JPH07174947A - Fiber optical plate - Google Patents

Abstract

PURPOSE:To eliminate the restriction in the cutting angle of an input end face and to obtain a fiber optical plate(FOP) thinner than heretofore by providing a fiber optical plate with a light absorber so as to cover the outer peripheral parts of respective clads. CONSTITUTION:This FOP is composed of a core 5 which propagates incident light, the clads 6 which covers the outer peripheral parts thereof and further an absorber 7 disposed to cover the outer peripheral part of each clad 6. The light leaking from the core 5 and the incident light on the clads 6 are absorbed by disposing the absorbers 7 in this position and, therefore, the adjacent optical fibers are held optically insulated by the absorber 7. The angle alpha of inclination of the input end face 2 is set at such an angle at which the incident light on the core 5 from the air does not generate total reflection at the boundary face with the clads 6 and, therefore, the output of the unnecessary light, such as background light, from the output end face does not arise and the image of only the part in tight contact therewith is outputted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber optic plate integrally formed with a plurality of optical fibers bundled together.

[0002]

2. Description of the Related Art A fiber optic plate (referred to as "FOP") as shown in FIG. 13 is conventionally known (US Pat. No. 4,932,776). The FOP 80 is formed by bundling and integrating a large number of optical fibers 85, and has an input end face 81 that is inclined and cut with respect to the optical axis at one end thereof. A finger 8 is placed on the input end face 81.
When 2 and the like are brought into close contact with each other, the concavo-convex pattern of the close contact portion is projected on the output end surface 83 on the opposite side, and as a result, the image of the fingerprint 84 can be read.

[0003]

The inclination angle θ of the input end face 81 disclosed herein is preferably about 30 ° to 60 ° from the viewpoint of occurrence of crosstalk, resolution, and the like. In order to set the cutting angle of the input end face 81 in this range and to secure a space where the fingertip or the like can be brought into close contact with the input end face 81, it is necessary to form the FOP to a certain thickness.

On the other hand, in recent years, miniaturization of electronic parts including optical devices has been further advanced, and further miniaturization of FOP is desired. However, in order to make the FOP more compact, that is, thinner, the cutting angle of the input end face 81 must be made sharper to secure a certain space in the input end face 81. However, as described above, the cutting angle of the input end face is limited, which is a great obstacle to miniaturization.

Therefore, an object of the present invention is to provide a FOP which is thinner than the conventional one, by eliminating the restriction on the cutting angle of the input end face in the FOP.

Another object of the present invention is to provide an FOP capable of clearly outputting an image of the closely contacted portion without unnecessary light such as background light being output from the output end face. .

[0007]

A fiber optic plate according to the present invention is provided so as to cover a plurality of cores that propagate incident light, a clad that covers the outer peripheral portion of each core, and a outer peripheral portion of each clad. And a light absorber that absorbs the light leaked from the core and the light incident on the clad. Then, one end of this plate is provided with an input end face that is a face for contacting the surface of the object and is inclined with respect to the optical axis of the optical fiber. The light incident on the core is set at an angle such that total reflection does not occur at the interface with the clad.

[0008]

By providing the light absorber so as to cover the outer peripheral portion of each clad, the light leaked from the core and the light propagating through the clad reach the light absorber. These lights are
Since the light is absorbed when it enters the light absorber, adjacent optical fibers are optically insulated by the light absorber. Therefore, the light propagating through each core is prevented from leaking and entering the other adjacent cores. This effect is independent of the tilt angle of the input end face,
No matter how acute the inclination angle of the input end face is, the light incident on each core is propagated through each core and output from the output end face.

When the inclination angle of the input end face is set to such a condition, a part of the light propagating through the air and entering the core from the input end face leaks from the core to the clad and is absorbed by the absorber. To be done. Therefore, unnecessary light such as background light is gradually attenuated in the process of propagating through the core, and is hardly output from the output end face. On the other hand, when the surface of the object is brought into close contact with the input end face, the light transmitted through this close contact portion enters the core, but this incident light meets the condition of total reflection at the interface with the cladding. There will also be light incident at an angle. That is, only the light incident from the close contact portion is output from the output end face.

[0010]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a fiber optic plate (hereinafter referred to as F
1 shows the appearance of 1). The FOP 1 is used in a fingerprint detecting device, etc., which will be described later, and is integrally formed in a state in which a plurality of optical fibers are bundled. An input end face 2 inclined with respect to the optical axis of the fiber is provided at one end of the FOP 1, and an output end face 3 formed substantially perpendicular to the optical axis is provided at the opposite end. .

As shown in FIG. 2, the FOP 1 includes a core 5 for propagating incident light, a clad 6 for covering the outer peripheral portion thereof, and an absorber 7 provided so as to cover the outer peripheral portion of each clad 6. It consists of three types. By providing the absorber 7 at this position, the light leaked from the core 5 and the light incident on the clad 6 are absorbed, so that the adjacent optical fibers are optically insulated by the absorber 7. Has become. The core 5, the clad 6 and the absorber 7 are each made of the material shown in FIG. 4, and as a result, the core 5 has a refractive index of 1.621 and the clad 6 has a refractive index of 1.519. Further, as an example of the size of the FOP 1, each dimension is shown in FIG.

By forming the FOP 1 with the optical fiber in which the outer peripheral portion of the clad 6 is covered with the absorber in this manner, the light incident on each core 5 leaks from the core 5 and enters another adjacent core 5. Incident is avoided, occurrence of crosstalk between adjacent fibers can be prevented, and the S / N ratio of the output image is improved. This action is independent of the inclination angle of the input end face, and no matter how acute the inclination angle of the input end face is, the light incident on each core is propagated through each core and output from the output end face. It is what is done.

Further, in the FOP 1 according to the present embodiment, by setting the inclination angle of the input end face 2 (the inclination angle with respect to the optical axis of the optical fiber) to a specific value, the excellent action and effect described later can be obtained. It plays.

FIG. 3 shows a vertical cross section of the FOP 1. In the figure,
n ₀ is the refractive index of the core, n ₁ is the refractive index of the cladding, and n is the refractive index of air. FOP1 of this embodiment
In the above, the inclination angle α of the input end face 2 is defined so that the light receiving angle becomes 0 °. That is, the inclination angle α is set to such an angle that total reflection does not occur at the boundary surface between the core 5 and the cladding 6 no matter what angle the light enters from the air into the core 5. .

This inclination angle α can be obtained from the following equation.

N ₀ sin β = n ₁ sin 90 ° (total reflection condition) (1) n ₀ sin γ = n sin 90 ° (light receiving angle 0 °) (2) α + (90 ° + γ) + (90 ° −β) = 180 ° (3) In this case, from FIG. 4, n ₀ = 1.621, n ₁ = 1.519, n
= 1, so α = 31.54 °. Therefore, when the inclination angle α in FIG.
The light propagating through the air and incident from the input end face 2 does not undergo total reflection at the interface between the core and the clad, regardless of the angle of incidence.

Therefore, the light incident on the FOP from the input end face 2 partially leaks from the core to the clad and is absorbed by the absorber in the process of repeating refraction and propagating, and then gradually attenuates and disappears. In this way, when the inclination angle of the input end face 2 is set to such an angle, the light propagating through the air and entering the FOP 1 from the input end face 2 is hardly output from the output end face 3.

On the other hand, as shown in FIG. 5, when a specific object, for example, the surface of the finger 10 is brought into close contact with the input end face 2 in this state, the close contact with the input end face 2 due to the unevenness of the fingerprint. A non-contact portion 12 that forms a gap between the portion 11 and the input end surface 2 is formed. In the close contact portion 11, the input end surface 2 and the surface of the finger 10 are in close contact with each other, and the refractive index of the finger surface is higher than the refractive index of air. Therefore, the input end face 2
The relationship between the incident angle of the light incident on and the condition for total reflection at the interface with the cladding changes from that before contact,
At the interface with the clad, some light enters at an angle that satisfies the condition of total reflection. For example, it is assumed that light is emitted from behind the finger 10 and the transmitted light reaches point A (FIG. 5). Of the light entering the FOP 1 from point A, as shown in the figure, the light entering in the range of 40.68 ° satisfies the condition of total reflection at the boundary surface between the core 5 and the clad 6 ((2) (From the equation), this incident light is repeatedly totally reflected at the boundary surface with the cladding and is output from the output end face 3 side. Light that has entered beyond this angle range is attenuated and disappears in the process of repeated propagation of refraction.

On the other hand, in the non-contact portion 12, a void portion 13 as shown in the drawing is formed, and air is present in this. That is, there is no difference from the state before the finger 10 is brought into close contact. Therefore, although the light enters the core 5 from the non-adhesive portion 12 of the input end face 2, no matter what angle the light enters, the condition of total reflection at the interface with the cladding is still not satisfied, and the core 5 It decays and disappears as it propagates inside.

Therefore, when detecting the surface image of the object in this way, only the light incident from the convex portion of the object surface that is in close contact with the input end surface 2 is output from the output end surface 3 and enters from the concave portion of the surface. Light is attenuated and disappears in the propagation process.
Therefore, unnecessary light such as background light is removed, and only the image of the portion in close contact with the input end face is transmitted and output.

The example explained above is NA (numerical aperture).
= 0.55, and Table 1 shows the tilt angles α with respect to other major NAs.

[0023]

[Table 1]

Further, the shape of the input end face 2 of the FOP 1 may be set as shown in FIG. The shape in FIG. 7 shows a cross section of the input end face 2 taken along the line 11 ′, and the arrow y in the drawing shows the optical axis of each fiber forming the FOP 1 (FIG. 6). FIG. 7A shows the input end face 2 having a planar shape as shown in FIG.
In (e), the input end surface 2 is concave, and the contact surface with the finger is large. In addition, in FIGS. 7F and 7G, the input end face 2 is formed in a slanted shape so that the image of the portion pressed by the input end face 2 is enlarged and output as compared with FIG. You can

Further, the FOP 40 may be formed as shown in FIG. In FOP40 in FIG. 8, FOP40
A hole is drilled for the through hole 4 diagonally to the body.
1 is formed and the inner surface is polished. When a finger is inserted into the through hole 41 along the arrow c, the finger is fixed in the through hole 41, and fingerprint detection with good reproducibility can be performed. In this case, the arrow d
Light for illumination is emitted from the direction. In the example of FIG. 8, FO
Although the P40 main body is processed and integrally formed, for example, the same applies even if a pressing portion for pressing the inserted finger to the input end face 2 side is provided at a position facing the input end face 2 in FIG. 1 described above. The effect of is obtained.

Here, a specific configuration of an apparatus having such a FOP 1 will be shown. FIG. 9 shows a fingerprint detecting device, which is composed of the above-mentioned FOP 1, CCD 20, computer 21, and the like. The input end face 2 of the FOP 1 is
It is formed so as to be inclined with respect to the optical axis, and this inclination angle is set to be equal to or less than the inclination angle α obtained by the equations (1) to (3) described above. Press your finger 22 against this surface for close contact,
Light is emitted from a light source 23 provided behind or on the side surface side. When they are brought into close contact with each other in this manner, the uneven pattern (fingerprint image) of the close contact portion is transmitted to the output end face 3, this image data is given to the CCD 20, and the signal thereof is subjected to image processing in the computer 21. .

FIG. 10 shows another example of the configuration. In this example, a lens 30 is arranged on the output end face 3 side of the FOP 1, an image output to the output end face 3 via this lens 30 is read by a line sensor 31, and the signal is processed by a computer 32. Has become.

Also in the illustrated apparatus of FIGS. 9 and 10,
The angle of the input end face 2 of the FOP 1 is preferably set to be equal to or less than the inclination angle α such that the light incident from the input end face 2 does not satisfy the condition of total reflection at the interface with the cladding. In this case, since the FOP 1 can be formed thin, the surface image of the object output from the output end face 3 can be reduced, and the CCD 20, the lens 30, the line sensor 31, and the like can be downsized, and the entire device can be downsized. It is possible to proceed.

Further, the FOP may have the shape shown in FIG. The FOP plate 50 is of a type in which the input end face 2 side of the FOP 1 in FIG. 1 is cut in parallel with the input end face 2, and the inclination angle θ between the optical axis of each optical fiber forming the FOP plate 50 and the input end face 52. Satisfies the condition of the inclination angle α shown in FIG. Further, the output end face of the FOP plate 50 is provided with a CCD 53 for detecting an image obtained from the output end face, and the output end face of the FOP plate 50 is fixed to an input face 53a of the CCD 53 to be integrally configured. There is. With this configuration, the fingerprint image can be detected with a compact configuration.

As an example of using the FOP, it is also possible to use two FOPs in cascade connection as shown in FIG. In this case, for FOP1a, F
OP1b is inclined by 90 ° and the input end face of FOP1b is fixed to the output end face of FOP1a. In this case, the tilt angles θ ₁ and θ ₂ of either one of the two FOPs 1a and 1b need only satisfy the condition of the tilt angle α described above. And, for example, F
By fixing the CCD 53 to the output end face of the OP 1b, it is possible to detect the fingerprint image of the finger and the like in the same manner.

In each of the embodiments described above, an example in which a finger is brought into close contact with the input end face such as FOP 1 in order to detect a fingerprint is shown, but the present invention is not limited to this example, and other examples are also possible. , Keep your palms and noses in close contact,
It can be used to detect palm choking, nose choking, etc. Also,
Although the output end face 3 is shown as being tilted perpendicularly to the optical axis, the present invention is not limited to this example, and the output end face 3 may be tilted arbitrarily with respect to the optical axis.

[0032]

According to the fiber optical plate of the present invention, since the light absorber is provided so as to cover the outer peripheral portion of each clad, adjacent optical fibers are optically insulated by this light absorber. It is possible to prevent the light propagating through each core from leaking and entering into another adjacent core. Since this effect is exhibited regardless of the inclination angle of the input end face, the inclination angle (cutting angle) of the input end face is not restricted as in the conventional case. Therefore, the fiber optic plate is made thinner than before,
Even when the inclination angle of the input end face is made acute, the surface image of the object brought into close contact with the input end face can be accurately transmitted to the output end face side.

At this time, the inclination angle of the input end face is set to such an angle that the light incident on the core from the air does not cause total reflection at the interface with the cladding, so that the surface of the object is set to the input end face. When they are brought into close contact with each other, unnecessary light such as background light is not output from the output end face, and it is possible to output an image of only the close contact portion.

[Brief description of drawings]

FIG. 1 is a perspective view showing a fiber optic plate according to an embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of a fiber optic plate.

FIG. 3 is a partial vertical cross-sectional view of a fiber optical plate.

[Fig. 4] Weight percentage of each material composition of core, clad, and absorber
2 is a table showing the refractive indexes of the core and the clad, as shown in FIG.

FIG. 5 is a vertical cross-sectional view of the fiber optic plate showing a partially enlarged state in which a finger surface is brought into close contact with the input end surface of the fiber optic plate.

FIG. 6 is a schematic view showing a side surface of a fiber optical plate.

FIG. 7 shows the fiber optic plate of FIG.
It is a figure which shows the cross section cut | disconnected by the 1'line, and FIGS. (a)-(g) is sectional drawing which illustrates the shape of an input end surface.

FIG. 8 is a schematic configuration diagram showing a fingerprint detection device provided with a fiber optical plate.

FIG. 9 is a diagram schematically showing another device configuration including a fiber optical plate.

FIG. 10 is a schematic view showing a side surface of a fiber optical plate.

FIG. 11 is a diagram schematically showing another device configuration including a fiber optic plate.

FIG. 12 is a diagram schematically showing another device configuration including a fiber optical plate.

FIG. 13 is a perspective view showing a conventional fiber optic plate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fiber optical plate, 2 ... Input end surface, 3 ... Output end surface, 5 ... Core, 6 ... Clad, 7 ... Absorber (light absorber).

Claims (1)

[Claims] 1. A fiber optic plate integrally formed with a plurality of optical fibers bundled together, wherein the fiber optic plate comprises a plurality of cores for propagating incident light and an outer peripheral portion of each core. A cladding to cover
A light absorber that is provided so as to cover the outer peripheral portion of each of the clads and that absorbs the light leaked from the core and the light that is incident on the clad is provided. It is a surface to be brought into contact with, and has an input end face that is inclined with respect to the optical axis of the optical fiber. A fiber optic plate that is angled to prevent total internal reflection on the surface.