JP2000193845A - Branching light coupler for input light into a plurality of fibers and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture a coupler having a desired branching ratio without wasting the fiber material by providing no dip between the core and the clad of a center fiber and a circumferential fiber. SOLUTION: In a branching light coupler which branches input light into a plurality of fibers to output, the input end is provided, a center fiber having clad provided on a core and the circumference of the core, and a circumferential fiber arranged on the circumference of the center fiber and having a clad provided on a core and the circumference of the core. The center fiber and the circumferential fiber are formed into construction having no dip between the core and the clad. The Fig. shows the profile of the fiber containing no dip between the core and the clad, the vertical axis shows specific refraction factor difference, and the lateral axis shows the distance from the center of the fiber. The term 'dip' means a layer having a refraction factor smaller than the refraction factor of the outermost circumference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a multi-branch optical coupler,
And its manufacturing method.

[0002]

2. Description of the Related Art With the rapid progress of fiber transmission technology,
2. Description of the Related Art An optical data link using a fiber for data transmission between a computer and a computer or a terminal has been actively researched and developed.
In configuring an optical data link, a multi-branch optical coupler that can distribute light input from one or a plurality of input fibers to a plurality of output fibers with low loss and evenly is indispensable. Device.

[0003] As such a multi-branch optical coupler, an optical star coupler in which a fiber bundle is inserted into a hollow glass tube, heated and stretched, and each fiber is arranged substantially evenly with respect to the center of the coupler is known. Japanese Patent Laid-Open No. 60-24505), 3
There is known a method of manufacturing an optical star coupler (Japanese Patent Application Laid-Open No. 63-205616) in which dB optical couplers are connected in multiple stages to realize many branch points. However, in the former case, it is difficult to obtain evenly split light, and in the latter case, the couplers are connected in multiple stages, so that the whole becomes large. There is also a method of manufacturing a fiber-type star coupler in which a fiber bundle is twisted, fused, drawn, and covered with a glass tube (Japanese Patent Application Laid-Open No. 63-70208). However, the arrangement of the fibers is not fixed. It is difficult to control variations in output intensity, and it is difficult to split light evenly.

Further, a multi-branch optical coupler (OE) having five fibers arranged in a plane in consideration of symmetry and having four branches.
C '94 (1994) pp. 364), but it is difficult to process a single fiber that does not contribute to the output, and the width is wide because the fibers are arranged in a horizontal line. The size of the coupler case becomes large.

In addition, N fibers are placed in a glass tube.
The fiber option to heat, draw and collapse the whole
Tick coupler and 1 × N fiber optic
A method of manufacturing a coupler (Japanese Patent Application Laid-Open No. 7-40346) is disclosed.
However, this method is a process of putting in a tube, collapse
Manufacturing process is not easy. Also,
It is extremely difficult to collapse Iva without distorting it
And the collapsed fiber is deformed,
Transmission characteristics, for example, polarization dependence may be affected.
Also, the refractive index of the core is n₁, The refractive index of the cladding n₂When
If n₁> N _i> N₂Index of refraction n_i
-Mode optical fiber with different refractive index pedestal
Fiber optic coupler consisting of
No. 22 discloses this.

[0006]

The present inventor has found that in producing a multi-branch optical coupler, the coupler to be produced cannot obtain a desired branch ratio depending on the type of single mode fiber used. Therefore, an object of the present invention is to prepare a single-mode fiber capable of obtaining a desired branching ratio and efficiently produce a coupler without wasting fiber material. Also, in the production of a multi-branch optical coupler, if the softening temperature of the fiber is different due to the difference in the amount of dopant in the fiber, etc., the stretching amount of the central fiber and the peripheral fiber during heating and stretching is different, so that the desired branching ratio is obtained. It is difficult to produce a coupler. Accordingly, an object of the present invention is to prepare a fiber having a desired branching ratio by preparing fibers having substantially the same softening temperature.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a method for manufacturing a branch optical coupler capable of manufacturing a branch optical coupler having a desired branch ratio. I do. In order to achieve such an object, the present invention is directed to a branch optical coupler that branches input light into a plurality of fibers and outputs the split light, having an input end for inputting the light, a core and the core. A central fiber having a cladding provided around the core, and a peripheral fiber disposed around the central fiber and having a core and a cladding provided around the core, wherein the central fiber and the peripheral fiber are the core And a branch optical coupler having no dip between the claddings.

Further, the present invention relates to a branch optical coupler for branching input light into a plurality of fibers and outputting the split light, comprising: a central fiber having an input end for inputting the light and exhibiting a predetermined softening temperature. A peripheral fiber disposed around the central fiber and exhibiting a softening temperature substantially equal to the predetermined softening temperature of the central fiber, the peripheral fiber comprising:
A branch optical coupler is provided, which is partially fused to the central fiber.

In one embodiment of the present invention, the central fiber has an output end for outputting the light. In another aspect of the present invention, the branch optical coupler may include a plurality of the peripheral fibers. In still another aspect of the present invention, the plurality of peripheral fibers may be arranged at substantially equal intervals along an outer periphery of the central fiber.
In yet another aspect of the present invention, the peripheral fiber comprises:
A portion thereof may be fused to the central fiber.

The present invention also relates to a method for manufacturing a branch optical coupler for manufacturing a branch optical coupler for splitting input light into a plurality of fibers and outputting the split light, comprising: a light input end; Having a cladding provided around the core, providing a single central fiber having no dip between the core and the cladding, comprising a core and a cladding provided around the core; And preparing a peripheral fiber having no dip between the cladding, and arranging the peripheral fiber along the outer periphery of the central fiber, and arranging the central fiber and the peripheral fiber arranged by the arranging step. A heating step of heating with a heating device, and the center fiber and the peripheral fiber heated in the heating step are connected to the center fiber. To extend in the axial direction of providing a branching optical coupler producing method characterized by each of said peripheral fiber and a stretching step for fusing the central fiber.

The present invention also relates to a method of manufacturing a branch optical coupler for manufacturing a branch optical coupler for branching input light into a plurality of fibers and outputting the split light, wherein the optical coupler has an input end of the light and has a predetermined softening property. Providing one central fiber having a temperature; providing a peripheral fiber having a softening temperature substantially equal to the softening temperature of the central fiber; and arranging the peripheral fibers along an outer periphery of the central fiber. Step, a heating step of heating the central fiber and the peripheral fiber arranged in the arranging step by a heating device, and the central fiber and the peripheral fiber heated in the heating step, in the axial direction of the central fiber Drawing each of the peripheral fibers to be fused to the central fiber. To provide a 岐光 coupler manufacturing method. In one aspect of the present invention, the step of preparing the center fiber may include preparing a center fiber having an input end of the light and an output end of the light and having a predetermined softening temperature.

In another aspect of the present invention, the step of preparing the peripheral fiber may include preparing a plurality of the peripheral fibers. In yet another aspect of the present invention,
The arranging the plurality of peripheral fibers along the outer periphery of the central fiber at substantially equal intervals,
Can be arranged. The above summary of the present invention does not list all of the necessary features of the present invention, and sub-combinations of these features may also constitute the present invention.

[0013]

1 (a) and 1 (b) are a plan view and a side view, respectively, of a multi-branch optical coupler manufacturing apparatus according to the present invention. The multi-branch coupler manufacturing apparatus includes a base 20,
Two stretching stages 35a supported by the base 20,
35b, rotating units 30a and 30b attached outside the stretching stages 35a and 35b, a stress adjusting unit 40b attached outside the rotating unit 30b,
A gas burner 22 as an example of a heating device, a monitor light output device 62 and two light receiving devices 64 and 66 are provided at the center of the two stretching stages 35a and 35b. In addition,
The "heating device" may be any device capable of heating the fiber 31, and may be, for example, a device for blowing hot air or an infrared radiation device.

The rotating unit 30a includes a plurality of fibers 3
1, a mask 34 a for holding the nozzles 1 at predetermined intervals, a rotation stage 33 a for rotating the rotation unit 30 a, a clamp table 32 a and a clamp 36 a as an example of a fixing unit for fixing the fiber 31, and the fiber 31 slidably. And a sliding holding portion 38a for holding. Further, the stretching stage 35a has a peripheral holding unit 37a that holds the rotating unit 30a freely in a peripheral movement. The configuration of the rotating unit 30b and the stretching stage 35b are respectively
0a and the configuration of the stretching stage 35a, so that the description is omitted.

First, the number of fibers 31 equal to the desired number of branches is supplied to the holding portions 37a and 37b and the masks 34a and 34.
b, and penetrate through the sliding holding parts 38a, 38b, and clamp one end of the fiber 31 by the clamp table 32a and the clamp 36a. The other end of the fiber 31 is
Hold at b. Next, the rotation stages 33a and 33b are grasped by hand, and the entire rotation units 30a and 30b are rotated several times in opposite directions to twist the fiber 31. In addition, as another method, only one of the rotation stages 33a and 33b may be rotated, or may be rotated by a motor instead of rotating by hand.

The stress adjusting section 40b has a stress adjusting table 42b and a plurality of elastic holding sections 44b for holding the respective fibers 31 independently. The elastic holding portion 44b has an elastic body such as a spring and can apply a desired tension to each fiber 31. Since the spring constant of the elastic body of the elastic holding portion 44b is sufficiently small with respect to the amount of movement of the fiber 31 when the rotation units 30a and 30b are rotated, even if the rotation units 30a and 30b are rotated, 31
Is maintained evenly. Thereby, each fiber 3
1 can be given an appropriate tension, and the fiber 31 can be prevented from being cut.

Next, the fiber 31 is clamped by the clamp 36b.
Is fixed, and the burner 22 is ignited to heat the fiber 31. After a predetermined time has elapsed since the burner 22 was ignited, the fiber 31 is drawn by moving at least one of the drawing stages 35a and 35b in a direction away from the other drawing stages by a motor (not shown). Before moving the stretching stages 35a and 35b, the stress adjusting section 40
Since the stress of each fiber 31 is equalized by b, each fiber 31 can be evenly stretched.

The center fiber 11 is located at the center of the fiber 31.
Are provided, and the other fibers 31 are arranged at equal intervals around the center fiber 11. In this specification, the fiber 31 disposed around the center fiber 11 is referred to as a peripheral fiber. In FIG. 1, four peripheral fibers 12, 1
Although only 3, 17, and 18 are shown, the number of peripheral fibers is not limited to four. The center fiber 11 has an input end 68 for inputting the monitor light output from the monitor light output device 62 and an output end 70 for outputting the input light. To the output terminal 70. The monitor light is input to the input end 68 of the central fiber 11, and the output end 7 of the central fiber 11 is
0 and the peripheral fibers 12, 13, 1
The amount of light output from any one of the output terminals 72 in 7 and 18 is monitored by the light receiving devices 64 and 66, respectively. When the amounts of light output from both fibers become substantially equal, the heating and moving stages 35a, 35
The movement of 5b is stopped.

Thereafter, the elastic holding portion 44b is once removed and the fiber 31 is held again, so that a uniform stress is applied to the fiber 31 between the clamp 36b and the elastic holding portion 44b. This stress value may be substantially zero. After a predetermined time elapses after the heating by the burner 22 is stopped and the fiber 31 is sufficiently hardened, the clamp 36b is removed. Further, the stretching stages 35a, 35
b is further moved by a predetermined distance to apply a desired tension to each fiber 31. Stretching stage 35a,
The amount of movement of 35b can be detected by monitoring the number of rotations of a motor that moves the stretching stages 35a and 35b with a computer connected to the multi-branch optical coupler manufacturing apparatus. With a predetermined tension applied to the fiber 31, both ends of the fused portion of the fiber 31 are fixed to a rigid member such as a quartz glass plate with resin, and further housed in a cylindrical metal case for protection, and a multi-branch optical coupler is provided. Completed.

FIG. 2A shows an example of a plan view of the masks 34a and 34b. At the center of the masks 34a and 34b,
A central hole 72 is provided, and a plurality of peripheral holes 74 are provided in the central hole 7.
2 at equal intervals. The central hole 72 penetrates the central fiber 11 for inputting the light to be branched, and the peripheral hole 74 penetrates the peripheral fiber. Thereby, the peripheral fibers can be arranged at equal intervals around the center fiber 11. Further, since the stress of each peripheral fiber is kept uniform by the stress adjusting mechanism 40b (FIG. 1), each peripheral fiber is fused to the center fiber 11 evenly, and light is evenly transmitted to each peripheral fiber. Can branch.

The inner diameters of the center hole 72 and the peripheral hole 74 are preferably about 1 μm larger than the cladding diameter of the fiber to be penetrated. It is preferable that the inner circumferences of the center hole 72 and the peripheral hole 74 are rounded so as not to damage the center fiber 11 and the peripheral fiber. When the center fiber 11 and the peripheral fiber have the same clad diameter, a maximum of six peripheral fibers can be arranged along the outer periphery of the central fiber 11. Therefore, the inner diameters of the center hole 72 and the peripheral hole 74 are made equal in order to penetrate the center fiber 11 and the peripheral fiber having the same diameter. That is, when the number of the peripheral holes 74 is six or less, the inner diameters of the center hole 72 and the peripheral holes 74 are equal.

FIG. 2B shows another example of a plan view of the masks 34a and 34b. When the number n of fibers is 8 or more (the number of peripheral fibers is 7 or more), in order to bring all the peripheral fibers into contact with the outer periphery of the central fiber 11, the diameter (cladding diameter) of the central fiber 11 is changed to the diameter of the peripheral fiber ( (Cladding diameter). When n is 8 or more, assuming that the outer diameter of the cladding of the peripheral fiber is CLDs, and the minimum outer diameter of the central fiber required to arrange the peripheral fiber along the outer periphery of the central fiber is CLDc (min),
CLDc (min) is represented by the following equation (1) using CLDs. CLDc (min) = (CLDs / sin (π / (n-1)))-CLDs (1) From equation (1), when n = 8 and the diameter of the peripheral fiber is 125 μm, the center is The diameter of the fiber 11 needs to be 163 μm or more. For example, the diameter of the central fiber 11 is 165 μm
If so, all the peripheral fibers can be arranged in close contact with the center fiber 11.

In order to penetrate the central fiber 11 and the peripheral fiber, the diameter of the central hole 72 needs to be larger than the diameter of the peripheral hole 74. That is, the peripheral hole 7
When the number of 4 is 7 or more, the diameter of the center hole 72 is made larger than the diameter of the peripheral hole 74. By changing the position of the peripheral hole 74 with respect to the center hole 72, the twisting of each fiber can be changed and the light branching ratio can be changed. Further, by changing the arrangement of the center hole 72 or the peripheral hole 74 in the opposing masks 34a and 34b, an unbalanced twist is generated in the fiber 31, and the light branching ratio can be changed.

FIG. 3 is a lateral view of the rotating unit 30a. The clamp table 32a and the mask 34a are fixed to the rotary stage 33a. In addition, the clamp 36a
It is attached to the clamp table 32a. Therefore, by rotating the rotary stage 33a, the clamp table 32a, the clamp 36a, and the mask 34a can be rotated together with the rotary stage 33a. The configuration of the rotation unit 30b is the same as the configuration of the rotation unit 30a, and thus the description is omitted. Since the rotating unit 30b is further provided with a stress adjusting unit 40b, by rotating the rotating stage 33b, the clamp table 32b, the clamp 36b, the mask 34b, and the stress adjusting unit 40b rotate as a pair.

FIGS. 4A to 4C are cross-sectional views of a 1-input × 8-output optical coupler according to the present invention before heating and stretching. From central fiber 11 to peripheral fibers 12-18
Each of the peripheral fibers 12 to 18 and the central fiber 11 are fused to branch the light. FIG.
In FIG. 4A, adjacent peripheral fibers 12 to 18 are in contact with each other, but as shown in FIG.
2 to 18 may be apart from each other.

By arranging the peripheral fibers 12 to 18 evenly around the center fiber 11, it is possible to reduce the variation of the light output intensity from each of the fibers 11 to 18.
However, even if the peripheral fibers 12 to 18 are arranged evenly around the center fiber 11 initially, the temperature difference between the fibers generated when heating and the temperature of each fiber 1
There is a case where the arrangement of the fibers is shifted due to a difference in the tensile strength between 1 and 18. To prevent this, the peripheral fibers 12 to 18 are pressed against the central fiber 11 by twisting the fiber bundle around the central fiber 11,
The center fiber 11 and the peripheral fibers 12 to 18 are brought into close contact with each other. FIG. 4C shows a case where the peripheral fibers 12 to 18 are twisted around the center fiber 11.
(A) is sectional drawing of the part from which the position of an axial direction differs.
When the peripheral fibers 12 to 18 are wound around the central fiber 11, the positions of the peripheral fibers 12 to 18 are displaced according to the positions in the axial direction.

FIGS. 5A to 5C show changes in the cross section in the step of heating and stretching the multi-branch optical coupler shown in FIG. 4C. In FIG. 5A, the peripheral fibers 12 to
Although 18 is fused to the central fiber 11, the peripheral fibers 12 to 18 are still separated. FIG. 5 (b)
FIG. 5C shows a state in which the fibers are further drawn and the peripheral fibers are fused together, but a slight gap is still left between the peripheral fibers. This shows a state where there is no gap between them. In these drawing steps, the output from one of the peripheral fibers and the center fiber 11 is monitored, and the drawing is stopped when the light intensities output from both fibers become equal. The state of the peripheral fiber when drawing is completed is
Even if it is not fused with other peripheral fibers as shown in FIG. 5A, it is fused with other peripheral fibers as shown in FIG. The state may be a state where a gap is slightly left, or a state where the gap is eliminated as shown in FIG.

When the cladding diameter of the central fiber 11 is increased, a gap is formed between the peripheral fibers before stretching. The difference ΔCLD between the actual center fiber cladding diameter CLDc and the minimum center fiber cladding diameter CLDc (min) required for arranging seven or more peripheral fibers along the outer circumference is apparent from equation (1). It is expressed by the following equation (2). △ CLD = CLDc-CLDc (min) = CLDc-(CLDs / sin (π / (n-1))) + CLDs ··· (2)

FIG. 6 shows the difference ΔC between the cladding diameter of the central fiber 11 and the cladding diameter of the peripheral fiber when n = 8 where seven peripheral fibers are arranged around the central fiber 11.
It is an experimental result which shows the change of uniformity with respect to LD. The “uniformity” is a value indicating the uniformity of light transmitted to each output fiber. When the maximum value of the power of the output light with respect to the input light is Pmax and the minimum value is Pmin, it is expressed by the following equation. You. Uniformity (dB) = 10 × (log ₁₀ Pmax−1
og ₁₀ Pmin)

As can be seen from the above equation, the smaller the value of the uniformity, the more uniformly branched output light can be obtained.
When the fiber bundle is heated and fused, the central fiber 11
Since the peripheral fiber becomes softer first and its cross section is deformed, it is preferable that there is a little gap between adjacent peripheral fibers. However, if the gap is too large, the degree of freedom in arranging the peripheral fibers is large, and it is difficult to arrange the peripheral fibers at equal intervals in the circumferential direction of the fiber bundle. As described above, ΔCLD has an optimum range, and in the experiment shown in FIG. 6, 38.6 to 40.1 μm was the optimum range, as indicated by the hatching in the figure.

The range of ΔCLD depends on the intensity of heating of the fiber bundle. As a result of an experiment in which the flame intensity of the gas burner was changed, when the heating was strong, the cross-section of the peripheral fiber deformed quickly, so that the optimum range of ΔCLD was shifted to a slightly larger range than the range indicated by the oblique line. Conversely, when the heating is weak, the cross section of the peripheral fiber is slowly deformed, so that the smaller the gap between adjacent peripheral fibers tends to be better coupled between the peripheral fiber and the center fiber, and the optimal range of ΔCLD is , Shifted slightly smaller than the shaded area. In a series of experiments in which the flame intensity of the gas burner was changed, the optimum value of ΔCLD for seven peripheral fibers (n = 8) having a cladding outer diameter of 125 μm was 38 to 41 μm.

FIG. 7A shows a change in the optical output intensity with respect to the drawing length of the fiber at the time of manufacturing the multi-branch optical coupler when the propagation constant β of the peripheral fiber and the center fiber 11 is largely different. FIG. 7B shows a change in the optical output intensity with respect to the drawing length of the fiber when the propagation constant β of the peripheral fiber and the center fiber 11 is substantially equal. The vertical axis indicates the light output intensity of light output from the central fiber 11 and any one of the peripheral fibers, and the horizontal axis indicates the central fiber 1
1 shows the draw length of one and any one of the peripheral fibers.

As is apparent from a comparison between FIGS. 7A and 7B, when the difference between the propagation constant β of the central fiber 11 and the peripheral fiber is large, the light incident on the central fiber 11 is sufficiently reduced. Does not transition to. Where the propagation constant β
Is different depending on the refractive index distribution profile of the fiber. For example, in the case of a step type fiber in which the refractive indices n1 and n0 of the core and the cladding are constant in the core and the cladding, respectively, it is expressed by the following equation. J0 (u) / u · J1 (u) = K0 (w) / w · K1 (w) (3) u2 + w2 = v2 (4) where u = ak2n12-β2 (5) w = aβ2-k2n02 (6) v2 = k2 (n12-n02) a2 (7)

Where a is the core diameter, k is the wave number, Jn
(X) is a Bessel function of the first kind, and Kn (x) is a modified Bessel function of the second kind. That is, the propagation constant β is the core diameter a,
This is a function determined by the refractive indexes n1 and n0 of the core and the clad, the wave number k, and the refractive index distribution profile. When fibers having different diameters are drawn from the same fiber preform, the core fibers of the peripheral fiber and the central fiber 11 are different, so that the propagation constant β is different, and a sufficient amount of light from the central fiber 11 does not transfer to the peripheral fiber. . Therefore, it is necessary to adjust the structural parameters of the fiber (core diameter a, refractive indices n1 and n0 of the core and clad, refractive index distribution profile), and make the propagation constant β of the central fiber 11 and the peripheral fiber equal.

The fiber has a cutoff wavelength λc determined according to the structural parameters. When light having a wavelength shorter than the cutoff wavelength λc of the fiber is incident, the fiber does not always operate in the single mode. For example, when using light having a wavelength of 1310 nm, the cutoff wavelength λc of the fiber is shorter, for example, about 1250 nm.
nm. So ordinary fibers are
The fiber is designed by adjusting the core diameter a and the relative refractive index difference Δn so that the cutoff wavelength λc is 1250 nm. Also in the multi-branch optical coupler of the present invention, it is preferable that the center fiber 11 and the peripheral fiber have substantially the same cutoff wavelength λc.

The cutoff wavelength λc is a function determined by the refractive index distribution profile, the core diameter a, and the refractive indices n1 and n0 of the core and the clad. For example, the cutoff wavelength λc in the case of a step type fiber is expressed by the following equation. Is done. λc = 2.61356a√ (n1 ² −n0 ² ) Therefore, for example, by making the core diameter a and the refractive indexes n1 and n0 of the core and the cladding the same, the cutoff wavelength λc of the center fiber 11 and the peripheral fiber becomes the same. Can be

In order for the center fiber 11 and the peripheral fiber to have substantially the same propagation constant β and cut-off wavelength λc, the ratio of the core diameter to the cladding diameter must be previously determined in the preform stage of the fiber. (Peripheral fiber). For example, it is assumed that a fiber having a core diameter of 9 μm manufactured by drawing a preform to a diameter of 125 μm is used as a peripheral fiber of the 8-branch optical coupler. A clad is further provided around the clad of the same preform, and the ratio between the core diameter and the clad diameter is changed in advance, for example, the clad diameter is 165 μm.
When the wire is drawn up to
A preform is manufactured to have a thickness of 9 μm. The center fiber 11 may be manufactured using this preform.
Since both fibers have the same core diameter, relative refractive index difference Δn, and refractive index profile, the propagation constant β is equal.

The relative refractive index difference Δn and the refractive index distribution profile may be slightly different depending on the preform.
When the peripheral fiber and the central fiber 11 are prepared from different preforms, the relative refractive index difference Δn and the refractive index distribution profile between the peripheral fiber and the central fiber 11 may be slightly different. In such a case, the core diameter a of each single mode fiber, the mode field diameter (the diameter of a region having an intensity of 1 / e ² of the maximum light intensity, which is called MFD), the cutoff wavelength λc, and the like are adjusted almost equally. Then, the propagation constant β (or Vvalue) can be made almost uniform.

FIG. 8 shows a multibranched optical coupler wire manufactured by heating and stretching the central fiber 11 and the peripheral fibers 12 and 13. The completed multi-branch optical coupler strand has a coupling region 82 in which the central fiber 11 and the peripheral fibers 12 and 13 are completely fused. On both outer sides in the axial direction of the coupling region 82, extension regions 78 and 86 where the peripheral fibers 12 and 13 are not stretched are provided. Between each of the extension regions 78 and 86 and the coupling region 82, there are provided tapered portions 80 and 84 in which each of the central fiber 11 and the peripheral fiber 12 is tapered. In addition, the end portions 76 of the peripheral fibers 12 and 13 on the input light side are subjected to non-reflection processing in order to suppress the amount of light reflected from the fiber ends.

As is clear from FIG. 8, the center fiber 1
1 has an input end 74 for inputting light and an output end 88 for outputting the light, and the light input to the input end 74 of the central fiber 11 outputs the light to the output end 88 of the central fiber 11 and the peripheral fiber 12; 13 and output. The core of the central fiber 11 is connected from the light input end 74 to the light output end 88, and a cladding is provided around the core. For ease of understanding, FIG. 8 shows only one central fiber 11 and two peripheral fibers 12 and 13, but more peripheral fibers are
May be evenly arranged around.

In ordinary optical communication, a fiber having a cladding diameter of 125 μm is used. If the center fiber 11 and the peripheral fiber have different cladding diameters, the cladding diameter of one of the fibers is different from the cladding diameter of a fiber used for ordinary optical communication. Therefore, a fiber having a normal clad diameter may be connected to the fiber of the present invention in advance. As shown in FIG. 8, when the center fiber 11 has a large clad diameter, ordinary single mode fibers 72 and 90 having a clad diameter smaller than the center fiber 11 are connected to both ends 74 and 88 of the center fiber 11. .

If the cladding diameter of the peripheral fibers 12 and 13 is smaller than that of a normal fiber, the peripheral fibers 12 and 13
An ordinary single mode fiber having a cladding diameter larger than the above cladding diameter is connected to the output light side of the peripheral fiber. If the end of the multi-branch optical coupler is required to be a tape fiber, a tape fiber may be connected to the output center fiber 11 and the peripheral fiber. Thus, a fiber having a diameter of 125 μm is connected to at least one end face of at least one of the central fiber 11 and the peripheral fiber. Thereby, a highly versatile multi-branch optical coupler can be provided. In order to increase the strength of the multi-branch optical coupler, it is desirable that the multi-branch optical coupler shown in FIG. 8 be covered with a rigid body such as a metal tube.

The eight-branch coupler manufactured by the above method has a peripheral fiber whose output end has a normal size of 125 μm in diameter, but the center fiber 11 has a large size of 165 μm. The fusion splicing was performed by electric discharge, and this was heated and stretched together with the peripheral fiber. Since the core diameter of the center fiber 11 and the core diameter of the connection fiber are designed to be substantially the same, the connection loss at the end face is small, and the increase in loss due to the connection of the fiber end face was almost negligible.

Example 1 Sixteen single mode fibers having a cladding diameter of 125 μm were prepared, and the coating on the fibers was partially removed. One fiber was placed in a glass tube, and the tube was heated and drawn to make it adhere to the outer periphery of the fiber. As a result, a central fiber 11 having a core diameter and a relative refractive index difference substantially equal to those of another single mode fiber (SMF) and a large cladding diameter was formed. Mask 34 of multi-branch optical coupler manufacturing apparatus shown in FIG.
A large central hole 72 is provided at the center of each of the holes a and 34b, and 15 peripheral holes 74 are provided around the central hole 72 at equal intervals. The central fiber 11 was passed through the central hole 72, and the single mode fiber was passed through a peripheral hole having an inner diameter of about 126 μm as a peripheral fiber.

One end of the fiber penetrated through the masks 34a and 34b was fixed by a clamp table 32a and a clamp 36a, and the other end was held by a stress adjustment table 42b and an elastic holding section 44b. Next, the two rotation units 30a and 30b are respectively rotated three times in opposite directions to twist the bundle of fibers 31, and the rotation units 30a and 30b are rotated so as not to be untwisted.
Was fixed with a stopper.

The fiber 31 was drawn while the center of the twisted portion of the fiber 31 was heated by the burner 22 of an oxyhydrogen flame. Light is input from the input end 68 of the central fiber 11, and the output from the output end 70 of the central fiber 11 and the output from one of the 15 peripheral fibers are monitored. When both outputs become equal, heating is performed. Then, the stretching was stopped to prepare a multibranched optical coupler strand. After this multi-branch optical coupler strand was fixed to a quartz glass substrate with a resin, it was housed in a cylindrical metal case to produce a 16-branch optical coupler. The size of the case of this coupler was 3.5 mm × 65 mmL, which was much smaller than that of a conventional multistage connected coupler case.

FIG. 9 shows the insertion loss for each output port of the 16-branch optical coupler manufactured according to the first embodiment. The insertion loss of each output port of the 16-branch optical coupler was 13.14 dB on average and the standard deviation was 0.53 dB, and a multi-branch optical coupler with good output balance was obtained.

(Embodiment 2) An example of a method of manufacturing a 1-input × 8-output branch optical coupler will be described. A fiber having a core diameter and a relative refractive index difference substantially equal to that of a single mode fiber (SMF) and having a diameter of 165 μm is placed in the center hole 72 of the masks 34a and 34b, and a normal single mode fiber having a diameter of 125 μm is placed in a peripheral hole
4, one end of the fiber was fixed by the clamp table 32a and the clamp 36a, and the other end was held by the stress adjustment table 42b and the elastic holding section 44b. Rotating unit 30a,
30b are rotated in opposite directions to each other,
A twist of rotation was added. Since the tension of the fiber 31 is adjusted by the stress adjuster 40b, the fiber 31 can be prevented from being cut.

Further, while the propane / oxygen flame burner 22 was shaken in the axial direction of the fiber at a width of 5000 μm, the center of the fiber 31 was heated and drawn at a speed of 120 μm per second. When the light amount of the central fiber 11 and the light amount of any one of the peripheral fibers became approximately equal, the heat drawing was stopped. Thereafter, the stress by the stress adjusting unit 40b was once released and then held again, and the clamp 36b was removed, the moving stage 35b was moved again, and tension was applied to the fiber 31. While tension was applied to the fiber 31, both ends of the fiber bundle fusion portion were fixed to a quartz glass plate with an adhesive to complete a multi-branch optical coupler.

(Example 3) A method of manufacturing a coupler for equally branching light having a wavelength of 1.31 µm will be described. First, clad diameter 125
Two identical fibers of μm were prepared, the coating covering the fibers was partially removed, the claddings were brought into contact with each other, and heated with an oxyhydrogen flame to draw the fibers. This heating
During the extension, the output light intensity is monitored by the light receiving units 64 and 66,
When the desired branching ratio was reached, the heat stretching was stopped. As a result, a multi-branch optical coupler having a branch ratio of 50.2% and an excess loss of 0.04 dB was produced.

When the temperature of the fiber 31 was sufficiently lowered, the stretching stage 35b was moved outward by 0.02 mm at a speed of about 100 μm / sec to pull the multibranch optical coupler strand. With tension applied to the multibranched optical coupler wires, both ends of the fused portion were fixed to a quartz glass substrate with a resin and placed in a metal case. The multi-branch optical coupler manufactured in this manner was subjected to a heat cycle test at −40 ° C. to + 85 ° C. A multi-branch optical coupler having a change in insertion loss during a test of a predetermined value or more was rejected, and a multi-branch optical coupler having a change of less than a predetermined value was passed. After the heating is completed, a multi-branch optical coupler manufactured by fixing the multi-branch optical coupler element wire to the quartz glass substrate by applying tension thereto, and a multi-branch optical coupler manufactured by fixing to the quartz glass substrate without applying tension, Table 1 shows the test results.

[Table 1] As is evident from the test results, by applying tension to the multibranched optical coupler wires after the completion of heating and fixing them to the glass substrate, the proportion of multibranched optical fibers that passed the heat cycle test was significantly increased.

(Embodiment 4) FIG. 10 shows a profile of a fiber having no dip between the core and the cladding. In FIG. 10, the vertical axis indicates the relative refractive index difference, and the horizontal axis indicates the distance from the center of the fiber. The term “dip” refers to a layer having a refractive index less than the outermost refractive index. A profile that does not include this dip is called a type A profile. This fiber is 125
This is a type A single mode fiber manufactured by ATT and having a diameter of μm.

In Example 4, a 1-input × 8-output multi-branch output optical coupler was manufactured using a fiber having a type A profile. A fiber having a core diameter and a relative refractive index difference substantially equal to that of a single mode fiber (SMF) and having a diameter of 165 μm having a type A profile is inserted into the center holes 72 of the masks 34a and 34b and having a diameter of 125 μm having a type A profile Is passed through the peripheral hole 74, and one end of the fiber is clamped to the clamp base 3.
2a and a clamp 36a, and the other end is
2b and the elastic holding portion 44b. The doping concentration in the 165 μm diameter fiber (center fiber) and the 125 μm single mode fiber (peripheral fiber) are almost equal, and the softening temperatures of the respective fibers are almost equal.

The rotation units 30a and 30b were rotated in opposite directions to twist the fiber 31 three times. Subsequently, propane / oxygen flame burner 22 is set to width 500
While oscillating in the axial direction of the fiber at 0 μm,
Was heated and stretched at a speed of 120 μm per second. FIG. 11 shows a change in the light output intensity with respect to the drawing length of the fiber at this time.

FIG. 11 shows the relationship between the output of the central fiber 11 and the output of one arbitrary peripheral fiber when 1.55 μm light is input to the central fiber 11. When the light amount of the central fiber 11 and the light amount of any one of the peripheral fibers became approximately equal, the heat drawing was stopped. This means that the input light is evenly distributed to the center fiber and the surrounding fibers. Thereafter, the stress by the stress adjusting unit 40b was once released and then held again, and the clamp 36b was removed, the moving stage 35b was moved again, and tension was applied to the fiber 31. While tension was applied to the fiber 31, both ends of the fiber bundle fusion portion were fixed to a quartz glass plate with an adhesive to complete a multi-branch optical coupler.

In the fourth embodiment, light is transferred from the central fiber to the peripheral fiber by using a fiber having no dip between the core and the cladding as the central fiber and the peripheral fiber. Also,
Although the softening temperature of a fiber is affected by the amount of dopant contained in the fiber, the softening temperature of each fiber becomes substantially equal by using fibers having substantially equal doping concentrations as the central fiber and the peripheral fiber. By using fibers having substantially the same softening temperature as the center fiber 11 and the peripheral fiber, when the fibers are heated and drawn, the drawn amounts of the respective fibers become substantially equal, and a uniform branching ratio can be obtained. Therefore, when generating a multi-branch optical coupler,
By preparing a fiber having a type A profile as the center fiber and the peripheral fiber in advance, it is possible to improve the yield.

FIG. 12 shows the wavelength characteristics of the insertion loss of the 1.55 μm 8-branch coupler manufactured in the fourth embodiment. As shown in FIG. 12, the insertion loss of the center fiber and the seven peripheral fibers is 1550 nm (1.55 nm).
μm). Therefore, by using the fiber having the type A profile, it is possible to efficiently generate an equally-branched multi-branch optical coupler.

FIG. 13 shows the profile of a fiber that includes a dip between the core and the cladding. A profile including this dip is called a type B profile. This fiber has an AT of 125 μm.
This is a type B single mode fiber manufactured by T Company, and has a layer (dip) having a small refractive index in a radius range of about 5 μm to 20 μm.

An example in which a 1-input × 8-output branch optical coupler is manufactured using a fiber having a type B profile as a peripheral fiber will be described below. The center fiber is a fiber having a type A profile that does not include a dip between the core and the cladding shown in FIG. Single mode fiber (SMF) with core diameter and relative refractive index difference
16 which is approximately equal to
The 5 μm fiber is inserted into the center hole 7 of the mask 34a, 34b.
Second, a single mode fiber having a type B profile and a diameter of 125 μm is passed through the peripheral hole 74, one end of the fiber is fixed by the clamp table 32a and the clamp 36a, and the other end is a stress adjustment table 42b and an elastic holding section. 44b
Held in. 165μm diameter fiber (center fiber)
And the single-mode fiber (peripheral fiber) having a diameter of 125 μm are different in doping concentration, and the softening temperatures of the fibers are different. Rotating unit 30
a and 30b are rotated in the opposite directions to each other,
Was twisted three times. Subsequently, the center of the fiber 31 was heated while the burner 22 of the propane / oxygen flame was shaken in the axial direction of the fiber at a width of 5000 μm, and was heated at 120 μm per second.
m.

FIG. 14 shows the change in the light output intensity with respect to the drawing length of the fiber at this time. Unlike the graph shown in FIG. 11, in FIG. 14, the light amount of the central fiber 11 does not become equal to the light amount of any one peripheral fiber. Therefore, when the center fiber 11 has the type A profile and the multi-branch optical coupler is generated using the peripheral fiber having the type B profile, the desired equal branch ratio cannot be obtained. Was.
It is considered that this is because the difference in the propagation constant β between the central fiber 11 and the peripheral fiber increases because the peripheral fiber has a dip.

Although the softening temperature of the fiber is affected by the amount of dopant contained in the fiber, the softening temperature of each fiber is different by using fibers having different doping concentrations as the central fiber and the peripheral fiber. . Therefore, when the fiber is heated and drawn, the drawing amount of each fiber is different. For example, when the softening temperature of the peripheral fiber is lower than the softening temperature of the central fiber, the peripheral fiber becomes thinner than the central fiber when stretched by heating, and the propagation constant β of the peripheral fiber decreases. Therefore, as a result, the difference in the propagation constant β between the center fiber and the peripheral fiber becomes large, and the coupling between the two becomes difficult to occur. Therefore, it is difficult to manufacture a multi-branch optical coupler having a desired uniform branch ratio. It is thought that it becomes.

From the above, it is apparent that when a fiber having a type B profile is used, it is difficult to generate a multi-branch optical coupler having a desired branching ratio, and the yield is deteriorated. Therefore, if the center fiber 11 and the peripheral fiber having no dip between the core and the clad are prepared, the yield of the multi-branch optical coupler having a desired branch ratio can be improved. Further, by preparing the center fiber 11 and the peripheral fiber having substantially the same softening temperature, the yield of the multi-branch optical coupler having a desired branch ratio can be improved.

Although the present invention has been described through the embodiments, the scope of the present invention is not limited by the description of the embodiments. Those skilled in the art can make various changes or modifications to the embodiments of the invention described in the embodiments. It is apparent from the description of the appended claims that embodiments with these changes or modifications can be included in the scope of the present invention. In particular, the total number of branched fibers may be two or more, and is not limited to eight or sixteen as described in the embodiments and examples of the invention.

As is apparent from the above description, according to the apparatus and method for manufacturing a multi-branch optical coupler of the present invention, a multi-branch optical coupler capable of branching light into a central fiber and a peripheral fiber at a desired ratio. The coupler can be easily manufactured.

The following invention is disclosed in the present application. 1. A multi-branch optical coupler manufacturing apparatus that manufactures a multi-branch optical coupler that splits light input to a single fiber into a plurality of fibers and outputs the branched light, wherein a central hole that penetrates a central fiber in the plurality of fibers, And a mask having peripheral holes that are arranged at equal intervals around the center hole, and a peripheral fiber that penetrates peripheral fibers that are fibers other than the central fiber in the plurality of fibers, and rotating the mask to form the peripheral fiber A rotating stage that twists around the central fiber, the peripheral fiber twisted around the central fiber by the rotating stage, and a heating device that heats the central fiber, and the central fiber that is heated by the heating device. And a drawing stage for drawing the peripheral fiber.

2. 2. The multi-item as set forth in claim 1, further comprising: a stress adjusting section for holding a stress generated in each of the center fiber and the peripheral fiber at a desired value when the plurality of fibers are twisted by the rotating stage. Branch optical coupler manufacturing equipment. 3. 3. The multi-branch coupler manufacturing apparatus according to item 2, further comprising a clamp provided between the stress adjustment unit and the heating device, the clamp fixing the fiber. 4. 2. The multi-branch optical coupler manufacturing apparatus according to item 1, wherein the mask has seven or more peripheral holes, and an inner diameter of the center hole is larger than an inner diameter of the peripheral hole.

5. A multi-branch optical coupler manufacturing apparatus that manufactures a multi-branch optical coupler that splits light input into one fiber into a plurality of fibers and outputs the branched light, wherein a rotation stage that twists the plurality of fibers, When twisting the plurality of fibers, a stress adjusting unit that holds a stress generated in each of the plurality of fibers at a desired value, a heating device that heats the plurality of fibers twisted by the rotating stage, And a drawing stage for drawing the fiber heated by the device. 6. The multi-branch optical coupler manufacturing apparatus according to item 5, further comprising a clamp provided between the stress adjusting unit and the heating device, the clamp fixing the fiber.

7. 6. The multi-branch optical coupler manufacturing apparatus according to item 5, wherein the stress adjusting unit has an elastic holding unit that elastically holds each of the plurality of fibers independently. 8. A central hole through which the central fiber in the plurality of fibers penetrates, and peripheral holes which are arranged at equal intervals around the central hole, through which peripheral fibers which are fibers other than the central fiber in the plurality of fibers penetrate. The multi-branch optical coupler according to item 5, further comprising a mask having: a stress adjusting unit that holds the central fiber penetrating the central hole and the peripheral fiber penetrating the peripheral hole. manufacturing device. 9. A monitor light output device for inputting monitor light to an input end of the central fiber for inputting the light, a light output from an output end of the central fiber, and a light output from one of the peripheral fibers; Item 9. The multi-branch optical coupler manufacturing apparatus according to item 8, further comprising a light receiving device.

10. Means for stopping the movement of the stretching stage when the intensity of light output from the output end of the central fiber and light output from one of the peripheral fibers becomes substantially equal. Item 10. The multi-branch optical coupler manufacturing apparatus according to item 9, which is a feature. 11. The multi-branch optical coupler manufacturing apparatus according to item 8, wherein the mask has seven or more peripheral holes, and an inner diameter of the center hole is larger than an inner diameter of the peripheral hole. 12. The difference ΔCLD between the cladding outer diameter of the central fiber and the cladding outer diameter of the peripheral fiber is 38 to 41 μm when the total number n of the central fiber and the peripheral fiber is 8.
m. The apparatus for manufacturing a multi-branch optical coupler according to item 11, wherein m is in a range of m.

13. A method for manufacturing a multi-branch optical coupler that splits input light into a plurality of fibers and outputs the split light, comprising: providing one central fiber connected from an input end to an output end of the light; Arranging the peripheral fibers at substantially equal intervals along the outer circumference of the fiber; heating the central fiber and the peripheral fibers arranged by the arranging step by a heating device; and Stretching the central fiber and the peripheral fiber heated in the axial direction of the central fiber and fusing each of the peripheral fibers to the central fiber. Production method.

14. The arranging step includes preparing a mask having a center hole and peripheral holes provided at equal intervals around the center hole, allowing the center fiber to penetrate the center hole, and 14. The method for manufacturing a multi-branch coupler according to item 13, comprising a step of penetrating a peripheral fiber. 15. 15. The method of claim 14, wherein the arranging step further comprises a step of twisting the peripheral fiber around the center fiber by rotating the mask. 16. In the disposing step, the stress generated in each of the central fiber and the peripheral fiber in the twisting step is desired by independently holding each of the central fiber and the peripheral fiber penetrating the mask with an elastic holder. 16. The method for producing a multi-branch optical coupler according to item 15, further comprising a step of maintaining the value of the optical coupler.

17. Item 16 is characterized in that the arranging step further includes a step of fixing the center fiber and the peripheral fiber after the twisting step by a clamp provided between the elastic body and the heating device. The method for producing a multi-branch coupler according to the above. 18. An input step of inputting monitor light from the input side of the central fiber, a step of monitoring an output from the output side of the central fiber and one of the peripheral fibers, and an output from the output side of the central fiber. And a stopping step of stopping the heating by the heating step and the stretching by the stretching step when the intensity of the light and the intensity of the light output from the one of the peripheral fibers become equal. 14. The method for manufacturing a multi-branch coupler according to item 13, wherein

19. Item 18 further comprising a tensioning step of applying a tension to the fused central fiber and the peripheral fiber after the stopping step.
3. The method for producing a multi-branch coupler according to item 1. 20. 20. The method for manufacturing a multi-branch optical coupler according to item 19, wherein the tensioning step includes a step of moving a stretching stage that moves at least one end of the central fiber and the peripheral fiber by a predetermined length. 21. 20. The method of claim 19, further comprising the step of fixing both ends of the fusion spliced portions of the central fiber and the peripheral fiber that have been tensioned by the tensioning step to rigid members.

22. 14. The method for manufacturing a multi-branch coupler according to item 13, further comprising connecting a fiber having a cladding diameter smaller than a cladding diameter of the center fiber to the input side and the output side of the center fiber. 23. 14. The method for manufacturing a multi-branch optical coupler according to item 13, further comprising a step of performing an anti-reflection process on an end of the peripheral fiber on a side closer to the input end.

[0075]

According to the present invention, it is possible to efficiently produce a coupler having a desired branching ratio without wasting fiber material.

[Brief description of the drawings]

1 (a) and 1 (b) are a plan view and a side view, respectively, of a multi-branch optical coupler manufacturing apparatus according to the present invention.

FIG. 2 is a plan view of a mask.

FIG. 3 is a detailed view of a rotary stage.

FIGS. 4A to 4C show an example of a cross-sectional shape of a multi-branch optical coupler of the present invention using eight fibers.

FIGS. 5A to 5C are cross-sectional views of a stretched bonding region.

FIG. 6 shows the relationship between the outer shape difference ΔCLD of the clad and the uniformity.

7A and 7B show the relationship between the extension length and the optical output intensity of the multi-branch optical coupler of the present invention.

FIG. 8 shows a multibranched optical coupler strand completed by stretching.

FIG. 9 shows the relationship between each output port and the insertion loss of the multi-branch optical coupler of the present invention.

FIG. 10 is a Type A refractive index profile with no dip between core and cladding.

11 shows the relationship between the extension length and the optical output intensity of a multi-branch optical coupler composed of a central fiber and a peripheral fiber having the type A profile shown in FIG.

FIG. 12 shows the wavelength characteristics of the insertion loss of the multi-branch optical coupler of the present invention.

FIG. 13 is a type B refractive index profile having a dip between a core and a cladding.

14 is a graph showing the extension length and optical output intensity of a multi-branch optical coupler composed of a central fiber having a type A profile shown in FIG. 10 and a peripheral fiber having a type B profile shown in FIG. Show the relationship.

DESCRIPTION OF SYMBOLS 11 Central fiber 12-18 Peripheral fiber 22 Burner 31 Fiber 32a, 32b Clamp base 36a, 36b Clamp 38a, 38b Sliding holder 33a, 33b Rotary stage 34a, 34b Mask 35a, 35b Stretching stage 40 Stress adjuster 44 Elastic holding part 72 Center hole 74 Peripheral hole

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Masaaki Shiroda 2-chome Isobe, Annaka-shi, Gunma Prefecture Shin-Etsu Kagaku Kogyo Co., Ltd. (72) Inventor Masatake Ejima 2-chome Isobe, Annaka-shi, Gunma Prefecture No. 1 Shin-Etsu Chemical Industry Co., Ltd.

Claims (11)

[Claims] 1. A splitting optical coupler for splitting input light into a plurality of fibers and outputting the split light, comprising: a central fiber having an input end for inputting the light, and having a core and a cladding provided around the core. And a peripheral fiber disposed around the central fiber and having a core and a cladding provided around the core, wherein the central fiber and the peripheral fiber do not have a dip between the core and the cladding. A branch optical coupler, characterized in that: 2. A branch optical coupler for splitting input light into a plurality of fibers and outputting the split light, comprising: a central fiber having an input end for inputting the light and exhibiting a predetermined softening temperature; And a peripheral fiber that exhibits a softening temperature substantially equal to the predetermined softening temperature of the central fiber, wherein the peripheral fiber is partially fused to the central fiber. Optical coupler. 3. The branch optical coupler according to claim 1, wherein the central fiber has an output end for outputting the light. 4. The branch optical coupler according to claim 1, further comprising a plurality of said peripheral fibers. 5. The branch optical coupler according to claim 4, wherein the plurality of peripheral fibers are arranged at substantially equal intervals along an outer periphery of the center fiber. 6. The branch optical coupler according to claim 1, wherein the peripheral fiber is partially fused to the center fiber. 7. A method of manufacturing a branch optical coupler for manufacturing a branch optical coupler for branching input light into a plurality of fibers and outputting the split light, comprising: a core; and a core provided around the core. Providing a central fiber having a clad that is not provided and having no dip between the core and the clad, comprising a core and a clad provided around the core,
Preparing a peripheral fiber having no dip between the core and the cladding; arranging the peripheral fiber along an outer periphery of the central fiber; and arranging the central fiber and the central fiber arranged by the arranging step. A heating step of heating the peripheral fiber by a heating device; and the central fiber and the peripheral fiber heated in the heating step are stretched in the axial direction of the central fiber, and each of the peripheral fibers is fused to the central fiber. A branching optical coupler manufacturing method. 8. A method for manufacturing a branch optical coupler for manufacturing a branch optical coupler for branching input light into a plurality of fibers and outputting the split light, comprising: a center having an input end of the light and having a predetermined softening temperature. Preparing a fiber, preparing a peripheral fiber having a softening temperature substantially equal to the softening temperature of the central fiber, arranging the peripheral fiber along the outer periphery of the central fiber, and arranging the peripheral fiber. A heating step of heating the arranged central fiber and the peripheral fiber by a heating device, and extending the central fiber and the peripheral fiber heated in the heating step in the axial direction of the central fiber; And a drawing step of fusing each to the center fiber. . 9. The method according to claim 7, wherein the step of preparing the central fiber includes preparing a central fiber having an input end of the light and an output end of the light and having a predetermined softening temperature. 9. The method for producing a branched optical coupler according to item 8. 10. The method according to claim 7, wherein the step of preparing the peripheral fiber includes preparing a plurality of the peripheral fibers. 11. The step of arranging the plurality of peripheral fibers at substantially equal intervals along an outer circumference of the center fiber.
3. The method for manufacturing a branched optical coupler according to item 1.