| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of recording a hard-to-forge pattern unique to a printer on a recording medium. SOLUTION: The image forming apparatus comprises an unique pattern exposure device 60 for exposing a unique interference pattern on a photosensitive drum wherein the unique pattern exposure device 60 comprises a laser light source 62 consisting of a surface emission laser, a parallel plate 64 constituting an etalon, and a projection lens 66. Laser light emitted from the laser light source 62 impinges on the parallel plate 64 and repeats multiplex reflection. It is split into laser lights having different optical path lengths which exit to the projection lens 66 side and passes through the projection lens 66 before being converged onto the photosensitive drum 16 and forming an interference fringe pattern. Since the parameters, i.e. the thickness d of the parallel plate 64, the refractive index n, the focal length f of the projection lens 66, the wavelengthλof laser light, and the like, are seldom combined to have totally identical values because of variation in production, an interference fringe pattern unique to the apparatus is generated. COPYRIGHT: (C)2005,JPO&NCIPI
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