JP2004240050A - Single-plate projector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a single-plate projector having the improved image quality of a projected image by enhancing the reflection efficiency of a total reflection prism. <P>SOLUTION: The projector 1 is provided with an illumination optical system 7, a TIR prism 8, a DMD 9, a Fresnel prism plate 10 and a projecting lens 11. A reflection surface for totally reflecting effective reflection light emitted from the DMD 9 is formed in the TIR prism 8. The reflection surface of the TIR prism 8 is formed at an angle of > 45° so as to secure the critical angle of the effective reflection light. Although the effective reflection light emitted from the TIR prism 8 is inclined with reference to a projection optical axis 11a, the light is efficiently projected through the projecting lens 11 by correcting the inclination of the effective reflection light by the Fresnel prism plate 10. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a single-panel projector having an optical element that efficiently totally reflects light from an image display element toward a projection optical system.
[0002]
[Prior art]
A projector for enlarging and projecting an image formed by an image display element on a large-screen screen is a single-panel type that uses one image display element to display a three-color image of RGB, and a three-image display element. It is roughly classified into a three-panel type that combines and displays the formed three-color images. Known single-panel projectors include those that sequentially display three-color images from illumination light in a time-division manner and those that project full-color images as they are. Most of the currently popular projectors use a liquid crystal display element as an image display element, and there are two types of liquid crystal display elements, a transmission type and a reflection type. Has become.
[0003]
2. Description of the Related Art In recent years, a DMD projector using a digital micromirror device (DMD) developed as a result of advances in semiconductor technology as an image display element has attracted attention (for example, see Patent Document 1). The DMD is a reflection-type display element in which a large number of micromirrors each having a side length of more than ten microns are arranged in a matrix, and the on / off of one pixel is switched by digitally controlling the inclination of the micromirrors. The DMD projector is capable of single-panel bright and precise projection depiction, and performs high-speed on / off control of one pixel by a micromirror to reproduce each RGB image in a time-division manner and to reproduce the gradation of one pixel. Perform in time division.
[0004]
In a projector having a built-in liquid crystal display element or DMD, the brightness of a projected image is greatly affected by the internal loss of illumination light. For this reason, a single-panel projector is provided with a total internal reflection prism (TIR prism: Total Internal Reflection prism) to reduce the reflection loss and reduce the angle of inclination of incident light with respect to the projection lens while reducing reflection loss. There is. In Patent Document 1, when the illumination light is guided to the image display device, the illumination light is totally reflected. Light emitted from the image display device is incident on the projection lens in parallel with its optical axis and is projected efficiently.
[0005]
Further, as shown in FIG. 4, there is a type in which light emitted from the image display element 30 is totally reflected toward the projection lens 32 by the reflection surface 31a of the TIR prism 31. The single-panel projector that totally reflects the light emitted from the image display device in the optical path between the image display device and the projection optical system has a layout in which the image display surface is parallel to the optical axis of the projection optical system in order to eliminate useless space. The reflection surface of the TIR prism is arranged at 45 degrees with respect to the image display element.
[0006]
[Patent Document 1]
JP 2001-042256 A
[Problems to be solved by the invention]
However, in the case of a TIR prism having a 45-degree reflecting surface, if the refractive index of the constituent material is small, a part of the light emitted from the image display element enters the reflecting surface at an angle smaller than the critical angle. There is a problem that the light is transmitted through the TIR prism and the illuminance of the projected image is reduced due to reflection loss.
[0008]
The present invention has been made in consideration of the above problems, and provides a single-panel projector in which the reflection surface of a TIR prism can be made larger than 45 degrees and the reflection loss between an image display element and a projection optical system can be made smaller. The purpose is to do.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, a single-panel projector according to the present invention includes a first optical element having a reflection surface which captures light emitted from an image display element and totally reflects the light toward a projection optical system. And a second optical element disposed between the reflecting surface and the projection optical system, for transmitting light emitted from the first optical element, and for bending the optical path thereof. The reflection surface of the first optical element is formed at an angle larger than 45 degrees with respect to the image display element so that the light emitted from the image display element is totally reflected efficiently. At this time, in order to eliminate the necessity of tilting and incorporating the projection optical system so that the principal ray of the light emitted from the first optical element becomes non-parallel to the image display surface, the second optical element The optical path of the light beam emitted from the first optical element is bent.
[0010]
The single-panel projector according to claim 2, wherein a plurality of triangular prisms having the same cross-sectional shape are arranged in a Fresnel prism plate in the same direction as the second optical element, so that an optical path at the time of transmission through the prism is used. The occurrence of astigmatism due to the difference is suppressed.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In FIG. 1, a projector 1 includes an illumination lamp 2 from which high-intensity light is emitted, a color wheel 3 including three primary color filters, an integrator rod 4, a relay lens 5, an illumination optical system 7 having a plane mirror 6, a TIR prism 8, A DMD 9, a Fresnel prism plate 10, and a projection lens 11 are provided.
[0012]
The illumination lamp 2 includes a high-intensity light source that emits white light at a first focal point of the elliptical reflecting mirror, and white light emitted from the high-intensity light source is reflected by the elliptical mirror and collected toward the second focal point. . The color wheel 3 is configured by arranging red (R), green (G), and blue (B) color filters in a disk shape. The white light emitted from the illumination lamp 2 is transmitted through the color wheel 3 rotating at high speed, becomes illumination light of three primary colors of RGB, and sequentially enters the integrator rod 4. The illumination light repeats total reflection inside the integrator rod 4, and the integrator rod 4 emits uniform illumination light without unevenness. Illumination light emitted from the integrator rod 4 passes through the relay lens 5 to become parallel light, and is reflected by the plane mirror 6 toward the TIR prism 8.
[0013]
The DMD 9 has a large number of micromirrors arranged in a matrix. Each micromirror is switched between an on state in which illumination light is reflected so as to be incident on the projection lens 11 and an off state in which illumination light is reflected so as to be incident on a light absorber (not shown). The brightness of one pixel of the projected image is determined by the time when the micromirror is turned on, and the illumination light becomes projection light having image information when the DMD 9 is driven in synchronization with the rotation of the color wheel 3. The DMD 9 is arranged with its image display surface parallel to the optical axis 11a of the projection lens 11.
[0014]
In FIG. 2, the TIR prism 8 includes a first prism 15 and a second prism 16 having a wedge shape. An air gap 17 is provided between the first prism 15 and the second prism 16. The first prism 15 has a first surface 15a on which illumination light reflected by the plane mirror 6 is perpendicularly incident, a second surface from which illumination light is emitted toward the second prism 16, and a third surface 15c. ing.
[0015]
The second prism 16 receives a first surface 16 a parallel to the image display surface of the DMD 9 and illumination light transmitted through the first prism 15, and the light emitted from the DMD 9 is totally reflected toward the projection lens 11. A second surface 16b and a third surface 16c from which light reflected by the total reflection surface 16b is emitted to the outside are formed. The air gap 17 is provided to generate total reflection on the second surface 16b of the second prism.
[0016]
The illumination light incident on the DMD 9 is effectively reflected by the on-state micromirror toward the projection lens 11 via the first surface 16a to the second surface 16c of the second prism, and is reflected by the off-state micromirror to a light absorber ( (Not shown), and travels along each optical path. The second prism 16 is formed such that the angle α between the first surface 16a and the second surface 16b is greater than 45 degrees. As a result, the effective reflected light reflected by the on-state micromirror 18 is incident on the second surface 16b at an incident angle equal to or greater than the critical angle.
[0017]
On the second surface 16b of the second prism 16, the effective reflection light emitted from the DMD 9 is totally reflected on the inner surface thereof, and travels straight in a direction inclined with respect to the optical axis 11a of the projection lens 11. The effective reflected light totally reflected by the second surface 16b is emitted from the third surface 16c and reaches the Fresnel prism plate 10.
[0018]
In FIG. 3, a Fresnel prism plate 10 has a structure in which a number of triangular prisms 19 are arranged on a thin flat plate, and a flat surface 10a on the incident side perpendicular to the projection optical axis 11a and a Fresnel surface on the emission side. 10b are formed. The Fresnel prism plate 10 has triangular prisms 19 arranged in parallel with their directions aligned, and has a refraction function equivalent to a wedge-shaped prism having the same angle as the inclined surface of the triangular prism 19.
[0019]
The effective reflected light emitted from the second prism 16 is incident on the Fresnel prism plate 10 with its principal ray having a certain inclination angle with respect to the projection optical axis 11a. When emitted from the Fresnel prism plate 10, the principal ray enters the projection lens 11 in parallel with the projection optical axis 11a.
[0020]
Since the Fresnel prism plate 10 is formed to be much thinner than a wedge-shaped prism having an equivalent refraction function, astigmatism and chromatic aberration due to transmission through an optical element having a biased thickness like a wedge-shaped prism are reduced. There is no occurrence, and there is no need to correct them in the projection lens 11.
[0021]
The distance on the optical path of the effective reflected light between the DMD 9 and the Fresnel prism plate 10 is set so that the spread of the light flux of the effective reflected light per pixel is sufficiently larger than the pitch of the triangular prism 19. Therefore, no stripe pattern is generated in the projected image by each triangular prism 19.
[0022]
The effective reflected light transmitted through the Fresnel prism plate 10 enters the projection lens 11. In the projector 1, the effective reflected light emitted from the DMD 9 is totally reflected by the second prism 16 without loss, and the effective reflected light having an inclination with respect to the projection optical axis is transmitted through the Fresnel prism plate 10 and is projected on the projection optical axis 11 a. It is corrected in parallel to and projected efficiently on the screen. The display image of the DMD 9 is enlarged and projected on the screen without losing illuminance and sharpness.
[0023]
In the above embodiment, a DMD is used as a reflective display element. However, a liquid crystal display element or other devices may be used as an image display element. The present invention may be applied to a projector using the image display element of the above. Further, the optical element that bends the light beam emitted from the first optical element is not limited to the refractive optical element.
[0024]
【The invention's effect】
As described above, the single-panel projector according to the present invention includes the first optical element that totally reflects the light emitted from the image display element and makes the light enter the projection optical system, and the optical path of the light emitted from the first optical element. And a second optical element that bends the first optical element, so that even if the first optical element is made of a material having a relatively small refractive index, the total reflection surface can be formed at an angle that can suppress reflection loss. Thus, there is no need to arrange the projection optical system at an angle, so that dead space does not occur. That is, the compactness, which is a feature of the single-panel projector, is not impaired, and the image quality of the projected image can be improved. Further, by using a Fresnel prism plate for the second optical element, occurrence of astigmatism due to bending of the optical path can be suppressed, and it is not necessary to correct them by the projection optical system.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a projector.
FIG. 2 is a plan view around a TIR prism.
FIG. 3 is an enlarged plan view of a Fresnel prism plate.
FIG. 4 is a plan view showing a configuration of a conventional TIR prism.
[Explanation of symbols]
1 Projector 8 TIR prism 9 DMD
Reference Signs List 10 Fresnel prism plate 11 Projection lens 15 First prism 16 Second prism 19 Triangular prism

Claims (2)

An image display element that modulates illumination light for each pixel;
A projection optical system for enlarging and projecting the light modulated by the image display element,
A first optical element that captures light emitted from the image display element and forms a reflection surface that totally reflects the light toward the projection optical system;
A second optical element disposed between the reflection surface and the projection optical system, for transmitting light emitted from the first optical element, and bending an optical path thereof. projector. 2. The single-panel projector according to claim 1, wherein the second optical element is a Fresnel prism plate in which a plurality of triangular prisms having the same cross-sectional shape are arranged in the same direction.

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