JP2001305318A - Color separation / synthesis optical system and liquid crystal display device having the color separation / synthesis optical system - Google Patents

Abstract

(57) [Summary] A bright and well-colored display can be realized irrespective of the characteristics of a dichroic thin film, and the dependence of the cut wavelength on the polarization direction and the variation in the incident angle can be reduced. Provided are a color separation / synthesis optical system that can be used, and a liquid crystal display device having the color separation / synthesis optical system. In a color separation / synthesis optical system including a plurality of prisms, incident light is made incident from a first surface, a predetermined color component light is reflected by a dichroic film formed on a second surface, and the remaining color component light is reflected. And a first prism configured to further reflect the predetermined color component light reflected by the dichroic film on the first surface and to pass through the third surface. The dichroic film formed on the second surface reflects green light and transmits other colors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color separation / synthesis optical system and a liquid crystal display device having the color separation / synthesis optical system.

[0002]

2. Description of the Related Art As a conventional full-color projector using a reflection type light valve, for example, Japanese Patent No.
A reflection type liquid crystal display device described in Japanese Patent Application Laid-Open No. 05758 is known. In FIG. 6, reference numeral 211 denotes a three-color color separation optical system.
The first prism 211A, the second prism 211B, and the third prism 211C are arranged as shown in the figure, and 211a corresponds to an incident surface, and 211b, 211c, and 211d correspond to emission surfaces of respective color component lights. Second surface 211e of first prism 211A
Is deposited with a dichroic interference thin film which reflects blue and transmits a longer wavelength region. First prism 21
An air gap is provided between the first prism 211A and the second prism 211B, and a gap between the second prism 211B and the third prism 211C.
On the 11f surface, a dichroic interference thin film of red reflection green transmission is deposited. Therefore, assuming that white light is incident on the incident surface 211a, the blue light is reflected on the dichroic thin film surface 211e, the inner surface is totally reflected on the surface 211a, and
Head to 1b. Of the light transmitted through the dichroic thin film surface 211e, the red light reflected by the dichroic thin film 211f is totally internally reflected by the surface in contact with the air gap and goes to the emission surface 211c, and the green light transmitted through the 211f surface is emitted by the emission surface 211d.
Head for.

Reference numerals 212, 213, and 214 denote two-dimensional reflective liquid crystal elements (light valves) for displaying a blue component video, a red component video, and a green component video, respectively. This reflection type liquid crystal element is provided with emission surfaces 211b and 211 of the color separation optical system.
c, 211d.

[0004] 211 is a polarizing beam splitter (PBS)
And is disposed on the setting optical axis O of the color separation optical system 211. Reference numeral 222 denotes a collimation lens, and a white light source 223 is disposed on the focal point of the collimation lens. Reference numeral 224 denotes a projection lens which is arranged so that its optical axis coincides with the optical axis passing through the PBS 221. 225
Is a screen, and the screen and each reflective liquid crystal element 21
2, 213 and 214 are adjusted to be conjugate with respect to the projection lens.

With the above configuration, the light beam emitted from the white light source 223 enters the collimation lens 222 to become a parallel light beam, and is reflected by the polarization splitting surface of the PBS 221.
Polarized light enters the three-color separation optical system. The linearly polarized light incident on the color separation optical system is decomposed into each color light and incident on each color light valve, spatially modulated by a video signal of each color light, reflected, reversed in the optical path, and subjected to color synthesis, and the color separation is performed. Only the component that has exited from the incident surface 211a of the optical system 211 and whose polarization direction has been changed passes through the PBS 221 and is projected on the screen 225 by the projection lens 224.

Japanese Patent Application Laid-Open No. Hei 9-166709 proposes a configuration in which a red dichroic mirror is formed as the dichroic thin film 211e of the first prism and a green dichroic mirror is formed as the dichroic thin film 211f of the second prism. I have.

[0007]

However, in the above-mentioned conventional apparatus, there is a problem in that the light amount is lost and the color is changed. This will be described with reference to FIG. FIGS. 7A and 7B respectively show the transmission characteristics of the dichroic thin film of the first prism and the dichroic thin film of the second prism in the conventional configuration. Since the first dichroic thin film reflects blue light (hereinafter referred to as B color) and transmits the other light, the cut wavelength (a wavelength having a transmittance of 50% in general) is set to 490 to 500 nm (FIG. 7A )). Further, the second dichroic thin film reflects red (hereinafter, referred to as R color) and transmits the other, so that the cut wavelength is set to 580 to 600 nm (FIG. 7B).

By the way, in a liquid crystal display device using a reflection type panel, light incident on the panel follows the same path as that at the time of incidence in the opposite direction after its polarization plane is modulated. Therefore, the same dichroic thin film is passed twice. In particular, when "white display" is performed in a mode in which the polarization is different before entering the panel and after reflection (for example, if the incident light is P-polarized light, the reflected light is S-polarized) (for example, it is generally used in a reflective liquid crystal panel) It is desirable that the characteristics of the dichroic mirrors of the S-polarized light and the P-polarized light coincide with each other.

In practice, the cut wavelength is shown in FIG.
As shown in (b), 10 to 30 n for S polarization and P polarization
A shift of about m occurs. For this reason, a loss of light amount and a change in tint occur. Further, since the light source used in the liquid crystal display device is not a perfect point light source, the incident light is incident on the dichroic thin film with a certain angle variation around the main incident optical axis. The cut wavelength of the dichroic film differs depending on the incident angle. This also causes a loss of light amount and a change in color. Furthermore, since the cut wavelength varies among the dichroic thin film solids, the brightness and color of the display device vary. However,
In the conventional configuration, both the characteristics in FIGS. 7A and 7B need to satisfy desired characteristics at the same time. Therefore, it is difficult to realize a display device that is bright and has good color with good reproducibility. There was a problem.

Therefore, the present invention solves the above-mentioned problems in the conventional art, and realizes a bright and well-colored display irrespective of the characteristics of the dichroic thin film. It is an object of the present invention to provide a color separation / synthesis optical system capable of reducing the dependence on the variation of the incident angle and a liquid crystal display device having the color separation / synthesis optical system.

[0011]

In order to achieve the above object, the present invention provides a color separation / synthesis optical system constructed as in the following (1) to (7), and a color separation / synthesis optical system. And a liquid crystal display device having the same. (1) In a color separation / synthesis optical system which is composed of a plurality of prisms, and separates and synthesizes incident light into component lights of each color by a dichroic film formed on the surface of the prism,
At least, the incident light is incident from a first surface, a predetermined color component light is reflected by a dichroic film formed on a second surface, and the remaining color component light is passed, and a predetermined color reflected by the dichroic film is reflected. A first component in which the component light is further totally reflected by the first surface and passes through the third surface.
And a dichroic film formed on the second surface of the first prism reflects green light and transmits other colors. (2) In a color separation / synthesis optical system configured of a plurality of prisms and separating or synthesizing incident light into component lights of respective colors by a dichroic film formed on a surface of the prism, at least the incident light is converted to a first surface. , The predetermined color component light is reflected by the dichroic film formed on the second surface and the remaining color component light is passed, and the predetermined color component light reflected by the dichroic film is converted into the first color component light.
A first prism that is further totally reflected by a surface and passes through a third surface, and the second prism of the first prism
The dichroic film formed on the surface reflects green light,
A color separation / synthesis optical system characterized by transmitting other colors. (3) The first prism is characterized in that an angle between the main axis of the incident light and a normal to the first surface of the prism has a constant angle. The color separation / synthesis optical system according to the above (1) or (2). (4) According to a color separation / synthesis optical system that separates and combines incident light into component lights of each color, and a video signal arranged on the side from which the component light of each color separated by the color separation / synthesis optical system is emitted. Reflective liquid crystal display element driven by
On the side where the incident light is incident on the combining optical system, a polarization beam splitter for making predetermined polarized light incident on the color separating / combining optical system as the incident light, and each color light combined by the color separating / combining optical system is projected. And a projection optical system, wherein the color separation / synthesis optical system is as described in (1) above.
A liquid crystal display device comprising the color separation / synthesis optical system according to any one of (1) to (3). (5) The shape of light emission of the polarizing beam splitter is
The liquid crystal display device according to the above (4), wherein the liquid crystal display device is formed in accordance with the shape of the first surface of the first prism. (6) According to a color separation / synthesis optical system that separates and combines incident light into component lights of respective colors, and a video signal arranged on the side from which the component light of each color separated by the color separation / synthesis optical system is emitted. Reflective liquid crystal display element driven by
A projection optical system for projecting each color light synthesized by the synthesis optical system, wherein the color separation / synthesis optical system is any one of the above (1) to (3). A liquid crystal display device comprising a system. (7) The reflective liquid crystal display element has three reflective liquid crystal panels, and the reflective panel rotates the polarization direction of light incident on the panel by approximately 90 ° during white display. The liquid crystal display device according to any one of 4) to 6).

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an embodiment of the present invention,
By applying the above-described configuration, the dichroic film formed on the second surface of the first prism can emit green light (hereinafter referred to as G light).
It is described as color. ) Is reflected to transmit other colors, for example, the second dichroic thin film for color-separating light transmitted through the first dichroic thin film transmits through the first dichroic thin film. Since the magenta color may be separated into R and B colors, it is possible to configure the second dichroic thin film so that the shift of the cut wavelength is not affected by the tint and brightness. Further, the cut wavelength of the second tychroic thin film can be easily manufactured, a wide margin for manufacturing variability can be secured, and a stable color separation / synthesis optical system and a liquid crystal display device can be provided at low cost. . Further, an angle between the main incidence axis of the incident light and a normal to the first surface of the prism is:
By making a certain angle, the incident angle of the incident light beam to the first dichroic mirror can be made shallower, and the dependence of the cut wavelength on the polarization direction and the variation of the incident angle can be reduced. In addition, it is possible to reduce a change in color tone. Further, by adjusting the shape of the light emitting portion from the polarization beam splitter to the shape of the incident surface of the first prism, the workability when mounting the optical member can be improved.

[0013]

Embodiments of the present invention will be described below. [Embodiment 1] FIG. 1 shows a configuration diagram of a liquid crystal display device in Embodiment 1 of the present invention. Reference numeral 11 denotes a three-color separation optical system, which includes a first prism 11A, a second prism 11B, and a third prism 1
1C is arranged as shown in the figure, 11a is the incident surface, 11b, 1
1c and 11d correspond to the emission surfaces of the respective color component lights. On the second surface 11e of the first prism 11A, a dichroic interference thin film that reflects green light and transmits longer and shorter wavelength regions than that is deposited. An air gap is provided between the first prism 11A and the second prism 11B.
A dichroic interference thin film that transmits green to red is deposited on the 11f surface between the first prism 11B and the third prism 11C. Since the light incident on the second dichroic thin film is a magenta color which is a complementary color of the G color, the second dichroic thin film substantially transmits the R color and reflects the B color.

The G color light reflected by the thin film surface 11e is
At 1a, the internal surface is totally reflected and travels toward the emission surface 11b. The blue light reflected by the dichroic thin film 11f is totally internally reflected on the surface in contact with the air gap and travels toward the emission surface 11c, and the red light transmitted through the 11f surface travels toward the emission surface 11d. 12, 13, 14
Is a two-dimensional reflective liquid crystal panel for displaying a video of the G color component, a video of the B color component, and a video of the R color component in this order. This reflection type liquid crystal panel is provided with emission surfaces 11b and 11 of the color separation optical system.
c, 11d. The liquid crystal used here is, for example, a vertically aligned liquid crystal, TN (Twisted Nem).
atic) type liquid crystal.

The following is the same as the conventional example, but will be described again. Reference numeral 11 denotes a polarizing beam splitter (hereinafter, referred to as PBS), which is arranged on the set optical axis O of the color separation optical system 11.
Reference numeral 22 denotes a collimation lens, and a white light source 23 is disposed on the focal point of the collimation lens. Reference numeral 24 denotes a projection lens which is arranged so that its optical axis coincides with the optical axis passing through the PBS 21. Reference numeral 25 denotes a screen, and the screen and each of the reflective liquid crystal elements 12, 13, 14 are adjusted so as to be conjugate with respect to the projection lens.

With the above configuration, the light beam emitted from the white light source 23 enters the collimation lens 22 to become a parallel light beam, and the S-polarized light reflected by the polarization splitting surface of the PBS 21 enters the three-color separation optical system. The linearly polarized light incident on the color separation optical system is decomposed into each color light and incident on each color light valve, spatially modulated by a video signal of each color light, reflected, reversed in the optical path, and subjected to color synthesis, and the color separation is performed. Only the component that has exited from the incident surface 11a of the optical system 11 and whose polarization direction has been changed passes through the PBS 21 and is projected on the screen 25 by the projection lens 24.

FIGS. 2A and 2B show transmission characteristics of the first dichroic thin film and the second dichroic thin film in this embodiment. The first dichroic thin film has a wavelength of 49
It has a property of transmitting light of 0 nm to 590 nm and reflecting others. As the cut wavelength, a value having a good light amount and a good tint for each color of R, G, and B is selected in consideration of the spectrum of the light source light. The light transmitted through the first dichroic thin film becomes a magenta color which is a complementary color of the G color. Next, the second dichroic thin film transmits light having a wavelength of 550 nm or more and reflects light having a wavelength less than 550 nm. Therefore, of the light transmitted through the first dichroic thin film, the R component is transmitted, and the B component is reflected.

The color and brightness of R and B are determined by the characteristics of the first dichroic thin film, and are not affected by the characteristics of the second dichroic thin film. Therefore, the cut wavelength of the second dichroic thin film may be any value within the range of 500 nm to 600 nm, and there is almost no need to consider the shift due to the incident angle and the shift due to the polarization direction. Therefore, the production margin of the film is large, and the production is easy.

Furthermore, a display device using a dichroic thin film has constant brightness and color for each device, and can maintain high quality. In this embodiment, the liquid crystal panel (reflection type liquid crystal element 14) at the position where incident light goes straight is used for R color, but this is used for B color and the reflection type liquid crystal element 13 is used for R color. And the effect of the present invention is not impaired at all. In this case, the transmission characteristics of the dichroic thin film shown in FIG. 2 (b) may be replaced with those in which "transmission" and "reflection" are inverted, that is, those which transmit wavelengths of 500 nm or less and reflect wavelengths of 600 nm or less.

According to the present embodiment, it is possible to provide a bright and well-colored display device which is not affected by the characteristics of the second dichroic thin film. In addition, since the cut wavelength of the second dichroic thin film can be easily manufactured and the margin for manufacturing variations is wide, a liquid crystal display device with stable quality can be provided at low cost.

[Embodiment 2] FIG. 3 shows a configuration diagram of a liquid crystal display device according to Embodiment 2 of the present invention. The components of the eleventh three-color color separation optical system are the same as those in the first embodiment, and the light path and the role of each film surface are the same as those in the first embodiment. The numbers of the components in FIG. 3 are the same as those in FIG.

The differences from the first embodiment are as follows. That is, (1) the incident surface 11a of the first prism is deviated from the perpendicular to the main optical axis of the incident light;
(2) The main optical axis of the incident light is at an angle closer to perpendicular to the surface of the dichroic thin film 11e of the first prism. (3) The dichroic thin film 1 of the first prism
The main optical axis of the incident light is at an angle farther from the vertical with respect to the 1e plane. The feature of this embodiment is derived from the above (2). That is, in the present embodiment, the incident angle dependence and the polarization direction dependence of the cut wavelength of the first dichroic thin film 11e that separates the G color from multiple colors by relaxing the incident angle of the light incident on the dichroic thin film. And a liquid crystal display device that is brighter and has a better color can be provided.

In this embodiment, the entrance surface 11 of the first prism
The example in which a is incident at 80 ° with respect to the main optical axis of the incident light is shown. As a result, the dichroic thin film 1 of the first prism
The main optical axis of the incident light with respect to the 1e surface enters at 78 °, which is closer to the vertical than 68 ° in the first embodiment.
FIGS. 4A and 4B show transmission characteristics of the first dichroic thin film and the second dichroic thin film in this embodiment. 2 (a) and 2 (b), the first dichroic thin film transmits light having a wavelength of 490 nm to 590 nm,
Others have the property of being reflected. The difference in the cut wavelength between the S-polarized light and the P-polarized light is smaller than that in FIG. Next, the second dichroic thin film transmits light having a wavelength of 550 nm or more and reflects light having a wavelength less than 550 nm. The polarization direction dependence of the second dichroic thin film characteristic is large because the incident angle of light is larger than in the first embodiment. However, as described in the first embodiment, since the cut wavelength of the second dichroic thin film is not related to the brightness and color of the display device, an increase in the incident angle on the second dichroic thin film does not matter.

The angle formed by the main optical axis of the incident light with respect to the incident surface 11a of the first prism is determined in consideration of the angle spread of the incident light, the refractive index of the prism material, the tolerance of each member, and the like. It is not limited to the embodiment. In this embodiment, the liquid crystal panel (reflection type liquid crystal element 14) at the position where incident light goes straight is used for R color, but this is used for B color and the reflection type liquid crystal element 13 is used for R color. And the effect of the present invention is not impaired at all. In this case, the transmission characteristics of the dichroic thin film shown in FIG. 4 (b) may be replaced with those in which "transmission" and "reflection" are inverted, that is, those which transmit wavelengths of 500 nm or less and reflect wavelengths of 600 nm or less.

In the present embodiment, in addition to the effect of the first embodiment, since the incident angle of light to the first dichroic thin film becomes closer to vertical, the dependence of the cut wavelength on the polarization and the incident angle is small. That is, the brightness and color of the display device are improved, and the variation in manufacturing is reduced.

Embodiment 3 FIG. 5 shows a configuration diagram of a liquid crystal display device according to Embodiment 3 of the present invention. This embodiment is a second embodiment.
This is another configuration example of “a configuration in which the incident surface 11a of the first prism is shifted from the vertical with respect to the main optical axis of the incident light”. The component elements of the three-color color separation optical system 11 are almost the same as those of the second embodiment, but the glass part of the polarization beam splitter 721 is extended to be close to the entrance surface 11a of the first prism. The light path and the role of each film surface are the same as those in the first and second embodiments, and a description thereof will be omitted. The numbers of the components in FIG. 5 are the same as those in FIGS. 1 and 3 except for the PBS 721. Also in the present embodiment, (1) to (1) shown in the second embodiment.
Although the feature of (3) remains as it is, according to the present embodiment, PB
By adjusting the shape of the light emitting portion from S to the shape of the incident surface of the first prism, it is possible to improve the workability when mounting the optical member.

The transmission characteristics of the first dichroic thin film and the second dichroic thin film can be the same as those of the second embodiment. As in the second embodiment, the difference in the cut wavelength between the S-polarized wave and the P-polarized wave is smaller than that in FIG. The cut wavelength of the second dichroic thin film is the brightness of the display device,
The second embodiment is the same as the second embodiment in that the angle of incidence on the second dichroic thin film does not matter because it has no relation to the color.

The angle formed by the main optical axis of the incident light with respect to the incident surface 11a of the first prism is determined in consideration of the spread of the incident light, the refractive index of the prism material, the tolerance of each member, and the like. It is not limited to the embodiment. In the present embodiment, the liquid crystal panel (reflection type liquid crystal element 14) at the position where the incident light goes straight is used for R color, but it can be used for B color and the reflection type liquid crystal element 13 can be used for R color. However, the effect of the present invention is not impaired at all.

In this embodiment, in addition to the effects of the second embodiment, the shape of the light emitting portion from the PBS is matched with the shape of the incident surface of the first prism, so that the optical member in mounting the optical member can be obtained. Workability can be improved.

[0030]

As described above, according to the present invention, the characteristics of the second dichroic thin film are not affected.
Bright and good-colored display can be realized. Further, according to the present invention, the cut wavelength of the second dichroic thin film can be easily manufactured, a wide margin for manufacturing variations can be secured, and a color separation / synthesis optical system and a liquid crystal display device with stable quality can be manufactured at low cost. Can be provided. Further, according to the present invention, the angle formed between the main incidence axis of the incident light and the normal to the first surface of the prism is set to a fixed angle, so that the first dichroic mirror can be moved to the first dichroic mirror. Can be made shallow, the dependence of the cut wavelength on the polarization direction and the dispersion of the incident angle can be reduced, and the loss of light quantity and the change in color tone can be reduced. Further, according to the present invention, by adjusting the shape of the light emitting portion from the polarization beam splitter to the shape of the incident surface of the first prism, it is possible to improve the workability when mounting the optical member. .

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating characteristics of a dichroic thin film of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a configuration diagram of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating characteristics of a dichroic thin film of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 5 is a configuration diagram of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional liquid crystal display device.

FIG. 7 is a diagram showing characteristics of a dichroic thin film of a conventional liquid crystal display device.

[Explanation of symbols]

 11: 3P prism 11A: first prism 11B: second prism 11C; third prism 11a: entrance surface of first prism 11b: exit surface of first prism 11c: exit surface of second prism 11d : Emission surface of the third prism 11 e: Dichroic thin film of the first pre-spun 11 f: Dichroic thin film of the first pre-spun 12: Reflective liquid crystal panel (G color) 13: Reflective liquid crystal panel (B color or R color) 14 : Reflective liquid crystal panel (R color or B color) 21: Polarization beam splitter (PBS) 22: Collimation lens 23: Light source (lamp) 24: Projection lens 25: Screen 211: 3P prism 211A: First prism 211B: First Second prism 211C: Third prism 211a: Incident surface of first prism 2 1b: Emission surface 211c: Emission surface 211d: Emission surface 211e: Dichroic thin film of the first stream 211f: Dichroic thin film of the second stream 212: Reflective liquid crystal element (B color) 213: Reflective liquid crystal element (R color) 214: Reflective liquid crystal element (G color) 221: Polarization beam splitter 222: Collimation lens 223: Light source (lamp) 224: Projection lens 225: Screen

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (reference) G03B 21/00 G03B 21/00 D 33/12 33/12 F term (reference) 2H042 CA08 CA14 CA17 2H048 GA14 GA23 GA24 GA61 2H088 EA14 EA15 EA16 HA13 HA20 HA21 HA23 2H091 FA05X FA10X FA21X FA26X FD14 FD24 HA07 HA09 LA03

Claims (7)

[Claims] 1. A color separation / synthesis optical system comprising a plurality of prisms and separating and synthesizing incident light into component lights of respective colors by a dichroic film formed on a surface of the prism, wherein at least the incident light is A predetermined color component light is reflected by the dichroic film formed on the second surface and the remaining color component light is passed through the dichroic film formed on the second surface, and the predetermined color component light reflected by the dichroic film is reflected on the first surface. In the first, the entire surface is further reflected to pass through the third surface.
And a dichroic film formed on the second surface of the first prism reflects green light and transmits other colors. 2. A color separation / synthesis optical system comprising a plurality of prisms and separating or synthesizing incident light into component lights of respective colors by a dichroic film formed on a surface of the prism, wherein at least the incident light is A predetermined color component light is reflected by the dichroic film formed on the second surface and the remaining color component light is passed through the dichroic film formed on the second surface, and the predetermined color component light reflected by the dichroic film is reflected on the first surface. In the first, the entire surface is further reflected to pass through the third surface.
And a dichroic film formed on the second surface of the first prism reflects green light and transmits other colors. 3. The method according to claim 1, wherein the first prism is arranged such that an angle formed by a normal to a first surface of the prism with respect to a main incident axis of the incident light has a constant angle. The color separation / synthesis optical system according to claim 1 or 2, wherein 4. A color separation / synthesis optical system for separating and synthesizing incident light into component lights of respective colors, and a video signal arranged on a side from which the component light of each color separated by the color separation / synthesis optical system is emitted. And a reflection type liquid crystal display element driven according to the color separation / combination optical system.
A liquid crystal display device comprising: a polarizing beam splitter that causes a predetermined polarized light to be incident on the combining optical system as incident light; and a projection optical system that projects each color light combined by the color separating / combining optical system. A liquid crystal display device, wherein the synthesis optical system is constituted by the color separation / synthesis optical system according to claim 1. 5. The liquid crystal display device according to claim 4, wherein a shape of light emitted from said polarization beam splitter is formed in accordance with a shape of said first surface of said first prism. 6. A color separation / synthesis optical system for separating and synthesizing incident light into component lights of respective colors, and a video signal arranged on a side from which the component light of each color separated by the color separation / synthesis optical system is emitted. Wherein the color separation / synthesis optical system is a liquid crystal display device comprising: a reflection type liquid crystal display element driven according to the following; and a projection optical system for projecting each color light synthesized by the color separation / synthesis optical system. A liquid crystal display device comprising the color separation / synthesis optical system according to any one of claims 1 to 3. 7. The reflection type liquid crystal display device has three reflection type liquid crystal panels, and the reflection panel rotates a polarization direction of light incident on the panel by approximately 90 ° when displaying white. The liquid crystal display device according to claim 4.