JP2000051182A - Fingerprint image input device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cost-effective and flat-shaped fingerprint image input device that features high resolution and high contrast to input various types of irregular patterns such as fingerprint, or the like. SOLUTION: This device is provided with a flat-shaped light-source 1 and a transparent parallel plate 3 in which one plane 30 of a transparent plate 31 of n1 of refractive index receives light from the light-source 1, at the other plane 40 side of this mother material (plate 31), multiple triangle prisms 4 of n2 of refractive index are embedded therein in parallel so that two faces of the triangle prisms are embedded, and boundary faces 41b, 42b... are incident and refractive planes while, boundary faces 41a, 42a... are refractive and outgoing planes, and boundary faces 41c, 42c... are flat-formed at the outside to make a detection plane. This device is also provided with a filtering plate 23 which selectively filters light from the outgoing planes 41a, 41a... and a light-receiving element 5 which receives the filtered light. The device reads fingerprint information from a finger touched on the detection planes 41c, 42c... on the transparent parallel plate 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fingerprint image input device, and more particularly to a fingerprint image input device capable of obtaining a thin and clear fingerprint image.

[0002]

2. Description of the Related Art Attention has been focused on biometric information having the highest security as a personal identification technique used for access control and cash services. Until now, information on fingerprints and other uneven surfaces has been input by applying ink and stamping it once on paper, and then inputting it using an image sensor, or using glass and air using an optical element such as a prism. There is a method of immediately obtaining a concavo-convex pattern by irradiating a light beam at an angle equal to or greater than the critical angle to the interface. The present invention relates to an apparatus for immediately detecting information on an uneven surface using the latter optical element.

FIG. 6 shows an example of input means using a prism according to the prior art, and is a principle diagram of a system called a total reflection method. In FIG. 6, a fingerprint (irregularity pattern) on the surface of the finger 9 is brought into contact with the hypotenuse of the prism 81, and when the irradiation light from the light source 1 is incident on the hypotenuse at a critical angle or more, the incident light at the projection 92 of the fingerprint Are scattered, and are totally reflected at the interface with the air at the concave portion 91 and are incident on the detector 55 such as an image sensor, so that an uneven pattern such as a fingerprint can be detected.

Japanese Patent Application Laid-Open No. 9-116128 entitled "Fingerprint Image Input Apparatus and Manufacturing Method Thereof" is disclosed as a conventional technique utilizing the principle of such a total reflection method. FIG. 7 is an exploded perspective view of the fingerprint image input device, FIG.
Fig. 3 shows a characteristic diagram of the diffraction grating. 7, a fingerprint image input device includes a diffraction grating 72 formed on a transparent substrate 71, a photoelectric conversion element (light receiving element) 5, a switch element not shown,
The two-dimensional image sensor 7 includes a switch wiring, a light shielding plate 73 formed of an opaque electrode disposed below the photoelectric conversion element 5, the planar light source 1, and the transparent protective film 8. ing.

In this configuration, the two-dimensional image sensor 7 is illuminated from the back with parallel rays from the planar light source 1,
The light that has passed through the diffraction grating 72 is diffracted by the order m (m = 1, 2, 3,...) And enters the transparent protective film 8 obliquely. In the disclosure example,
Since the critical angle theta _c is not totally reflected and not about 34 ° or more, the order m = 4 or higher order diffracted light is utilized. That is, the transparent protective film 8
Is brought into contact with a fingerprint (irregular pattern) of a finger 9 and the transparent protective film 8 is irradiated with the diffracted light at a critical angle or more.
The incident light is scattered at the convex part 92 of the fingerprint, and the light is totally reflected at the interface with the air at the concave part 91 and is incident on the light receiving element 5, so that a concavo-convex pattern such as a fingerprint can be detected.

In FIG. 8, a two-dimensional image sensor 7
Is a light shielding plate 73 composed of opaque electrodes on a transparent substrate 71.
The photoelectric conversion element 5 disposed on the upper surface of the substrate and a diffraction grating 72 forming a slit 75 by two opaque materials (constituting a lower electrode and a wiring material) with an interlayer insulating film 76 interposed therebetween are integrally formed. I have. A part of the parallel light beam emitted from the lower part of the two-dimensional image sensor 7 passes through the diffraction grating 72 and is deflected at an angle θ _m corresponding to the order m of the diffraction grating. Of the deflected light, the critical angle θ of the transparent protective film 8
Light of _c or more is used for detecting a concavo-convex pattern such as a fingerprint. Figure 9 is the angle theta _m being deflected by the diffraction grating in the horizontal axis shows the light intensity on the vertical axis. As the order m of the diffraction grating increases, the luminous intensity of the light beam deflected by the diffraction grating 72 decreases.

[0007]

As described above, a diffraction grating and a photoelectric conversion element are integrally formed as a two-dimensional image sensor, and the parallel light is irradiated from the back of the two-dimensional image sensor by the diffraction grating. Is diffracted to irradiate a transparent protective film against which an uneven surface such as a fingerprint is pressed. The deflected light is scattered in the convex portion of the uneven surface, deflecting light diffracted above the critical angle theta _c in the recess is received by a photoelectric conversion element is totally reflected, the signal processing line as uneven pattern information Will be Since the diffraction grating serving as the light deflecting unit and the photoelectric conversion element that receives light having uneven pattern information such as a fingerprint are integrally formed, a thin fingerprint image input device can be configured.

However, light components are scattered by the convex portion is received by the photoelectric conversion element, degrade the resolution with respect to the optical component to be received by the total reflection at the critical angle theta _c or more recesses in the photoelectric conversion element It becomes a noise component. In particular, a low degree deflected light diffraction deteriorates the signal-noise ratio since the light intensity is higher with respect to light components totally reflected by the critical angle θ _c (S / N ratio). Also, among the critical angle theta _c above deflected light, also contribute to deteriorating the resolution when the higher order deflection light is received by the total reflection to the photoelectric conversion elements in other recesses. That is, when detecting a concavo-convex pattern such as a fingerprint in a comparatively wide range, the concave portion information from another position apart from the mixture is mixed, thereby deteriorating the contrast of the concavo-convex pattern.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to solve the above-mentioned problems and to effectively convert a parallel light beam from a light source without using a diffraction grating as light deflecting means. It is an object of the present invention to provide an economical thin fingerprint image input device having high resolution and high contrast for an image of a concavo-convex pattern such as a fingerprint in a relatively wide range by deflecting the image.

[0010]

In order to achieve the above object, in the present invention, a flat or linear light source and light emitted from the light source are applied to one surface of a transparent plate having a refractive index of n1. , A plurality of parallel to the other surface side of this base material
Two surfaces of a triangular prism of n2 (<n1) are buried in this base material to form an interface, and one of the two interfaces is an entrance / refraction surface, the other interface is a refraction / emission surface, and the remaining interface is a refraction / emission surface. A transparent parallel plate of a refractive index distribution type, one surface of which is formed outwardly and smoothly in a planar shape to be an inspection surface; a light shielding plate for selectively passing light emitted from an emission surface of the transparent parallel plate; A light-receiving element that receives light passing through the plate.

Further, two interfaces (incident / refracting surface and refracting / emission surface) formed by the base material of the transparent plate and the triangular prism and an interface between the other interface of the triangular prism and air (refractive index n3) (hereinafter referred to as an inspection surface) ), The light incident on the transparent parallel plate is totally reflected at the first interface (incident surface), refracted at the next interface (refractive surface) adjacent to this incident surface, enters the triangular prism, and becomes smooth. It is assumed that a point that reaches the inspection surface of the polished transparent parallel plate totally reflects when forming an interface with the air layer.

[0012] With this configuration, fingerprint image information from a finger in contact with the inspection surface of the transparent parallel plate polished smoothly can be read as follows. That is, the light incident on the transparent parallel plate is totally reflected at the first interface (incident surface), and enters the triangular prism at the next interface (refractive surface) adjacent to this interface,
When reaching the inspection surface of the transparent parallel plate polished smoothly in the triangular prism, it is totally reflected when it is a concave portion of a concavo-convex pattern such as a fingerprint, and travels through the triangular prism to the next interface (refractive surface).
, And is totally reflected again at the interface (exit surface) of the next adjacent triangular prism, and is detected as a signal component by each element of the light receiving element 5.

On the other hand, when the portion reaching the inspection surface of the transparent parallel plate in the triangular prism is a projection of the uneven pattern, this light is scattered. Of the scattered light, the light component scattered at the same angle and direction that is totally reflected by the concave portion and detected as a signal component is detected by the corresponding light receiving element and becomes noise, but compared with the entire scattered light. Its share is small. Light components scattered at other angles are shielded and absorbed by the light shielding plate 23 or the surface of the finger. That is, since only the weak optical signal scattered is detected at the convex portion, the concave / convex pattern such as the fingerprint can be identified with good contrast.

The transparent parallel plate has a plurality of triangular V-shaped grooves arranged in parallel on the other surface of the base material of the transparent plate having a refractive index of n1, and the V-groove has a refractive index smaller than the refractive index n1. A transparent parallel plate can be formed by filling a transparent resin having n2 and polishing the filled transparent resin side smoothly. Further, the triangular prism having the refractive index n2 can be an isosceles triangle having an inspection surface of the transparent parallel plate as a base (an angle formed with the base is α).

The isosceles triangle can be an equilateral triangle. With this configuration, a parallel light beam incident on the transparent parallel plate from the light source is incident on the first interface (incident surface) of the triangular prism, is totally reflected, and is interfaced with the next adjacent triangular prism (refractive surface).
, Reaches the inspection surface of the triangular prism that has been polished smoothly, undergoes light intensity modulation based on the information on the uneven pattern of the fingerprint on this surface, and is further refracted at the interface (refractive surface) of the triangular prism. The light is totally reflected by the (emission surface) and can be received by the light receiving element.

The light source may include a lens and emit parallel light to a transparent parallel plate, or may be a surface emitting laser. With this configuration, a parallel light beam can be used as a light source, so that total reflection at the interface of the triangular prism of the transparent parallel plate at the entrance surface, total reflection at the concave portion of the fingerprint in contact with the inspection surface of the transparent parallel plate, and light reception are performed. Due to the total reflection at the light-emitting surface that receives light at the element, diffusion of light at the light-receiving surface of the light-receiving element can be prevented.

In addition, the transparent parallel plate is replaced with a triangular prism embedded in the transparent plate, and instead of four surfaces of a plurality of quadrangular pyramids having a refractive index n2 (<n1) on the other surface side of the transparent plate having a refractive index n1. One interface in each of the left, right, and depth directions is called an incidence / refraction surface, and the remaining interface is called a refraction / exit surface).
The remaining quadrangular surface is outwardly formed to be smooth and flat, so that a refractive index distribution type transparent parallel plate serving as an inspection surface can be obtained.

With this configuration, it is possible to maintain high resolution not only in the horizontal direction but also in the depth direction. That is, when the transparent parallel plate is formed of a triangular prism, when there is a divergence of light from the light source in the depth direction of the triangular prism, there is a possibility that information on other positions in the depth direction is mixed into the detected concave portion information to lower the resolution. is there. Such a problem can be solved by forming a triangle in the depth direction in the same manner as in the horizontal direction. That is, forming a triangle in the horizontal direction and the depth direction can be performed by arranging a plurality of quadrangular pyramids regularly.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram of a main part of a fingerprint image input device as one embodiment of the present invention, FIG. 2 is a block diagram of a main portion of a fingerprint image input device as another embodiment, and FIG. FIG. 4 is an explanatory diagram illustrating the operation principle of the present invention, FIG. 4 is an explanatory diagram illustrating light diffusion when a divergent light source is used, and FIG. 5 is a diagram illustrating a fingerprint image input device as another embodiment of the present invention. FIG.
The same members corresponding to FIGS. 6 to 9 are denoted by the same reference numerals.

In FIG. 1, a fingerprint image input device includes a planar or linear light source 1 (11, 12,... 1n) and a light source (11, 12,... 1n).
12n), the light (11a, 12b
Received on one side 30 of n1 transparent plate 31, inspection surface 40 of this base material
A triangular prism with a refractive index n2 (<n1) (41,42
・ 4n + 2) ((41a, 42a ・ ・ 4n + 2a), (41b, 42b ・ ・ 4n
+ 2b)) is embedded in this base material to form an interface. One of the two interfaces (41b, 42b... 4n + 2b) is the incident / refracting surface, and the other interface (41a, 42a.・ 4n + 2a) is the refraction / outgoing surface, and the other surface (41c, 42c ・ ・ 4n + 2c) is outwardly formed in a flat and smooth plane and becomes the inspection surface 40. 3 and the exit surface of this transparent parallel plate 3 (41a, 42a... 4n
+ 2a), a light-shielding plate 23 for selectively passing light (11 g, 12 g,... 1 ng) emitted therefrom, and a light-receiving element 5 (51, 52,... 5n) for receiving light passing through the light-shielding plate 23. It is comprised including.

With this configuration, the inspection surface of the transparent parallel plate 3
The fingerprint image information from the finger 9 that has come into contact with 40 can be read as follows. For the sake of simplicity of description, the tracing of the light beam is indicated by the light beam 11a emitted from the light source 11, and the other light beams are indicated by parentheses.
Note that the ray tracing in FIG. 1 is illustrated with the outgoing light 11a as the center.
Other lights have been omitted. The base material of the transparent plate 31 and the triangular prism 4 (41,42
・ Two interfaces with (4n + 2) ((41a, 42a, ... 4n + 2a), (41b, 42
b, .. 4n + 2b)) and incident on the transparent parallel plate 3 at the interface (41c, 42c, .. 4n + 2c) between the triangular prism 4 (41,42..4n + 2) and air (refractive index n3). The reflected light 11a (12a... 1na) is totally reflected at the first interface (incident surface) 41b (42b,.
..1nb), and is refracted at the next interface (refractive surface) 42a (43a..4n + 1a) adjacent to the incident surface 41b (42b,... 4nb) and triangular prism 42 (43..4n + 1) And enters into light 11c (12c... 1nc). And the inspection surface of the transparent parallel plate 3 polished smoothly
Inspection surface 42c of the point that reached 40 (triangular prism 42 (43 ... 4n + 1)
When (43c... 4n + 1c) forms an interface with the air layer, it is totally reflected and becomes light 11d (12d... 1nd).

Here, the following is detected by the uneven pattern information such as the fingerprint from the finger 9 contacting the inspection surface 40 of the transparent parallel plate 3 polished smoothly. That is, triangular prism 4
The point (inspection surface 42c (43c... 4n + 1c)) of 2 (43... 4n + 1) which reaches the inspection surface 40 of the transparent and polished transparent parallel plate 3 is the concave portion of the uneven pattern such as a fingerprint. At this time, as described above, the light is totally reflected and becomes light 11d (12d... 1nd), and this triangular prism 42 (43.
・ 4n + 1) and the interface (refractive surface) 42b (43b 4n + 1)
b) is refracted into light 11f (12f ... 1nf), and is totally reflected again by the emission surface 43a (44a ... 4n + 2a) of the next adjacent triangular prism 43 (44. (12g ... 1ng)
Are detected as concave signal components by the corresponding elements 51 (52,... 5n).

On the other hand, a point (inspection surface 42c (43c... 4n) of the transparent parallel plate 3 in the triangular prism 42 (43.
+ 1c)) is the light 11c (12c,.
・ 1nc) is scattered and becomes light 11e (12e,... 1ne). Of the scattered light 11e (12e, 1ne), a light component 11d '(12d', 1nd ') scattered at the same angle and direction that is totally reflected by the concave portion and detected as a signal component is: The corresponding light receiving element 51 (52,
・ Noise is detected by 5n), but its proportion is small compared to the total scattered light. Light components scattered at other angles are shielded and absorbed by the light shielding plate 23 or the surface of the finger. That is, since only the weak optical signal scattered is detected at the convex portion, the concave / convex pattern such as the fingerprint can be identified with good contrast.

[0024]

Embodiment 1 FIG. 2 shows another embodiment of the present invention. The difference from the embodiment shown in FIG. 1 is that the light emitting element (light source 1) (11, 12,
.. 1n) and the light receiving element 5 (51, 52... 5n) are integrally formed, and the light shielding plate 22 is omitted. Light emitting element (1
The trajectories of the light beams emitted from (1, 12,... 1n) are the same as those described in the embodiment of FIG.

In the present invention, the light emitting elements (11, 12,...) Extend in the depth direction of the triangular prism 4 (hereinafter, this direction is referred to as the depth).
1n) is composed of a plurality of linear or dotted light emitting elements. The light receiving elements 5 (51, 52,..., 5n) are configured by regularly arranging a plurality of light receiving elements also in the depth direction. Thus, the light-emitting elements (11, 12,
.. 1n) and the light receiving elements 5 (51, 52... 5n) are alternately arranged in the horizontal direction to form a two-dimensional light emitting / receiving element.

In one embodiment, in the horizontal direction, the light-emitting and light-receiving elements are 50 μm for one set, and the width of the triangular prism 3 in the horizontal direction is 50 μm.
m, in the depth direction, a light-receiving element or a point-shaped light-emitting element constitutes a light-receiving element or a point-shaped light-emitting element at intervals of 50 μm, so that a fingerprint such as a finger has a resolution of 50 μm or a resolution of 500 DPI (500 dots / inch). , And can accurately identify personal information.

As described above, the width of the triangular prism 3 in the lateral direction is
Instead of making it 50 μm, the triangular prism 3 is made a little larger and a plurality of light receiving elements or
A plurality of pixels can be captured using a two-dimensional image sensor such as a CCD. In this case, the arrangement of the plurality of pixels captured for one triangular prism 3 is inverted. Therefore, when reproducing the original image (fingerprint pattern) based on the data obtained from the plurality of triangular prisms 3, , The direction of the data taken in from the triangular prism 3 can be inverted, the whole can be combined, and the original image can be synthesized.

[0028]

[Embodiment 2] The transparent parallel plate 3 constituting the optical system means of the fingerprint image input apparatus according to the present invention will be described. FIG. 1 or FIG.
The transparent parallel plate 3 has a plurality of triangular V-grooves (interfaces) arranged in parallel on the inspection surface 40 side of the base material of the transparent plate 31 having the refractive index n1.
(41a, 41b), (42a, 42b), ... (4n + 2a, 4n + 2b)), and this V-groove is filled with a transparent resin having a refractive index n2 smaller than the refractive index n1, and this filling is performed. 4n + 2c, the inspection surface (41c, 42c,... 4n + 2c), and a refractive index distribution type transparent parallel plate having triangular prisms 41, 42,. An optical surface 40 for inspecting the concave and convex pattern information of the fingerprint by contacting the finger 3 and the finger 9 can be formed.

Also, a triangular prism 41, 42... 4n + 2 having a refractive index n2
Are the inspection surfaces (41c, 42c,
・ Construct an isosceles triangle with 4n + 2c) as the base. With this configuration, the light (11a, 12a... 1na) perpendicularly incident on one surface 30 of the transparent parallel plate 3 passes through the transparent parallel plate 3 through the optical system means. The light exits vertically from one surface 30 and enters the light receiving element 5 (51, 52... 5n). That is, the design of the optical system is simplified.

Next, the triangular prism 4 having the refractive index n2 is
The inspection plane (41c, 42c... 4n + 2c) is the base, and the angle between the base and the base is an isosceles triangle of α. In FIG. 3, a triangular prism 4 having a refractive index n2 is shown by ΔABC, ΔCDE, ΔEFG, and an inspection surface 40 of the transparent parallel plate 3 to be inspected by contacting an uneven surface such as a fingerprint is point A, C, E, G. Exist on a straight line.

Light 11a emitted perpendicularly to the transparent parallel plate 3 from the light source 11 is totally reflected at the intersection P of the side BC of ΔABC. That is,
The condition for total reflection at the entrance surface 11b is that the incident angle (90-β
= Α) is greater than or equal to the critical angle. Assuming that the refractive index of the base material of the transparent parallel plate 3 is n1,

[0032]

Α ≧ sin ⁻¹ (n2 / n1) (1) The value of the angle α is a necessary condition that satisfies the expression (1). Next, the light 11b totally reflected at the intersection P is the intersection Q of the side CD of ΔCDE.
Incident on. Since the angle of incidence θ CQP is given by equation (2),

[0033]

数 CQP = 180−β− (180−2α) = 3α−90 (2)

[0034]

Θ = 90− (3α−90) = 180−3α (3) When this angle θ = 180−3α is within the critical angle, the light enters the ΔCDE according to the law of refraction and is refracted. It reaches the intersection R with the inspection surface 40 at the angle x.

[0035]

## EQU4 ## θ = 180−3α <sin ⁻¹ (n2 / n1) (4) The relationship between the refraction angles x is expressed by the following equation (5).

[0036]

## EQU00005 ## n2 sinx = n1 sin (180-3.alpha.) (5) That is, the refraction angle x is expressed by equation (6).

[0037]

X = sin ^-1 ｛(n1 / n2) sin (180-3α)｝ (6) When the unevenness information of the fingerprint on the inspection surface 40 at the intersection R with the inspection surface 40 is a concave portion , The refractive index n3 of this recess (air)
The angle of incidence at this intersection R is

[0038]

90−∠CRQ = 90− (180−α−90−x) = α + x (7) Therefore, for total reflection at the intersection R,

[0039]

Α + x ≧ sin ⁻¹ (n3 / n2) (8) That is, the angle x needs to satisfy the condition expressed by the equation (9).

[0040]

X ≧ sin ⁻¹ (n3 / n2) −α (9) The refractive index n1 of the base material of the transparent parallel plate 3 and the refractive index n2 of the triangular prism 4
By appropriately selecting the value of the refractive index n3 of the air and the angle α with the base, the above expressions (1), (4), (6), and (9) can be satisfied. That is, the basic conditions of the transparent parallel plate constituting the optical system means of the fingerprint image input device can be satisfied.

In the trajectory of the light beam after the intersection R, since the triangular prism 4 is an isosceles triangle, the incident angle and the reflection angle of the intersection S are the same angles as the light traveling at the intersection Q is reversed. Similarly, the angle of incidence and the angle of reflection at the intersection T also travel at the same angle as when the light at the intersection P is reversed. That is, the light 11d totally reflected at the intersection R travels within ΔCDE, intersects at the intersection S of the side DE at the same angle (incident angle x) as the refraction angle x obtained by the equation (6), and the light 11f at the refraction angle θ. And enters the base material of the transparent parallel plate 3. This light 11f is the intersection T of the interface (side EF) of ΔEFG.
, The light is totally reflected at the incident angle α, passes through the transparent parallel plate 3 vertically, and reaches the light receiving element 5.

Although the triangular prism 4 has been described as an isosceles triangle, for example, when the angles ∠CAB, ∠ECD, ∠GEF,... Take a value different from the angle α, the expressions after the expression (2) are slightly modified. Can be used.

[0043]

Embodiment 3 Next, a case where the triangular prism 4 is an isosceles triangle and particularly an angle α = 60 °, that is, an equilateral triangle will be described. In FIG. 3, for example, as one embodiment, the refractive index of the base material n1 = 1.5,
Assuming that the refractive index of the triangular prism 4 is n2 = 1.2 and the refractive index of air n3 = 1.0, and the angle α is 60 °, the central portion (optical axis) of the light 11a emitted perpendicularly to the transparent parallel plate 3 from the light source 11 is ΔABC Side BC
At the middle point P. At this time, the light 11b totally reflected at the middle point P is refracted at the intersection Q, and
At the intersection R of The position of the intersection R at this time is the middle point of the side CE. That is, the light 11b emitted from the light source 11 and totally reflected at the midpoint P is totally reflected at the midpoint R of the side CE, further refracted at the intersection S, totally reflected at the midpoint T of the side EF, and Can be received at the central part of Considering the width of the parallel ray of the light 11a emitted from the light source 11, all the light 11a incident on the side BC is incident on the side CE, and the light 11c incident on the side CE is
When the portion is the concave portion of the concavo-convex pattern, the light is totally reflected on all sides CE and all the light is incident on the side EF as light 11f. The light 11f is totally reflected by the side EF and can be received by the light receiving element 51. That is, the light 11a emitted from the light source 11 can be most efficiently received by the light receiving element 51.

Next, the case where the light source 1 is divergent light will be considered with reference to FIG. Light emitted from the light source 1 is an intersection P, P ', P "of the side BC.
It is assumed that the light is totally reflected. The light totally reflected at each point P, P ', P "is refracted at the intersection point Q, Q', Q" of the side CD, and the concave and convex pattern of the fingerprint is at the intersection R, R ', R "of the side CE. Total reflection, intersection of side DE
The light is refracted at S, S ', S "and further totally reflected at the intersection T, T', T" of the side EF and proceeds to the light receiving element 5. When the light source 1 is a divergent light, as the reflection and refraction progress, that is, from the intersection P, P ', P "to the intersection T, T', T", and further, the distance between the light at the light receiving point of the light receiving element 5 Spreads with the optical path length of light, and in the worst case, the light receiving element 5 may not be able to receive light.

Therefore, for example, when the divergence of light emitted from the light source 1 such as a light emitting diode is predicted in advance, the light source 1
It is preferable that a condensing lens 21 is provided, and that the outgoing light be converted into a parallel beam by the lens 21 and output to a transparent parallel plate. Also,
If the light source 1 has a small light divergence such as a surface emitting laser, the condenser lens 21 is unnecessary.

As described above, the transparent parallel plate 3 and the light beams (11a to 11a) constituting the optical system means of the fingerprint image input device.
g), (12a to 12g)... (1na to 1ng) indicate that the light emitted from the light source 1 is efficiently received by the light receiving element 5 as much as possible when the concave portion of the uneven pattern information such as a fingerprint is a transparent parallel. The parallel rays incident on the plate 3 are perpendicular to the inspection surface 40 of the transparent parallel plate 3, and the light incident on the transparent parallel plate 3 is a triangular prism 41 (42,...).
4n), the ray totally reflected at the central part (P) of the first interface 11b (12b1nb) becomes the next adjacent triangular prism 42 (43, 4n + 1)
At the interface 12a (13a ... 1n + 1a), and this triangular prism 42 (43,
..4n + 1) central part (R) of inspection surface 40 polished smoothly
It is desirable to reach.

[0047]

Fourth Embodiment In FIG. 5, a transparent parallel plate 3A is formed of a triangular prism 4 embedded in a transparent plate 31 as shown in FIGS. A plurality of square pyramids 4A (4ijA, i = 1, 2,...) Having a refractive index n2 (<n1)
n, j = 1,2, .m)) (one interface in each of the left and right direction and the depth direction is called an entrance / refraction surface, and the other interface is called a refraction / exit surface). It can be configured as a refractive index distribution type transparent parallel plate that is buried and the remaining quadrangular surface is outwardly formed to be smooth and flat and becomes the inspection surface 40.

With this configuration, high resolution can be maintained not only in the horizontal direction but also in the depth direction. That is, when the transparent parallel plate is formed of a triangular prism, when there is a divergence of light from the light source in the depth direction of the triangular prism, there is a possibility that information on other positions in the depth direction is mixed into the detected concave portion information to lower the resolution. is there. Such a problem can be solved by forming a triangle in the depth direction in the same manner as in the horizontal direction. For example, as described in the first embodiment, not only in the horizontal direction but also in the depth direction, the width of the triangle forming the quadrangular pyramid is 50 μm, and the interval between the corresponding light receiving elements or point-like light emitting elements is 50 μm. Sometimes, a fingerprint such as a finger can be read at a resolution of 50 μm or a resolution of 500 DPI (500 dots / inch), and personal information can be accurately identified.

[0049]

As described above, according to the present invention, the optical system means which deflects a light beam emitted from a planar light source and enters the inspection surface for inspecting the unevenness of a fingerprint at a critical angle or more is refracted. A plurality of parallel V-grooves are formed on the inspection surface (inspection surface) side of the base material of the transparent plate having a refractive index n1, and a plurality of refractive indices n2 (<
n1) The two surfaces of the triangular prism are adhered to each other, and the other side (the inspection surface side) is made smooth and flat to form a refractive index distribution type transparent parallel plate. By using the total reflection of light to deflect light rays, images of uneven patterns such as fingerprints in a relatively wide area can be resolved at high resolution.
An economical thin fingerprint image input device having a high contrast of 500 DPI and being economical can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of a fingerprint image input device as one embodiment of the present invention.

FIG. 2 is a main part configuration diagram of a fingerprint image input device as another embodiment.

FIG. 3 is an explanatory diagram illustrating the operation principle of the present invention.

FIG. 4 is an explanatory diagram illustrating light diffusion when a divergent light source is used.

FIG. 5 is a main part configuration diagram of a fingerprint image input device as another embodiment of the present invention.

FIG. 6 is a diagram illustrating the principle of the total reflection method according to the related art.

FIG. 7 is an exploded perspective view of a conventional fingerprint image input device.

FIG. 8 is a diagram illustrating the operation of a diffraction grating.

FIG. 9 is a characteristic diagram of a diffraction grating.

[Explanation of symbols]

1,11,12 ... 1n Light source 11a, 11b, 11c, ... 11g, Light 21 Lens 22,23 Light shielding plate 3,3A Transparent parallel plate 30 Surface 31,31A Transparent plate 4,41,42 ... 4n Triangular prism 4A , 411A, ... 4ijA ... 4nmA Square pyramids 41a, 42a, 43a, ... 4na, 4n + 1a, 4n + 2a Refraction / outgoing surfaces 41b, 42b, 43b,・ Refractive surface 41c, 42c, 43c, ... 4nc, 4n + 1c, 4n + 2c, 40 Inspection surface 5,51,52 ・ 5n Light receiving element ΔABC, ΔCDE, ... Triangle α, β, θ, x angle P , P ', P ", Q, Q', Q", T, T ', T "Intersection 7 Two-dimensional image sensor 71 Transparent substrate 72 Diffraction grating 73 Light shielding plate 75 Opaque material 76 Interlayer insulating film θ _c Critical angle θ _m Diffraction grating deflection angle 8 Transparent protective film 81 Prism 9 Finger 91 Concave part 92 Convex part n, n1, n2, n3 Refractive index

Claims (8)

[Claims] 1. A flat or linear light source, and light emitted from the light source is received on one surface of a transparent plate having a refractive index of n1, and a plurality of light beams are refracted in parallel to the other surface of the base material. Rate n2 (<n1)
The two surfaces of the triangular prism are embedded in this matrix to form an interface,
Of these two interfaces, one is an entrance / refraction surface, the other is a refraction / exit surface, and the other surface is outwardly directed outward and is formed in a smooth and flat shape to be an inspection surface. A transparent parallel plate, a light-shielding plate for selectively passing light emitted from an emission surface of the transparent parallel plate, and a light-receiving element for receiving light passing through the light-shielding plate; and an inspection surface of the transparent parallel plate. A fingerprint image input device, which reads fingerprint image information upon contact. 2. The fingerprint image input device according to claim 1, wherein the transparent parallel plate comprises a plurality of triangular V-shaped grooves arranged in parallel on the other surface side of the base material of the transparent plate having a refractive index of n1. This V
A fingerprint image input device comprising: filling a groove with a transparent resin having a refractive index n2 smaller than the refractive index n1; and smoothing the filled transparent resin side to form a transparent parallel plate. 3. The fingerprint image input device according to claim 1, wherein two interfaces (incidence / refraction surface and refraction / emission surface) formed by the base material of the transparent plate and the triangular prism and another of the triangular prism. Light incident on the transparent parallel plate at the interface between the interface and air (refractive index n3) (hereinafter referred to as the inspection surface) is totally reflected at the first interface (incident surface), and the next interface adjacent to this incident surface A fingerprint image input characterized by being refracted by the (refractive surface) and incident on the triangular prism and reaching the inspection surface of the smooth polished transparent parallel plate and totally reflecting when forming the interface with the air layer. apparatus. 4. The fingerprint image input device according to claim 1, wherein the triangular prism having a refractive index of n2 is an isosceles triangle having a base of an inspection surface of the transparent parallel plate. A fingerprint image input device, wherein the angle is α). 5. The fingerprint image input device according to claim 1, wherein the isosceles triangle is an equilateral triangle. 6. The fingerprint image input device according to claim 1, wherein the light source includes a lens and emits a parallel light beam to a transparent parallel plate. Input device. 7. The fingerprint image input device according to claim 1, wherein the light source is a surface emitting laser. 8. The fingerprint image input device according to claim 1, wherein the transparent parallel plate is the other of the transparent plates having the refractive index n1 instead of the triangular prism embedded in the transparent plate. On the surface side of a square pyramid 4 of refractive index n2 (<n1)
The surface (one interface in the left and right and depth directions is called the entrance / refraction surface, and the remaining interface is called the refraction / exit surface) is regularly embedded in the base material, and the remaining square surface comes out outward and is smooth. A fingerprint image input device, comprising a transparent parallel plate of a refractive index distribution type formed in a planar shape and serving as an inspection surface.