JP2009265310A - Optical fiber module - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber module obtained by melt-connecting an optical fiber bundle composed of three thin fibers to a large-diameter fiber, in which optical loss in a melting part is suppressed. <P>SOLUTION: The optical fiber module 1 is constituted by melt-connecting the optical fiber bundle 10 where three thin-diameter optical fibers 11 are bundled in a triangular shape, to the large-diameter optical fiber 20. The optical fiber module 1 satisfies the following inequalities: R1>(r2/cos30°)+r1 and 47.2<3r2<SP>2</SP>/R2<SP>2</SP><61.8, wherein r1 denotes the core radius of the thin-diameter optical fiber at the melting part 25, r2 denotes the clad radius thereof, R1 denotes the core radius of the large-diameter fiber, R2 denotes the clad radius thereof. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber module in which a plurality of small-diameter optical fibers and a single large-diameter optical fiber are fusion-spliced, and in particular, three small-diameter optical fibers and a single large-diameter optical fiber. The present invention relates to an optical fiber module in which and are fused.

  Conventionally, an optical fiber module in which a plurality of small-diameter optical fibers and a single large-diameter optical fiber are fused and connected includes an optical fiber amplifier, a coupler (multiplexer), a splitter (demultiplexer), and a clad amplification laser. Is used in a wide range of optical applications including Among them, the optical coupler is a technology that contributes to high output of light, and by combining a plurality of laser lights through a fiber, a high output laser light source can be easily obtained, so that laser processing, laser heating, Used in laser exposure devices and the like.

  Also, in recent years, in industrial equipment such as exposure devices, higher output of laser light sources has been demanded, and when the output of a single semiconductor laser is insufficient, light emitted from multiple laser elements is combined. High output light. In this case, high output light can be obtained by coupling a laser element to each end of a plurality of fibers and converging the multiple ends into a narrow area.

  However, if only a plurality of optical fibers are bundled to increase the brightness, there are a plurality of cores, so that uneven exposure may occur in the irradiation area, resulting in non-uniform area illumination. In addition, when picking up one of these fibers, the optical density of each fiber core is large, and when light with a wavelength near the ultraviolet is guided, organic matter etc. is collected on the light emitting end face. However, it is known that there are problems such as cloudiness.

  In order to solve these problems, an optical fiber module in which an optical fiber bundle composed of a plurality of optical fibers and a single fiber having a large diameter are fusion-connected may be used. An optical fiber bundle in which adjacent fiber strands are melt-adhered in advance in the vicinity of the emission end is also known.

Thus, when creating an optical fiber module by fusing an optical fiber bundle formed by bundling a plurality of small-diameter optical fibers and a single large-diameter optical fiber, the cladding diameter of the large-diameter optical fiber, In many cases, fusion splicing is performed so that the circumscribed circle of the fiber bundle has substantially the same diameter (see Patent Document 1). For example, as shown in FIG. 10, when an optical fire bar bundle 91 in which three small-diameter optical fibers 90 are bundled and a single large-diameter optical fiber 92 are fused and connected, the optical fiber is used in the fused portion. In many cases, the thickness of each optical fiber is set so that the circumscribed circle of the bundle 91 and the outer diameter of the large-diameter optical fiber 92 are substantially the same.
Special table 2002-506225 gazette

  The present inventor measured the light transmittance at the fused portion using the optical fiber module as shown in FIG. From this measurement, it was found that in such an optical fiber module, the loss of light at the fused portion is large and the transmittance is considerably low.

  From this, it is conceivable that the diameter of the thin optical fiber is too large compared to the diameter of the thick optical fiber, but in order to suppress the loss of light at the fused portion, It is unclear how much the diameter of the thin optical fiber should be made smaller than the diameter, and there is a problem of affecting the reliability of the optical fiber module of this form.

    The present invention has been made in view of the above circumstances, and in an optical fiber module in which an optical fiber bundle composed of three small-diameter fibers and a large-diameter fiber are fusion-bonded, light loss at the fusion portion is reduced. An object of the present invention is to provide an optical fiber module that can be suppressed.

The optical fiber module of the present invention is an optical fiber module in which an optical fiber bundle in which three small-diameter optical fibers are bundled in a triangular shape and one large-diameter optical fiber are fusion-bonded.
The core radius of the small-diameter optical fiber at the fused portion is r1, the cladding radius is r2, the core radius of the large-diameter fiber is R1, and the cladding radius is R2.
R1> (r2 / cos30 °) + r1
And 47.2 <3r2 ² / R2 ² <61.8
It is characterized by being.

  Moreover, if the said thin diameter optical fiber is a taper type fiber, it is preferable that a taper rate is 85% or more. Here, the taper rate is defined by a ratio obtained by dividing the outermost fiber diameter of the tapered portion of the thin fiber by the initial fiber outer diameter which is not tapered.

In the optical fiber module of the present invention, in the optical fiber module in which an optical fiber bundle in which three small-diameter optical fibers are bundled in a triangular shape and one large-diameter optical fiber are fusion-bonded, The core radius of the small-diameter optical fiber is r1 and the cladding radius is r2, and the core radius of the large-diameter fiber is R1 and the cladding radius is R2.
R1> (r2 / cos30 °) + r1
Therefore, the core portion of the small-diameter fiber can be fused to the core portion of the large-diameter fiber, and 47.2 <3r2 ² / R2 ² <61.8
Therefore, the optical loss at the fused part is suppressed.

  Further, by tapering the tip of the small-diameter optical fiber, it is possible to easily adjust so as to satisfy the above relationship, and in order to satisfy the above relationship, the fiber is manufactured from 1 (drawing production from a preform). If the degree of freedom of the diameter of the small-diameter fiber used is improved and the taper rate is 85% or more, the loss in the tapered portion can be suppressed.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical fiber module 1 according to the first embodiment. As shown in FIG. 1, an optical fiber module 1 includes an optical fiber bundle 10 in which three small-diameter optical fibers 11 are bundled in a triangular shape and a single optical fiber 20 which are fusion-bonded at a fusion portion 25. Yes. FIG. 2 is a schematic diagram of the fusion part 25. As shown in FIG. 2, the small-diameter fiber 11 includes a core 12 and a cladding 13. The radius of the core 12 is r1, and the radius of the cladding 13 is r2. The optical fiber 20 is composed of a core 21 and a clad 22, and the radius of the core 21 is R1 and the radius of the clad 22 is R2.

  By the way, as described above, the inventor of the present invention has a considerable loss of light at the fused portion in an optical fiber module in which an optical fiber bundle composed of three small diameter fibers and a large diameter fiber are fusion-connected. The present inventors examined how to determine the cladding diameter of a thin optical fiber relative to the cladding diameter of a large optical fiber. First, the cause of the loss in the fusion part is examined, and one of the causes of the loss is that the fiber is not sufficiently melted at the time of fusion in the vicinity of the center of the large-diameter fiber. It has been found that there is an area 99 in which the cores are not fused. Fusion splicing is performed by applying heat energy from the outside, but when connecting an optical fiber bundle formed by bundling three small-diameter optical fibers and a large-diameter optical fiber, the cross-section of the optical fiber bundle is Since it is not a stable shape like a circle, it is likely to be thermally deformed. When the cross-sectional area of the optical fiber bundle is large, in order to prevent the deformation of the cross-sectional shape, sufficient heat energy cannot be applied to completely melt the cross-section, and such an unfused area 99 occurs. Conceivable.

  Prior to the measurement, the present inventor first defined a splice ratio S, which is a ratio of a cross-sectional area at the fused portion of the optical fiber, as in the following formula (3).

S = 3 · r1 ² / R1 ² (3)
The splice ratio S was varied in various ways, and the relationship between the splice ratio S and the transmittance at the fused portion was measured. In this measurement, light was incident from the small-diameter optical fiber side of the optical fiber bundle, and the transmittance of the light transmitted to the large-diameter fiber side was measured. The result is shown in FIG. In the figure, black dots are measurement points. A solid line is an asymptotic line obtained from a measurement point having a large splice ratio S and a low transmittance among the measurement points indicated by black dots, and a dotted line is an asymptotic value obtained from a measurement point having a low splice ratio S and a low transmittance. Is a line.

  As shown by the solid line, it can be seen that when the splice ratio S is larger than a predetermined value, the transmittance is lowered. When the transmittance is T, the solid line can be expressed by the following formula (4).

T = -2.99 ・ S + 2.85 (4)
From this equation (4), it can be seen that the transmittance T is close to 1 (100%) when the splice ratio S is smaller than 61.8. Therefore, it can be seen that the splice ratio S <61.8 is desirable.

  Further, as shown by the dotted line, it can be seen that when the splice ratio S is smaller than a predetermined value, the transmittance is lowered. FIG. 5 shows a schematic diagram of the fused part in such a case. The inventor examined the cause of the loss when the splice ratio S is small, and one of the causes of the loss is that, when the splice ratio is small, fiber melting during discharge fusion causes diffusion of the boundary between the core and the clad. I found out. This dotted line can be expressed by the following formula (5).

T = 0.66 ・ S + 0.69 (5)
From this equation (5), it can be seen that when the splice ratio S is greater than 47.2, the transmittance T is close to 1 (100%). Therefore, it can be seen that the splice ratio S> 47.2 is desirable.

From these equations (4) and (5), it can be said that the splice ratio S = 3 · r2 ² / R2 ² is desirably larger than 47.2 and smaller than 61.8.

  In the present embodiment, the radius r1 of the core 12 of the thin fiber 11, the radius r2 of the cladding 13, the radius R1 of the core 21 of the thick fiber 20, and the radius R2 of the cladding 22 are the following formulas (1) and (1): Satisfies (2).

R1> (r2 / cos30 °) + r1 (1)
47.2 <3 · r2 ² / R2 ² <61.8 (2)
In addition, said Formula (1) is conditions for the core part of a small diameter fiber to be able to fuse | melt all to the core part of a large diameter fiber, and when satisfy | filling this Formula (1), it is fused. If there is no loss in the part, all the light emitted from the core 12 of the thin fiber 11 can enter the core 21 of the thick fiber 20.

Further, in the optical fiber module 1, since the splice ratio S = 3 · r2 ² / R2 ² satisfies the formula (2), it is possible to suppress the loss of light at the fused portion.

  Next, the optical fiber module 2 which is the 2nd Embodiment of this invention is demonstrated with reference to FIG. FIG. 6 is a schematic configuration diagram of an optical fiber module 1 according to the second embodiment. As shown in FIG. 6, in the optical fiber module 2, a tapered optical fiber bundle 30 in which three tapered fibers 31 are bundled in a triangular shape and a single optical fiber 20 are fusion-bonded at a fusion part 35. ing. FIG. 7 is a schematic diagram of the fusion part 35. As shown in FIG. 7, the tapered fiber 31 includes a core 32 and a clad 33, and the radius of the core 32 in the fused part 35 is r1, and the radius of the clad 33 is r2. The optical fiber 20 is composed of a core 21 and a clad 22, and the radius of the core 21 is R1 and the radius of the clad 22 is R2.

  Also in the present embodiment, as in the first embodiment, the core radius r1 and the cladding radius r2 at the fusion part of the tapered fiber 31 and the core radius R1 and the cladding radius R2 of the large-diameter fiber 20 are as follows. Expressions (1) and (2) are satisfied.

R1> (r2 / cos30 °) + r1 (1)
47.2 <3 · r2 ² / R2 ² <61.8 (2)
Hereinafter, a method for manufacturing the optical fiber module 2 will be described. First, the tapered optical fiber bundle 31 is created. Three identical optical fibers are bundled in a triangular shape, and a part of the three fiber bundles is heated by a drawing heater to apply a tension tension to melt and adhere adjacent portions. By this melt drawing, a tapered portion as shown in FIG. 8 is generated in a part of the three-fiber bundle. Then, the center part of this taper part is cut | disconnected.

  When cutting, first, the tip of the diamond blade is brought into contact with the center of the tapered portion, and a scratch is made on the circumference of any one of the three fibers. Thereafter, the fiber bundle is stretched at a speed of 1 mm / second or less while being stretched in a straight line. Repeat intermittently pull → stop → pull → stop → ... until the fiber breaks. When the fiber is cut, a cleaved surface is obtained. The taper rate can be controlled by the amount of stretching at the time of melting. That is, the fiber diameter after taper can be controlled.

  Observe and clean the cut (cleaved) end face, and finish the end face without contamination. In addition, a thick fiber is prepared, and one end is cut (cleaved) to remove dirt on the end face. The creep surface of the optical fiber bundle and the creep surface of the large-diameter fiber are set in a face-to-face contact state, and fusion splicing is performed by electrode (arc) discharge using an optical fiber fuser (FSM-40PM manufactured by Fujikura). At that time, the discharge profile (intensity, time, etc.) is created and adjusted in accordance with the fiber form.

  As shown in FIG. 8, when an optical fiber having a tapered portion formed in one part is incident on one side and the light emitted from the other side is received by a photodetector, the output changes depending on the taper rate. (Loss) can be measured. The inventor measured the relationship between the taper rate and the loss using a laser light source having a wavelength of 400 to 410 nm with various changes in the taper rate. The result is shown in FIG. From this figure, it can be seen that when the taper ratio is less than 85%, the loss due to the taper becomes significant.

  In the present embodiment, since the tapered optical fiber bundle 30 is used, the degree of freedom of the diameter of the tapered fiber 31 is improved and the taper rate is 85% or more, so that loss in the tapered portion is also suppressed. ing.

Schematic configuration diagram of an optical fiber module according to the first embodiment Schematic diagram of fused part Schematic diagram of fused part Diagram showing the relationship between splice ratio and transmittance Schematic diagram of fused part Schematic configuration diagram of an optical fiber module according to the first embodiment Schematic diagram of fused part State diagram for taper formation Diagram showing the relationship between taper ratio and transmission loss Schematic diagram of conventional fused part of optical fiber module

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Optical fiber module Combined light source 10 Optical fiber bundle 11 Small diameter optical fiber 12, 21, 32 Core 13, 22, 33 Cladding 20 Large diameter optical fiber 25, 35 Fusion part 30 Taper type optical fiber bundle 31 Taper type Optical fiber r1, R1 Core radius r2, R2 Clad radius

Claims (2)

In an optical fiber module in which an optical fiber bundle in which three small-diameter optical fibers are bundled in a triangular shape and one large-diameter optical fiber are fusion-bonded,
The core radius of the small-diameter optical fiber at the fused portion is r1, the cladding radius is r2, the core radius of the large-diameter fiber is R1, and the cladding radius is R2.
R1> (r2 / cos30 °) + r1
And 47.2 <3r2 ² / R2 ² <61.8
An optical fiber module characterized by the above.   The optical fiber module according to claim 1, wherein the small-diameter optical fiber is a tapered fiber, and the taper ratio is 85% or more.

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