Fingerprint sensing device and method

[0002] This application is a continuation-in-part application for a prior filed and currently pending U.S. patent application, Ser. No. 09/339,464 filed on Jun. 23, 1999.

[0003] This invention is in the field of three dimensional object sensing apparatuses and methods and more particularly in the field of apparatuses and methods for sensing fingerprints.

[0004] Fingerprint sensing devices typically consist of a glass plate or prism upon which the finger of the subject is pressed, an illuminating light source which directs the light through the prism to the contact zone between the finger and the glass plate or prism, an image producing lens and an image capturing device such as a charge couple device (CCD). Most of these known devices function on the basic principle that if the angle of incidence of the illuminating light with the contact zone between the finger of the subject and the glass plate or prism, is adjusted to within a certain range which is dependent on the frequency of the light used, the illuminating light will be internally reflected from the contact zone at fingerprint valley points where there is no contact between the finger and the glass surface, and will not be internally reflected from the ridge points where the finger contacts the glass surface. The reflected light is focused into an image by an image producing lens and the image is transformed into an electrical signal by a CCD or other sensing device.

[0005] These known devices have inherent problems and limitations relating to the accuracy of the valley and ridge information defining the subject fingerprint. Known methods require the use of an image producing lens and require an optical sensor such as a CCD to receive the image and convert it to an electrical signal. Improvements are needed in the means and method of illuminating the contact zone between the finger and glass surface, the physical geometry of the sensing unit and the means and method of receiving and digitizing the fingerprint information.

[0006] An object of the present invention is to provide a simpler, more accurate and more reliable method and apparatus for extracting and digitizing a fingerprint for imaging and identification purposes. It is a further object of the present invention to provide a method and apparatus for utilizing a surface-emitting laser as the source of illuminating radiation. It is a further object of the present invention to provide a method and apparatus for utilizing a Liquid Crystal Display (LCD) for emitting point source radiation as the source of illuminating radiation. It is a further object of the present invention to provide a fingerprint sensing device that is durable, inexpensive and simpler to manufacture and maintain. It is a further objective of the present invention to provide an apparatus and method for the direct digitization of a fingerprint without the use of an image producing lens and optical image sensor.

[0007] Preferred embodiments of the apparatus of the present invention comprises a prism, a pixilated source of radiation, and a photoelectric sensor. For certain preferred embodiments, the prism is wedge-shaped, but it can be of any shape that provides for differentiation between fingerprint ridges and valleys. The finger of the subject is pressed to the prism top surface. For preferred embodiments, either a radiation source and a LCD or a surface-emitting laser having a network of laser vertical surface cavities, lines the prism bottom surface and the photoelectric sensor lines the prism end surface.

[0008] For embodiments using the surface emitting laser, the vertical surface cavities of the surface emitting laser are arranged in a grid network with the spacing between the cavities being selected to provide for the desired accuracy of the fingerprint extraction and digitization. Each of the surface cavities emits a laser sub-beam into the prism bottom surface when activated and each of these sub-beams is orthogonal to the top surface of the surface emitting laser and the prism bottom surface. The wedge angle between the prism top surface and the prism bottom surface determines the angle of incidence for each of the laser sub-beams. The angle of incidence of the sub-beams is selected so that the points where the fingerprint ridges of the subject contact the prism top surface will not internally reflect the laser radiation, and the points corresponding to the fingerprint valleys of the subject where the finger of the subject does not contact the prism top surface will reflect the laser radiation.

[0009] Each of the laser sub-beams illuminates a unique point on the prism top surface. Similarly, except for those points in the contact zone where the fingerprint ridges of the subject contact the prism top surface, each laser sub-beam is reflected to a unique point on the photoelectric sensor. The number of pixels and thus the accuracy of the resolution of the fingerprint extraction, is determined by the density of the surface cavities of the surface-emitting laser.

[0010] The sub-beams may be emitted sequentially in a burst and therefore sensed sequentially by a single-receptor photoelectric sensor. The photoelectric sensor may have a filter or may be tuned to detect only the frequency of radiation emitted by the laser so as to prevent interference from radiation from other sources. Alternatively, filters or shields may be installed on all exposed exterior surfaces of the prism to prevent admission of radiation to the prism from any source other than the surface emitting laser.

[0011] Each sub-beam received in its assigned time slot indicates a fingerprint valley at its corresponding point of illumination and each sub-beam not received in its assigned time slot indicates a fingerprint ridge at its corresponding point of illumination. Alternatively the photoelectric sensor may have a grid of receptors, each receptor sensing the reception of a sub-beam. The reception or non-reception of a sub-beam again indicates a fingerprint valley or ridge at the corresponding point of illumination. Either version provides for a very accurate digitization of the fingerprint, which can then be used for imaging or identification purposes. This provides for the direct digitization of the subject fingerprint without the need for an image producing lens or an optical image sensing device.

[0012] For either of the foregoing embodiments, the fingerprint apparatus of the present invention may be connected to an external computer to process the data, or may be equipped with its own computer circuit, particularly for remote applications.

[0013] For embodiments utilizing a radiation source and a LCD, the present invention functions in a manner very similar to that described above for the embodiments utilizing a surface emitting laser. Each pixel of the LCD is activated in a desired sequence thereby transmitting the light into the bottom surface of the prism and illuminating a corresponding point on the top contact surface of the prism. However, unlike the embodiments utilizing the surface emitting laser, the illuminating radiation is not confined to the corresponding point of illumination. Accordingly, the photoelectric sensor will receive reflected radiation for each pixel. If the pixel corresponds to a fingerprint ridge point, the amount of illuminating radiation reflected to the photoelectric cell will be measurably less than that reflected if the pixel corresponds to a fingerprint valley point. The difference can be increased by incorporating a minute lens at each pixel point, which lenses are affixed to the LCD or the prism or are interposed between the LCD and the prism as a lens wafer. These lenses can also be incorporated as an integral part of the prism. These lenses provide for the focusing of the radiation transmitted through each pixel of the LCD on the corresponding point of illumination on the top contact surface of the prism. For these embodiments, the non-reflection of the illuminating radiation will be near total from fingerprint ridge points and the reflection of the illuminating radiation will be near total for the fingerprint valley points. This enhances differentiation between ridge points and valley points.

[0014] For embodiments utilizing either a surface emitting laser or a radiation source and a LCD, an additional lens or lens arrangement, a sensor lens, may be included between the prism and the photoelectric sensor, to provide for focusing the reflected radiation for sensing. This allows the use of a smaller photoelectric sensor or a smaller grid of receptors for the photoelectric sensor. The sensor lens may be affixed to or incorporated into the prism end surface, or may be interposed between the prism and the photoelectric sensor.

[0015] The following drawings illustrate preferred embodiments of the apparatus of the present invention.

[0016] FIG. 1 is a side perspective view of a preferred embodiment of the apparatus of the present invention utilizing a surface emitting laser.

[0017] FIG. 2 is a side view of a preferred embodiment of the apparatus of the present invention utilizing a surface emitting laser.

[0018] FIG. 3 is a side perspective view of a preferred embodiment of the apparatus of the present invention utilizing a radiation source and a LCD.

[0019] Embodiments of the present invention utilize one of several pixilated means for internally illuminating points of illumination on a contact surface of a prism. Referring first to FIG. 1, a preferred embodiment of the apparatus of the present invention which comprises a wedge-shaped prism 1, a surface-emitting laser 2, a sensor lens 26, and a photoelectric sensor 3, is illustrated therein. Referring also to FIG. 2, a finger 4 of the subject is pressed to the prism top surface 5, the contact surface, contacting the prism top surface in a contact zone 18. The surface-emitting laser, having a network of laser vertical surface cavities 6, is affixed to the prism bottom surface 7 and the photoelectric sensor is affixed to the prism end surface 8. The vertical surface cavities of the surface emitting laser are arranged in a grid network 9 with the spacing 10 between the cavities being selected to provide for the desired accuracy of the fingerprint extraction and digitization. Each of the surface cavities emits a laser sub-beam 11 into the prism bottom surface when activated and each of these sub-beams is orthogonal to the top surface 12 of the surface emitting laser and the prism bottom surface. The wedge angle 13 between the prism top surface and the prism bottom surface determines the angle of incidence 14 for each of the laser sub-beams. The angle of incidence of the sub-beams is selected so that the points where the fingerprint ridges 15 of the subject contact the prism top surface will not internally reflect the laser radiation, and the points corresponding to the fingerprint valleys 16 of the subject where the finger of the subject does not contact the prism top surface will reflect the laser radiation.

[0020] While certain preferred embodiments utilize a wedge shaped prism as illustrated in FIGS. 1 and 2, other embodiments may utilize prisms with a different shape or may utilize any medium which allows for the internal reflection of illuminating radiation at an angle which will provide for differentiation of the fingerprint ridges and valleys.

[0021] Each of the laser sub-beams illuminates a unique illumination point 17 on the prism top surface. Similarly, except for those points in the contact zone 18 where the fingerprint ridges of the subject contact the prism top surface, each laser sub-beam is reflected to a unique sensing point 19 on the photoelectric sensor. The number of pixels and thus the accuracy of the resolution of the fingerprint extraction, is determined by the density of the surface cavities of the surface-emitting laser. The sensor lens 26 focuses the sub-beams on the photoelectric sensor. The sensor lens may be affixed to or incorporated in the prism end surface or may be interposed between the prism and the photoelectric sensor.

[0022] The sub-beams may be emitted sequentially in a burst and therefore sensed sequentially by a single-receptor photoelectric sensor. The photoelectric sensor may have a filter 20 or may be tuned to detect only the frequency of radiation emitted by the laser so as to prevent interference from radiation from other sources. Alternatively, filters or shields may be installed on all exposed exterior surfaces of the prism to prevent admission of radiation to the prism from any source other than the surface emitting laser. Each sub-beam received in its assigned time slot indicates a fingerprint valley at its corresponding point of illumination and each sub-beam not received in its assigned time slot indicates a fingerprint ridge at its corresponding point of illumination.

[0023] Alternatively the photoelectric sensor may have a grid of receptors or sensors, each receptor or sensor sensing the reception of a unique sub-beam. For these embodiments, the sub-beams can be emitted simultaneously. The reception or non-reception of a sub-beam again indicates a fingerprint valley or ridge at the corresponding point of illumination. The sensor lens will reduce the size of the photoelectric sensor or the size of the grid of receptors needed for the photoelectric sensor.

[0024] The photoelectric sensor generates electric signals based upon the sub-beams received. Either of the preferred embodiments of the apparatus of the present invention described above provides for a very accurate digitization of the fingerprint, which can then be used for imaging or identification purposes. Each of these embodiments provides for the direct digitization of the subject fingerprint without the need for an image producing lens or an optical image sensing device.

[0025] Referring now to FIG. 3, a preferred embodiment utilizing a radiation source 21 and a pixilated LCD 22 is illustrated. This embodiment functions in a manner very similar to that described above for the embodiments utilizing a surface emitting laser. Each pixel of the LCD is activated in a desired sequence thereby transmitting the illuminating radiation into the bottom surface of the prism and illuminating a corresponding point on the top contact surface of the prism. However, unlike the embodiments utilizing the surface emitting laser, the LCD sub-beam 25 illuminating radiation may not be confined to the corresponding discrete point of illumination. Accordingly, the photoelectric sensor will receive reflected radiation for each LCD pixel 24. If the pixel corresponds to a fingerprint ridge point, the amount of illuminating radiation reflected to the photoelectric cell will be measurably less than that reflected if the pixel corresponds to a fingerprint valley point. The difference can be increased by incorporating a minute lens at each pixel point. These lenses can be affixed to the LCD or the prism or can be interposed between the LCD and the prism as a lens wafer 23 as shown in FIG. 3. These lenses provide for the focusing of the radiation transmitted through each pixel of the LCD on the corresponding point of illumination on the top contact surface of the prism. The focal length of the lenses varies based upon the pixel location, to provide for focusing on the point of illumination. For these embodiments, the percentage of non-reflection of the illuminating radiation will be high from fingerprint ridge points and the percentage of reflection of the illuminating radiation will be high for the fingerprint valley points. This enhances differentiation between ridge points and valley points. The sensor lens 26 focuses the reflected radiation as desired for the photoelectric sensor.

[0026] Any of the preferred embodiments of the fingerprint sensing apparatus of the present invention may be connected to an external computer to control the emission of the laser sub-beams and to process the electric signals generated by the photoelectric sensor or sensors, or may be equipped with its own computer circuit, particularly for remote applications where a support computer with required software is not available.

[0027] Other embodiments of the invention and other variations and modifications of the embodiments described above will be obvious to a person skilled in the art. Therefore, the foregoing is intended to be merely illustrative of the invention and the invention is limited only by the following claims.