Patent ID: 7626687
Filing Date: 2009-12-01
Classification: G06K

Abstract:
1. A compact optical imaging device suitable for forming optical images of fingerprints, the device comprising: an optical plate having first and second opposite main faces, and first and second side faces respectively at opposite first and second ends of said plate, a finger-press surface is defined in at least a portion of said first main face in the vicinity of said first end of the plate; at least one light source facing a face of said plate at said first end thereof, and having an illumination direction directed to said finger-press surface through the plate; and imaging means including a focusing lens that has an inlet surface and an outlet surface determining a magnification factor, and that is situated downstream from the optical plate; wherein said first and second main faces, said face in front of which the light source is situated, and the illumination direction of said light source are arranged mutually in such a manner that a light beam, reflected by a finger pressed against said finger-press surface illuminated by said light source, propagates thereafter inside the plate with multiple reflections alternately on the first and on the second main faces thereof toward said second side face; wherein said second end face of said plate is inclined, at least in part, so that the light beam leaves the plate via said inclined end face without being subjected to significant refraction or reflection; the focusing lens is disposed facing said inclined face of the second end of the plate, said focusing lens having an optical axis which extends substantially in a midplane of the plate between said main faces and which extends substantially parallel to said inclined face; and a first mirror is placed facing an inlet surface of said focusing lens and is oriented so as to receive a portion of the light beam from said second end face of the plate and reflect said portion of the light beam along the optical axis of said focusing lens.