JPH0534683A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To protect a polarizing plate by a preliminary polarizing plate and to eliminate a 1/2 wavelength plate from a gap between the preliminary polarizing plate and the polarizing plate. CONSTITUTION:The preliminary polarizing plate 2, the polarizing plate 4, a liquid crystal panel 5, the polarizing plate 6, and a lens 7 are arranged on the optical path axis O of beam projected from a light source 1 subsequently to the source 1. The preliminary polarizing plate 2 is constituted of a glass plate with a TiO2 vapor-deposited film. The transmitting axis of the preliminary polarizing plate 2 is inclined forward by 30 degrees in order to transmit P-wave, and the angle of rotation around the optical path axis O is set 45 degrees which is the same as the angle of rotation around the optical path axis O of the transmitting axis on the polarizing plate 4. The P-wave which is transmitted the preliminary polarizing plate 2 is transmitted through the polarizing plate 4 without loss and is made incident on the liquid crystal panel 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector for projecting an image displayed on a liquid crystal panel onto a screen or the like. More specifically, a polarizing plate arranged on the incident side of the liquid crystal panel is provided with a TiO ₂ vapor deposition film. The present invention relates to a liquid crystal projector protected by a pre-polarizing plate made of a glass plate.

[0002]

2. Description of the Related Art Due to its characteristics, a liquid crystal panel needs to enter a polarized wave whose polarization axis is inclined by 45 degrees with respect to the vertical direction of the screen. Therefore, in the liquid crystal projector, a polarizing plate is arranged on the incident side of the liquid crystal panel, and in some models, the polarizing plate is protected by a pre-polarizing plate made of a glass plate with a TiO ₂ vapor deposition film. FIG. 5 schematically shows a conventional example of a liquid crystal projector in which a polarizing plate arranged on the incident side of a liquid crystal panel is protected by a pre-polarizing plate made of a glass plate with a TiO ₂ vapor deposition film.

The light emitted from the light source 1 passes through a pre-polarizing plate 2, a half-wave plate 3, a polarizing plate 4, a liquid crystal panel 5, a polarizing plate 6 and a lens 7 in this order and is applied to a screen.
The pre-polarizing plate 2 is made of a glass plate with a TiO ₂ vapor deposition film,
It tilts forward about 20 degrees and transmits only P waves. Pre-polarizer 2
The polarization axis of the P wave transmitted through is oriented in the vertical direction of the screen. On the other hand, the transmission axis of the polarizing plate 4 is inclined 45 degrees with respect to the vertical direction of the screen. The half-wave plate 3 disposed between the pre-polarizing plate 2 and the polarizing plate 4 serves to match the polarization axis angle of the P wave transmitted through the pre-polarizing plate 2 with the transmission axis angle of the polarizing plate 4. It is a thing. The characteristics are shown in FIG.

When the polarization axis of the half-wave plate is tilted with respect to the polarization axis (incident polarization axis) of the polarization wave incident on the half-wave plate, the polarization wave passes through the half-wave plate. Rotates about the optical path axis, and a polarized wave whose polarization axis is inclined at an angle twice the tilt angle of the half-wave plate is emitted from the half-wave plate. That is, if the tilt angle of the polarization axis of the half-wave plate with respect to the polarization axis of the incident polarized wave (incident polarization axis) is θ, then
The inclination angle of the polarization axis (emitted polarization axis) of the polarized wave emitted from the wave plate is 2θ. Therefore, as shown in FIG. 7, the half-wave plate 3 disposed between the pre-polarizer 2 and the polarizer 4 has its polarization axis aligned with the polarization axis of the P-wave transmitted through the pre-polarizer 2. It is tilted 22.5 degrees with respect to
The polarization axis angle of the P wave emitted from the half-wave plate 3 is 45 degrees (the angle with respect to the vertical direction of the screen), which is the same as the angle of the transmission axis of the polarizing plate 4.

[0005]

In such a conventional liquid crystal projector, although the polarizing plate is protected by the pre-polarizing plate, the structure of the optical system is improved by the half-wave plate interposed therebetween. It cannot avoid being complicated. The half-wave plate has wavelength characteristics, and for example, G
1 if the polarization axis of the half-wave plate is aligned with the light
The R component and the B component of the polarized wave emitted from the / 2 wavelength plate have a deviation of the polarization axis with respect to the G component. for that reason,
The quality of the image projected by the liquid crystal projector is also inevitable.

The present invention was devised in view of the above circumstances, and an object of the present invention is to provide a liquid crystal projector in which a polarizing plate is surely protected, a structure is simple, and a high-quality image can be projected. ..

[0007]

In a liquid crystal projector according to the present invention, a polarizing plate is arranged on the incident side of a liquid crystal panel,
Further, in a liquid crystal projector in which a pre-polarizing plate made of a glass plate with a TiO ₂ vapor deposition film is arranged on the incident side, the polarization axis angle of the polarized wave pre-polarized by the pre-polarizing plate is arranged on the emitting side of the pre-polarizing plate. It is characterized in that the pre-polarizing plate is rotated around the optical path axis so as to match the transmission axis angle of the polarizing plate.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a perspective view showing a structure of a liquid crystal projector according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing a spectral transmittance of a pre-polarizing plate, FIG. 3 is a characteristic diagram showing a spectral transmittance of a polarizing plate,
FIG. 4 is an explanatory diagram of the inclination of the polarization axis.

A liquid crystal projector, as shown in FIG.
The pre-polarizing plate 2, the polarizing plate 4, the liquid crystal panel 5, the polarizing plate 6, and the lens 7 are arranged in this order on the optical path axis O of the light emitted from the light source 1. In the middle
No wave plate is placed. Therefore, the P wave transmitted through the pre-polarizer 2 is directly incident on the polarizer 4.

The pre-polarizer 2 is made of a glass plate with a TiO ₂ vapor deposition film, the transmission axis is tilted forward by about 20 ° with respect to the screen, and the optical path axis O is rotated at an angle of 45 ° with respect to the vertical direction of the screen. Leaning on. Then, due to the forward tilt, in the pre-polarizing plate 2, as shown in FIG. 2, about 90% of the P wave is transmitted, and about 20% of the S wave whose polarization axis is inclined by 90 degrees with respect to the P wave is transmitted. .. Further, due to the inclination around the optical path axis O, the polarization axis of the P wave transmitted through the pre-polarizing plate 2 is inclined by 45 degrees with respect to the vertical direction of the screen.

The polarization axis of the polarizing plate 4 is inclined by 45 degrees with respect to the vertical direction of the screen in order to allow the polarized wave whose polarization axis is inclined by 45 degrees with respect to the vertical direction of the screen to enter the liquid crystal panel 5. Therefore, the P-wave transmitted through the pre-polarizer 2 has a polarization axis angle that matches the transmission-axis angle of the polarizer 4 as shown in FIG. 4, and as a result, the P-wave travels through the polarizer 4 without loss. To Penetrate. As shown in FIG. 3, the transmittance of the polarizing plate 4 is about 40%, and the rest is almost absorbed and becomes heat.
Since this is the heat generated by the component orthogonal to the transmission axis,
About 20% of the heat generated by the polarizing plate 4 is transmitted through the pre-polarizing plate 2.
It is only due to the S wave of.

The P wave transmitted through the polarizing plate 4 is transmitted through the liquid crystal panel 5 and the polarizing plate 6 and then projected onto the screen by the lens 7. The transmission axis of the polarizing plate 6 is inclined 45 degrees in the reflection direction with respect to the transmission axis of the polarizing plate 4.

In such a liquid crystal projector, the polarizing plate 4 is protected by the pre-polarizing plate 2. Since the half-wave plate is not interposed between the pre-polarizing plate 2 and the polarizing plate 4,
The structure of the optical system becomes simple. P transmitted through the pre-polarizer 2
Even though the wave is directly incident on the polarizing plate 4, the polarization axis angle of the P wave matches the transmission axis angle of the polarizing plate 4, so that the P wave transmits through the polarizing plate 4 without loss. In addition, the elimination of the half-wave plate eliminates the axis deviation for each wavelength. Therefore, a high quality projected image quality can be obtained.

Although the above embodiment is a single-plate type liquid crystal projector, the present invention can be applied to a two-panel type or three-panel type liquid crystal projector.

[0015]

As described above, the liquid crystal projector according to the present invention has a structure in which the polarizing plate is protected by the pre-polarizing plate, but the polarization axis angle of the polarized wave pre-polarized by the pre-polarizing plate is transmitted through the polarizing plate. Since the half-wave plate is excluded from between the pre-polarizing plate and the polarizing plate by matching the axial angle, the structure of the optical system becomes simple. Further, when the half-wave plate is provided, there is no axis deviation for each wavelength, and a high-quality image can be projected.

[Brief description of drawings]

FIG. 1 is a perspective view showing a structure of a liquid crystal projector according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a spectral transmittance of a pre-polarizing plate.

FIG. 3 is a characteristic diagram showing a spectral transmittance of a polarizing plate.

FIG. 4 is a schematic diagram showing a relationship between a polarization axis and a transmission axis.

FIG. 5 is a perspective view showing a structure of a conventional liquid crystal projector.

FIG. 6 is a schematic diagram showing characteristics of a half-wave plate.

FIG. 7 is a schematic diagram showing a relationship between a polarization axis and a transmission axis.

[Explanation of symbols]

 1 light source 2 pre-polarizing plate 4, 6 polarizing plate 5 liquid crystal panel 7 lens O optical path axis

Claims (1)

Claim: What is claimed is: 1. A liquid crystal projector comprising a liquid crystal panel, a polarizing plate disposed on the incident side, and a pre-polarizing plate made of a glass plate with a TiO ₂ vapor deposition film disposed on the incident side. The polarization axis angle of the polarized wave pre-polarized by
A liquid crystal projector characterized in that the pre-polarizing plate is arranged so as to rotate about the optical path axis so as to match the transmission axis angle of the polarizing plate arranged on the emission side of the pre-polarizing plate.