JPH0574804B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical star coupler that distributes a light beam transmitted through an optical fiber to a plurality of optical fibers, and a method for manufacturing the same.

[Background of the invention]

With the rapid advancement of optical fiber transmission technology,
2. Description of the Related Art Optical data links that use optical fibers for data transmission between computers and between computers and terminals are actively being researched and developed. In configuring this optical data link, an optical star coupler is an essential device that can mix optical signals from multiple input optical fibers and distribute them evenly and with low loss to multiple output optical fibers. It is.

Conventionally, a typical example of an optical star coupler is the biconical taper type shown in Figure 9 (see pages 324-325 of the 1st printing of ``Optical Communication Handbook'' edited by Hisayoshi Yanai, published by Asakura Shoten, September 1, 1982). . this is,
A large number of optical fibers 1 are put together in one place, heated and fused by applying a twist, and a tapered region 5 is formed in the center of the optical fibers 1 for input (the left side of the tapered region 5). ) is distributed to a plurality of output optical fibers (on the right side of the tapered region 5). In addition, in Figure 9,
The arrow indicates the direction of travel of the optical signal. It has been reported that in this biconical taper type optical star coupler, good characteristics can be obtained when multimode optical fibers are used and the number of optical fibers is four or more. However, there are few reports on cases in which a single mode optical fiber capable of long-distance, high-capacity transmission is used and the number of input ports is 2 to 2, and the characteristics shown in the reported examples are good. It can not be said. According to research conducted by the present inventors, it has been found that it is extremely difficult to realize a uniformly distributed optical star coupler, especially using a single mode optical fiber.

That is, the present inventors used the configuration shown in FIG. 10 to variously change the number of twists, stretching ratio, and fusion range of the twisting/fusion/stretching section 7 (corresponding to the tapered region 5 in FIG. 9). (In FIG. 10, 1i is the input optical fiber and 1o is the output optical fiber). However, it has not been possible to achieve low insertion loss and little distribution variation. This is because if an attempt is made to obtain a low insertion loss, the distribution variation will be extremely large at 10 dB or more, and an attempt to reduce the distribution variation will result in an insertion loss of 10 dB or more, which is a trade-off. Also, twisting, fusing,
The outer diameter of each optical fiber (cladding diameter: 125 μm) corresponding to the stretched portion 7 is etched to 20 μm.
and the core between each optical fiber (core diameter approximately 10 μm:
In order to realize a single-mode optical fiber, the core diameter needs to be reduced in this way). In this case, it was possible to reduce the distribution variation relatively easily when the optical fiber outer diameter was about 20 μm, but on the other hand, because the optical fiber outer diameter was small, the twisting, fusing, and drawing process required twisting, fusing, and stretching. It was found that the center portion of the stretched portion 7 was bent or bent, resulting in a significant decrease in reliability. Considering this point, the outer diameter of the optical fiber that can be handled with this method is at least
It was about 60 μm. However, the outer diameter of the optical fiber
At about 60 μm, the core spacing was too wide, so sufficient coupling could not be obtained, and when the insertion loss was 6 dB or less, the distribution variation was more than 10 dB.

For the reasons mentioned above, it is difficult to apply a biconical taper type optical star coupler as a single mode optical fiber capable of long-distance and large-capacity transmission by simply forming twisted, fused, and stretched parts. , It was also found that it is difficult to have a two-to-two ratio of input ports to output ports.

In addition, in terms of manufacturing, as mentioned above, when forming a single optical mode fiber, it is necessary to stretch the outer diameter of the tapered region 5 to a thinness of 10-odd μm to 100-odd μm. Stretched parts may be damaged or bent during handling. Furthermore, although an oxyhydrogen burner is usually used as a heating source for stretching, the wind pressure of the oxyhydrogen burner may bend or deform the molten part, or it may melt too much, making it impossible to control the outer diameter to the desired value. There is a problem that the yield is very low. In particular, when the number of input-to-output ports is small, the outer diameter of the above region must be set from several tens of micrometers to several tens of micrometers (this value varies depending on the thickness of the cladding).
Each of the above problems is more serious.

As a conventional example of a 2:2 optical branch circuit (optical star coupler) using a single mode optical fiber, the first
There are those shown in FIGS. 1 and 12. First of all
In FIG. 1, optical fibers 1a and 1b are embedded in blocks 31a and 31b, fixed with adhesive, and surfaces 32a and 32b are polished, and then these are assembled. Figure 11b is A in Figure 11a.
This is an enlarged view of the -A' cross section, and by doing so, the distance between the cores 2a and 2b of each of the optical fibers 1a and 1b is brought very close to increase the coupling efficiency. However, the controllability of the polishing thickness is poor and the manufacturing time is long. Therefore, there is a problem that the manufacturing cost becomes extremely high. Note that 3a and 3b in FIG. 11b are clads of the optical fibers 1a and 1b, respectively.

FIG. 12 shows the optical fibers 33a, 3 of the eccentric core.
3b, the distance S (several μm) between the respective cores 2 ₃₃ a and 2 ₃₃ b is made close to each other.
Note that FIG. 12b is an enlarged view of the section A-A' in FIG. 12a. However, in this configuration, it is difficult to make the eccentric core optical fibers 33a, 33b, and the manufacturing cost increases. Also, when fusing the cores so that they are close to the minimum, it is not possible to judge whether or not the core spacing is close to the minimum.
Manufacturing yield becomes an issue.

As explained above, in the conventional method, optical star couplers for single-mode optical fibers capable of long-distance and large-capacity transmission, especially single-mode optical fibers with equal distribution of n to n input/output ports, are used. It has been difficult to achieve low insertion loss, low distribution variation, and low cost.

[Purpose of the invention]

An object of the present invention is to solve the problems of the prior art as described above, and to provide an optical star coupler for single mode and multimode optical fibers, especially when the number of input/output ports is n.
It is an object of the present invention to provide an optical star coupler for a single mode optical fiber with equal distribution of n pairs, which can realize low insertion loss, low distribution variation, and low cost, and a method for manufacturing the same.

[Summary of the invention]

The object of the present invention is to provide a biconical tapered optical star coupler having a tapered twisted, fused, and stretched portion in the center of a bundle of a plurality of optical glass fibers, which twist, fused, and stretched portion. An optical star coupler characterized in that a twist/fusion part is provided on both sides of the extension part, and the twist/fusion part and the twist/fusion/extension part are suspended in a glass protective tube, and A method for manufacturing a biconical tapered optical star coupler having a tapered twisted/fused/stretched part in the center of a plurality of bundled optical glass fibers, the method comprising: (1) a plurality of bundled optical glass fibers; A step of twisting the optical glass fiber bundle, (2) a step of applying only heat treatment to the optical glass fiber bundle twisted in the step to form a twisted/fused part, and (3) a step of forming a twisted/fused part by the step. (4) forming the twisted/fused part and the twisted/fused part by subjecting the formed twisted/fused part to heat treatment, twisting process, and stretching process in parallel; This is achieved by a method for manufacturing an optical star coupler characterized by including a step of suspending the bonding/stretching portion in a glass protective tube.

[Embodiments of the invention]

Hereinafter, the configuration of the present invention will be explained in detail using examples.

FIG. 1 is a block diagram of an optical star coupler according to an embodiment of the present invention.

1a and 1b are silicone coated single mode optical glass fibers (core diameter 10μm, cladding diameter 125μm)
4 is a coating material (silicone) for the optical fiber 1, 6a and 6b are twisting/fusion parts, 7 is a twisting/fusion/stretching part, and 8 is a protection tube (this example). In this case, a Pyrex tube or a quartz glass tube with an outer diameter of 6 mm and an inner diameter of 4 mm is used.) 9 is an adhesive for bonding and fixing the protective tube 8 and the optical fibers 1a and 1b. In this example, an epoxy-based "Araldite" (trade name: Epoxy Technology, Inc., USA) was used as the adhesive 9.

As the protective tube 8, it is also possible to use quartz glass or Vycor glass tube, and dopants (for example, B ₂ O ₃ , GeO ₂ , P ₂ It is also effective to use a glass tube containing O ₅ , etc.).

In addition, as shown in FIG. 1, the optical fiber 1
Out of a, 1b, the covering material 4 corresponds to the twisted/fused parts 6a, 6b and the twisted/fused/stretched part 7
Although the silicone is exfoliated, it is also possible to use an optical fiber that is uncoated and consists only of a core and a cladding.

The number of twists of the twist/fused parts 6a, 6b is approximately several times, and the greater the number of twists, the smaller the distribution variation. Also, the twisted/fused part 6a,
The length of 6b is preferably about several cm. Furthermore, unless the twist pitch is several mm or more, it may cause breakage or increase microbending loss.

The length of the twisting/fusion/stretching section 7 should be approximately several centimeters at most, and the stretching ratio of this section should preferably be approximately 1.5 to 15 times. The larger the stretching ratio, the smaller the distribution variation, but as the core diameter in this part becomes smaller, the normalized frequency V becomes less than 2 (V < 2.4 in the case of a single mode optical fiber), and the surface condition of this part becomes smaller. Therefore, characteristic fluctuations are likely to occur. That is, the normalized frequency V is V=2πa/λ√ ₁ ² − ₂ ² ...(1) where a: core diameter, λ: wavelength, n ₁ : refractive index of the core, n ₂ :
This is because the normalized frequency V is expressed by the refractive index of the cladding and is proportional to the core diameter a. Therefore, the twisted/fused parts 6a, 6
b and the twisted/fused/stretched portion 7 are suspended in the protective tube 8 to keep the surface clean and to prevent boundary conditions from changing.

Note that the number of optical fibers is not limited to two, and may be two or more, or more than one hundred. It goes without saying that this embodiment can also be applied to multimode optical fibers other than single mode optical fibers. Further, the present invention is not limited to the case where the number of input/output ports is equally distributed n to n, and it goes without saying that it can be applied to an optical star coupler with any branching ratio.

Next, an example of measuring the optical characteristics of the optical star coupler shown in FIG. 1 will be described.

First, the length of the part of the optical fibers 1a and 1b from which the coating material 4 (silicone or silicone coated with nylon) is peeled off is 40 mm.
Twisting was applied five times within this 40 mm length.
Next, the twisted and fused portion 6a (length approximately 15 mm) was heated with a heat source to be fused. Thereafter, while heating the twisting, fusing, and stretching part 7 (length: about 10 mm), fusing and stretching were performed while adding two more twists, so that the length was about 40 mm (stretching ratio: 4 times). Then, the twisted and fused portion 6b (about 15 mm in length) was heated and fused.
Thereafter, it was inserted into a protective tube 8 (length 70 mm) and glued and fixed.

When we measured the characteristics of this optical star coupler, we found that
At the He-Ne laser wavelength, insertion loss is 2.1 dB,
The distribution variation was 2.8dB.

In addition, the conditions were the same as above except for the twisting, welding, and stretching part 7, and the twisting, welding, and stretching part 7 (length approximately 10
fusing and stretching the length (mm) by twisting it three times,
60mm (stretching ratio 6.0x), insertion loss
2.7dB and distribution variation of 1.4dB.

Furthermore, coating material 4 is applied to the optical fibers 1a and 1b.
After twisting 4 times within the length of the peeled part (40 mm), manufacturing was performed under the same conditions as the first one, and the insertion loss was 1.8 dB and the distribution was uneven.
Obtained 4.1dB. That is, the twisted/fused portion 6a,
It was found that as the number of twists of 6b decreased, the distribution variation increased.

In this way, the optical star coupler of this embodiment has twisted/fused parts 6 on both sides of twisted/fused/stretched part 7.
By providing a and 6b, it is possible to realize low insertion loss and low distribution variation even in an optical star coupler for a single mode optical fiber capable of long-distance, large-capacity transmission. It was also found that since the protective tube 8 held the tube suspended in the air, there was almost no change in characteristics due to changes in environmental conditions.

Next, a method of manufacturing an optical star coupler according to an embodiment of the present invention will be described.

FIG. 2 is a diagram showing a method of manufacturing an optical star coupler according to the first embodiment of the present invention.

First, as shown in FIG. 2a, the coating material (silicone) 4 near the center of the silicone-coated optical fibers 1a, 1b is peeled off by chemical or mechanical treatment. As a result, the cross-sectional views taken along lines A-A', B-B', and C-C' in FIG. 2A are as shown by the arrows. In addition, 2 has an outer diameter of 10μ
3 is a cladding with an outer diameter of 125 μm.
The optical fiber 1 used in this example is a single mode optical fiber with a refractive index difference of 0.27% and a cutoff wavelength of 1.2 μm.

FIG. 2b shows an optical fiber obtained by etching the portion from which the coating material 4 was removed in FIG. 2a. Etching is done with 50% hydrofluoric acid.
This was done for 16 minutes, and the outer diameter of Clad 3 was made 60 μm.

Next, the two optical fibers 1a, which have been etched as described above, are etched using the apparatus shown in FIG.
Bundle 1b and add a twist. In FIG. 2c, 10 is a base, 11a and 11b are chucks for fixing optical fibers 1a and 1b, and 12 is a chuck portion 11b in the direction of arrow 14 (optical fibers 1a and 1b).
A chuck rotation mechanism 13 supports the chuck 11b and the chuck rotation mechanism 12, and supports the chuck 11b and the chuck rotation mechanism 12.
The chuck moving mechanism moving above, 15 is a heating source.

With this device, first, bundled optical fibers 1
Both ends of a and 1b are fixed by chucks 11a and 11b, and only one of them is rotated and twisted by chuck rotation mechanism 12. In this embodiment, the chuck rotation mechanism 12 is provided only in the chuck 11b, but
The chuck 11a may also be provided with a chuck rotation mechanism, and both rotation mechanisms may be rotated in opposite directions to add a twist.

Next, the heating source 15 is moved from the direction of the chuck 11a to the direction of the chuck 11b along the axial direction of the twisted optical fibers 1a and 1b.
However, the heating source 15 is moved so as to heat only the portions of the optical fibers 1a and 1b from which the coating material 4 has been peeled off. Optical fiber 1 with a twist
By heating the parts a and 1b on the left side of the drawing, the optical fibers 1a and 1b in this part are fused and twisted.
A fused portion 6a is formed. When the heating source 15 comes near the center of the optical fibers 1a, 1b, the chuck 11b is rotated. This rotation forms the twisted/fused/stretched portion 7. Check 11 after passing through the twisting/fusion/stretching section 7.
By stopping the rotation of b and further moving the heat source 15 in the direction of the chuck 11b, the twisted and fused portion 6b is formed.

The heat source 15 used in this step is specifically an oxyhydrogen burner, and the oxygen nozzle has an inner diameter of 0.65.
mm, gap between oxygen nozzle outer diameter and hydrogen nozzle inner diameter
A 2.0 mm double tube type was used. The flow rates of oxygen and hydrogen gas were both set to minute amounts of 1/min or less. The moving speed of the oxyhydrogen burner was several mm/sec in the twisting/welding parts 6a and 6b, and a slower speed in the twisting/welding/stretching part 7. In addition, as the heat source 15, an electric furnace, a high frequency heating furnace, etc. can be used in addition to an oxyhydrogen burner.

After forming the twisted/fused parts 6a, 6b on both sides of the twisted/fused/stretched part 7 in this way, these twisted/fused parts 6a, 6b and the twisted/fused/stretched part 7 are connected to the protective tube. The optical fibers 1a and 1b are inserted into the protective tube 8 at both ends of the protective tube 8 and held in the air.
Glue and fix.

FIG. 3 is a diagram showing an embodiment of the second method for manufacturing an optical star coupler of the present invention.

The feature of this embodiment is that the entire device is surrounded by a box 17 with an exhaust port 18. In this way, by surrounding the optical fibers 1a and 1b with the box 17, uneven heating of the optical fibers 1a and 1b due to fluctuations in the flame of the heat source (oxyhydrogen burner) 15 can be suppressed. Further, 19 is a light source, for example, a He-Ne laser is used. The optical star coupler can be manufactured by shining the emitted light 20 from the output ports of the two optical fibers 1a and 1b onto the screen 21 and checking its characteristics.

FIG. 4 is a diagram showing a third embodiment of the method for manufacturing an optical star coupler according to the present invention.

A feature of this embodiment is that the optical fibers 1a and 1b are heated indirectly. The reason for indirect heating is the heating source (oxygen hydrogen burner) 1
This is to prevent deformation and bending of the optical fibers 1a and 1b due to the wind pressure described in No. 5, and to improve manufacturing yield.

As a method of indirect heating, a semicircular tube glass (in this case, quartz glass) 22 is placed on a support 23.
The optical fibers 1a and 23b are supported at positions below the optical fibers 1a and 1b, and heating is performed through the semicircular glass tube 22. In this case, oxyhydrogen is supplied to the oxyhydrogen burner 15 at a rate of several minutes per minute or more.

Note that the first to third manufacturing methods described above were for a 2:2 optical star coupler, but in each of the above embodiments, the number of optical fibers was two or more, that is, n:n.
It can also be applied to the production of optical star couplers (n>2).

Unlike the conventional techniques shown in FIGS. 11 and 12, these manufacturing methods do not require polishing the joint surfaces of blocks in which optical fibers are embedded, or use optical fibers with eccentric cores that are difficult to manufacture. Therefore, it is possible to reduce manufacturing costs and improve manufacturing yield.

FIG. 5 is a diagram showing a fourth embodiment of the method for manufacturing an optical star coupler of the present invention.

FIG. 5a is a diagram showing the first step of this embodiment. Before explaining the first step, the apparatus used in this example will be explained.

1 is an optical fiber, and 1c is an optical fiber bundle in which optical glass fibers 1 are bundled. The optical fiber 1 used in this example is a single mode optical fiber with a core diameter of 10 μm and a cladding diameter of 40 μm. 8 is a protection tube made of a hollow glass tube, the outer diameter of which is made thinner at both ends so that the optical fiber bundle 1c and both ends of the protection tube 8 can be bonded and fixed in the final step. be. The protection tube 8 used in this example is a quartz glass tube with an outer diameter of 6 mm and a wall thickness of 1 mm.

24a and 24b are the chucks 11c and 24b, respectively.
11d, a headstock 25a and 25b support chucks 11e and 11f, respectively;
26a and 26b are headstocks 25a and 25, respectively.
headstock moving mechanism for moving b, 27,2
8 and 29 are an oxygen inlet, a hydrogen inlet, and a heat source moving mechanism of the heat source 15, respectively. Check 11
c, 11d, 11e, and 11f are each equipped with a chuck rotation mechanism (not shown). heating source 1
5 uses an oxyhydrogen burner and is equipped with an oxygen inlet 27 and a hydrogen inlet 28.

First, the protection tube 8 is held by the chucks 11c and 11d of the headstocks 24a and 24b. The optical fiber bundle 1c is inserted into the protected tube 8 held. Thereafter, the optical fiber bundle 1c is moved to the outer headstock 25 so that the optical fiber bundle 1c is suspended in the protection tube 8.
It is held by chucks 11e and 11f of a and 25b. Note that the center axes of the inner headstocks 24a, 24b and the outer headstocks 25a, 25b are aligned. Therefore, the optical fiber bundle 1c can be suspended in the air without contacting the protective tube 8 at all.

FIG. 5b is a diagram showing the next step.

As shown by arrows in the figure, the optical fiber bundle 1c is twisted by rotating the chucks 11e and 11f in opposite directions around the axis of the optical fiber bundle 1c. The number of twists depends on the total length of the optical fiber bundle 1c and the degree of coupling between the optical fibers 1, but usually the total length of the optical fiber bundle 1c is 200
If it is about mm, twist it about 1 to 30 times. Generally, the number of twists needs to be increased in proportion to the total length of the optical fiber bundle 1c. The greater the number of twists, the more it becomes possible to maintain the core 2 of each optical fiber 1 in a circular shape within the radial cross section of the twist/fusion/stretch portion 7 shown in FIGS. 2a and 2b. However, if the number is too large, the loss will increase and the stretching length must be increased, so it should be set depending on the number of optical fibers, the outer diameter of the optical fibers, etc. As a result, it is possible to realize an optical star coupler with no mode dependence in the degree of coupling.

Next, as shown in FIG. 5c, the optical fiber bundle 1c in the protection tube 8 is fused on both sides and twisted, fused, and stretched in the center using the heating source 15. At this time, by rotating the chucks 11c and 11d in the same direction, the protective tube 8 is rotated to uniformly heat its outer periphery, and the twisting, fusing, and stretching processes are performed symmetrically, quickly, and smoothly.

That is, while rotating the protection tube 8, the ignited heat source 15 is moved along the axial direction of the protection tube 8 at a predetermined speed by the heat source moving mechanism 29. As a result, the twisted optical fiber bundle 1c inside the protection tube 8 is softened and fused. In this example, the moving speed was set to about 0.000 mm/sec. When the ignited heat source 15 passes through the left portion of the protective tube 8, the twisted and fused portion 6a shown in FIG. 1 is formed. When the ignited heat source 15 is near the center, the chucks 11e and 11f are rotated in opposite directions for a predetermined number of rotations and for a predetermined period of time, and at the same time, the headstocks 25a and 25b are rotated by the headstock drive mechanisms 26a and 26b. The optical fiber bundle 1c is moved at a predetermined speed in the direction of stretching. This speed has a linear or nonlinear function between time and distance traveled. As a result, the twisted, fused, and extended portion 7 shown in FIG. 1 is formed.

After the ignited heating source 15 passes near the center, twisting of the optical fiber bundle 1c by the chucks 11e and 11f and stretching by the headstock drive sources 26a and 26b are stopped. The twisted and fused portion 6b shown in FIG. 1 can be formed by further moving the ignited heat source 15 to the right while the twisting and stretching process is stopped. In addition, first, a twisted and fused part is formed in a predetermined part of the optical fiber inside the protection tube.
Next, the vicinity of the center of the upper twisted/fused portion may be stretched.

As mentioned above, the moving speed of the heating source 15 is set to 0.
When mm/sec, all processes in Figure 5 a to d are 30
I was able to finish it within minutes. We made 37 prototype optical star couplers using this method, but the insertion loss was
We were able to achieve a distribution variation of less than 3dB and a distribution variation of less than 2dB.

In order to reduce distribution variations as much as possible, as in the second manufacturing example shown in Fig. 3, a He-Ne laser beam is input into the optical fiber 1, and heating is performed while observing the emitted light. , twisting, fusing, stretching, etc. may be performed. When observing the emitted light, it is better to stop the rotation of the chuck 11e.

FIG. 5d is a diagram showing the next step.

The optical fiber bundle 1c in the protection tube 8 is fused,
After twisting, fusing, stretching, and fusing, both ends of the protective tube 8 are filled with adhesive 9 to bond and fix the optical fiber bundle 1c and the protective tube 8.

In addition, when the heat source 15 is configured to heat the protection tube 8 sequentially from one end to the other end,
Alternatively, if the flame of the oxyhydrogen burner is expanded to widen the heating range of the protection tube 8, there is no need to move the protection tube 8, and if the protection tube 8 is configured to be heated uniformly from its outer periphery, the protection tube There is no need to rotate 8.

After the protective tube 8 has been bonded and fixed, an oxidizing or inert gas is sealed through the hole 30 in FIG.
It may also be filled with silicone material, plastic material). These liquids and resins have the functions of removing cluttering mode and reinforcing the optical fiber. As adhesives, thermoplastic, thermosetting, elastomer, and mixed types can be used. The specific method for the twisting, fusing, and stretching process is to first twist, then stretch while observing the emitted light, and finish the stretching when equal distribution is reached.
Although any method of simultaneously stretching and twisting may be used, the former method provides better controllability.

The twisting process of the optical fiber bundle 1c is as follows:
It is also possible to provide a chuck circuit mechanism only in either chuck 1e or chuck 11f. Further, the stretching process can also be performed by providing a headstock moving mechanism only on either the headstock 25a or the headstock 25b.

The protective tube 8 can also be supported by only one headstock and chuck. That is,
Even if the protection tube 8 is supported only on one side and heated at a temperature that does not deform the protection tube 8, the twisted/fused portion 6
This is because experiments have revealed that a, 6b, and the twisted/fused/stretched portion 7 can be sufficiently formed.

As shown in FIG. 6, the shape of the protective tube 8 can be made narrower near the center to facilitate heat transfer to the optical fiber bundle 1c. Further, as shown in FIG. 7, holes 30 may be provided near both ends of the tube to facilitate insertion of the adhesive 9 into the tube in the step of FIG. 5d. Furthermore, a straight protection tube as shown in FIG. 8 may be used.

In this fourth embodiment, the optical star coupler can be manufactured in an integrated process. That is, the process of twisting the optical fiber bundle 1c, forming the twisting/fusion parts 6a and 6b, and twisting/fusion/stretching part is carried out without taking the optical fiber bundle 1c out even once while it is inserted into the protection tube 8. The forming step 7 and the step of forming the twisted/fused portions 6a, 6b and the twisted/fused/stretched portion 7 in a suspended state in the protective tube 8 can be performed continuously, making mass production possible. Also,
Because it is an indirect heating method, even when exposed to heating sources such as oxyhydrogen burners, the molten part will not bend or deform due to the wind pressure, and will not twist or deform.
The outer diameter of the fused/stretched portion 7 can be easily controlled. Furthermore, since it does not break or break during manufacturing, manufacturing yield can be improved and costs can be reduced. In addition, since the optical fiber is heated in a protective tube, it is possible to suppress the infiltration of airborne impurities (transition metals, alkali metals, alkaline earth metals, etc.), and since there is no adhesion of dust, etc., the optical fiber has low loss. You can make a star coupler.
Furthermore, since it is an indirect heating method through a hollow glass tube, a large amount of H ₂ O generated from an oxyhydrogen burner is
Since there is no diffusion and infiltration of the twisted, fused, and stretched parts, absorption loss due to OH ions can be significantly reduced, making it possible to realize a low-loss optical star coupler. In particular, optical star couplers for long wavelengths (1.3μm, 1.55μm,
1.2 μm), it is possible to obtain extremely good characteristics. Furthermore, since the stretching length could be precisely controlled, an optical star coupler with lower loss and distribution variation could be obtained.

Each of the first to fourth embodiments described above can be applied to optical star couplers having a structure other than that shown in FIG. That is, the twisted/fused parts 6a and 6b shown in FIG. 1 are not present, and the twisted/fused part 7 is not present.
It can be applied to the production of optical star couplers having only In this case, the step of FIG. 5b and the second
The twisting process before heating in Figures c, 3, and 4 is omitted.

As a result of making a prototype of such an optical star coupler, we obtained values of insertion loss and distribution variation of around 2 dB when using a multimode optical fiber, and similar values when using a single mode optical fiber. That is, the optical fiber bundle was twisted while heating the protection tube. Thereafter, the film was stretched while observing the emitted light. In this case, the number of twists is several times and the length of stretching is several times.
It was 10mm. The greater the number of optical fibers, the greater the number of twists and the longer the drawn length.

Furthermore, it goes without saying that each of the above embodiments can be applied not only to a single mode optical fiber but also to a multimode optical fiber. In the case of multimode optical fiber, the core diameter is about 50 μm or 80 μm, so
The outer diameter of the optical fiber after etching is preferably about 70 μm or 90 μm.

Further, in each of the above embodiments, the branching ratio is 1:1, but the present invention is not limited to this, and can be applied to the manufacture of an optical star coupler having any branching ratio. For example, in FIG. 2b, the branching ratio can be arbitrarily set by making the outer diameters of the clads 3 of the optical fibers 1 to be bundled different. Specifically, when there are two optical fibers, the outer diameter of the cladding of one optical fiber is 125 μm.
and the outer diameter of the cladding of the other optical fiber is 60μm.
It's fine if you do this.

Also, during the process shown in Fig. 5c, N ₂ was added to the protective tube.
If this is done while flowing a gas such as O ₂ , Ar, or He, a lower-loss optical star coupler can be realized. In this case, gas is supplied from one end of the protection tube.

〔Effect of the invention〕

As explained above, the optical star coupler and the manufacturing method thereof of the present invention can be used not only for optical star couplers for multimode optical fibers, but also for optical star couplers for single mode optical fibers, especially for input/output ports. It is also possible to achieve low insertion loss, low distribution variation, and low cost even for an optical star coupler for a single mode optical fiber with equal distribution of n to n.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an optical star coupler according to an embodiment of the present invention, and FIGS. 2, 3, 4, and 5 are diagrams showing first, second, third, and fourth embodiments of the present invention. Figures 6, 7, and 8 are diagrams illustrating a method of manufacturing an optical star coupler according to an example. diagram showing,
FIG. 9, FIG. 10, FIG. 11, and FIG. 12 are diagrams showing a conventional optical star coupler and its manufacturing method. 1, 1a, 1b: Optical glass fiber, 1c: Optical glass fiber bundle, 6a, 6b: Twisting/fusion part, 7: Twisting/fusion/stretching part, 8: Protection tube,
9: Adhesive, 11a, 11b, 11c, 11d,
11e, 11f: chuck, 12: chuck rotation mechanism, 13: chuck moving mechanism, 15: heating source,
26a, 26b: Headstock moving mechanism.

Claims (1)

[Scope of Claims] 1. A biconical tapered optical star coupler having a tapered twisted/fused/stretched part in the center of a plurality of bundled optical glass fiber bundles, wherein the twisted/fused/stretched part is An optical star coupler characterized in that a twist/fusion part is provided on both sides of the extension part, and the twist/fusion part and the twist/fusion/extension part are suspended in a glass protective tube. 2. The optical star coupler according to claim 1, wherein the protection tube is made of quartz glass and has a circular or semicircular cross section. 3. A method for manufacturing a biconical tapered optical star coupler having a tapered twisted, fused, and stretched portion in the center of a plurality of bundled optical glass fibers, comprising: (1) the plurality of bundled optical glass fibers; (2) a step of applying only heat treatment to the optical glass fiber bundle twisted in the step to form a twisted/fused portion; (3)
a step of performing heat treatment, twisting treatment, and stretching treatment on the twisted/fused portion formed by the step in parallel to form the twisted/fused/stretched portion; (4) the twisted/fused portion and the above-mentioned twisted/fused portion; A method for manufacturing an optical star coupler, characterized by including a step of suspending the twisting, fusing, and stretching parts in a glass protective tube. 4. Claim 3, characterized in that the steps (1) to (3) are performed on a plurality of bundled optical glass fiber bundles inserted in advance into the glass protection tube. A method of manufacturing the optical star coupler described. 5 At least the plurality of bundled optical glass fiber bundles, means for fixing both ends of the optical glass fiber bundles and applying twisting/stretching to the optical glass fiber bundles, and means for heating the optical glass fiber bundles are integrated. Claim 3 or 4, characterized in that the above-mentioned steps are executed while enclosing
2. Method for manufacturing the optical star coupler described in Section 1. 6. A step of forming a twisted/fused portion by only heating the optical glass fiber bundle and a subsequent step of forming a twisted/fused/stretched portion are performed on each of the optical glass fiber bundles constituting the optical glass fiber bundle. Claims 3 to 5 are characterized in that the process is executed while inputting an optical signal into the optical glass fibers and checking the light emitted from each optical glass fiber.
A method for manufacturing an optical star coupler according to any one of paragraphs. 7. The heating means used here is used to perform a step of forming a twisted/fused portion by only heating the optical glass fiber bundle, and a subsequent step of forming a twisted/fused/stretched portion. Claims 3 to 6 are characterized in that the process is carried out while moving the fiber bundle along the axial direction.
A method for manufacturing an optical star coupler according to any one of paragraphs.