the single-sapphire substrate has an inclination of about 3° to about 7° with respect to one reference side selected from the perpendicularly intersecting two sides of the nearly rectangular shape. The application of the single-crystal sapphire substrate having such a c-axis to a projector makes it possible to easily manufacture the projector without deteriorating too much the optical characteristics of the projector. 
     As will be understood from the foregoing description, the first to third liquid crystal light valves  300 R,  300 G, and  300 B of this embodiment correspond to the first to third electro-optical devices in the present invention, respectively. In general, the word “electro-optical device” sometimes means an electro-optical device in a narrow sense, indicating only a liquid crystal panel, whereas it means an electro-optical device in a wider sense including liquid crystal panels and polarizers in this specification. 
     B. Second Embodiment: 
     FIG. 9 illustrates a principal part of a second embodiment of a projector to which the present invention is applied. In the first embodiment, as shown in FIG. 2, only the second polarizers  302 Ro,  302 Go, and  302 Bo provided on the side of the light emission surfaces of the liquid crystal light valves  300 R,  300 G, and  300 B are bonded to the single-crystal sapphire substrates  308 R,  308 G and  308 B. 
     On the other hand, in this embodiment, first polarizers  302 Ri,  302 Gi, and  302 Bi provided on the side of the light incidence surfaces of the liquid crystal light valves  300 R,  300 G, and  300 B are also bonded to single-crystal sapphire substrates  307 R,  307 G and  307 B. The single-crystal sapphire substrates  307 R,  307 G and  307 B to which the first polarizers  302 Ri,  302 Gi, and  302 Bi are bonded are the same as the single-crystal sapphire substrates  308 R,  308 G and  308 B. 
     As shown in FIG. 9, according to this embodiment, the polarizer  302 Ri provided on the single-crystal sapphire substrate  307 R is disposed on the side of the light incidence surface of the liquid crystal panel  301 R so that light emitted from the single-crystal sapphire substrate  307 R enters the polarizer  302 Ri. If the polarizer  302 Ri and the single-crystal sapphire substrate  307 R are disposed so that light enters in this order, the polarization state of a linear polarized light beam emitted from the polarizer  302 Ri is changed by passing through the single-crystal sapphire substrate  307 R, and light that is not a linear polarized light beam enters the liquid crystal panel  301 R. If such light enters the liquid crystal panel  301 R, contrast of an image light emitted from the liquid crystal light valve  300 R is lowered. That is, by the disposition as shown in FIG. 9, even if the polarization state of light is changed by the single-crystal sapphire substrate  307 R, the light passes through the polarizer  302 Ri thereafter, so that a linear polarized light beam can enter the liquid crystal panel  301 R. This avoids lowering of contrast of the image light emitted from the liquid crystal light valve  300 R. 
     As described above, according to the projector of this embodiment, the liquid crystal light valves  300 R,  300 G, and  300 B include the single-crystal sapphire substrates each having nearly a rectangular shape, and the polarizers on the side of the light incidence surfaces and on the side of the light emission surfaces. Since the single-crystal sapphire substrates are the same as the single-crystal sapphire substrates of the first embodiment, it is also possible in this embodiment to easily manufacture the projector without deteriorating too much the optical characteristics of the projector. 
     This invention is not limited to the above embodiments and modes for carrying out the invention, and can be carried out in various forms without departing from the spirit and scope of the invention. For example, the following modifications can be made. 
     (1) In the first embodiment, as shown in FIG. 2, while the liquid crystal light valves  300 R,  300 G, and  300 B include the polarizers on both sides of the light incidence surfaces and the light emission surfaces, only the second polarizers on the side of the light emission surfaces are provided on the single-crystal sapphire substrates  308 R,  308 G and  308 B. On the other hand, in the second embodiment, as shown in FIG. 9, the liquid crystal light valves  300 R,  300 G, and  300 B include the polarizers on both sides of the light incidence surfaces and the light emission surfaces, and both polarizers are provided on the single-crystal sapphire substrates  307 R,  307 G and  307 B and  308 R,  308 G and  308 B. 
     In addition, in the first and second embodiments, since the projector  1000  includes the illuminating optical system  100  for emitting a linear polarized light beam, the first polarizers  302 Ri,  302 Gi, and  302 Bi provided on the side of the light incidence surfaces of the liquid crystal light valves  300 R,  300 G, and  300 B may be omitted. 
     In this way, electro-optical devices of the present invention may include the single-crystal sapphire substrates each having a substantially rectangular shape, and the polarizers provided on the single-crystal sapphire substrates on at least one side of the light incidence surfaces and the light emission surfaces. 
     (2) While the projector  1000  (FIG. 1) includes the illuminating optical system  100  for emitting a linear polarized light beam in the above embodiments, an illuminating optical system for emitting unpolarized light may be included instead. In this case, however, since the first polarizers  302 Ri,  302 Gi, and  302 Bi provided on the side of the light incidence surfaces produce a large amount of heat, the first polarizers may preferably be provided on the single-sapphire substrates as in the second embodiment (FIG.  9 ). 
     (3) While the temperature rise of the polarizers is reduced by bonding the polarizers to the single-crystal sapphire substrates in the above embodiments, a cooling device for forcibly cooling the polarizer may additionally be used. For example, the polarizers bonded to the single-crystal sapphire substrates may be cooled with a cooling fan. In addition, the polarizers may be cooled by placing the single-crystal sapphire substrates having the polarizers bonded thereto in a liquid, and by circulating the liquid between the single-crystal sapphire substrates and a heat changer. Alternatively, the polarizers may be cooled by bringing a Peltier element into contact with corners of the polarizers or the single-crystal sapphire substrates. The use of such a cooling device makes it possible to fairly reduce the temperature rise of the polarizers. When the polarizers are forcibly cooled as described above, not only the polarizers, but also the overall liquid crystal light valves, may be cooled. 
     (4) While an example has been described in the above embodiments in a case where the present invention is applied to a transmissive projector, it is possible to apply the present invention to a reflective projector. 
     Here, “transmissive” means that an electro-optical device serving as an optical modulation means, such as a transmissive liquid crystal panel, is of a type for transmitting light, and “reflective” means that an electro-optical device serving as an optical modulation means, such as a reflective liquid crystal panel, is of a type for reflecting light. When this invention is applied to the reflective projector, advantages that are substantially similar to those of the transmissive projector can be obtained. 
     (5) While the projector  1000  for displaying a color image is described in the above embodiments, the description also applies to a projector for displaying a monochrome image. 
     (6) As will be understood from the graph in FIG. 8, the single-crystal sapphire substrate has the characteristics of decreasing transmittance of a linear polarized light beam according to the wavelength. According to the graph in FIG. 8, for example, the transmittance of the linear polarized light beam having a wavelength of about 450 nm is decreased. 
     If the characteristics are utilized, there is a possibility that the wavelength of the emitted linear polarized light beam can be suitably selected by entering light emitted from the single-crystal sapphire substrate into the polarizer. For example, of light emitted from the illuminating optical system, if intensity of light having a predetermined wavelength is remarkably high, it is possible to decrease the intensity of light of the wavelength.