JPH04329526A - Liquid crystal projector - Google Patents

Abstract

PURPOSE:To suppress the heat generation of polarizing plates due to the irradiation light from a light source by providing a flat plate polarization beam splitter between the light source and polarizing plate. CONSTITUTION:The liquid crystal projector is provided with the light source 1, a condenser lens 3 which converges the irradiation light from the light source 1, a light valve 10 composed of the polarizing plates 4 and 6 and a liquid crystal panel 5, and a projection lens. Then the flat plate polarization beam splitter 9 of TiO2, etc., is provided between the light source 1 and incidence-side polarizing plate 4. This flat plate polarization beam splitter 9 is arranged slantingly to the optical axis while the angle of incidence of the irradiation light is the Brewster angle of the flat plate polarizing splitter 9 so that an S wave which is an unnecessary polarized component is reflected and separated with good efficiency. Further, the heat generation of the polarizing plate 4 is suppressed by matching the plane of polarization of a P wave transmitted through the flat plate polarization beam splitter 9 with the transmission axis of the incidence-side polarizing plate 4. Further, a light absorption member 11 is formed of an aluminum plate painted in black and is provided at the position where the S wave reflected by the flat plate polarization beam splitter 9 is efficiently absorbed.

Description

[Detailed description of the invention]

0010

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal projector such as a liquid crystal projection television or an overhead projector (OHP) using a liquid crystal panel as a light valve.

[0020]

2. Description of the Related Art Recently, liquid crystal projectors using a liquid crystal panel as a light valve have become widely used as liquid crystal projection televisions that project OHP or television images onto a large screen.

FIG. 5 shows the basic structure of a conventional liquid crystal projector, in which 1 is a light source such as a metal halide lamp, 2 is a parabolic mirror that focuses the irradiated light from the light source 1 in a predetermined direction, and 3 is a condenser. A lens 10 is a light valve consisting of an incident side polarizing plate 4, a liquid crystal panel 5 and a projection side polarizing plate 6, and 7 is a projection lens system. 8 is a screen on which images from the liquid crystal projector are projected.

Therefore, the irradiated light from a strong light source 1 such as a metal halide lamp is focused in a predetermined direction by the parabolic mirror 2, and then further focused by the condenser lens 3, and then the incident side polarizing plate 4 and the liquid crystal panel. 5 and a projection-side polarizing plate 6 efficiently enter the light valve 10. On the other hand, when information such as a video signal is supplied to the liquid crystal panel 5 and the light valve 10 consisting of the liquid crystal panel 5 and polarizing plates 4 and 6 is driven to change the amount of light transmitted in accordance with the information such as the video, the liquid crystal The light transmitted through a light valve 10 consisting of a panel 5 and polarizing plates 4 and 6 is enlarged and projected onto a screen 8 by a projection lens system 7, and displayed as an image.

[0050]

[Problem to be Solved by the Invention] Recently, there has been a strong demand for larger screens and higher brightness in the conventional devices mentioned above, but in order to meet these demands, it is necessary to use a more powerful light source. be. However, the polarizing plate used in a liquid crystal projector converts about 1/2 of the incident light into heat, generates heat by itself, and has the drawback of having low heat resistance. Therefore, in order to use a more powerful light source, a cooling device for the polarizing plate must be large-scale, resulting in increased noise, weight, volume, and cost, and there are also problems in that the cooling capacity is limited.

[0060]

[Means for Solving the Problems] In order to solve the above problems, the present invention provides a light source, a condenser lens for condensing irradiated light from the light source, a light valve consisting of a polarizing plate and a liquid crystal panel, and a projection lens. In the liquid crystal projector, a flat polarizing beam splitter is provided between the light source and the polarizing plate.

Further, the plane of polarization of the transmitted light of the flat plate polarizing beam splitter is made to coincide with the transmission axis of the polarizing plate, and
The structure includes a light absorbing member that absorbs the light reflected and separated by the flat plate polarizing beam splitter.

[0080]

[Operation] According to the above configuration, the strong light emitted from the light source is separated into P waves and S waves by the flat plate polarizing beam splitter before entering the polarizing plate, and the transmitted light entering the polarizing plate is significantly attenuated. Suppresses the heat generated by polarizing plates that generate a large amount of heat. and,
The light reflected and separated by the flat plate polarizing beam splitter is absorbed by the light absorbing member.

[0090]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of an embodiment of the present invention. The same parts as those in the conventional example shown in FIG. 5 are given the same reference numerals, and their explanation will be omitted. In FIG. 1, 9 indicates the light source 1 and the incident side polarizing plate 4.
In order to efficiently reflect and separate S waves, which are unnecessary polarization components, in advance, the incident angle of the irradiation light is set to the flat plate polarizing beam splitter 9. It is arranged with an inclination to the optical axis so that the Brewster's angle is . Further, the polarization plane of the P wave transmitted through the flat plate polarizing beam splitter 9 is made to coincide with the transmission axis of the incident side polarizing plate 4, so that heat generation of the polarizing plate 4 is suppressed.

Reference numeral 11 denotes a light absorbing member made of a black-painted aluminum plate, and is provided at a position where it can efficiently absorb the S waves reflected by the flat plate polarizing beam splitter 9.

FIG. 4 shows the dependence of the transmittance of the TiO2 flat plate polarizing beam splitter on the incident angle, where a indicates the transmittance of P-polarized light and b indicates the transmittance of S-polarized light. When light is incident at the Brewster angle shown in c, about 100% of the P wave shown in a is transmitted, but about 25% of the S wave shown in b is transmitted.
Only the light passes through and the rest is reflected.

That is, as in the embodiment shown in FIG.
The angle of incidence of the irradiated light on the flat plate polarizing beam splitter 9 is as shown in FIG.
When installed so that the Brewster angle (approximately 70 degrees) as shown by c in FIG. Since the heat generation in the polarizing plate 4 is caused by the transmitted S waves, it is suppressed to about 1/4.

In the embodiment shown in FIG. 1, the Brewster angle of the TiO2 flat polarizing beam splitter 9 is approximately 70° as shown in c in FIG. Since they are arranged at an angle of about 70 degrees, the optical path length becomes long, and the loss of light quantity becomes large along the way.

FIG. 2 is intended to improve this.
The flat plate polarizing beam splitter 91 is folded into two. FIG. 3 shows yet another embodiment in which the flat plate polarizing beam splitter 92 is divided into a plurality of pieces. In this case, the optimum number of divisions may be determined based on the loss due to division and the loss due to the optical path length. Each of the above flat plate polarizing beam splitters 9
The angle of incidence of the irradiation light onto 1 and 92 is set to the Brewster angle of the flat plate polarizing beam splitter.

[0150]

As the present invention has the above-described structure, the irradiated light from the light source can be polarized in advance by the flat plate polarizing beam splitter, and the heat generation of the polarizing plate can be significantly reduced. Therefore, the cooling device for the polarizing plate can be simplified, and the cost and noise can be reduced.
Furthermore, it becomes possible to use a stronger light source. In addition, since the irradiated light from the light source is polarized before entering the polarizing plate, the polarizing plate can be made to have low orthogonal transmittance, that is, low contrast. losses can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of another embodiment of the main part of the present invention.

FIG. 3 is a configuration diagram of still another embodiment of the main part of the present invention.

FIG. 4 is an explanatory diagram of the operation of the present invention.

FIG. 5 is a configuration diagram of a conventional example.

[Explanation of symbols]

1 Light source 3 Condenser lens 4 Incident side polarizing plate 5 Liquid crystal panel 6 Projection side polarizing plate 7 Projection lens system 9, 91, 92 Flat plate polarizing beam splitter 10
Light valve 11 Light absorption member

Claims (3)

[Claims] 1. A liquid crystal projector comprising a light source, a condenser lens for condensing light irradiated from the light source, a light valve consisting of a polarizing plate and a liquid crystal panel, and a projection lens, wherein a flat plate is provided between the light source and the polarizing plate. A liquid crystal projector characterized by being equipped with a polarizing beam splitter. 2. A liquid crystal projector comprising a light source, a condenser lens for condensing light irradiated from the light source, a light valve consisting of a polarizing plate and a liquid crystal panel, and a projection lens, wherein a flat plate is provided between the light source and the polarizing plate. 1. A liquid crystal projector comprising a polarizing beam splitter and a light absorbing member for absorbing light reflected and separated from the flat polarizing beam splitter. 3. The liquid crystal projector according to claim 1, wherein the plane of polarization of the transmitted light of the flat plate polarizing beam splitter is made to coincide with the transmission axis of the polarizing plate.