JPH10208022A - Fiber optical plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fiber optical plate which outputs a bright rugged image, is easily attached to a photodetector and is compact even after it is attached. SOLUTION: In this fiber optical plate, recessed parts 20 are provided on ends which are located on the side of input end planes 2 of the fiber optical plate between both ends of unit fibers 6, and light is made incident through the side planes 22 of the parts 20. Because the planes 22 are inclined at angles that can eliminate diffused external light in the air, this fiber optical plate outputs a rugged image that has high contrast. Because the fiber optical plate has an output edge plane 4 that is perpendicular to an axis line 14 of the unit fibers, a bright rugged image is acquired when the plane 4 is matched to an input plane of the photodetector and fixed. Also, it has a shape that perpendicularly extends from the plane 4, it is easily attached to a photodetector and is compact after the attachment.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fiber optical plate used as an optical image transmitting means in a fingerprint detecting device or the like.

[0002]

2. Description of the Related Art FIG. 11A is a side view showing a conventional fiber optical plate (hereinafter referred to as "FOP") 50, and FIG. 11B is a partially enlarged sectional view showing the structure of the FOP 50. It is. The FOP 50 is usually used as a concave / convex image transmission unit of a concave / convex image detecting device (for example, a fingerprint detecting device).

[0003] As shown in FIG.
Numeral 0 has a structure in which a plurality of optical fibers 56 are bundled so that their axes are substantially parallel to each other and are integrally assembled. When this optical fiber is referred to as a unit fiber, each unit fiber is aligned such that both end faces thereof are substantially one plane. Input end face 52
The output end surface 54 is a surface for inputting and outputting an optical image. These end faces are mutually parallel faces formed by assembling both end faces of each unit fiber. The input end face 52 and the output end face 54 are inclined at an angle α with respect to the axial direction of the unit fiber. When this FOP 50 is used in the uneven image detection device, a subject such as a finger is placed on the input end face 52.

[0004] As shown in FIG. 11 (b), the unit fiber 56 has a core 60, which is a light propagation region, at the center.
1 and a light absorber 62 closely surrounding the clad 61. Both end faces of each unit fiber are inclined at an angle α with respect to the axis 64 of the unit fiber. In other words, both end faces of each unit fiber are inclined so that the angle between the normal to both end faces of each unit fiber and the axis 64 is (90 ° −α). This inclination angle (slant angle) α
The angle is set so that even when light enters the core 60 from the air, the incident light is not totally reflected at the boundary surface between the core 60 and the clad 61. In other words, the slant angle α
Is set so that the angle of incidence of light incident on the core 60 from the air with respect to the interface between the core and the clad is less than or equal to the critical angle at this interface.

As is well known, such a range of the slant angle α can be expressed as α ≦ α _C using a specific angle α _C. Here, α _C is an angle that satisfies the following three equations. n ₀ · sin θ _C = n ₁ · sin 90 ° (condition of total reflection between core and clad) n ₀ · sin β = n _a · sin 90 ° (law of refraction between air and core) α + (90 ° + β) + ( in _{90 ° -θ C) = 180 °} ( triangles of the sum of the interior angles) where, n ₀ is the refractive index, n ₁ of the core 60 is the refractive index of the cladding 61, the n _a is the refractive index of air. Further, θ _C is a critical angle at a boundary surface between the core and the clad, and β is light incident on the input end face 52 at an incident angle of 90 ° (FIG. 11).
(B) indicates the angle formed by the normal to the input end face 52, that is, the refraction angle of the light incident at an incident angle of 90 °.

Considering α _C obtained from the above three equations,
It said slant angle range of the alpha ^{_{is, α ≦ α C = sin -1}} (n 1 / n 0) -sin -1 (n a / n 0) ... represented as (1).

When the subject is illuminated with illumination light while the subject is placed on the input end face 52, the unevenness of the subject surface is transferred to the core 60 of the unit fiber through the convex part which comes into contact with the input end face 52. The incident light propagates through the core 60 and is emitted from the emission end face 54 while being totally reflected at the boundary surface between the core and the clad. On the other hand, the light incident on the core 60 through the concave portion on the surface of the subject passes through the air layer existing between the surface of the subject and the input end face 52, and then enters the core 60.
Since the input end face 52 of the P50 is inclined at the slant angle in the above angle range, this incident light is not totally reflected at the interface between the core and the clad, and a part of the incident light leaks to the clad 61. . Every time the incident light from the concave portion of the subject reaches the interface between the core and the clad, a part of the light leaks into the clad, and the light leaked into the clad 61 is absorbed by the light absorber 62. Gradually attenuates and cannot reach the output end face 4. Therefore, the output end face 54
Substantially emits only light that has entered through the projections on the surface of the object, and as a result, a bright and dark image with high contrast corresponding to the unevenness on the surface of the object can be obtained.

As described above, the bright and dark images (irregular images) corresponding to the irregularities on the surface of the object are transmitted by the FOP 50,
The light exits from the output end face 54. Therefore, as shown in FIG.
The output end face 54 of the FOP 50 is connected to a photodetector (C in FIG. 12).
If the FOP 50 is attached to the photodetector in a state where the FOP 50 is in contact with the input surface of the CD detector 70 (in FIG. 12, the input surface 74 of the CCD chip 72), it is possible to detect the uneven image on the surface of the subject.

[0009]

In the conventional FOP 50, since the output end face 54 is inclined with respect to the axis 64 of the unit fiber, the medium outside the output end face 54 has a lower refractive index than the core 60 like air. If the medium has a high efficiency, total reflection may occur between the medium and the core 60, and even light incident from the convex portion of the subject may not be emitted from the output end face 54 in some cases. Therefore, in the conventional FOP50,
In many cases, a sufficiently bright concavo-convex image is obtained only when a matching liquid or an adhesive having a refractive index matching is filled between the output end face 54 and the input face 74 of the CCD detector 70.

Further, since the uneven image of the object is emitted substantially along the axis 64 of the unit fiber, the conventional FOP5
At 0, the uneven image does not exit perpendicular to the output end face 54, so that the uneven image of the subject does not enter the input surface 74 of the CCD detector 70 perpendicularly, and is therefore detected by the CCD detector 70. The resulting uneven image is dark overall.

The input end face 5 set as described above
The slant angle of 2 is typically quite small, so F.sub.1 along the plane containing each axis 64 of each unit fiber.
The cross-sectional shape of OP50 is a parallelogram having a steep inclination as shown in the figure. As a result, the width of the conventional FOP 50 tends to be large, so that the input recess 76 of the CCD detector 70 is not provided.
There is a problem that it is difficult to attach to the device.
Further, even after mounting on the CCD detector 70, the FOP50
Of the FOP, the tip of the FOP protrudes to the side of the CCD detector 70, and so on.
It is easy to increase the size of the composite device including the D detector.

The present invention has been made in view of the above,
It is an object of the present invention to provide a fiber optic plate that outputs a bright uneven image, is easy to attach to a photodetector, and is compact even after attaching.

[0013]

The invention according to the present application comprises a plurality of unit fibers assembled with their respective axes substantially parallel to each other, and both end faces of each of these unit fibers are assembled. A fiber optical plate having an input end face and an output end face, wherein each of the unit fibers includes a core which is a light propagation region having a predetermined refractive index. At the end on the side of the end surface, there are provided depressions having side surfaces inclined with respect to the axis of the unit fiber, and the inclination angle of the side surface of each depression is such that the light incident on the unit fiber from the air through the side surface into the air. Is the angle that prevents propagation in the unit fiber of
The output end surface is a fiber optical plate that is a surface orthogonal to the axis of each unit fiber.

As described above, by providing the recess having the side surface inclined at the above angle at the input end face of the both ends of the core of the unit fiber, the propagation of the disturbance light from the air in the unit fiber is provided. Is prevented, the fiber optical plate according to the present application can output a concavo-convex image with high contrast as before. In addition, since the fiber optical plate according to the present application has an output end face perpendicular to the axis of the unit fiber, the emission direction of the concavo-convex image of the subject becomes substantially the normal direction of the output end face, and An uneven image can be output without interposing a matching liquid or the like between the input surface of the photodetector and the fiber optical plate. Further, since the emission direction of the uneven image is the normal direction of the output end face, when the output end face of the fiber optical plate is fixed against the input face of the photodetector, the output end face of the optical fiber plate with respect to the input face of the photodetector is The uneven image is incident substantially vertically, and as a result, a bright uneven image can be obtained. Furthermore, since this fiber optical plate has a shape extending in the vertical direction from the output end face, it can be attached to the photodetector relatively easily and with high precision as compared with the conventional fiber optical plate. , Compact after installation.

In the fiber optical plate of the present invention, each unit fiber closely surrounds the core, and has a clad having a lower refractive index than the core, and closely surrounds the clad.
And a light absorber that absorbs light leaked from the core, and the inclination angle of the side surface of the dent provided at the end of each core is incident on the unit fiber from the air through this side surface. The angle may be such that total reflection of the light in the unit fiber is blocked.

In this case, the disturbance light entering the core from the air through the side surface of the depression enters the interface between the core and the clad at an incident angle smaller than the critical angle and is not totally reflected. Part leaks into the cladding. This leaked light
Since the light is absorbed and removed by the light absorber, the disturbance light from the air gradually attenuates and cannot be propagated to the output end face. Since the disturbance light from the air is removed in this way, an uneven image with high contrast is output from the output end face.

In the fiber optical plate of the present invention, each unit fiber may further include a light absorber that closely surrounds the core and absorbs light from the core, and is provided at an end of each core. The angle of inclination of the side surface of the hollow may be an angle at which light incident on the unit fiber from the air through the side surface in a direction deviated from the axis direction of the position fiber.

Since this unit fiber has no cladding, only light traveling in the axial direction of the unit fiber can propagate in the core, and light traveling in other directions is absorbed by the light absorber. Removed. Since the side surface of each depression has the above-mentioned inclination angle, disturbance light from the air travels in a direction deviated from the axial direction of the unit fiber, and as a result, is absorbed and removed by the light absorber,
It cannot propagate in the unit fiber. Since the disturbance light from the air is removed in this way, an uneven image with high contrast is output from the output end face.

Next, in the fiber optical plate according to the present invention, a predetermined light shielding member may be attached to the bottom of the depression. Accordingly, even when the bottom of the depression is rounded and the effect of removing disturbance light due to the inclination angle of the side surface of the depression is not sufficiently obtained, disturbance light from the air is transmitted to the core through the bottom of the depression. Is prevented from being incident on the image, so that an uneven image with high contrast is output.

[0020]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description. Also, the dimensional ratios in the drawings do not always match those described.

(First Embodiment) FIG. 1 is a schematic perspective view showing a fiber optical plate (hereinafter referred to as "FOP") 1 according to a first embodiment. Like the conventional FOP, the FOP 1 of the present embodiment also includes a plurality of unit fibers 6.
Has an input end face 2 and an output end face 4 which are formed by bundling and assembling such that their respective axes are substantially parallel to each other. I have. For simplicity of the drawing, only one of the two side surfaces shown in FIG. 1 shows the unit fiber 6, and the other side surface is omitted. Also, at the input end face 2, only a part of the unit fiber 6 is used.
Are shown, and other portions are omitted.

FIG. 2 is an enlarged plan view partially showing the input end face 2 of the FOP 1, and FIG. 3 is a sectional view taken along line II-II of FIG. As shown in these figures, the unit fiber 6
Has a core 10 which is a light propagation region having a predetermined refractive index at the center, and further has a clad 11 having a lower refractive index than the core 10 and tightly surrounding the core 10, and a clad 11. It has a light absorber 12 that is tightly enclosed. When the FOP 1 of the present embodiment is used in a concavo-convex image detecting device, the light absorber 12 is usually made of a material capable of absorbing illumination light applied to the subject.

Hereinafter, of the two end faces of the unit fiber 6, the end face located on the input end face 2 side of the FOP 1 is called the input end face of the unit fiber 6, and the end face located on the output end face 4 side is the output end face of the unit fiber 6. Call. In accordance with this designation, the end faces of the core 10, the clad 11, and the light absorber 12 located on the input end face 2 side are called these input end faces, and the end faces located on the output end face 4 side are called these output end faces. .

As shown in FIGS. 2 and 3, the end of each unit fiber 6 located on the input end face 2 side of the core 10 has a conical shape in which the deepest part is located on the axis 14 of the unit fiber 6. A depression 20 is provided. Therefore, the input end face 22 of the core 10 is the side face of the depression 20 (conical side face). On the other hand, the output end face of the core 10 of each unit fiber 6 is perpendicular to the axis 14 similarly to the input end face and the output end face of the clad 11 and the light absorber 12.

As shown, the input end face 2 of each core 10
2, that is, the side surface of the depression 20 is inclined at a predetermined acute angle α with respect to the axis 14. In other words, the normal passing through any point on the input end face 22 of the core 10 and the axis 14 always intersect at an acute angle (90 ° -α). As with the conventional FOP, this inclination angle (slant angle) α
The angle is set so that even if light enters the core 10 from the air through the interface 2, total reflection of the incident light on the boundary surface between the core 10 and the clad 11 is prevented. As described in the “Prior Art” section, the range of the slant angle α is such that the angle of incidence of light incident on the core 10 from the air with respect to the interface between the core and the clad is equal to or less than the critical angle at this interface. It can be said that such a range.

The range of the slant angle is represented by the following inequality. The ^{_{α ≦ α C = sin -1 (}} n 1 / n 0) -sin -1 (n a / n 0) ... (1) Hereinafter, this alpha _C, referred to as the critical slant angle.

FIGS. 4 (a) and 4 (b) show the F of this embodiment.
It is a diagram and graphs for explaining the relationship between the critical slant angle alpha _C refractive index and the core 10 for OP1.
In FIG. 4A, α is the slant angle of the input end face 22 of the core 10, and β is the light incident on the core 10 at an incident angle of 90 ° (FIG.
The angle of refraction θ _C is the core 10 and clad 1
A critical angle at the boundary surface between the 1, n ₀ is the refractive index, n ₁ of the core 10 is the refractive index of the cladding 11, the n _a is the refractive index of air. FIG. 4A shows a case where the slant angle α is equal to the critical slant angle α _C.

In the following, the refractive index n _{1 of the} clad is set to 1.
It is fixed at 52. As shown in FIG.
When the refractive index n ₀ of the core 10 is 1.56, the above (1)
Based on the equation, the critical slant angle α _C is 37.1 °. Therefore, the slant angle α of the end face of the core 10 is 37.1.
If it is less than or equal to °, the light incident on the core 10 from the air does not satisfy the condition of total reflection, leaks to the cladding 11, is absorbed by the light absorber 12, and is removed.

An object (such as a finger) is input to the input end face 2 of the FOP 1
Considering the case where illumination light is irradiated by a known method in a state where the core is pressed against the input end face 2 of the core 10.
2 does not come into contact with the core 10
Since air intervenes between the input end face 22 and the input end face 22, the light incident through the concave portion of the subject is removed. On the other hand, of the light incident on the core 10 through the convex portion of the subject that is in close contact with the input end face 22 of the core 10, the core 10
The light whose incident angle to the cladding 11 is larger than the critical angle θ _C shown in FIG. 4A repeats total reflection at the interface between the core and the cladding, and proceeds toward the output end face of the core 10. Then, the light exits from the output end face of the core 10. As described above, similarly to the conventional FOP, only the light incident through the convex portion of the subject is substantially propagated to the output end face 4, so that a high-contrast uneven image is emitted from the output end face 4.

Next, referring to FIG.
The attachment to the CD detector 70 will be described. Here, FIG.
3 is a schematic side view showing the FOP1 attached to the CCD detector 70. FIG. As shown in this figure, FOP1
Is fixed by bonding the output end face 4 to the input face 74 of the CCD chip 72 provided in the concave portion 76 of the CCD detector 70. When the subject is placed on the input end face 2 and then irradiated with illumination light, an uneven image of the subject exits from the output end face 4 and enters the CCD chip 72 via the input face 74.
Thus, the uneven image of the subject is converted into an electric signal and output. If a signal processing device and a display device are sequentially connected to the CCD detector 70, an uneven image of the subject can be displayed on the screen of the display device.

As described above, in the present embodiment, by providing the recess 20 at the end of the core 10 of each unit fiber 6 on the input end face 2 side, the light passing through the surface of the subject can be transmitted from the air. Depression inclined at slant angle that can remove disturbance light 2
0 and the output end face 4 perpendicular to the axis 14 of the unit fiber 6 is FOP
Is possible to have. Therefore, the FOP 1 of the present embodiment can output a concavo-convex image with high contrast as before, but unlike the conventional FOP, the emission direction of the concavo-convex image of the subject is substantially the same as the normal direction of the output end face 4. Therefore, an uneven image is emitted from the FOP 1 without interposing a matching liquid or the like between the FOP 1 and the input surface of the photodetector. Further, since the emission direction of the uneven image is the normal direction of the output end face 4, when the FOP 1 is fixed to the CCD chip 72 as shown in FIG. Since an uneven image is incident, a bright uneven image can be obtained. Further, since the FOP 1 has a substantially rectangular parallelepiped shape extending vertically from the output end face 4,
The attachment of the CCD detector 70 to the concave portion 76 can be performed relatively easily and with high accuracy as compared with the conventional FOP.

(Second Embodiment) In the first embodiment, an optical fiber comprising a core 10, a clad 11, and a light absorber 12 is used as the unit fiber 6, but instead,
A unit fiber (NA = 0) composed of the core 10 and the light absorber 12 and having no cladding can also be used.
FIG. 6 is an enlarged plan view partially showing the input end face of the FOP according to the present embodiment composed of such unit fibers, and FIG. 7 is a sectional view taken along line VI-VI of FIG. In the following, components similar to FOP1 of the first embodiment are denoted by the same reference numerals as FOP1 except that a suffix a is added.

As shown in FIGS. 6 and 7, the unit fiber 6a in the present embodiment has a core 10a which is a light propagation region having a predetermined refractive index at the center. It has a light absorber 12a that is tightly enclosed. As in the first embodiment, the FOP of this embodiment
When 1a is used in the uneven image detecting device, the light absorber 12a
Is usually made of a material capable of absorbing illumination light applied to the subject.

As in the first embodiment, each unit fiber 6
a at the end of the core 10a on the input end face 2a side,
A conical depression 20a whose deepest portion is located on the axis 14a of the unit fiber 6a is provided, and the output end face of the core 10a of each unit fiber 6a is perpendicular to the axis 14a.

Also in this embodiment, the input end face 22a of each core 10a, that is, the side face of the depression 20a is
is inclined at a predetermined slant angle α with respect to a, and this slant angle α is set to an angle range equal to or less than a predetermined critical slant angle α _C.

FIGS. 8A and 8B are diagrams and graphs showing the relationship between the refractive index of the core 10a and the critical slant angle α _C for the FOP 1a of the present embodiment composed of the unit fiber 6a without cladding. It is. In FIG. 8A,
α is the slant angle of the input end face of the unit fiber 6a without cladding, β is the refraction angle of light (arrow in FIG. 8A) incident on the core 10a at an incident angle of 90 °, and n ₀ is the refractive index of the core 10a. , n _a is the refractive index of air. FIG. 8 (a)
Shows a case where the slant angle α is equal to the critical slant angle α _C.

It should be noted that the critical slant angle for the unit fiber having no cladding is slightly different from the critical slant angle for the unit fiber having the cladding. That is, the critical slant angle of the unit fiber without cladding is an angle at which light incident on the core at an incident angle of 90 ° with respect to the input end face travels in the axial direction of the unit fiber.
As is clear from FIG. 8A, this critical slant angle α
_{C is, α C = 90 ° -β =} 90 ° -sin -1 (n a / n 0) ... (2) can be expressed as in the. When the slant angle α is equal to the critical slant angle α _C , the refraction angle β is given by β _C (= 90 ° −
α _C ), the core 1 is removed from the air at an incident angle of less than 90 °.
The refraction angle of the light incident on 0 is less than β _C. Therefore, such incident light travels in a direction deviated from the axial direction of the unit fiber, travels to the boundary surface between the core 10a and the light absorber 12a, and is absorbed and removed by the light absorber 12a. When the slant angle α is smaller than the critical slant angle α _C , the refraction angle of all light incident within an incident angle of 90 ° becomes less than β _C, and all the incident light from the air is absorbed by the light absorber. Absorbed and removed by 12a. As a result, if the slant angle α is equal to or smaller than the critical slant angle α _C , the propagation of the incident light from the air in the unit fiber 6a can be substantially prevented.

As shown in FIG. 8B, the core 10a
For the refractive index n ₀ is 1.92, the critical slant angle alpha _C 5
8.6 °. Therefore, the cladding-free unit fiber 6
If the slant angle α of the input end surface 22a of a is equal to or less than 58.6 °, disturbance light incident on the core 10a from the air is absorbed by the light absorber 12a and removed.

When illumination light is irradiated by a well-known method in a state where a subject (such as a finger) is pressed against the input end face 2a of the FOP 1a, the concave portion of the subject does not contact the input end face 22a of the core 10a. Air is interposed between the input end face 22 of the core 10a and the light incident through the concave portion of the subject is removed. On the other hand, of the light incident on the core 10a through the convex portion of the subject that is in close contact with the input end face 22a of the core 10a, the light traveling in the direction parallel to the axis 14a of the unit fiber 6a is the output end face 4a.
, And exits from the output end face 4a. Therefore, similarly to the FOP1 of the first embodiment, the FOP1a of the present embodiment composed of the unit fiber 6a without the cladding also transmits substantially only the light incident through the convex portion of the subject to the output end face. Thus, an uneven image having high contrast can be output from the output end face. Further, as is apparent from a comparison between FIG. 8B and FIG.
In OP1a, the slant angle of the input end face of the unit fiber can be set to be larger than the slant angle of FOP1 of the first embodiment, so that the contact area between the convex portion of the subject and the input end face of the core can be increased. As a result, a clearer uneven image can be output.

Next, the FOP of the first and second embodiments will be described.
A method of manufacturing the first and first embodiments will be described. In these FOPs, a columnar FOP (both the input end face and the output end face are perpendicular to the axis of the unit fiber) is prepared as a matrix, and the flat input face of the core of the unit fiber constituting the matrix FOP is processed. To form the above-mentioned depressions 20 and 20a.

The depressions 20 and 20a can be formed by, for example, etching using an acid such as hydrochloric acid or nitric acid as an etchant. In this case, when fabricating the matrix FOP, the composition of the core of the unit fiber is set so that the etching rate of the core with respect to the acid monotonously changes depending on the radial distance r from the center of the core. Specifically, the composition of the core is adjusted so that the etching rate of the core decreases as the radial distance r increases. As a result, the core of the unit fiber of the parent FOP is
It has a concentric cylindrical composition distribution centered on the axis of the unit fiber.

Hereinafter, an example of the composition of the core of the unit fiber of the parent FOP will be described. In this composition example, the core of the unit fiber is composed of SiO ₂ , B ₂ O ₃ , BaO, La ₂ O ₃ and P _2.
It is composed of bO. Table 1 below shows the composition at the center (A) of the core and the side (B) of the core of the unit fiber, respectively.

[0043]

[Table 1]

In Table 1, the proportion of each composition is as follows:
Expressed as a weight percent concentration (wt%).

FIG. 9 is a diagram showing the concentration distribution of BaO and La ₂ O ₃ contained in the core of the unit fiber. In this figure, r ₀ indicates the radius of the core.
As shown in this figure, the BaO concentration decreases monotonically from 55 to 50 from the center (A) of the core toward the side surface (B), and conversely, the concentration of La ₂ O ₃ decreases in the center (A) of the core. ) Monotonically increases from 10 to 15 from the side (B). Since BaO has a higher etching rate for hydrochloric acid and nitric acid than La ₂ O ₃ , Table 1 and FIG.
Has a structure in which the farther away from the center, the lower the etching rate of the core with respect to the acid.

When fabricating the FOP according to the above embodiment, a unit fiber preform having such a core (when fabricating the FOP of the first embodiment, a structure in which the core is surrounded by a clad and a light absorber) In the case of fabricating the fiber preform of the second embodiment and the FOP of the second embodiment, after preparing the above-mentioned fiber preform having a structure in which the core is surrounded by a light absorber, this is drawn until a desired fiber size is obtained. . As a material for the clad, soda-lime glass or borosilicate glass is used, and as a material for the light absorber, a glass obtained by adding an oxide such as Fe, Ni, Co, Cr, or Mn to such a glass is used. use.

Next, the long fiber obtained by the drawing is cut into a predetermined length to obtain a plurality of unit fibers having a uniform length. These unit fibers are placed in a mold, aligned, and heated and fused to form a fiber block. Then
After cutting this fiber block body to a certain thickness,
By polishing both end faces, a matrix FOP having an input end face and an output end face perpendicular to the axis of the unit fiber is produced. The above process is a well-known process for manufacturing an FOP.

The end face to be etched of the both end faces of the base FOP thus obtained (the face to be the input end face)
With regard to (2), the portion excluding the end face of the core of the unit fiber is masked using an acid-resistant masking agent. In addition, mother body F
The other end face of the OP is entirely masked using a masking agent. Thereafter, the base FOP is immersed in an acid solution to perform etching. As described above, the composition of the core of the unit fiber has a higher etching rate toward the center and a lower etching rate toward the side, so that one end of the core of the unit fiber is formed by this etching.
A conical depression coaxial with the axis of the unit fiber will be formed. After the etching is completed, the FOP is washed with water and then the mask layer is removed. As described above, the FOP of the above embodiment can be manufactured.

In this manufacturing method, the slant angle α of the slope of the depression formed at the end of the unit fiber is affected by (1) the combination of the core composition and (2) the etching conditions. In particular, (2) the etching conditions are related to the type, concentration and temperature of the acid, the immersion time, and the use conditions of the ultrasonic waves (ultrasonic intensity and ultrasonic irradiation time). The ultrasonic wave is irradiated into the etchant in which the base FOP is immersed during the etching, and promotes uniform etching by diffusing the etchant. As described above, in order to form a depression having a slope with a desired slant angle, it is necessary to adjust the above conditions.

(Third Embodiment) FIG. 10 is a partial sectional view showing the structure of an FOP according to a third embodiment, and is similar to FIGS. 3 and 7. The FOP of the present embodiment is obtained by applying a black resin 30 to the bottom of the depression 20 of the unit fiber 6 in the FOP 1 of the first embodiment. this is,
This is an effective process when the bottom of the depression 20 is round. In other words, if the bottom of the depression 20 is rounded, the effect of removing the disturbance light due to the slant angle α (≦ α _C ) described above cannot be sufficiently obtained in this rounded portion, and the core 10 cannot be removed from the air.
May be able to propagate through the core 10. In the present embodiment, in view of this, the black resin 30 which is a light-absorbing type light shielding member is applied to the rounded bottom of the recess 20 to prevent the incidence of disturbance light from the air, A high-contrast uneven image can be output.

The attachment of the light shielding member to the bottom of the depression as in the present embodiment is similarly effective in the FOP 1a of the second embodiment.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the shape of the recess provided at the end of the core of the unit fiber is not limited to the shape having a single surface inclined at a predetermined angle as the side surface, such as the conical shape of the embodiment, and is inclined at the above angle A shape having a plurality of side surfaces (for example, a polygonal pyramid such as a triangular pyramid) may be used.

[0053]

As described in detail above, according to the present invention, the fiber optics is provided by providing, at the end of the core of the unit fiber, a depression having a side surface inclined at an angle capable of removing disturbance light from the air. The plate enables the output of a concavo-convex image with high contrast as before, and also allows the fiber optic plate to have an output end face perpendicular to the axis of the unit fiber. For this reason, the fiber optical plate according to the present application can emit a concavo-convex image without interposing a matching liquid or the like between the input surface of the photodetector and the output end face of the input surface of the photodetector. A bright uneven image can be obtained when fixed against the surface. Further, since the fiber optical plate according to the present application has a shape extending in the vertical direction from the output end face, it is relatively easy and highly accurate to attach to the photodetector as compared with the conventional fiber optical plate. And compact after installation.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view showing an FOP 1 according to a first embodiment.

FIG. 2 is an enlarged plan view partially showing an input end face 2 of the FOP1.

FIG. 3 is a partial sectional view taken along line II-II of FIG. 2;

FIG. 4 is a diagram and a graph for explaining a relationship between a core refractive index and a critical slant angle α _C when a unit fiber has a cladding.

FIG. 5 is a schematic side view showing the FOP1 attached to the CCD detector 70.

FIG. 6 shows a second structure composed of unit fibers without cladding.
FIG. 10 is an enlarged plan view partially showing an input end face 2a of the FOP 1a according to the embodiment.

FIG. 7 is a sectional view taken along line VI-VI of FIG. 6;

FIG. 8 is a diagram and a graph for explaining the relationship between the refractive index of the core and the critical slant angle α _C when the unit fiber has no cladding.

FIG. 9 is a view showing a concentration distribution of a core composition.

FIG. 10 is a partial sectional view showing a structure of an FOP according to a third embodiment.

11A is a side view showing a conventional FOP 50, and FIG. 11B is a partially enlarged sectional view showing a structure of the FOP 50.

FIG. 12 is a side view showing the FOP 50 attached to the CCD chip 72 of the CCD detector 70.

[Explanation of symbols]

1. Fiber optic plate (FOP) 2: Input end face
4 ... output end face, 6 ... unit fiber, 10 ... core, 11 ...
Cladding, 12: light absorber, 14: axis of unit fiber, 20: depression, 22: input end face of core 10.

Claims (4)

[Claims] 1. An input end face and an output end face each comprising a plurality of unit fibers assembled in a state in which respective axes are substantially parallel to each other, and both end faces of each of these unit fibers are assembled. Wherein each of the unit fibers includes a core which is a light propagation region having a predetermined refractive index, and an end of the core on both sides of the input end face side, A depression having a side surface inclined with respect to the axis of the unit fiber is provided, and the inclination angle of the side surface of each depression is the unit fiber of light incident on the unit fiber from air through the side surface. A fiber optical plate, wherein the output end face is a plane orthogonal to the axis of each unit fiber. 2. The unit fiber, wherein the unit fiber closely surrounds the core and has a lower refractive index than the core, and a light absorber which closely surrounds the clad and absorbs light leaked from the core. The angle of inclination of the side surface of each of the depressions is an angle that prevents total reflection in the unit fiber of light incident on the unit fiber from the air from the air through the side surface. A fiber optic plate as described. 3. The unit fiber further includes a light absorber that tightly surrounds the core and absorbs light from the core, and a tilt angle of a side surface of each of the depressions is set through the side surface. The fiber optical plate according to claim 1, wherein the angle is such that light incident on the unit fiber from the air travels in a direction deviated from an axial direction of the unit fiber. 4. The fiber optic plate according to claim 1, wherein a predetermined light shielding member is attached to a bottom of the depression.