JP2003262918A - Image projecting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, high-luminance, and high picture quality image projecting device. <P>SOLUTION: The image projecting device is provided with an illumination optical system which generates illumination light by passing the luminous flux from a light source part, a spatial optical modulating element which varies in reflection characteristics to the illumination light according to a control signal, and a projecting means which projects video light reflected by the spatial optical modulating element on a screen; and the light source part and projecting means are arranged having their optical axes almost in parallel to each other, the optical axes and the optical axis of the spatial optical modulating element are arranged almost at right angles to each other, and an optical deflecting means which changes the traveling directions of the illumination light and video light are arranged adjacently to the spatial optical modulating element. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image projection device using a spatial light modulator.

[0002]

2. Description of the Related Art As one of spatial light modulators used in an image projection apparatus, a digital micromirror device (hereinafter referred to as "DM") in which a large number of minute mirrors are two-dimensionally arranged.
D ”).

FIG. 6 shows a pixel structure of a DMD, in which each pixel is responsive to a control signal from the outside.
The movable mirror is capable of changing the tilt angle by ± 10 degrees or ± 12 degrees with the diagonal direction of the pixel as the rotation axis.

The DMD produces an image by changing the reflection direction of illumination light by turning on and off the two states shown in FIG.

As a method of applying the DMD to the image projection apparatus, an optical system using a critical angle prism as shown in FIG. 7 is known. The operation of this optical system will be described below.

The light beam generated by the light source unit 701 passes through a rod integrator 702 and a condenser lens 703, is reflected by a mirror 704, and is guided to a critical angle prism 705.

The critical angle prism 705 has an air gap 705a whose inclination angle is set so that the illumination light is totally reflected and the image light is transmitted.

The critical angle prism 705 has an air gap 7
It is arranged at an angle of 45 degrees with respect to the horizontal direction of the device so that the direction of 05a coincides with the swing direction of the mirror of the DMD 706.

As a result, the illumination light 708 enters from the direction of 45 degrees with respect to the horizontal direction of the apparatus, and the image light is turned on.
The mirror in this state reflects the light in the front direction of the DMD 706.

Image light 709 reflected by the DMD 706
Passes through the air gap of the critical angle prism, and an image is displayed on the screen by the projection lens 707.

The drive circuit 710 controls the DMD mirror by digital signal processing, and is arranged on the back surface of the DMD.

The DMD is controlled by extremely high-speed signal processing, and it is desirable to integrally arrange the drive circuit 710 and the DMD 706 in this way for stable operation of the device.

[0013]

The image projection apparatus according to the above-mentioned prior art has a drawback that the circuit board for driving the DMD is arranged orthogonal to the optical system, and the apparatus size becomes large. There is.

Also in the optical system, the structure in which the illumination light is incident on the critical angle prism from the direction of 45 degrees is a cause of hindering the miniaturization of the apparatus.

Further, the critical angle prism between the spatial light modulator and the projection lens has a problem that it causes astigmatism when the image light passes through the air gap and deteriorates the quality of the projected image. There is.

If an optical system as shown in FIG. 8 disclosed in Japanese Patent Laid-Open No. 2000-47328 is used, it is possible to avoid the occurrence of the above-mentioned astigmatism.
Since the image light is totally reflected twice by the prism, there is a drawback that the optical path length of the prism portion becomes longer and the size of the projection lens becomes larger than that of the above-mentioned conventional technique.

Further, as in the above-mentioned prior art, the drive circuit and the D
When the MDs are integrally arranged, they are orthogonal to the optical system, and many elements that hinder miniaturization remain in the layout of the entire device.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a small-sized, high-luminance and high-quality image projection apparatus.

[0019]

According to a first aspect of the present invention, a light source section, an illumination optical system for passing a light beam from the light source section to generate illumination light, and a reflection characteristic of the illumination light according to a control signal. Is a spatial light modulation element and a projection means for projecting the image light reflected by the spatial light modulation element onto a screen, wherein the light source section and the optical axis of the projection means are substantially mutually Light deflection that is arranged in parallel, the optical axis and the optical axis of the spatial light modulation element are arranged substantially at right angles, and is adjacent to the spatial light modulation element and changes the traveling directions of the illumination light and the image light. Means are arranged.

In a second aspect of the present invention, in addition to the configuration of the first aspect of the present invention, a mirror adjacent to the spatial light modulator for reflecting the illumination light toward the spatial light modulator, and the illumination are provided. A critical angle prism that transmits light and totally reflects the image light is arranged.

In the third aspect of the present invention, in addition to the configuration of the second aspect of the present invention, the chief ray of the image light is inclined in a direction in which the angle of incidence on the total reflection surface of the critical angle prism increases.

In the fourth aspect of the present invention, in addition to the configuration of the second or third aspect of the present invention, a field lens having a positive power is disposed adjacent to the incident portion of the critical angle prism.

In the fifth aspect of the present invention, in addition to the structure of the fourth aspect of the present invention, the field lens is bonded to the critical angle prism.

In the sixth aspect of the present invention, in addition to the configuration of the fourth or fifth aspect of the invention, the optical axis of the field lens is decentered with respect to the optical axis of the illumination light incident on the critical angle prism.

In the seventh aspect of the present invention, in addition to any one of the third to sixth aspects of the present invention, the chief ray of the image light is inclined in the long side direction of the spatial light modulator, and The illumination light has a larger spread angle in the short side direction than in the long side direction of the spatial light modulator.

In the eighth aspect of the present invention, in addition to the configuration of the seventh aspect of the present invention, the illumination optical system has a rod integrator, and the cross section of the rod integrator has a shape in which an incident portion is closer to a square than an emission portion. Is.

According to a ninth aspect of the present invention, a light source section, and an illumination optical system for passing a light flux from the light source section to generate illumination light,
An image projection apparatus comprising: a spatial light modulation element in which a reflection characteristic of the illumination light changes according to a control signal; and a projection means for projecting image light reflected by the spatial light modulation element onto a screen, A critical angle prism that transmits the illumination light and totally reflects the image light is disposed adjacent to the light modulation element, and the projection means is disposed on an optical axis that blocks a light beam less than a critical angle of the critical angle prism. On the other hand, it has an asymmetric diaphragm.

[0028]

FIG. 1 is an optical path diagram of an image projection apparatus showing an embodiment of the present invention, FIG. 1 (a) is a top view and FIG. 1 (b) is a side view.

In this embodiment, the optical system includes a light source unit 10.
1. Illumination optical system 102 that passes the light flux from the light source unit to generate illumination light, DMDs 103 and D that are spatial light modulators
The projection lens 104, the reflection mirror 105, and the field lens 10 that project the image light reflected by the MD on the screen.
6 and the critical angle prism 107.

Then, these constituent elements are arranged according to the relationship described below.

The light source section 101 and the projection lens 104 are arranged so that their optical axes are substantially parallel to each other.

With respect to these optical axes, the DMD 103
They are arranged so that their optical axes are substantially right angles.

On the rear surface of the DMD 103, the drive circuit 111
Are arranged. Since the arrangement of the drive circuit 111 is substantially parallel to the optical system, the increase in the device width is minimized.

On the front surface of the DMD 103, a reflection mirror 105 for reflecting the illumination light 108 toward the DMD, the illumination light 1
A critical angle prism 107 that transmits 08 and totally reflects image light 109 is arranged so that the illumination light and the image light travel in a predetermined direction.

The total reflection surface 107a of the critical angle prism 107
Is arranged so that its normal vector is aligned with the horizontal direction of the device, thereby making the device thinner.

As the deflecting means for changing the traveling directions of the illumination light 108 and the image light 109, the above-mentioned reflection mirror 105 is used.
In addition to the critical angle prism 107, an optical element such as a polarization beam splitter or a hologram may be used.

The light source section 101 uses an elliptical reflector 101a as a light collecting means. Reflector 101
A color wheel 101b that switches while rotating a color filter including the three primary colors of light is disposed at the light collecting position 102a of a, and it is possible to display a color image.

The condensing means of the light source section 101 may be realized by a combination of a parabolic reflector or a condenser lens in addition to the elliptical reflector 101a.

Further, the color wheel may be arranged at the emitting portion 102b of the rod integrator 102 or the like.

The optical axis of the light source section 101 is the projection lens 104.
Does not necessarily have to be perfectly parallel to the optical axis of.

Considering the space occupied by the entire optical path, it may be better to provide a slight inclination angle. In the present embodiment, the inclination angle θ1 of the optical axis of the light source section 101 is 5 relative to the projection lens 104. As a degree, the light source unit 101 is configured not to project more than the others.

Image light 109 incident on the projection lens 104
, The chief ray has a predetermined inclination angle with respect to the optical axis.

This inclination angle is set in such a direction that the angle of incidence on the total reflection surface 107a of the critical angle prism 107 increases, whereby the illumination light 1 in the critical angle prism 107 is increased.
The transmission of 08 and the total reflection of the image light 109 are ensured.

In the present embodiment, the DMD 103 having a mirror deflection angle of ± 12 degrees is used as the spatial light modulator, and a general optical glass having a refractive index of about 1.52 is used as the glass material of the prism 107. Assuming that, the apex angle θ2 of the prism is 46 degrees and the inclination angle θ3 of the chief ray is 5 degrees.

A field lens 106 having a positive power is arranged at the incident portion of the critical angle prism 107.

The field lens 106 is the DMD 103.
The illumination light for irradiating light is made telecentric, the uniformity of the illuminance distribution is good, and the fact that it is arranged at the incident part of the critical angle prism 107 serves to significantly shorten the optical path length.

FIG. 2 shows details of the critical angle prism 107 and the field lens 106.

When a spatial light modulator such as the DMD 103 is used, the illumination light 108 needs to be incident on the device at a predetermined inclination angle.

In the present embodiment, this is achieved by making the illumination light 108 incident on the critical angle prism 107 from obliquely above, and in accordance with this, the prism 10 is matched.
The incident surface 107b of No. 7 is inclined.

The field lens 106 holds the prism 10 so as to stably hold it against such an inclined surface.
It is adhered to the incident surface of No. 7.

The critical angle prism and the field lens may have a configuration as shown in FIG.

In this example, unlike the above example, the prism 3
The field lens 302 is arranged eccentrically with respect to the illumination light 303 without tilting the incident surface 301a of No. 01.

The decentered field lens 302 has a function equivalent to the refracting power of the inclined surface of the prism 301, and the prism 301 can have a columnar shape.

As a result, the plurality of critical angle prisms 30
Since it becomes possible to polish 1 at a time, it becomes possible to greatly improve productivity.

The projection lens 104 is designed to have a bright F number so as to be able to take in all the image light having the above-mentioned inclination angle. In addition to this, as shown in FIG. A diaphragm 104a that is asymmetric with respect to the axis is provided.

This diaphragm 104a is provided with the critical angle prism 10
In FIG. 7, the light beam 110 that does not satisfy the condition of total reflection is cut off.

For example, when using a rod-shaped rod integrator 401 as shown in FIG.
As shown in b, the image light 4 incident on the projection lens 104
02 passes through the diaphragm surface in a state of being eccentric with respect to the circular diaphragm shape 403 originally possessed by the projection lens 104.

Since a light beam less than the critical angle transmits on the side opposite to the eccentric direction, a diaphragm 404 asymmetric about the optical axis is provided according to the position.

As a result, stray light mixed in from the illumination optical system is not projected on the screen, and a high-quality image with an excellent contrast ratio can be obtained.

As the integrator of the illumination optical system, a taper type one as shown in FIG. 5a may be used.

In this case, by making the cross-sectional shape of the entrance portion 501a of the rod integrator 501 closer to a square than the exit portion 501b, it is possible to improve the efficiency of taking in the light flux at the integrator entrance portion.

At the same time, the angular intensity distribution at the time of emitting the rod spreads in the short side direction of the spatial light modulator, and the passing range 502 of the image light on the diaphragm surface of the projection lens becomes large vertically as shown in FIG. 5b.

With such a structure, the effective area of the projection lens can be utilized without waste and the brightness of the projection screen can be increased.

Incidentally, such an illumination optical system having different vertical and horizontal angular spreads may be constructed by using a cylindrical lens or the like.

In the above description, the example in which the rod integrator is used for the illumination optical system has been described, but an element such as a fly-eye lens may be used as the integrator.

If screen uniformity is not an issue, the integrator need not be used.

Regarding the spatial light modulator, the DMD
Besides, an element such as a reflective liquid crystal may be used.

[0068]

According to the first aspect of the invention, the light sources and the projection means are arranged so that their optical axes are substantially parallel to each other, and the optical axis and the optical axis of the spatial light modulator are substantially perpendicular to each other. By arranging, the protrusions in the height and width directions due to the drive circuit of the optical system components and the spatial light modulator are minimized,
An image projection device that is slim and has excellent portability is provided.

According to the second aspect of the invention, since the image light is totally reflected by the critical angle prism, no astigmatism is generated when the image light is transmitted through the air gap, and the image projection apparatus is excellent in image forming performance. Will be provided.

According to the third aspect of the present invention, the chief ray of the image light is inclined in the direction in which the incident angle on the total reflection surface of the critical angle prism increases, so that the light amount loss occurs in the critical angle prism. And a bright projection image can be obtained.

According to the invention described in claim 4, by disposing the field lens having a positive power adjacent to the incident portion of the critical angle prism, the optical path length of the illumination system is effectively shortened, and the image projection. Further miniaturization of the device can be achieved.

According to the fifth aspect of the present invention, by bonding the field lens to the critical angle prism, the optical path length is further shortened, and the lens holding mechanism is not required and the structure of the optical system is simplified. can do.

According to the sixth aspect of the invention, since the field lens is arranged eccentrically, the critical angle prism has a columnar shape, and the productivity can be greatly improved.

According to the seventh aspect of the invention, in the optical system in which the chief ray of the image light is inclined in the long side direction of the spatial light modulation element, the illumination light is directed in the short side direction rather than the long side direction of the spatial light modulation element. By having a large divergence angle, the effective area of the component is effectively utilized in the projection means, and the brightness of the image projection apparatus can be increased.

According to the eighth aspect of the present invention, since the rod integrator whose cross-sectional shape of the incident part is closer to square than that of the exit part is used, the efficiency of taking in the light flux at the integrator incident part is improved, and the image projection device Further higher brightness can be achieved.

According to the invention described in claim 9, the projection means is provided with a stop asymmetric with respect to the optical axis for blocking a light beam less than the critical angle of the critical angle prism, whereby stray light mixed from the illumination optical system is provided. Is no longer projected on the screen,
It is possible to obtain a high-quality image with an excellent contrast ratio.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical system showing an embodiment of an image projection apparatus according to the present invention, FIG. 1 (a) is a top view and FIG. 1 (b) is a side view.

FIG. 2 is a diagram showing the shapes of a field lens and a critical angle prism of the present invention.

FIG. 3 is a diagram showing a decentered field lens and a critical angle prism of the present invention.

FIG. 4 is a diagram showing a distribution of diaphragm surfaces of a rod integrator and a projection lens according to an embodiment of the present invention.

FIG. 5 is a diagram showing distributions of a rod integrator and a diaphragm surface of a projection lens according to another embodiment of the present invention.

FIG. 6 is a diagram showing a structure of a pixel of a DMD.

FIG. 7 is a configuration diagram of an optical system of an image projection device according to a conventional technique.

FIG. 8 is a configuration diagram of an optical system of an image projection device according to another conventional technique.

[Explanation of symbols]

101 ... Light source part, 101a ... Reflector, 101b ...
Color wheel, 102 ... Illumination optical system, 102a ... Rod entrance section, 102b ... Rod exit section, 103 ... DMD,
104 ... Projection lens, 104a ... Aperture, 105 ... Mirror, 106 ... Field lens, 107 ... Critical angle prism, 107a ... Total reflection surface, 108 ... Illumination light, 109 ... Image light, 110 ... Luminous flux less than critical angle, 111 ... drive circuit, 301 ... prism, 301a ... prism entrance surface, 3
02 ... Field lens, 303 ... Illumination light, 401 ... Rod integrator, 402 ... Image light, 403 ... Circular diaphragm, 404 ... Asymmetric diaphragm, 501 ... Rod integrator, 501a ... Rod entrance section, 501b ... Rod exit section, 502 ... image light, 503 ... diaphragm, 701 ... light source section, 702 ... rod integrator, 703 ... condenser lens, 704 ... mirror, 705 ... critical angle prism,
705a ... Air gap, 706 ... DMD, 707 ... Projection lens, 708 ... Illumination light, 709 ... Image light, 710 ...
Drive circuit

Claims (9)

[Claims] 1. A light source section, an illumination optical system for generating illumination light by passing a light flux from the light source section, a spatial light modulator for changing the reflection characteristic of the illumination light according to a control signal, and the space. An image projection apparatus comprising: a projection means for projecting image light reflected by a light modulation element onto a screen, wherein the light source section and the projection means are arranged so that their optical axes are substantially parallel to each other. An optical axis of the spatial light modulation element is arranged at a substantially right angle, and a light deflecting means for changing the traveling directions of the illumination light and the image light is arranged adjacent to the spatial light modulation element. Image projection device. 2. A mirror for reflecting the illumination light toward the spatial light modulator and a critical angle prism for transmitting the illumination light and totally reflecting the image light are arranged adjacent to the spatial light modulator. The image projection apparatus according to claim 1, wherein the image projection apparatus is provided. 3. The image projection apparatus according to claim 2, wherein the chief ray of the image light is inclined in a direction in which the incident angle on the total reflection surface of the critical angle prism increases. 4. The image projection apparatus according to claim 2, wherein a field lens having a positive power is arranged adjacent to the incident portion of the critical angle prism. 5. The image projection apparatus according to claim 4, wherein the field lens is bonded to the critical angle prism. 6. The image projection apparatus according to claim 4, wherein an optical axis of the field lens is decentered with respect to an optical axis of illumination light incident on the critical angle prism. 7. The chief ray of the image light is inclined in the long side direction of the spatial light modulation element, and the illumination light has a larger spread angle in the short side direction than in the long side direction of the spatial light modulation element. The image projection apparatus according to any one of claims 3 to 6, wherein 8. The image projection apparatus according to claim 7, wherein the illumination optical system has a rod integrator, and a cross section of the rod integrator has a shape in which an entrance portion is closer to a square than an exit portion. . 9. A light source section, an illumination optical system that passes the light flux from the light source section to generate illumination light, a spatial light modulator that changes a reflection characteristic of the illumination light according to a control signal, and the space. An image projection device comprising: a projection means for projecting image light reflected by a light modulation element onto a screen, wherein a critical angle is provided adjacent to the spatial light modulation element for transmitting the illumination light and for totally reflecting the image light. An image projection apparatus in which a prism is arranged, and the projection means has a diaphragm that is asymmetric with respect to an optical axis that blocks a light beam less than a critical angle of the critical angle prism.