JPS6165204A - Optical star coupler and its manufacture - Google Patents

Abstract

PURPOSE:To realize a low distributing dispersion and a low cost with respect to an optical star coupler for a single mode optical fiber, as well, by providing a twisted/welded part on both sides of a tapered twisted/welded/drawn part of the center part of plural bundled optical glass fibers. CONSTITUTION:A covering material 4 being in the vicinity of the center part of optical fibers 1a, 1b covered with silicone is peeled off, the peeled part is brought to an etching processing, and two processed optical fibers 1a, 1b are bundled and twisted. Along the axial direction of the optical fibers 1a, 1b, a heating source 15 is moved from the direction of a chuck 11a to the direction of a chuck 11b. The heated part is welded, a twisted/welded part 6a is formed, and at the time point when the heating source 15 has come to the vicinity of the optical fibers 1a, 1b, a twisted/welded/drawn part 7 is formed by rotating the chuck 11b. The twisted/welded parts 6a, 6b and the twisted/welded/drawn part 7 are inserted into a protective pipe 8, and are stuck and fixed in both ends. In this way, a low insertion loss, a low distributing dispersion and a low cost can be realized.

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 rapid progress in optical fiber transmission technology, research and development of optical data links that use optical fibers for data transmission between computers or between one computer terminal and another are being actively conducted. In configuring this optical data link,
An optical star coupler is an essential device that can mix optical signals from a plurality of input optical fibers and distribute them evenly to a plurality of output optical fibers with low loss.

Conventionally, a typical example of an optical star coupler is the biconical taper type shown in Figure 9.
(see pages 324-325).

This is done by heating a large number of optical fibers 1 together at one location, then adding a "twist" to fuse them, and forming a tapered region 5 in the center of the optical fibers 1 for input (tapered region The optical signal from the left side of the tapered region 5 is distributed to a plurality of output optical fibers (the right side of the tapered region 5). Note that in FIG. 9, arrows indicate the traveling direction of the optical signal.

In this biconical taper type optical star coupler,
It has been reported that good characteristics can be obtained when multimode optical fibers are used and the number of optical fibers is 11 or more. However, there are few cases of complaints regarding the case where a single mode optical fiber capable of long-distance and large-capacity transmission is used and the number of input ports is 2:2, and the characteristics shown in the reported examples are According to the research conducted by the present inventors, it has been found that it is extremely difficult to realize an optical star coupler with equal distribution using a single mode optical fiber.

That is, 1. The present inventors used a configuration as shown in FIG. 1O, and variously changed the number of twists, stretching ratio, and fusion range of the twisting/fusion/stretching portion 7 (corresponding to the tapered region 5 in FIG. 9). However, we were unable to achieve low insertion loss and little distribution variation.

This is because an attempt to obtain a low insertion loss results in extremely large distribution variations of 10 dB or more, and an attempt to reduce the 1-distribution variation results in an insertion loss of 10 dB or more, which is a trade-off. In addition, the outer diameter of each optical fiber (cladding diameter: 125μ) corresponding to the twisted, fused, and stretched portion 7
m) to 20 μm, and the core between each optical fiber (core diameter approximately 10 μm = the core diameter must be reduced in this way to realize an east mode optical fiber).
An attempt was made to make the bond closer by bringing them closer together. 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 if the central portion of the stretched portion 7 was bent or bent, the reliability was significantly reduced. Considering this point, the outer diameter of the optical fiber that can be handled by this method is at least about 60 μm. However, when the outer diameter of the optical fiber was 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 10 dB or more.

For the reasons mentioned above, it is difficult to apply biconical taper type optical star couplers to single mode optical fibers capable of long-distance, high-capacity transmission by simply forming twisted, fused, and stretched parts. , and the number of input to output ports is 2 to 2.
I also found it difficult.

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 part 1 is damaged or broken 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 manufacturing yield is very low. In particular, when the number of input vs. output ports is small, the outer diameter of the above area is
It is necessary to set the thickness from several μm to several tens of μm (this value varies depending on the thickness of the cladding), and each of the above problems becomes more serious.

Conventional examples of 2:2 optical branching circuits (optical star couplers) using single mode optical fibers are shown in Figures 1f and 1.
There is one shown in Figure 2. First, FIG. 11 shows a structure in which optical fibers la and lb are embedded in blocks 31a and 31b, respectively, and fixed with adhesive, and after polishing surfaces 32a and 32b, these are combined. Figure 11(b) shows the first
This is an enlarged view of the AA' cross section in Figure 1 (,). By doing this, the distance between the cores 2a and 2b of each of the optical fibers la and lb is made extremely close to increase the coupling efficiency. ing. 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. In addition, Fig. 11 (b
) 3a and 3b are the claddings of the optical fibers la and lb, respectively.

FIG. 12 shows the distance S (several μ
m) are brought closer to each other. Note that FIG. 12(b) is an enlarged view of the AA' cross section of FIG. 12(a). However, in this configuration, it is difficult to make the eccentric core optical fibers 33a, 33b, and the manufacturing cost increases. Furthermore, when fusion bonding is performed so that the core spacing approaches the minimum, it is not possible to determine whether or not the core spacing is close to the minimum, which poses a problem in manufacturing yield.

As explained above, the conventional method is to use an optical star coupler for single mode optical fiber, which enables long-distance and large-capacity transmission.
In particular, it has been difficult to realize a single mode optical fiber in which the number of input and output ports is evenly distributed (n:n) with 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, particularly for single mode optical fibers with equal distribution of input/output ports of n to n. Low insertion loss and low distribution variation even for fiber optic star couplers.

An object of the present invention is to provide an optical star coupler that can realize low cost and a method for manufacturing the same.

[Summary of the invention]

In order to achieve the above object, the present invention provides 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.・Twist on both sides of the stretched part・
It is characterized by the provision of a fused part.

(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.

la and lb are silicone-coated single-mode optical glass fibers (core diameter 10 μm, cladding diameter 125 μm, hereinafter referred to simply as optical fibers); 4 is the coating material of optical fiber l (
silicone), 6a and 6b are twisted/fused parts, 7 is twisted/fused/stretched parts, and 8 is a protective tube (in this example, the outer diameter is 6
A Pyrex tube or a quartz glass tube with an inner diameter of 4 mm is used.) 9 is an adhesive for bonding and fixing the protective tube 8 and the optical fibers la and lb. In this embodiment, the adhesive 9
The epoxy type "Araldite" (trade name: Epoxy Technology Company, USA) was used as the material.

As the protection tube 8, it is also possible to use quartz glass or Vycor glass tube, and the inner or outer wall of the tube,
or an index-controlling dopant in the wall (e.g. B
203, G e02, P205, etc.) is also effective.

In addition, as shown in FIG. 1, the optical fiber la.

Of tb, the silicone covering material 4 of the parts corresponding to the twisted/fused parts 6a, 6b and the twisted/fused/stretched part 7 has been peeled off, but there is no covering at all, only the core and cladding. It is also possible to use an optical fiber consisting of

The number of twists of the twist/fused parts 6a and 6b is approximately several times, and the greater the number of twists, the smaller the distribution variation. Also, the twist/fusion part 6a.

The length of 6b is preferably about several cm. Furthermore, unless the twist pitch is several mm or more, breakage may occur or microbending loss may increase.

The length of the twisting/fusion/stretching part 7 is about several cm at most.
The stretching ratio of this part is preferably about 1.5 to 15 times. The larger the stretching ratio, the smaller the distribution variation, but the core diameter in this area becomes smaller and the normalized frequency V is less than 2 (
In the case of a single mode optical fiber, V<2.4), and the characteristics tend to fluctuate depending on the surface condition of this portion.

That is, the normalized frequency V is.

However, a: core diameter, λ: wavelength, nl: refractive index of the core,
nl: refractive index of cladding.

This is because the normalized frequency V is proportional to the core diameter a. Therefore, the twisted/fused parts 6a, 6b and the twisted/fused/stretched part 7 are held suspended in the protective tube 8 to keep the surface clean and to prevent the boundary conditions from changing.

Note that the number of optical fibers is not limited to two;
It may be more than 100 books or 10 books. It goes without saying that this embodiment can also be applied to multimode optical fibers other than single mode optical fibers. Furthermore, it goes without saying that the number of input/output ports is not limited to the case where the number of input/output ports is evenly distributed in n:n, but can also be distributed to optical star couplers with arbitrary branching ratios.

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 4"1, and this 40m+m
Twists were applied five times within the length range.

Next, the twisted and fused portion 6a (about 15 cm in length) was heated with a heat source to be fused. After that, the twisting/fusion/stretching part 7
(length: approximately 101,111 mm) was heated and further twisted twice while being fused and stretched to a length of approximately 40 mm (stretching ratio: 4 times). Then, the twisted and fused portion 6b (length approximately L5a+g+) was heated and fused. Thereafter, it was inserted into a protective tube 8 (70 mm in length) and bonded and fixed.

The characteristics of this optical star coupler were measured.

Insertion loss 2.1 dB at He-Ne laser wavelength
, the distribution variation was 2.8 dB.

In addition, the conditions other than the twisting/fusion/stretching part 7 were the same as above, and the twisting/fusion/stretching part 7 (length approximately 10+m+m) was twisted three times and fused/stretched to a length of 60cm ( When the stretching ratio was set to 6.0 times, the insertion loss was 2.7 dB.
, distribution variation of 1.4 dB was obtained.

Furthermore, the optical fibers la and lb were twisted four times within the length range of the part (40 ma+) where the coating material 4 was peeled off, and then the MT3 was crushed under the same conditions as the first, and the insertion loss was 1. .8dB and distribution variation of 4.1dB. In other words, it was found that as the number of twists of the twist/fused portions 6a + 6b decreases, the distribution variation increases.

In this way, the optical star coupler of this embodiment has the twisted/fused parts 6a on both sides of the twisted/fused part 7.

By providing 6bti, it is possible to achieve low insertion loss and low distribution variation even for optical star couplers for Ql-mode optical fibers capable of long-distance and 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 a first embodiment of the present invention.

First, as shown in FIG. 2(a), the coating material (silicone) 4 near the center of the silicone-coated optical fibers la, Ib is peeled off by chemical or mechanical treatment. As a result, the lines A-A' and B in FIG.
-8' line and c-c' line sectional views are as shown by arrows. Note that 2 is a core with an outer diameter of IO μm, and 3 is a core with an outer diameter of 125 μm.
It is a μm cladding. Furthermore, the optical fiber I used in this example had a refractive index difference of 0.27% and a cutoff wavelength of 1.2%.
It is a μm stick-mode optical fiber.

FIG. 2(b) shows that the covering material 11 in FIG. 2(,) is
FIG. 3 is a diagram showing an optical fiber obtained by etching the portions separated by I=lJ. Etching is performed using 50% hydrofluoric acid for about 16 minutes, and the outer diameter of the cladding 3 is set to 60 μm.

Next, the two optical fibers Ia were etched as described above using the apparatus shown in FIG. 2(c).

Bundle the tb and add a twist. In Figure 2(c),
10 is the base, lla, llb are optical fibers la, lb
The chuck 12 fixes the chuck part 11b in the direction of arrow 1.
chuck rotation mechanism for rotating in direction 4 (optical fiber) a, 1 direction of rotation around axis b; 13;
1 is a chuck moving machine end that supports the chuck Ilb and the chuck rotating machine gt12 and moves on the base 10;
5 is a heating source.

With this device, first, the bundled optical fibers la.

Both ends of 1b are fixed by chucks lla and llb, and only one side is rotated and twisted by chuck rotation mechanism 12. In this embodiment, the chuck rotation mechanism 12 is provided only on the chuck 11b, but the chuck rotation mechanism 12 may also be provided on the chuck 11a, and both rotary grooves may be rotated 13 times in opposite directions to add a twist.

Next, along the axial direction of the twisted optical fiber la, ]L+ part, from the direction of the chuck ILa to the chuck llb
Move the heat source 15 in the direction of. However, the heating source 15 is one of the two optical fibers la and Ib.

It is moved so that only the area where the covering material 4 is applied is heated. Optical fiber la with a twist.

By heating the portion on the left side of Ib in the drawing, the optical fibers la and lb in this portion are fused and a twisted/fused portion 6a is formed. When the heating source I5 comes near the center of the optical fibers la and lb, the chuck 11b is rotated. This rotation forms the twisted/fused/stretched portion 7. Once it has passed through the twisting, fusing, and stretching section 7, the chuck l is
lb rotation, and then turn the heat source I5 on to the chuck 1.
By moving in the direction of 1b, the twisted/fused part 6
b is formed.

The heating fFAtS used in one process is specifically an oxyhydrogen burner, with an oxygen nozzle inner diameter of 0.65 m + i.
, Gear Ip2 of oxygen nozzle outer diameter and hydrogen nozzle inner diameter,
On++i double tube type was used. The flow rates of oxygen and hydrogen gas were both set to very small amounts of till/lll1n or less. The moving speed of the oxyhydrogen burner is
In a and 6b, several Iam/sec, twisting, fusion,
In the stretching section 7, the speed was slower than that. 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. 8, and the optical fibers 1a and 1b are glued and fixed at both ends of the protective tube 8 to keep it in a closed room.

FIG. 3 is a diagram showing an embodiment of the second method for manufacturing an optical star coupler according to the present invention. A 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 heating 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 output light 20 from the output boats of the two optical fibers la 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.

The feature of this embodiment is that the optical fibers la and lb are heated indirectly. The reason for indirect heating is to prevent deformation and bending of the optical fibers la and lb due to the wind pressure of the heating source (oxyhydrogen burner H5) and to improve manufacturing yield.

As a method of indirect heating, a semicircular tube glass (in this case, 1 quartz glass) 22 is heated using a support l-23a.

The optical fibers la and lb are supported by the optical fibers la and lb by the glass semicircular tube 23b, and heated through the semicircular glass tube 22.

In this case, the oxyhydrogen burner 15 contains several II oxyhydrogens.
/min 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, several optical fiber companies produced two or more fibers, that is, n:n (n > 2). ) can also be applied to one type of optical star coupler.

These manufacturing methods differ from the conventional techniques shown in Figures 1 and 12 in that they require polishing the joint surface of the block in which the optical fiber is embedded, or use an optical fiber with an eccentric core that is difficult to manufacture. Since there are no defects, 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. 5(a) is a diagram showing the first step of this embodiment.

Before explaining the first step, the apparatus used in this example will be explained.

(2) is an optical fiber, and lc is an optical fiber bundle in which optical glass fibers 1 are bundled. The optical fiber I used in this example is a single mode optical fiber with a core diameter of 10 μm and a cladding diameter of 40 μm. Reference numeral 8 denotes a protection tube made of a hollow glass tube, and both ends of the protection tube have a thin outer diameter so that the optical fiber bundle 1c and both ends of the protection tube 8 can be bonded and fixed in the final step. It is. The protective tube 8 used in this example is a quartz glass tube with an outer diameter of 61 and a wall thickness of 1 u+m.

24a and 24b are chucks 11c, respectively.

The headstocks 25a and 25b that support the lid are the headstocks 26a and 26 that support the chucks lle and llf, respectively.
27, 28 and 29 are the oxygen inlet, hydrogen inlet, and heat source moving mechanism of the heat source 15, respectively. Chuck Ilc.

The lid, lie, and llf are each equipped with a chuck rotation mechanism (not shown). As heating g15, an oxyhydrogen burner is used, and oxygen inlet 27 and hydrogen inlet 2
It has 8.

First, the protective tube 8 is attached to the chuck Il of the headstock 24a, 24b.
c, held by lid. The optical fiber bundle 1c is inserted into the protected tube 8 held. after that.

so that the optical fiber bundle 1c is suspended in the protection tube 8,
The optical fiber bundle 1c is held by chucks lle and llf of the outer headstock 25a25b.

Note that the center axes of the inner headstocks 24a, 24b and the outer headstocks 25a, 25b are made to coincide. Therefore, the optical fiber bundle 1c can be suspended in the air without contacting the protective tube 8 at all.

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

As shown by the arrows in the figure, chuck lla, chuck l
A twist is added to the optical fiber bundle 1c by rotating lf in opposite directions about 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 number of twists is
If the total length is 200 mm, twist it about 1 to 30 times. Generally speaking, the number of twists must be increased in proportion to the total length of the optical fiber east IC. As the number of twists increases, it becomes possible to maintain the core 2 of each optical fiber 1 in a circular shape within the radial cross section of the twisting/fusion/stretching section 7 shown in FIGS. 2(a) and 2(b). . 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. 5(c), the optical fiber bundle 1c in the protective tube 8 is fused on both sides by a heating source [5].
Twist, fuse, and stretch the center part. At this time, by rotating the chuck llc and lid in the same direction,
The protection tube 8 is rotated to uniformly heat its outer periphery, and twisting, fusing, and stretching processes are performed symmetrically, quickly, and smoothly.

That is, the heating-1 is ignited while rotating the protection tube 8.
1J115 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 is set to 0. Several mm/
It was set to about . 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 heating source I5 is near the center, the chucks lla and chucks llf are rotated in opposite directions to each other for a predetermined number of rotations for 1 hour, and at the same time, the headstock 25a
, 25b are moved at a predetermined speed in the direction of extending the optical fiber east IC by the headstock 1 east moving mechanisms 26a, 26b. This speed is a linear or nonlinear function between two hours and the distance traveled. As a result, the twisted, fused, and extended portion 7 shown in FIG. 1 is formed.

After the heated heating source 15 passes near the center,
Twisting of the optical fiber bundle 1c by chuck lie and chuck llf, and headstock drive sources 26a, 2
6b is 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. Note that it is also possible to first form a twisted/fused portion in a predetermined portion of the optical fiber within the protective tube, and then to stretch the vicinity of the center of the upper twisted/fused portion.

As mentioned above, the moving speed of the heating source 15 is set to O0 number ram
/sec, all steps shown in Figures 5(a)-(d) should be completed within 30 minutes/? did it. We fabricated 37 optical star splinters using this method, and were able to achieve insertion loss of less than 3 dB and distribution variation of less than 2 dB.

In addition, in order to reduce distribution variations as much as possible, as in the second manufacturing example shown in FIG.
Heating, twisting, fusing, stretching, etc. may be performed while inputting a He-Ne laser beam into the substrate and observing the emitted light. The output light is I! When measuring, it is better to stop the rotation of the chuck lle.

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

The optical fiber bundle 1c in the protection tube 8 is fused, twisted,
After fusing/stretching and processing WA:v, both ends of the protective tube 8 are filled with adhesive 9, and the optical fiber bundle 1c and the protective tube 8 are bonded together.
Glue and fix.

Note that the heat source I5 may be moved if it is configured to heat the protection tube 8 sequentially from one end to the other, or if the flame of the oxyhydrogen burner is expanded to widen the heating range of the protection tube 8. Further, if the protection tube 8 is configured so that it can be heated uniformly from its outer periphery, there is no need to rotate the protection tube 8.

After sealing the protective tube 8 with adhesive and fixing, oxidizing or inert gas is sealed through the hole 30 in FIG. material) may be filled. These liquids and resins have the functions of removing cluttering modes and reinforcing optical fibers. As the adhesive, types of adhesives such as thermoplastic, thermosetting, elastomeric, and mixed types can be used. In addition,
The specific method for the twisting, fusing, and stretching process is to first add a twist, then stretch while observing the emitted light, and finish the stretching when uniform distribution is reached.

Either method of simultaneously applying a twist and stretching may be used, but the former method provides better controllability).

It is also possible to twist the optical fiber bundle 1c by providing a chuck rotation mechanism only on either the chuck 11e or the chuck Ilf.

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 protection tube 8 can also be supported by only one headstock and chuck. Namely.

Even if the protective tube 8 is supported on only one side and heated at a temperature that does not deform the protective tube 8, the twisted/fused portion 6a remains intact.

This is because experiments have revealed that it is possible to form the twisted/fused/stretched portion 7 sufficiently.

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, it is also possible to provide holes 30 near both ends of the tube to facilitate insertion of the adhesive 9 into the tube I\ in the step of FIG. 5(d). Furthermore, a straight protection tube as shown in FIG. 8 may be used.

In this fourth embodiment, the optical star coupler can be manufactured by the process. That is, the process of twisting the γ-r fiber bundle 1c while the optical fiber bundle 1c is inserted into the protective tube 8 without ever taking it out.
- Formation of fused parts Ga and 6b.

The process of forming the twisted/fused/stretched portion 7 can be performed continuously, and the steps of forming the twisted/fused portions 6a, 6b and the twisted/fused/stretched portion 7 in a suspended state on the protective tube 8 can be performed continuously. , xk production becomes possible. In addition, since it is an indirect heating method, the molten part does not bend or deform due to the wind pressure even when exposed to a heat source such as an oxyhydrogen burner, and the outside of the twisted, fused, and stretched part 7 is prevented. The diameter 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 heat-treated in a protective tube, it is possible to suppress the intrusion of impurities in the air (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 using a hollow glass tube, a large amount of F (20) generated from an oxyhydrogen burner does not diffuse into the twisting, welding, and stretching parts.
Absorption loss due to ions can be significantly reduced, and a lossy optical star coupler can be realized. In particular, extremely good characteristics can be obtained as an optical star coupler for long wavelengths (1.3 μm, +55 μm, 1.2 it m). Also, the stretched length is 1? Since it can be precisely controlled, an optical star coupler with lower loss and distribution variation can 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, it can be applied to the production of an optical star coupler that does not have the twisted/fused parts 6a and 6b shown in FIG. 1 but only has the twisted/fused/stretched part 7.

In this case, the process of FIG. 5(b) and FIG. 2(C
), the twisting process before heating in FIGS. 3 and 4 is omitted.

As a result of making a prototype of such a star coupler, when a multimode optical fiber was used, the values after 2 dBirf for both insertion loss 1 distribution variations were obtained, and similar values were obtained for a QL-mode optical fiber. That is, the optical fiber bundle was twisted while heating the protective tube. Thereafter, the film was stretched while applying light. In this case, the number of twists was several times and the number of stretching lengths was 1OIII11. 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 the above embodiments can be applied not only to 1N and -mode optical fibers but also to multimode optical fibers. For multimode optical fiber, the core diameter is 50
.mu.m or 80 .mu.m at 8 degrees, so the outer diameter of the optical fiber by etching is preferably about 70 .mu.m or 90 .mu.m.

Furthermore, although each of the above embodiments is a case where the 0 branching ratio is 1:1, 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. 2(b, ), the branching ratio can be set arbitrarily by setting the outer diameters of the claddings 3 of the optical fibers 1 to be bundled to different values. Specifically, when the number of optical fibers is two, the cladding outer diameter of one optical fiber is set to 1.
25μm, and the other optical fiber has a crut outer diameter of 60μm.
It suffices if it is μm.

Also, during the process shown in FIG. 5(C), N2 was added to the protective tube.

If this is carried out while flowing a gas such as 02, 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, according to the optical star coupler and the manufacturing method thereof of the present invention, an optical star coupler for a single mode optical fiber, particularly for a single mode optical fiber in which the number of input and output ports is evenly distributed n to n. This makes it possible to achieve low insertion loss, low distribution variation, and low cost even for optical star couplers6.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical star coupler according to an embodiment of the present invention, and FIGS.
Second. Third. Figures 6, 7, and 8 are diagrams illustrating the manufacturing method of the optical star coupler according to the fourth embodiment.
FIG. 6 is a diagram showing another embodiment of the protection tube used in FIGS. 4 and 5. FIG. FIG. 9, FIG. 1O, FIG. 11, and FIG. 12 are diagrams showing a conventional optical star coupler and its manufacturing method. 1, la, lb: optical glass fiber, lc: optical glass fiber bundle, 6a, 6b: twisted/fused portion. 7: Twisting/fusion/stretching part, 8: Protective tube, 9: Adhesive,
lla, llb, lc, lid, lie. 11f: Chuck, 12: Chuck rotation mechanism, 13: Chuck moving mechanism, I5: Heat source, 26a. 26b: Headstock movement ma. Figure 2 (a) A B C (b) A I3 C Figure 5 (a) Figure 5 (C) Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 (a) (b ) 1a,,51b Fig. 12 (a) (b) 33a 33b

Claims (6)

[Claims] (1) In 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, the twisted, fused, and
An optical star coupler characterized by having twisted and fused parts on both sides of the extended part. (2) The optical star coupler according to claim 1, wherein the twisted/fused portion and the twisted/fused/stretched portion are suspended in a protective tube. (3) In the 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, the plurality of bundled optical glass fibers are A process of adding a twist to the fiber, a process of applying only heat treatment to the twisted optical glass fiber to form a twisted/fused part, and a process of simultaneously performing the twisting process, heat treatment, and stretching process. A method for manufacturing an optical star coupler, comprising a step of forming the twisted/fused/stretched portion, and a step of suspending the twisted/fused portion and the twisted/fused/stretched portion in a protective tube. . (4) The step of twisting the bundled plurality of optical glass fibers and the step of forming the twisting/fusion/stretching part are performed on the bundled plurality of optical glass fibers that have been inserted into the protection tube in advance. 4. A method of manufacturing an optical star coupler according to claim 3, wherein the method is carried out for: (5) A patent claim characterized in that the step of forming the twisted/fused portion and the step of forming the twisted/fused/stretched portion are performed in parallel with the input of the optical signal into the optical fiber. A method for manufacturing an optical star coupler according to item 3. (6) A method for manufacturing an optical star coupler as set forth in claim 4, characterized in that no twisting/fusion portions are provided on both sides of the twisting/fusion/stretching portion.