Importance

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Abstract

A tapered FOB (20) obtained by forming optical absorbers on the outer surfaces of fibers and bundling these fibers is joined to a slant FOB (10) obtained by bundling fibers, and a CCD (60) is arranged at the output end face of the tapered FOB (20). The slant angle (.beta..sub.0) of a detection surface (11) of the slant FOB (10) on which a fingertip is to be placed is set to an angle at which background light incident from air on the slant FOB (10) is not reflected as total internal reflection at the interface between the core and cladding of the slant FOB (10). The slant angle (.beta..sub.1) of the tapered FOB (20) is set such that background light reaching the tapered FOB (20) becomes incident at the interface between the core and the cladding at an angle smaller than the critical angle at which total internal reflection occurs. Unwanted background light and illumination light are eliminated, and the S/N ratio of a fingerprint image to be detected can be increased.

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First Claim