1. Field of the Invention
This invention relates to an image exposure, and more particularly to an image exposure system and an image exposure method which pass light modulated by a spatial light modulator element through an imaging optical system to form an image of light on a photosensitive material and expose the photosensitive material.
2. Description of the Related Art
Conventionally, there has been known an image exposure system in which light modulated by a spatial light modulator element is passed through an imaging optical system to form an image of light on a photosensitive material to expose the photosensitive material to the image of light. The image exposure system of this kind basically comprises a spatial light modulator element comprising a number of two-dimensionally arranged pixel portions each modulating according to a control signal light projected thereon, a light source which projects light onto the spatial light modulator element and an imaging optical system which forms on a photosensitive material an image of light modulated by the spatial light modulator element. An example of such a basic arrangement of the image exposure system of this kind is disclosed in “Shortening of Development and Application of Mass Production by Maskless Exposure” (“Electronics Mounting Technology” Technology Investigation Co. Ltd. by Akihito Ishikawa vol. 18, No. 6, 2002, pp. 74–79) or in our Japanese Patent Application No. 2002-149886.
In the image exposure systems of this kind, LCDs (liquid crystal display) or DMDs (a distal micro mirror device) are suitably employed as the spatial light modulator element. “DMD” is a mirror device comprising a number of micro mirrors each of which changes the angle of its reflecting surface according to the control signal and which are two-dimensionally arranged on a semiconductor substrate such as silicon.
In such image exposure systems, there often follows a demand for enlargement of the image projected onto the photosensitive material. In this case, an enlarging imaging optical system is employed as the imaging optical system. However, when the light modulated by the spatial light modulator element is simply passed through the enlarging imaging optical system, the light bundles from the spatial light modulator element are enlarged and the pixel size in the projected image is increased, whereby the sharpness of the image deteriorates.
In order to overcome this problem, it is conceivable to dispose a first imaging optical system on the optical path of light modulated by the spatial light modulator element and to dispose a micro lens array on the imaging plane of the first imaging optical system so that each of the micro lenses of the micro lens array corresponds to each of the pixel portions of the spatial light modulator element as disclosed in the above identified Japanese patent application. In the image exposure system disclosed in the Japanese patent application, a second imaging optical system is disposed on the optical path of light passing through the micro lens array to form an image by the modulated light on the photosensitive material or a screen, and the image is enlarged by the first and second imaging optical systems. With this arrangement, though the size of the image projected onto the photosensitive material or the screen is enlarged, light from each of the pixel portions of the spatial light modulator element is converged by the micro lens of the micro lens array. Accordingly, the pixel size (spot size) in the projected image is kept small and the sharpness of the image can be held high.
Japanese Unexamined Patent Publication No. 2001-305663 discloses an example of the image exposure system in which a DMD is employed as the spatial light modulator element and a combination of the DMD and a micro lens array is employed. However, in the conventional image exposure system which employs a combination of the spatial light modulator element and the micro lens array, there has been a problem that the shape of the light beam collected by each of the micro lenses of the micro lens array is distorted in the light collecting position. This problem is more serious when the DMD is employed as the spatial light modulator element.