Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1999-05-12
2001-09-11
Lester, Evelyn A (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S224200, C355S067000
Reexamination Certificate
active
06288830
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical image forming method and device for forming a light image on an object, and more particularly to an optical image forming method and device for forming a light image on an object which moves in one direction relative to reflected light irradiated thereto from a spatial light modulator including a plurality of mirrors each capable of independently controlling the inclination of its reflecting surface, as well as to a printer, an image forming apparatus such as a copying machine, and an aligner for lithography, all of which may utilize the device.
2. Description of the Related Art
Conventionally, a device named a digital micromirror device (hereinafter referred to as the “DMD”) is known as a spatial light modulator of the type mentioned above. Specifically, the DMD has a multiplicity of micromirrors, referred to as micromirrors, each rotatable about a fixed axis, formed on a semiconductor substrate of Si or the like. The DMD is irradiated with light from a light source which is deflected by each of the micromirrors, the rotation of which is controlled by an electrostatic action or the like. Each of the micromirrors is selectively rotated to change the inclination of its reflecting surface to selectively irradiate an object with reflected light from each of the micromirrors to form a light image on the object.
Originally, the DMD has been proposed for applications in a display such as a digital large screen projector or the like. Recently, however, applications proposed for the DMD have been increasingly directed to an optical writing system for writing a laser beam onto a photosensitive material in an image forming apparatus such as an electrophotographic printer, as described in, for example, Laid-open Japanese Patent Applications Nos. 8-318641, 7-232458 and 9-300701. Particularly, the Application No. 8-318641 describes a method of forming all pixels in the axial direction of a photosensitive material using a DMD having a small number of mirrors and a reduced device length in the axial direction (longitudinal direction). Specifically, the DMD is composed of a plurality of mirror columns arranged in a direction in which the surface of a photosensitive material, as an object, is moved, wherein each of the mirror columns includes a plurality of mirrors arranged in an axial direction, orthogonal to the surface moving direction, and effective reflecting surfaces of mirrors in each mirror column are shifted in the axial direction, so that one line portion of a light image on a photosensitive material is formed using the plurality of mirror columns of the DMD.
In the method disclosed in the above-mentioned Laid-open Japanese Patent Application No. 8-318641, the object is irradiated only with a portion of reflected light from each mirror in order to prevent reflected light images of the respective mirrors from overlapping with each other in the direction orthogonal to the direction of the relative movement of the object, so that the irradiating light having only a reduced intensity reaches each of pixels on the object (photosensitive material). This also leads to a requirement for a technique of irradiating respective pixels with reflected light from the mirrors a plurality of times.
On the other hand, while the pixel density tends to be higher in the field of modern image forming apparatus or the like, the present inventors have found that the pixel density can be significantly improved in the formation of a light image on an object such as a photosensitive material even without the need for increasing the number of mirrors in the direction orthogonal to the direction of the relative movement of the object in a spatial light modulator such as the above-mentioned DMD.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made in view of the problems mentioned above, and its object is to provide an optical image forming method and device which are capable of forming a light image in a high pixel density and of enhancing the intensity of light irradiated to each pixel by effectively utilizing reflected light from respective mirrors of a spatial light modulator. Another object of the present invention is to provide an image forming apparatus and an aligner for lithography using the device.
To achieve the above objects, in a first aspect, the present invention provides an optical image forming method for forming a light image on an object which includes the steps of irradiating light from a light source to a spatial light modulator including a plurality of mirrors, wherein each of the mirrors is capable of independently controlling the inclination of a reflecting surface thereof, irradiating reflected light from the spatial light modulator to an object which moves in one direction relative to the reflected light, arranging the respective mirrors of the spatial light modulator to reflect light therefrom such that reflected light images from the mirrors of the spatial light modulator are aligned on the object in a direction orthogonal to the direction of the relatively movement with a pitch smaller than the pitch p of the mirrors, and converging reflected light from the respective mirrors of the spatial light modulator onto the object.
In this optical image forming method, reflected light images from the mirrors of the spatial light modulator are aligned on the object in the direction orthogonal to the direction of the relative movement with a pitch smaller than the pitch p of the mirrors, and reflected light from each of the mirrors of the spatial light modulator is converged onto the object, thereby forming a light image at a high pixel density on the object. Here, the reflected light from the respective mirrors of the spatial light modulator is converged onto the object to effectively utilize the reflected light from the respective mirrors, thereby enhancing the intensity of irradiated light in respective pixels.
In a second aspect, the present invention provides an optical image forming device for forming a light image on an object, which includes a light source, a spatial light modulator including a plurality of mirrors, each of which is capable of independently controlling the inclination of a reflecting surface thereof for reflecting light from the light source, wherein reflected light from the spatial light modulator is irradiated to an object which moves in one direction relative to the reflected light, a controller which controls the inclination of the reflecting surface of each of the mirrors such that reflected light images from the respective mirrors of the spatial light modulator are aligned on the object in a direction orthogonal to the direction of the relative movement with a pitch smaller than the pitch p of the mirrors, and a plurality of lenses each for converging reflected light from a corresponding mirror of the spatial light modulator onto the object.
In the optical image forming device, the respective mirrors are arranged at predetermined positions, and the controller controls the inclination of the reflecting surface of each of the mirrors such that reflected light images from the respective mirrors of the spatial light modulator are aligned on the object in a direction orthogonal to the direction of the relative movement with a pitch smaller than the pitch p of the mirrors. Then, the reflected light from the respective mirrors is converged onto the object by the plurality of lenses to form a light image at a high pixel density on the object. In this event, the reflected light from the respective mirrors is converged by the lenses to effectively utilize the reflected light from the respective mirrors, thereby enhancing the intensity of irradiated light in respective pixels.
The reflected light from the respective mirrors may be converged on the object in such a degree to prevent overlapping, or may be converged to permit slight overlapping.
The spatial light modulator may include n mirror rows arranged in the direction of the relative movement, wh
Lester Evelyn A
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh Microelectronics Company, Ltd.
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