JPH0239084A - Image projector - Google Patents

Abstract

PURPOSE:To improve a light utilizing efficiency by combining a polarized beam splitter and a prism. CONSTITUTION:A natural light radiated from a light source 2 is reflected at an ellipse reflecting mirror 1, converged to another focus, made into parallel lights by a lens 3 and made incident on a polarized beam splitter 4. Reflected S polarized components 12 are reflected at a prism 5 and transmitted through a 1/2 wavelength plate 6, thereby, a polarizing surface is rotated by 90 deg., and P polarized components 11 and a polarizing direction are made parallel. Respective components are converged by lens 14A and 14B, they are totally reflected two times in parallelogram type prisms 15A and 15B, both lights are made approach, they can be made incident on a liquid crystal layer 7 as the parallel lights by a superposing lens 16, and they are projected through a polarizer 8 onto a screen 10 by a lens 9. Thus, the energy consumption of the light source necessary for obtaining the picture of the brightness of the screen can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of an optical system that provides high efficiency for an image projection device.

[Conventional technology]

The optical system of a conventional image projection device will be explained using figures.

FIG. 4 is a principle diagram showing the optical system of the image projection device.

The image projection device can be thought of as a conventional slide projector in which a liquid crystal panel is arranged in place of the slide.

The light emitted from the light source 2 is reflected by the reflecting mirror 1, enters the heat ray absorbing glass 19 and the lens 6, becomes almost parallel light, is converted into image information by the liquid crystal panel 20, and is projected onto the screen 10 by the projection lens 9. be done. The liquid crystal panel 20 is composed of polarizing plates 8A, 8B and a liquid crystal 7 as shown in FIG. Figure 4 shows the case of black and white display.
The liquid crystal panel 20 is also used for color display using the three-color separation method as shown in FIG. The same elements as in FIG. 4 are given the same numbers, 21 is a dichroic mirror (blue reflection), 22 is a dichroic mirror, 23 is a mirror 24 is a dichroic prism.

[Problem to be solved by the invention]

In conventional configurations, when obtaining linearly polarized light from natural light, like a Polaroid polarizing plate, a polarizing plate that absorbs orthogonal linearly polarized light components is used, so in principle, at least half of the light incident from the light source is Since the light is absorbed, the light utilization efficiency is less than 50%, which is low efficiency.

For general use, since the power of the light source cannot be increased excessively, it is difficult to obtain a high-brightness screen, and it is usually used in a darkened room.

Therefore, the present invention provides a high-brightness image projection device that is sufficiently visible even in a normal bright room.

[Means to solve problems]

The present invention improves the light utilization efficiency of a polarizer by utilizing polarized light components that are absorbed by conventional polarizing plates, thereby improving screen brightness. To accomplish this, a combination of a polarizing beam splitter and a prism is used. A polarizer uses two orthogonal polarization components to polarize incident light.
The P-polarized light component and the S-polarized light component are separated, the P-polarized light is transmitted, the S-polarized light is reflected, and the reflected light passes through a prism and a half-wave plate and enters the liquid crystal panel together with the transmitted light. Here, the polarizing beam splitter is used in the visible range (400 nm to 500 nm).
), which is designed to separate polarized light.
An elliptical reflector is used as the light source reflector.

Further, a liquid crystal panel is used as a spatial light modulator, and a liquid crystal cell is used as an optical rotation element.

[Example of real sister]

(Example 1) FIG. 1 shows an optical system of an image projection apparatus as an example of the present invention. The arrow and focal point in the figure indicate the polarization direction. Natural light emitted from a light source 2 (metal halide or halogen lamp) is reflected by an elliptical reflector 1, condensed at another focal point, turned into parallel light by a lens 6, and incident on a polarizing beam splitter 4. Of these, the S polarization component 12 is
The remaining P-polarized light component 11 is reflected and transmitted. The reflected S-polarized light component 12 is reflected by the prism 5 and transmitted through the half-wave plate 6, so that the plane of polarization is rotated by 90 degrees and the polarization direction becomes parallel to that of the P-polarized light component 11. Then, attach each lens to the lens 14A.
, 14B, and a parallelogram-shaped prism 15A.
, 15B, both lights approach each other, and can be made incident on the superimposing lens 16 as parallel light) W8 layer 7, pass through the polarizer 8, and are reflected on the screen 1 by the lens 9.
Project onto 0. With this configuration, the efficiency can be increased to 2 times because it utilizes the polarized light component that was conventionally absorbed by the liquid crystal panel.

(Example 2) FIG. 2 is a diagram showing a second example of the present invention. Natural light emitted from a light source 2 (metal halide lamp or halogen lamp) is reflected by an elliptical reflector 1, condensed at another focal point, turned into parallel light by a lens 3, and enters a polarizing beam splitter 4. Of these, the S-polarized component 12 is reflected, and the remaining P-polarized component 11 is transmitted. Reflection S polarization component 12
is reflected by the prism 5 and transmitted through the 1/2 wavelength plate 6, so that the plane of polarization is rotated by 90 degrees, and the polarization direction becomes parallel to the P polarization component 11. As a result, after the polarization planes of the two separated polarization components are aligned, they are made incident on the pressure liquid crystal layer 7 in parallel, transmitted through the polarizer 8, and projected onto the screen 10 by the projection lens 9. In the case of this configuration as well, since the polarized light components that were conventionally absorbed can be used, twice the efficiency can be obtained. Also,
Characteristics of the polarizing beam splitter A slight difference in the spectral characteristics of reflected light and transmitted light caused by the characteristics of the half-wave plate can be resolved by using a color correction filter.

(Embodiment 3) FIG. 3 is a diagram showing a third embodiment of the present invention. In order to support color display, an optical system is constructed by combining the part from the light source to the front lens of the liquid crystal layer shown in FIG. 1 with the color display part shown in FIG. Similarly to FIG. 1, the light from the light source is converted into parallel light by a lens, and is incident on the optical system of the color display section, and a color image is projected onto the screen by the projection lens. Note that the same elements as in FIGS. 1 and 5 are given the same numbers, and their explanations will be omitted.

〔Effect of the invention〕

As is clear from the above explanation, by separating the polarizer from the liquid crystal, the influence of heat transfer to the liquid crystal due to light absorption by the polarizer is eliminated, and by using a non-absorbing polarizer for the polarizer, it is possible to It would be possible to use the polarized light component that had been absorbed and eliminate the loss in the polarizer. As a result, the power consumption of the light source required to obtain a screen with the same brightness as a conventional screen can be approximately halved. Also, without changing power consumption, screen performance can be doubled.

[Brief explanation of the drawing]

FIGS. 1, 2, and 3 are block diagrams showing the optical system of an image projection device that is an actual case of the present invention, and FIG. The figure is a configuration diagram showing each m configuration in the case of color display. 1... Elliptical reflector, 2... Light source, 4... Polarizing beam splitter, 5...
Prism, 6... Half wavelength plate, 7... Liquid crystal layer, 8... Polarizer, 9... Projection lens, 10... ... Screen, 19 ... Heat ray absorption filter, 20 ... Liquid crystal panel, 21 ... Dichroic mirror (blue reflection), 2
2...Dichroic mirror (green reflection), 23
...Mirror 24...Dichroic prism.

Claims (3)

[Claims] (1) In an image projection device comprising a light source, a projection lens, and a plurality of spatial light modulation elements, a rotating reflecting mirror whose first focus is the light source, a lens whose focal point is a second focal point of the spheroidal reflecting mirror; A prism separates the light emitted from the lens as almost parallel light into reflected light and transmitted light according to the polarization direction, and a 2/2 prism for rotating the polarization direction of either the reflected light or the transmitted light by 90 degrees. An image projection device comprising a one-wavelength plate or a 90° optical rotation element, and a reflecting mirror or prism for aligning the traveling directions of the reflected light and the transmitted light. (2) The image projection device according to claim 1, wherein a liquid crystal panel is used as the spatial light modulation element. (3) The image projection apparatus according to claim 1, wherein a liquid crystal cell is used as the optical rotation element.