JP3499384B2 - Image projection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image projection apparatus such as an exposure apparatus and a projection display in a printer. 2. Description of the Related Art There is known a projection type image exposure apparatus which forms an image on a CRT on a photosensitive material and records the image on the photosensitive material. Has a problem that it takes a long time to record on a photosensitive material because the beam diameter is small and the amount of light is small. Therefore, FIG.
The spatial light modulator 20 (spatial light modula
ter: SLM), polarizing beam splitter 35 (PBS),
Using a readout light irradiation means 40 and a projection optical system 50, a CRT
An exposure apparatus that amplifies light from 10 or the like and irradiates the photosensitive material 60 with the light has recently been adopted. The configuration shown in FIG. 5 is a basic configuration of a general image projection apparatus using an SLM. In addition to an exposure apparatus, an image on a CRT 10 is once written on an SLM 20 and read out from the SLM 20 to be irradiated from a light irradiation means 40. It is also used in a projector or the like that enlarges and projects a bright image on the screen 60 by reading out with high luminance light such as halogen lamp light. The SLM is an element that amplifies and displays an image signal by spatially modulating the amplitude and phase of the readout light.
There are an optical writing type in which optical signals are input in time series or in parallel, and an electric writing type in which electric signals are input in time series. As shown in FIG. 2, the basic structure of the optical writing type is a structure in which a flat optical sensor 21, a dielectric mirror 22, and a light modulating layer 23 are successively brought into close contact and sandwiched between two transparent electrodes 24, 25. .
On the other hand, in the electric writing type, the optical writing type optical sensor is replaced with an electron beam scanning system or an integrated electronic circuit. For the light modulation layer of these SLMs, a material such as an electro-optic crystal or a liquid crystal, whose optical properties such as refractive index, scattering, and optical rotation are changed according to an applied electric field, is used. When an exposure apparatus using such an SLM is used, light from a CRT or the like can be easily amplified, and the exposure time to a photosensitive material can be shortened. In the above-mentioned image projection apparatus, an optical apparatus in which the SLM 20 and the PBS 35 are integrally formed is proposed in JP-A-8-122808 in order to reduce the light quantity loss and suppress the occurrence of flare and ghost due to the optical axis shift. Have been. [0007] However, optical axis deviation from an optical system other than the SLM and the PBS occurs, and the PB
Adhesion of dust and dirt to the surface on which readout light is incident by the S condenser lens or the surface from which light is emitted to the projection optical system causes image quality degradation such as noise on a reproduced image. There were problems. The present invention has been made in view of the above circumstances, and is an image projection apparatus capable of projecting a reproduced image which is unlikely to cause optical axis shift and has no image quality deterioration such as noise caused by dust or dust. The purpose is to provide. According to an image projection apparatus of the present invention, image information is two-dimensionally written on a plane, and the polarization state of reflected light of readout light incident on the plane is determined by the image projection apparatus. A spatial light modulation element that spatially modulates the information, image information writing means for writing the image information to the spatial light modulation element, and a spatial light modulation element disposed to face the plane; A polarizing beam splitter, a light source for emitting the readout light, a condenser lens for condensing the readout light and entering the polarization beam splitter, and a linearly polarized readout light in which the readout light is polarized by the polarization beam splitter. Was incident on the spatial light modulator, and the reflected light spatially modulated by the spatial light modulator was polarized by the polarizing beam splitter. Thereafter, in an image projection apparatus comprising: a projection lens for enlarging and projecting linearly polarized reflected light having a polarization plane orthogonal to the polarization plane of the linearly polarized light readout light to an external projection plane, the plane of the spatial light modulator, The surface of the polarizing beam splitter facing the flat surface is integrally fixed and fixed, and the light condensing lens and / or the projection lens receives light passing through the lens of the polarizing beam splitter, respectively. It is characterized by being integrally formed on the surface or the surface from which the light is emitted. [0010] As the condenser lens, for example, a condenser lens or a Fresnel lens can be used. The "external projection surface" is, for example, a photosensitive material or a screen. According to the image projection apparatus of the present invention, not only the spatial light modulator (SLM) and the polarizing beam splitter (PBS) are integrated, but also the condenser lens and / or the projection lens can be mounted on the PBS. Integrally formed with PBS
It is possible to prevent dust and dirt from adhering to the surface, and to prevent image quality deterioration due to these, and as a result, a reproduced image without image quality deterioration can be projected on the projection surface. The integration of the PBS and each optical system eliminates optical axis deviation between the elements, simplifies adjustment of the position and axis between the elements, and facilitates mounting. . Further, the apparatus can be made compact as a whole. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific embodiment of an image projection apparatus according to the present invention will be described with reference to the drawings. As shown in FIG. 1, an image projection apparatus 1 according to the present invention includes a CRT 11 for irradiating a spatial light modulator 20 with a writing light Lw carrying image information and a writing lens 12 for writing image information. Readout light irradiation comprising means 10 and a light source 41 such as a halogen lamp for generating the readout light Li, and a condenser lens 42 for condensing the readout light Li emitted from the light source 41 and irradiating the light to a polarization beam splitter 35 described later. Means 40, and writing light Lw is irradiated from one surface by the image information writing means 10, and spatial light that spatially reflects and modulates light incident from the other surface based on the image information of the writing light Lw. A modulating element (SLM) 20, a linearly polarized readout light Li ′ is made incident on the SLM 20, and a polarization beam splitter (PBS) 35 that linearly polarizes and emits the reflected light Lr from the SLM 20, and the PBS 35. Consisting projection plane (photosensitive material or screen) consists of a projection lens 51 for projecting the 60 projection optical system 50. The linearly polarized light reflected light Lr ', which is allowed to polarization. The AC power supply 30 in the figure is an SLM drive voltage source. The SLM 20, the condenser lens 42 of the reading light irradiation means 40, the lens 51 as the projection optical system 50, and the PBS
35 is integrally formed as shown in detail in FIG. The PBS 35 is formed by joining the inclined surfaces of two triangular prisms, and the incident light is separated into light reflected on the joining surface 35c and light transmitted through the joining surface 35c.
Note that these two light components have polarization planes orthogonal to each other. In this embodiment, one surface 35 of the PBS is used.
An SLM 20 is formed using d as a substrate. That is, PB
The transparent electrode 25 is formed on the surface 35d of S, and the alignment layer 26a, the liquid crystal layer 23, the alignment layer 26b, the dielectric mirror 22, the light-shielding layer 28, the photoconductive layer 21, and the transparent electrode 24 are arranged in this order, and the surface 35d of PBS is formed. The SLM 20 is sandwiched between the SLM 20 and the glass substrate 29. The liquid crystal layer 23 is made of vertical alignment type liquid crystal, and the liquid crystal is sealed by a spacer 27. The photoconductive layer 21 is made of a material such as hydrogenated amorphous silicon or a CdS thin film which has a large resistivity when light is not irradiated and a material whose resistivity is significantly reduced by light irradiation. 21 works as an optical sensor. The dielectric mirror 22 plays a role of spatially separating the writing light and the reading light, and the degree of optical isolation determines the signal amplification factor of the SLM. The light-shielding layer 28 is provided to enhance the isolation between the two lights. The projection surface 60 is a photosensitive material when the present image projection device 1 is used as an exposure device such as a printer, and is a screen when it is used as a projector. The operation of the image projection device 1 will be described below. The image on the CRT 11 is projected onto the SLM 20 by the writing lens 12 and written. On the other hand, the read light Li emitted from the light source 41 is condensed by the condenser lens 42 and radiated to the PBS 35, and the linearly polarized read light Li ′ linearly polarized by the PBS 35 and reflected by the bonding surface 35c of the PBS 35 is transmitted to the SLM 20. Irradiated. The operation principle of the SLM 20 is as follows. When there is no writing light, almost no AC electric field is applied to the liquid crystal layer 23 because the impedance of the photoconductive layer 21 is large. Even when the linearly polarized light readout Li ′ is incident on the liquid crystal layer 23, the optical axis of the liquid crystal is substantially parallel to the traveling direction of the linearly polarized light readout light Li ′ because the liquid crystal layer 23 is a vertically aligned liquid crystal. Is reflected by the dielectric mirror 22 as it is and reciprocates through the liquid crystal layer 23, and the output light Lr from the SLM 20 is returned to the PBS 35 as linearly polarized light having the same polarization plane as the incident light Li '. On the other hand, when the writing light Lw is irradiated, the resistance of the photoconductive layer 23 is greatly reduced, and an electric field is applied to the liquid crystal layer 23. This electric field changes the orientation of molecules in the liquid crystal layer, and the incident light
The direction of travel of Li 'and the direction of the optical axis of the molecule are shifted from parallel. Therefore, a birefringence effect occurs, and the reflected light Lr is generally returned to the PBS 35 as elliptically polarized light. In a state where a predetermined electric field is applied and the orientation of the molecules is tilted by 45 degrees with respect to the polarized light, the liquid crystal layer 23 has the same effect as the quarter-wave plate, and when the light reciprocates through the liquid crystal layer 23. , This light is 1/2
The same effect as transmitting through the wave plate is produced. Therefore, the linearly polarized light readout light Li 'reciprocates through the liquid crystal layer 23, whereby its polarization direction is rotated by 90 degrees.
As linearly polarized light having a plane of polarization perpendicular to that of Li '
Returned to BS35. In the PBS 35, the reflected light Lr is linearly polarized, and only the component of the reflected light Lr having a plane of polarization parallel to the paper surface is selectively transmitted through the bonding surface 35c (the others are reflected), and the light Lr '
It becomes. That is, the linearly polarized reflected light Lr ′ having a plane of polarization perpendicular to the plane of polarization of the linearly polarized light readout light Li ′ is transmitted through the joint surface 35c and irradiated onto the projection lens 51. The linearly polarized reflected light Lr ′ reflects the writing light Lw, and the reproduced image is enlarged and projected on the photosensitive material 60 by the projection lens 51. In the above-described image projection apparatus 1, the embodiment in which both the condenser lens 42 and the projection lens 51 are formed integrally with the polarization beam splitter 35 has been described. However, as shown in FIG. Only the lens 42 is formed integrally with the surface of the polarization beam splitter 35 on which the readout light is incident, or only the projection lens 51 is integrated with the linearly polarized light reflected light emission surface of the polarization beam splitter 35 as shown in FIG. It can also take the form of forming it. In the above embodiment, the optical writing type S
Although the LM is used, the image projection apparatus of the present invention is not limited to this, and an electric writing type SLM may be used. The electric writing type SLM is obtained by replacing the optical sensor section of the above-mentioned optical writing type SLM with an electron beam scanning system or an integrated electronic circuit, and has a configuration in which image information is directly and electrically written to the SLM. Further, the condenser lens is used as the condenser lens for condensing the light in the reading light irradiation means in the above embodiment, but a Fresnel lens may be used instead of the condenser lens. Also, a configuration may be adopted in which a parabolic mirror is provided behind the light source without using a lens, and light emitted from the light source is efficiently incident on the PBS. In this embodiment, the SLM is formed using one surface of the PBS as a substrate. However, the SLM sandwiched between two glass substrates is fixedly adhered to one surface of the PBS so that the PBS and the SLM are combined. They may be integrated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of an image projection device of the present invention. FIG. 2 shows a polarizing beam splitter, a spatial light modulator, and a lens formed integrally in the image projection device of the present invention. FIG. 3 is a diagram showing an element in which a polarization beam splitter, a spatial light modulation element, and a readout light focusing lens are integrated. FIG. 4 is an illustration in which a polarization beam splitter, a spatial light modulation element, and a projection lens are integrated. FIG. 5 shows a basic configuration of an image projection device. FIG. 6 shows a basic configuration of a spatial light modulation device. [Description of References] 1 Image projection device 10 Image information writing means 11 CRT 12 Writing Lens 20 Spatial light modulator (SLM) 35 Polarizing beam splitter (PBS) 40 Readout light irradiation optical system 41 Light source 42 Condenser lens 50 Projection optical system 51 Projection lens 60 Photosensitive material (screen)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-8-82780 (JP, A) JP-A-8-62564 (JP, A) JP-A-4-125538 (JP, A) JP-A-4-125538 232904 (JP, A) JP-A-5-188325 (JP, A) JP-A-5-66368 (JP, A) JP-A-8-149493 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03B 21/00-21/30 G02F 1/13

Claims (1)

(57) [Claim 1] Image information is two-dimensionally written on a plane, and the polarization state of the reflected light of the readout light incident on the plane is spatially determined based on the image information. A spatial light modulation element that modulates the spatial light modulation element; an image information writing unit that writes the image information into the spatial light modulation element; a polarization beam splitter disposed to face the plane of the spatial light modulation element; A light source that emits read light, a condenser lens that collects the read light and makes it enter the polarization beam splitter, the read light is polarized by the polarization beam splitter, and the linearly polarized read light is the spatial light modulator. And the reflected light spatially modulated by the spatial light modulator is polarized by the polarization beam splitter, and then the linearly polarized light is read. An image projection apparatus comprising: a projection lens for enlarging and projecting linearly polarized reflected light having a polarization plane orthogonal to the light plane onto an external projection plane, wherein the plane of the spatial light modulator and the plane of the polarization beam splitter An opposing surface is integrally and closely fixed thereto, and the condensing lens and / or the projection lens allow the light transmitted through the lens of the polarizing beam splitter to enter or emit the light, respectively. An image projection device, which is formed integrally on a surface.