Title of Invention	AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS
Abstract	The invention relates to an optical imaging device (1) for forming an optical image of fingerprints of a finger, comprising: an optical plate (2) with a part (5) at one end (A) of a main face (3) provided for placing the finger upon; a light source (S) for illuminating the finger through the plate (2), the reflected light beam propagating with multiple reflections in the plate up to the other end (B) thereof having an inclined end face (8); a focalization lens (9) oriented toward the end face with its axis situated in the median plane of the plate, and; a mirror (10) for directing the light beam exiting the end face (8) in the axis of the lens (9).

Title of Invention

AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS

Abstract

The invention relates to an optical imaging device (1) for forming an optical image of fingerprints of a finger, comprising: an optical plate (2) with a part (5) at one end (A) of a main face (3) provided for placing the finger upon; a light source (S) for illuminating the finger through the plate (2), the reflected light beam propagating with multiple reflections in the plate up to the other end (B) thereof having an inclined end face (8); a focalization lens (9) oriented toward the end face with its axis situated in the median plane of the plate, and; a mirror (10) for directing the light beam exiting the end face (8) in the axis of the lens (9).

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) 'AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS' SAGEM DEFENSE SECURITE, Le Ponant de Paris 27, rue Leblanc 75015 Paris, FRANCE The following specification particularly describes the invention and the manner in which it is to be performed. X AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS. The present invention generally relates to the field 5 of taking fingerprints, and the invention relates more particularly to improvements provided to optical imaging devices suitable for forming optical images of fingerprints of a finger, such a device comprising: • an optical plate having first and second opposite 10 main faces, at least a portion of said first main face situated in the vicinity of a first end of the plate constituting a finger-press surface for a finger; • at least one light source situated facing a face of said plate at said first end thereof, in order to 15 illuminate said finger through the plate; and • imaging means including a focusing lens that has an inlet surface and a outlet surface determining a magnification factor, and that is situated downstream from the optical plate. 20 It is explicitly emphasized herein that the invention relates exclusively to an optical device suitable for forming optical images of fingerprints, and that it does not relate to equipment situated downstream from said device for the purposes of scanning/recording 25 the resulting image, detecting characteristic points of fingerprints, and providing information about the person concerned. In particular, devices for detecting fingerprints can be used to authenticate a person so as to authorize 30 that person to perform some determined operation: under such circumstances, the device for detecting fingerprints is often accompanied by some other apparatus that the authenticated person is to be authorized to use (a computer, an automated teller machine (ATM), . . . ) . The 35 space available for receiving the fingerprint detector device is then small, and in particular the optical imaging device incorporated in the fingerprint detection -2- X device must be made to be as compact as possible, and in particular with thickness (or height) that is as small as possible. By way of concrete example, at least certain specifications require the optical imaging device to 5 present a thickness (or height) that does not exceed about 5 millimeters (mm). Various embodiments of optical imaging devices for forming optical images of fingerprints are already known, including for example the device disclosed in 10 document EP 0 308 162 which presents the dispositions set out in the introduction. Nevertheless, those known devices do not enable practical requirements to be satisfied completely. An object of the invention is to provide an optical 15 imaging device for optically sensing fingerprints that can be made in a form that is as compact as possible, and in particular with small thickness not exceeding about 5 mm, and that is structurally as simple as possible with a minimum number of components so that it is caused to be 20 as simple, as fast, and as inexpensive as possible to fabricate and assemble. For these purposes, the invention provides an optical imaging device suitable for forming optical images of fingerprints of a finger, the device, when 25 arranged in accordance with the invention, being characterized in that: 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 30 mutually in such a manner that the light beam emitted by the source and then reaching the finger pressed against said portion of the first main face in order to illuminate said finger, propagates thereafter inside the plate with multiple reflections alternately on the first 35 and on the second main faces thereof in order to reach the second end of the plate opposite from said first end; -3- sf said plate possesses an end face at its second end that 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; 5 the focusing lens is disposed facing said inclined face of the second end of the plate with its optical axis extending substantially in the midplane of the plate between said main faces and extending substantially parallel to said inclined face; and 10 a first mirror is placed facing the inlet surface of said focusing lens and is oriented in such a manner as to receive a portion of the light beam coming from said end face of the second end of the plate and reflect it towards said inlet surface of the focusing lens along the 15 axis thereof. By means of the above dispositions, a device can be constituted in which the bulkiest element is constituted by the optical plate and in which all of the other component elements that are functionally associated with 20 the plate can be shaped and dimensioned in such a manner as to be disposed in line with the plate and remain dimensionally within the limits set by the thickness of the plate. In particular, this arrangement, and in particular the transmission of the light beam from one 25 end of the plate to the other, can remain compatible with the plate having a thickness that does not exceed about 5 mm, in compliance with practical requirements. To make the apparatus for sensing and analyzing fingerprints as compact as possible, it is desirable in 30 particular for the imaging device not to be excessive in extent, and for this purpose, provision can be made for the image focal point of the focusing lens not to be situated in line with the optical plate: for this purpose, the optical imaging device further includes a 35 second mirror disposed facing the outlet surface of said focusing lens and oriented in such a manner that the light beam coming from the focusing lens is reflected -it- A' transversely (typically perpendicularly) relative to the plate. Advantageously, said second mirror is then oriented in such a manner that the light beam is reflected in a direction going away from the finger-press 5 surface. In the context of an arrangement of the device that is as simple as possible, the first and second main faces of the plate are mutually parallel. In order to constitute a device including a minimum 10 number of component parts, and thus being inexpensive to fabricate and install, it is possible to provide for the first mirror to belong to a first projecting part fitted on the end face of the second end of the plate, in such a manner as to extend in line with said plate. In the same 15 manner and for the same reasons, it is also possible to provide for the second mirror to belong to a second projecting part fitted on the end face of the second end of the plate in such a manner as to extend in line with said plate. 20 In a preferred embodiment, in order to obtain a well-contrasted high-quality image, the optical imaging device includes a diaphragm situated upstream from and close to the focusing lens. Advantageously, the focusing lens is secured to the 25 end face of said second end of the plate via support means, and in preferred manner, the support means of the focusing lens are arranged to allow the focusing lens to move along its optical axis. In which case, and advantageously, the support means of the lens are 30 constituted in one piece with said second projecting part incorporating the second mirror. The arrangement of the optical imaging device in accordance with the invention presents the advantage of leaving a choice between various possible solutions for 35 implanting one or more light sources. In a first possibility, at its first end the plate includes an end face that is inclined at an acute angle -5- jr relative to said first main face, and the light source is situated facing said inclined end face: the light source then remains within the dimensional limits of the thickness of the plate, such that the device overall is 5 small in thickness. In a second possibility, at said finger-press portion of the first main face of the plate, at least one side face of the plate is inclined at an angle that is acute relative to said first main face, and the light 10 source is situated facing said inclined side face. Under such circumstances, it is advantageous for both opposite side faces of the plate to be inclined, and for two light sources to be situated facing respective ones of said two inclined side faces, so that the finger is then 15 illuminated bilaterally, thus encouraging the formation of better quality images of fingerprints. Also in this solution, the light source(s) remain(s) within the dimensional limits set by the thickness of the optical plate. 20 Whichever solution is retained for implanting the light source(s), it is possible to obtain an illuminating light beam that diverges more and that is therefore better adapted to cover the finger by making provision for the inclined face(s) of the plate situated towards 25 the first end thereof to be curved in the thickness of the plate with their concave faces facing outwards. In a preferred variant embodiment, provision can be made for the light source not to be a point source, presenting a significant surface area and being placed 30 facing the bottom main face of the plate, substantially facing said finger-press portion provided on the top main face, and directed towards it, in which case, advantageously, the light source is a matrix of light-emitting diodes, with a ground surface interposed between 35 the light source and the bottom face of the plate. The invention will be better understood on reading the following detailed description of certain detailed -I- embodiments given purely by way of illustration. In the description, reference is made to the accompanying drawings, in which: • Figures 1 and 2 are respectively a plan view and a 5 side view of an optical imaging device arranged in accordance with the invention; • Figure 3 is a view from beneath of the device of Figures 1 and 2, with an end portion shown in section on line III-III of Figure 2; 10 • Figure 4 is an end view showing the left-hand end of the Figure 1 device; Figure 5 is a section view on line V-V of the Figure 1 device; • Figure 6 is an end view showing the right-hand end 15 of the Figure 1 device; • Figures 7 and 8 are side views analogous to the view of Figure 2, respectively showing two variant embodiments of the device in accordance with the invention; 20 • Figure 9 is an end view analogous to the view of Figure 6, showing a variant embodiment of the device in accordance with the invention; and • Figure 10 is a fragmentary side view analogous to that of Figure 2, showing a preferred variant embodiment 25 of the device in accordance with the invention. Reference is made initially to Figures 1 to 6 while describing a preferred embodiment of an optical imaging device suitable for forming optical images of fingerprints. 30 The optical imaging device in accordance with the invention, given overall reference 1, mainly comprises: • an optical plate 2 having a first main face 3 and a second main face 4 opposite the first main face, and in order to make the device simpler to design both 35 mechanically and optically, the two faces 3 and 4 are advantageously parallel to each other as shown in all of the figures; at least one portion 5 (shown shaded in -7- sf Figure 1 to distinguish it more clearly from the remainder of the plate) of said first main face 3, situated in the vicinity of a first end A (to the right in Figures 1 to 3) of the plate 2 constitutes a finger-5 press surface for a finger 6; overall, the plate 2 is generally in the form of a rectangular parallelepiped; • at least one light source - described in greater detail below - situated facing a face of the optical plate 2, at said first end A thereof, in order to 10 illuminate the finger through the plate 2; • the first and second main faces 3 and 4 of the plate 2, the face of the plate situated facing the light source, and the direction of illumination of said light source being arranged relative to one another in such a 15 manner that the light beam emitted by the source reaches (7X) the finger 6 pressed against said portion 5 of the first main face 3 so as to illuminate said finger 6, then propagates (72) inside the plate 2 with multiple reflections taking place alternatively on the first and 20 second main faces 3 and 4 thereof in order to reach the second end B of the plate 2 opposite from the end A; • at its second end B, the plate 2 having an end face 8 which is inclined so as to be struck substantially perpendicularly by the light beam 72 so that it leaves the 25 plate through said inclined face 8 without being subjected to any significant amount of refraction or reflection; and imaging means as described in greater detail below. 30 By channeling the light beam within the plate 2, using multiple reflections on its opposite main faces 3 and 4, and for a given length of light path, it is possible to bring the two ends of the light path closer together, and thus to provide a device that is shorter 35 and more compact. Since the two main faces 3 and 4 are mutually parallel, they provide reflections that are identical and symmetrical on the two faces, thereby -£- X simplifying the optical design and the manufacture of the plate; nevertheless, if the need were to be felt, the two faces 3 and 4 need not be parallel. The imaging means situated after the second end B 5 mainly comprise a focusing objective lens 9 (e.g. in the form of a thick converging lens) presenting an inlet surface 9X that collects the light beam that has passed through the inclined face 8 of the plate 2, and an outlet surface 92 through which the focused beam leaves; the 10 inlet and outlet surfaces 9X and 92 of the focusing lens 9 define a magnification factor between the finger and its image. In order to ensure that the device 1 is as thin as possible, it is advantageous, as can be seen more clearly 15 in Figures 3 and 5, for the focusing lens 9 to be placed in a prone position and thus to lie within the dimensional limits defined between the two main faces 3 and 4 of the plate 2. It is then appropriate for the beam that has passed through the inclined end face 8 of 20 the plate 2 to be reflected along the axis 11 of the focusing lens 9. For this purpose, a mirror 10 is provided that has two inclinations, both relative to the normal to the face 8 and relative to the axis 11 of the focusing lens 9, as can be seen more clearly in 25 Figures 3, 4, and 5. In the typical arrangement shown more specifically in Figures 1 to 6, the inclination of the mirror 10 is about 45° on both occasions. In Figure 3, the path of the beam within the plate 2 is referenced 72, and its path after being reflected on the 30 mirror and on going through the focusing lens 9 is referenced 73. The focused beam coming from the focusing lens 9 then needs to reach a sensor (not shown) suitable for detecting the image of a fingerprint, said sensor being 35 situated at the image focus of the focusing lens. To avoid the device 1 being excessively bulky, the sensor is not situated on the optical axis of the focusing lens 9, -9- y but rather under the device 1 (for example the sensor is integrated in a processor unit having the device 1 surmounted thereon). For this purpose, another mirror 11 is provided facing the outlet surface 92 of the focusing 5 lens 9 and is inclined (e.g. at about 45°) to reflect the beam 73 transversely to the plate 2 (and in particular substantially perpendicularly relative thereto). By means of these dispositions, an optical imaging device is constituted that can be made particularly 10 compact, with the focused beam directed away from the finger-press surface. In addition, it is possible to devise various arrangements leading to remarkable compactness. The first mirror 10 and/or the second mirror 11 may 15 be formed on respective parts 12 and 13 which are fitted to the inclined end face 8 of the plate 2 and from which they project in line with the plate. Advantageously, in order to limit the influence of parasitic light and in order to obtain an image of better 20 quality, a diaphragm is provided situated upstream from and close to the focusing lens. In practice, the front face 14a of the support means described below can act as a diaphragm. The focusing lens 9 is also secured to the end B of 25 the plate 2 by the support means 14. By way of example, these support means 14 may be in the form of a sleeve that is secured (in particular by adhesive) to the inclined end face 8 of the plate 2, said sleeve having the lens 9 inserted therein. The lens 9 can preferably 30 be moved axially inside the sleeve so as to make it possible to adjust the position of the image focal plane relative to the sensor. By way of example, provision can be made for the lens 9 to be secured to a plate 15 provided with a finger 16 that projects radially through 35 a lateral slot 17 in the sleeve, as can be seen more clearly in Figures 4 and 5. In this concrete embodiment, it should be observed that the support means "are made - /A - yf integrally with the projecting part 13 that incorporates the second mirror 11, said part 13 having a bore in which the above-mentioned sleeve is inserted. The sleeve can be locked in position, e.g. by using a radial lock screw 5 engaged through the part 13 in a position 13a. The arrangement of the optical imaging device in accordance with the invention provides the advantage of allowing various possible locations for the light source(s) as a function of available space. 10 In the preferred embodiment shown in Figures 1 to 6, the plate 2 includes at least one side face 18 towards its end A and approximately in register with the above-mentioned portion 5 of the first main face 3 forming a finger-press surface, which side face 18 is inclined at 15 an acute angle relative to the first main face 3 of the plate 2. Preferably, the two opposite side faces 18 are inclined so as to ensure that the finger is illuminated symmetrically. In the example shown, which is best seen in Figure 6, the inclination of both side faces 18 is 20 about 45°. Two light sources S (e.g. in the form of light-emitting diodes) are disposed respectively facing the inclined faces 18 with their respective axes approximately perpendicular to the faces 18. In this example, the faces 8 are plane. The arrangement as 25 proposed in this way provides bilateral illumination of the finger placed on the portion 5, i.e. illumination that is more uniform and more effective. It is possible to obtain illumination cones that are wider open using the same light sources by making the 30 inclined faces in curved form with their concave faces facing outwards, as referenced at 19 in Figure 9. Another possible configuration, shown in Figure 7, consists in illuminating the finger through the end face 20 situated at the first end A of the plate 2. For this 35 purpose, said end face 20 is inclined at an acute angle relative to the first main face 3 of the plate 2, and the light source S is disposed facing the face 20, with its # axis approximately perpendicular thereto. In the example shown, the inclination of the face 20 is about 45°. A plurality of sources S may be disposed facing the face 20 across the width of the plate 2. 5 A wider illumination cone can be obtained, as shown in Figure 8, by providing an end face 21 that is inclined and curved with its concave side facing outwards. In a variant embodiment that is presently the preferred embodiment, the finger is illuminated, as shown 10 in Figure 10, by placing a non-point light source having a significant surface area in front of the bottom face 4 of the plate 2, facing said finger-press portion 5 and directed towards said portion. In practice, this light source may advantageously be a matrix 20 of light- 15 emitting diodes, with a ground or frosted surface interposed between the matrix and the bottom face 4 of the plate 2, or formed on said plate. From the above description, it can be understood that the projecting parts 12 and 13 respectively 20 incorporating the mirrors 10 and 11, and also the support means 14 for supporting the focusing lens 9 can be made with dimensions that do not exceed the top and bottom limits defined by the main faces 3 and 4 respectively of the plate 2. This makes it possible to provide a device 25 that is more compact, and above all that presents small thickness, which may be no greater than 5 mm, thus satisfying practical requirements. The device has a very small number of component parts, thereby making it easy and inexpensive to produce. -12.- >^ 1. An optical imaging device (1) suitable for forming optical images of fingerprints of a finger (6), the 5 device comprising: an optical plate (2) having first and second opposite main faces (3, 4), at least a portion (5) of said first main face (3) situated in the vicinity of a first end (A) of the plate (2) constituting a finger- 10 press surface for a finger (6); • at least one light source (S) situated facing a face of said plate (2) at said first end (A) thereof, in order to illuminate said finger (6) through the plate (2); and 15 • imaging means including a focusing lens (9) that possesses an inlet surface (9X) and a outlet surface (92) determining a magnification factor, and that is situated downstream from the optical plate (2); characterized in that: 20 • said first and second main faces (3, 4), said face in front of which the light source (S) is situated, and the illumination direction of said light source (S) are arranged mutually in such a manner that the light beam emitted by the source and then reaching (7X) the finger 25 (6) pressed against said portion (5) of the first main face (3) in order to illuminate said finger, propagates (72) thereafter inside the plate (2) with multiple reflections alternately on the first and on the second main faces (3, 4) thereof in order to reach the second 30 end (B) of the plate (2) opposite from said first end (A); • said plate (2) has an end face (8) at its second end (B) that is inclined, at least in part, so that the light beam leaves the plate via said inclined end face 35 (8) without being subjected to significant refraction or reflection; -13- Jrt the focusing lens (9) is disposed facing said inclined face (8) of the second end (B) of the plate (2) with its optical axis extending substantially in the midplane of the plate between said main faces and 5 extending substantially parallel to said inclined face (8); and a first mirror (10) is placed facing the inlet surface (9X) of said focusing lens (9) and is oriented in such a manner as to receive a portion of the light beam 10 coming from said end face (8) of the second end (B) of the plate (2) and reflect it (73) towards said inlet surface (9X) of the focusing lens (9) along the axis thereof. 15 2. An optical imaging device according to claim 1, characterized in that it further includes a second mirror (11) disposed facing the outlet surface (92) of said focusing lens (9) and oriented in such a manner that the light beam coming from the focusing lens (9) is reflected 20 transversely relative to the plate (2). 3. An optical imaging device according to claim 2, characterized in that said second mirror (11) is oriented in such a manner that the light beam is reflected in a 25 direction going away from the finger-press surface (5). 4. An optical imaging device according to any one of claims 1 to 3, characterized in that the first and second main faces (3, 4) of the plate (2) are mutually parallel. 30 5. An optical imaging device according to any one of claims 1 to 4, characterized in that the first mirror (10) belongs to a first projecting part (12) fitted on the end face (8) of the second end (B) of the plate (2), 35 in such a manner as to extend in line with said plate. —i-- J^ 6. An optical imaging device according to any one of claims 2 to 5, characterized in that the second mirror (11) belongs to a second projecting part (13) fitted on the end face (8) of the second end (B) of the plate (2) 5 in such a manner as to extend in line with said plate. 7. An optical imaging device according to any one of claims 1 to 6, characterized in that it further includes a diaphragm situated upstream from and close to the 10 focusing lens. 8. An optical imaging device according to any one of claims 1 to 7, characterized in that the focusing lens (9) is secured to the end face (8) of said second end (B) 15 of the plate (2) via support means (14). 9. An optical imaging device according to claim 8, characterized in that the support means (14) of the focusing lens (9) are arranged to allow the focusing lens 20 (9) to move along its optical axis. 10. An optical imaging device according to claim 6 and claim 8 or claim 9, characterized in that the support means (14) of the lens (9) are constituted in one piece 25 with said second projecting part (13) incorporating the second mirror (11). 11. An optical imaging device according to any one of claims 1 to 10, characterized in that at its first end 30 (A) the plate (2) includes an end face (20) that is inclined at an acute angle relative to said first main face (B) , and in that the light source (S) is situated facing said inclined end face (20). 35 12. An optical imaging device according to any one of claims 1 to 10, characterized in that at said finger-press portion (5) of the first main face (3) of the plate -lfc_ ^ (2) , at least one side face (18) of the plate (2) is inclined at an angle that is acute relative to said first main face (3) , and in that the light source (S) is situated facing said inclined side face (18). 5 13. An optical imaging device according to claim 12, characterized in that both opposite side faces (18) of the plate (2) are inclined, and in that two light sources (S) are situated facing respective ones of said two 10 inclined side faces. 14. An optical imaging device according to any one of claims 11 to 13, characterized in that the at least one inclined side face (18) of the plate (2) situated towards 15 the first end (A) thereof is curved in the thickness of the plate (2), with its concave face facing outwards. 15. An optical imaging device according to any one of claims 1 to 10, characterized in that the light source 20 (S) is not a point source, presenting a significant surface area and being placed facing the bottom main face (4) of the plate (2), substantially facing said finger-press portion (5) provided on the top main face (3), and directed towards it. 25 16. An optical imaging device according to claim 15, characterized in that the light source (S) is a matrix (20) of light-emitting diodes, with a ground surface interposed between the light source and the bottom face 30 (4) of the plate (2). -IL~ 17. An optical imaging device (1) suitable for forming optical images of fingerprints of a finger (6) substantially as herein described with reference to and as illustrated in the accompanying drawings. Dated this 22nd day of May, 2006 (G. DEEPAK SRINIWAS) OF K & S PARTNERS AGENT FOR THE APPLICANTS -17- y ABSTRACT AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS 5 An optical imaging device (1) for forming optical images of fingerprints of a finger, the device comprising: an optical plate (2) having a portion (5) at one end (A) of a main face (3) that is provided for 10 illuminating the finger through the plate (2), the reflected light beam propagating with multiple reflections inside the plate to the other end (B) thereof, which end presents an inclined end face (A) ; a focusing lens (9) facing the end face with the lens 15 having its axis situated in the midplane of the plate; and a mirror (10) for directing the light beam leaving the end face (8) onto the axis of the lens (9). — Ifc-

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
'AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF
FINGERPRINTS'
SAGEM DEFENSE SECURITE, Le Ponant de Paris 27, rue Leblanc 75015 Paris, FRANCE
The following specification particularly describes the invention and the manner in which it is to be performed.

X
AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS.
The present invention generally relates to the field
5 of taking fingerprints, and the invention relates more
particularly to improvements provided to optical imaging
devices suitable for forming optical images of
fingerprints of a finger, such a device comprising:
• an optical plate having first and second opposite
10 main faces, at least a portion of said first main face
situated in the vicinity of a first end of the plate constituting a finger-press surface for a finger;
• at least one light source situated facing a face
of said plate at said first end thereof, in order to
15 illuminate said finger through the plate; and
• imaging means including a focusing lens that has
an inlet surface and a outlet surface determining a
magnification factor, and that is situated downstream
from the optical plate.
20 It is explicitly emphasized herein that the invention relates exclusively to an optical device suitable for forming optical images of fingerprints, and that it does not relate to equipment situated downstream from said device for the purposes of scanning/recording
25 the resulting image, detecting characteristic points of fingerprints, and providing information about the person concerned.
In particular, devices for detecting fingerprints can be used to authenticate a person so as to authorize
30 that person to perform some determined operation: under such circumstances, the device for detecting fingerprints is often accompanied by some other apparatus that the authenticated person is to be authorized to use (a computer, an automated teller machine (ATM), . . . ) . The
35 space available for receiving the fingerprint detector device is then small, and in particular the optical imaging device incorporated in the fingerprint detection
-2-

X
device must be made to be as compact as possible, and in particular with thickness (or height) that is as small as possible. By way of concrete example, at least certain specifications require the optical imaging device to 5 present a thickness (or height) that does not exceed about 5 millimeters (mm).
Various embodiments of optical imaging devices for forming optical images of fingerprints are already known, including for example the device disclosed in
10 document EP 0 308 162 which presents the dispositions set out in the introduction. Nevertheless, those known devices do not enable practical requirements to be satisfied completely.
An object of the invention is to provide an optical
15 imaging device for optically sensing fingerprints that can be made in a form that is as compact as possible, and in particular with small thickness not exceeding about 5 mm, and that is structurally as simple as possible with a minimum number of components so that it is caused to be
20 as simple, as fast, and as inexpensive as possible to fabricate and assemble.
For these purposes, the invention provides an optical imaging device suitable for forming optical images of fingerprints of a finger, the device, when
25 arranged in accordance with the invention, being characterized in that:
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
30 mutually in such a manner that the light beam emitted by the source and then reaching the finger pressed against said portion of the first main face in order to illuminate said finger, propagates thereafter inside the plate with multiple reflections alternately on the first
35 and on the second main faces thereof in order to reach the second end of the plate opposite from said first end;
-3-

sf
said plate possesses an end face at its second end
that 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;
5 the focusing lens is disposed facing said inclined
face of the second end of the plate with its optical axis extending substantially in the midplane of the plate between said main faces and extending substantially parallel to said inclined face; and
10 a first mirror is placed facing the inlet surface
of said focusing lens and is oriented in such a manner as to receive a portion of the light beam coming from said end face of the second end of the plate and reflect it towards said inlet surface of the focusing lens along the
15 axis thereof.
By means of the above dispositions, a device can be constituted in which the bulkiest element is constituted by the optical plate and in which all of the other component elements that are functionally associated with
20 the plate can be shaped and dimensioned in such a manner as to be disposed in line with the plate and remain dimensionally within the limits set by the thickness of the plate. In particular, this arrangement, and in particular the transmission of the light beam from one
25 end of the plate to the other, can remain compatible with the plate having a thickness that does not exceed about 5 mm, in compliance with practical requirements.
To make the apparatus for sensing and analyzing fingerprints as compact as possible, it is desirable in
30 particular for the imaging device not to be excessive in extent, and for this purpose, provision can be made for the image focal point of the focusing lens not to be situated in line with the optical plate: for this purpose, the optical imaging device further includes a
35 second mirror disposed facing the outlet surface of said focusing lens and oriented in such a manner that the light beam coming from the focusing lens is reflected
-it-

A'
transversely (typically perpendicularly) relative to the plate. Advantageously, said second mirror is then oriented in such a manner that the light beam is reflected in a direction going away from the finger-press 5 surface.
In the context of an arrangement of the device that is as simple as possible, the first and second main faces of the plate are mutually parallel.
In order to constitute a device including a minimum
10 number of component parts, and thus being inexpensive to fabricate and install, it is possible to provide for the first mirror to belong to a first projecting part fitted on the end face of the second end of the plate, in such a manner as to extend in line with said plate. In the same
15 manner and for the same reasons, it is also possible to provide for the second mirror to belong to a second projecting part fitted on the end face of the second end of the plate in such a manner as to extend in line with said plate.
20 In a preferred embodiment, in order to obtain a well-contrasted high-quality image, the optical imaging device includes a diaphragm situated upstream from and close to the focusing lens.
Advantageously, the focusing lens is secured to the
25 end face of said second end of the plate via support means, and in preferred manner, the support means of the focusing lens are arranged to allow the focusing lens to move along its optical axis. In which case, and advantageously, the support means of the lens are
30 constituted in one piece with said second projecting part incorporating the second mirror.
The arrangement of the optical imaging device in accordance with the invention presents the advantage of leaving a choice between various possible solutions for
35 implanting one or more light sources.
In a first possibility, at its first end the plate includes an end face that is inclined at an acute angle
-5-

jr
relative to said first main face, and the light source is situated facing said inclined end face: the light source then remains within the dimensional limits of the thickness of the plate, such that the device overall is 5 small in thickness.
In a second possibility, at said finger-press portion of the first main face of the plate, at least one side face of the plate is inclined at an angle that is acute relative to said first main face, and the light
10 source is situated facing said inclined side face. Under such circumstances, it is advantageous for both opposite side faces of the plate to be inclined, and for two light sources to be situated facing respective ones of said two inclined side faces, so that the finger is then
15 illuminated bilaterally, thus encouraging the formation of better quality images of fingerprints. Also in this solution, the light source(s) remain(s) within the dimensional limits set by the thickness of the optical plate.
20 Whichever solution is retained for implanting the light source(s), it is possible to obtain an illuminating light beam that diverges more and that is therefore better adapted to cover the finger by making provision for the inclined face(s) of the plate situated towards
25 the first end thereof to be curved in the thickness of the plate with their concave faces facing outwards.
In a preferred variant embodiment, provision can be made for the light source not to be a point source, presenting a significant surface area and being placed
30 facing the bottom main face of the plate, substantially facing said finger-press portion provided on the top main face, and directed towards it, in which case, advantageously, the light source is a matrix of light-emitting diodes, with a ground surface interposed between
35 the light source and the bottom face of the plate.
The invention will be better understood on reading the following detailed description of certain detailed
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embodiments given purely by way of illustration. In the description, reference is made to the accompanying drawings, in which:
• Figures 1 and 2 are respectively a plan view and a
5 side view of an optical imaging device arranged in
accordance with the invention;
• Figure 3 is a view from beneath of the device of
Figures 1 and 2, with an end portion shown in section on
line III-III of Figure 2;
10 • Figure 4 is an end view showing the left-hand end of the Figure 1 device;
Figure 5 is a section view on line V-V of the Figure 1 device;
• Figure 6 is an end view showing the right-hand end
15 of the Figure 1 device;
• Figures 7 and 8 are side views analogous to the
view of Figure 2, respectively showing two variant
embodiments of the device in accordance with the
invention;
20 • Figure 9 is an end view analogous to the view of Figure 6, showing a variant embodiment of the device in accordance with the invention; and
• Figure 10 is a fragmentary side view analogous to
that of Figure 2, showing a preferred variant embodiment
25 of the device in accordance with the invention.
Reference is made initially to Figures 1 to 6 while
describing a preferred embodiment of an optical imaging
device suitable for forming optical images of
fingerprints. 30 The optical imaging device in accordance with the
invention, given overall reference 1, mainly comprises:
• an optical plate 2 having a first main face 3 and
a second main face 4 opposite the first main face, and in
order to make the device simpler to design both
35 mechanically and optically, the two faces 3 and 4 are advantageously parallel to each other as shown in all of the figures; at least one portion 5 (shown shaded in
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Figure 1 to distinguish it more clearly from the remainder of the plate) of said first main face 3, situated in the vicinity of a first end A (to the right in Figures 1 to 3) of the plate 2 constitutes a finger-5 press surface for a finger 6; overall, the plate 2 is generally in the form of a rectangular parallelepiped;
• at least one light source - described in greater
detail below - situated facing a face of the optical
plate 2, at said first end A thereof, in order to
10 illuminate the finger through the plate 2;
• the first and second main faces 3 and 4 of the
plate 2, the face of the plate situated facing the light
source, and the direction of illumination of said light
source being arranged relative to one another in such a
15 manner that the light beam emitted by the source reaches
(7X) the finger 6 pressed against said portion 5 of the
first main face 3 so as to illuminate said finger 6, then
propagates (72) inside the plate 2 with multiple
reflections taking place alternatively on the first and
20 second main faces 3 and 4 thereof in order to reach the second end B of the plate 2 opposite from the end A;
• at its second end B, the plate 2 having an end
face 8 which is inclined so as to be struck substantially
perpendicularly by the light beam 72 so that it leaves the
25 plate through said inclined face 8 without being subjected to any significant amount of refraction or reflection; and
imaging means as described in greater detail below.
30 By channeling the light beam within the plate 2, using multiple reflections on its opposite main faces 3 and 4, and for a given length of light path, it is possible to bring the two ends of the light path closer together, and thus to provide a device that is shorter
35 and more compact. Since the two main faces 3 and 4 are mutually parallel, they provide reflections that are identical and symmetrical on the two faces, thereby
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simplifying the optical design and the manufacture of the plate; nevertheless, if the need were to be felt, the two faces 3 and 4 need not be parallel.
The imaging means situated after the second end B 5 mainly comprise a focusing objective lens 9 (e.g. in the form of a thick converging lens) presenting an inlet surface 9X that collects the light beam that has passed through the inclined face 8 of the plate 2, and an outlet surface 92 through which the focused beam leaves; the
10 inlet and outlet surfaces 9X and 92 of the focusing lens 9 define a magnification factor between the finger and its image.
In order to ensure that the device 1 is as thin as possible, it is advantageous, as can be seen more clearly
15 in Figures 3 and 5, for the focusing lens 9 to be placed in a prone position and thus to lie within the dimensional limits defined between the two main faces 3 and 4 of the plate 2. It is then appropriate for the beam that has passed through the inclined end face 8 of
20 the plate 2 to be reflected along the axis 11 of the focusing lens 9. For this purpose, a mirror 10 is provided that has two inclinations, both relative to the normal to the face 8 and relative to the axis 11 of the focusing lens 9, as can be seen more clearly in
25 Figures 3, 4, and 5. In the typical arrangement shown more specifically in Figures 1 to 6, the inclination of the mirror 10 is about 45° on both occasions. In Figure 3, the path of the beam within the plate 2 is referenced 72, and its path after being reflected on the
30 mirror and on going through the focusing lens 9 is referenced 73.
The focused beam coming from the focusing lens 9 then needs to reach a sensor (not shown) suitable for detecting the image of a fingerprint, said sensor being
35 situated at the image focus of the focusing lens. To avoid the device 1 being excessively bulky, the sensor is not situated on the optical axis of the focusing lens 9,
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but rather under the device 1 (for example the sensor is integrated in a processor unit having the device 1 surmounted thereon). For this purpose, another mirror 11 is provided facing the outlet surface 92 of the focusing 5 lens 9 and is inclined (e.g. at about 45°) to reflect the beam 73 transversely to the plate 2 (and in particular substantially perpendicularly relative thereto).
By means of these dispositions, an optical imaging device is constituted that can be made particularly
10 compact, with the focused beam directed away from the finger-press surface. In addition, it is possible to devise various arrangements leading to remarkable compactness.
The first mirror 10 and/or the second mirror 11 may
15 be formed on respective parts 12 and 13 which are fitted to the inclined end face 8 of the plate 2 and from which they project in line with the plate.
Advantageously, in order to limit the influence of parasitic light and in order to obtain an image of better
20 quality, a diaphragm is provided situated upstream from and close to the focusing lens. In practice, the front face 14a of the support means described below can act as a diaphragm.
The focusing lens 9 is also secured to the end B of
25 the plate 2 by the support means 14. By way of example, these support means 14 may be in the form of a sleeve that is secured (in particular by adhesive) to the inclined end face 8 of the plate 2, said sleeve having the lens 9 inserted therein. The lens 9 can preferably
30 be moved axially inside the sleeve so as to make it possible to adjust the position of the image focal plane relative to the sensor. By way of example, provision can be made for the lens 9 to be secured to a plate 15 provided with a finger 16 that projects radially through
35 a lateral slot 17 in the sleeve, as can be seen more clearly in Figures 4 and 5. In this concrete embodiment, it should be observed that the support means "are made
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integrally with the projecting part 13 that incorporates the second mirror 11, said part 13 having a bore in which the above-mentioned sleeve is inserted. The sleeve can be locked in position, e.g. by using a radial lock screw 5 engaged through the part 13 in a position 13a.
The arrangement of the optical imaging device in accordance with the invention provides the advantage of allowing various possible locations for the light source(s) as a function of available space.
10 In the preferred embodiment shown in Figures 1 to 6, the plate 2 includes at least one side face 18 towards its end A and approximately in register with the above-mentioned portion 5 of the first main face 3 forming a finger-press surface, which side face 18 is inclined at
15 an acute angle relative to the first main face 3 of the plate 2. Preferably, the two opposite side faces 18 are inclined so as to ensure that the finger is illuminated symmetrically. In the example shown, which is best seen in Figure 6, the inclination of both side faces 18 is
20 about 45°. Two light sources S (e.g. in the form of light-emitting diodes) are disposed respectively facing the inclined faces 18 with their respective axes approximately perpendicular to the faces 18. In this example, the faces 8 are plane. The arrangement as
25 proposed in this way provides bilateral illumination of the finger placed on the portion 5, i.e. illumination that is more uniform and more effective.
It is possible to obtain illumination cones that are wider open using the same light sources by making the
30 inclined faces in curved form with their concave faces facing outwards, as referenced at 19 in Figure 9.
Another possible configuration, shown in Figure 7, consists in illuminating the finger through the end face 20 situated at the first end A of the plate 2. For this
35 purpose, said end face 20 is inclined at an acute angle relative to the first main face 3 of the plate 2, and the light source S is disposed facing the face 20, with its

#
axis approximately perpendicular thereto. In the example shown, the inclination of the face 20 is about 45°. A plurality of sources S may be disposed facing the face 20 across the width of the plate 2. 5 A wider illumination cone can be obtained, as shown in Figure 8, by providing an end face 21 that is inclined and curved with its concave side facing outwards.
In a variant embodiment that is presently the preferred embodiment, the finger is illuminated, as shown
10 in Figure 10, by placing a non-point light source having a significant surface area in front of the bottom face 4 of the plate 2, facing said finger-press portion 5 and directed towards said portion. In practice, this light source may advantageously be a matrix 20 of light-
15 emitting diodes, with a ground or frosted surface interposed between the matrix and the bottom face 4 of the plate 2, or formed on said plate.
From the above description, it can be understood that the projecting parts 12 and 13 respectively
20 incorporating the mirrors 10 and 11, and also the support means 14 for supporting the focusing lens 9 can be made with dimensions that do not exceed the top and bottom limits defined by the main faces 3 and 4 respectively of the plate 2. This makes it possible to provide a device
25 that is more compact, and above all that presents small thickness, which may be no greater than 5 mm, thus satisfying practical requirements. The device has a very small number of component parts, thereby making it easy and inexpensive to produce.
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1. An optical imaging device (1) suitable for forming optical images of fingerprints of a finger (6), the 5 device comprising:
an optical plate (2) having first and second
opposite main faces (3, 4), at least a portion (5) of
said first main face (3) situated in the vicinity of a
first end (A) of the plate (2) constituting a finger-
10 press surface for a finger (6);
• at least one light source (S) situated facing a
face of said plate (2) at said first end (A) thereof, in
order to illuminate said finger (6) through the plate
(2); and
15 • imaging means including a focusing lens (9) that possesses an inlet surface (9X) and a outlet surface (92) determining a magnification factor, and that is situated downstream from the optical plate (2); characterized in that:
20 • said first and second main faces (3, 4), said face in front of which the light source (S) is situated, and the illumination direction of said light source (S) are arranged mutually in such a manner that the light beam emitted by the source and then reaching (7X) the finger
25 (6) pressed against said portion (5) of the first main
face (3) in order to illuminate said finger, propagates
(72) thereafter inside the plate (2) with multiple
reflections alternately on the first and on the second
main faces (3, 4) thereof in order to reach the second
30 end (B) of the plate (2) opposite from said first end (A);
• said plate (2) has an end face (8) at its second
end (B) that is inclined, at least in part, so that the
light beam leaves the plate via said inclined end face
35 (8) without being subjected to significant refraction or reflection;
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the focusing lens (9) is disposed facing said
inclined face (8) of the second end (B) of the plate (2)
with its optical axis extending substantially in the
midplane of the plate between said main faces and
5 extending substantially parallel to said inclined face
(8); and
a first mirror (10) is placed facing the inlet surface (9X) of said focusing lens (9) and is oriented in such a manner as to receive a portion of the light beam 10 coming from said end face (8) of the second end (B) of the plate (2) and reflect it (73) towards said inlet surface (9X) of the focusing lens (9) along the axis thereof.
15 2. An optical imaging device according to claim 1, characterized in that it further includes a second mirror (11) disposed facing the outlet surface (92) of said focusing lens (9) and oriented in such a manner that the light beam coming from the focusing lens (9) is reflected
20 transversely relative to the plate (2).
3. An optical imaging device according to claim 2,
characterized in that said second mirror (11) is oriented
in such a manner that the light beam is reflected in a
25 direction going away from the finger-press surface (5).
4. An optical imaging device according to any one of
claims 1 to 3, characterized in that the first and second
main faces (3, 4) of the plate (2) are mutually parallel.
30
5. An optical imaging device according to any one of
claims 1 to 4, characterized in that the first mirror
(10) belongs to a first projecting part (12) fitted on
the end face (8) of the second end (B) of the plate (2),
35 in such a manner as to extend in line with said plate.
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6. An optical imaging device according to any one of
claims 2 to 5, characterized in that the second mirror
(11) belongs to a second projecting part (13) fitted on
the end face (8) of the second end (B) of the plate (2)
5 in such a manner as to extend in line with said plate.
7. An optical imaging device according to any one of
claims 1 to 6, characterized in that it further includes
a diaphragm situated upstream from and close to the
10 focusing lens.
8. An optical imaging device according to any one of
claims 1 to 7, characterized in that the focusing lens
(9) is secured to the end face (8) of said second end (B)
15 of the plate (2) via support means (14).
9. An optical imaging device according to claim 8,
characterized in that the support means (14) of the
focusing lens (9) are arranged to allow the focusing lens
20 (9) to move along its optical axis.
10. An optical imaging device according to claim 6 and
claim 8 or claim 9, characterized in that the support
means (14) of the lens (9) are constituted in one piece
25 with said second projecting part (13) incorporating the second mirror (11).
11. An optical imaging device according to any one of
claims 1 to 10, characterized in that at its first end
30 (A) the plate (2) includes an end face (20) that is inclined at an acute angle relative to said first main face (B) , and in that the light source (S) is situated facing said inclined end face (20).
35 12. An optical imaging device according to any one of claims 1 to 10, characterized in that at said finger-press portion (5) of the first main face (3) of the plate
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(2) , at least one side face (18) of the plate (2) is inclined at an angle that is acute relative to said first main face (3) , and in that the light source (S) is situated facing said inclined side face (18). 5
13. An optical imaging device according to claim 12,
characterized in that both opposite side faces (18) of
the plate (2) are inclined, and in that two light sources
(S) are situated facing respective ones of said two
10 inclined side faces.
14. An optical imaging device according to any one of
claims 11 to 13, characterized in that the at least one
inclined side face (18) of the plate (2) situated towards
15 the first end (A) thereof is curved in the thickness of the plate (2), with its concave face facing outwards.
15. An optical imaging device according to any one of
claims 1 to 10, characterized in that the light source
20 (S) is not a point source, presenting a significant surface area and being placed facing the bottom main face (4) of the plate (2), substantially facing said finger-press portion (5) provided on the top main face (3), and directed towards it.
25
16. An optical imaging device according to claim 15,
characterized in that the light source (S) is a matrix
(20) of light-emitting diodes, with a ground surface
interposed between the light source and the bottom face
30 (4) of the plate (2).
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17. An optical imaging device (1) suitable for forming optical images of fingerprints of a finger (6) substantially as herein described with reference to and as illustrated in the accompanying drawings.
Dated this 22nd day of May, 2006

(G. DEEPAK SRINIWAS)
OF K & S PARTNERS
AGENT FOR THE APPLICANTS
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ABSTRACT
AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS
5
An optical imaging device (1) for forming optical images of fingerprints of a finger, the device comprising: an optical plate (2) having a portion (5) at one end (A) of a main face (3) that is provided for
10 illuminating the finger through the plate (2), the reflected light beam propagating with multiple reflections inside the plate to the other end (B) thereof, which end presents an inclined end face (A) ; a focusing lens (9) facing the end face with the lens
15 having its axis situated in the midplane of the plate; and a mirror (10) for directing the light beam leaving the end face (8) onto the axis of the lens (9).
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AN OPTICAL IMAGING DEVICE SUITABLE FOR FORMING IMAGES OF FINGERPRINTS

Documents:

Inventors:

PCT Conventions: