JP3009746B2 - Optical fiber coupler and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber coupler capable of efficiently and inexpensively manufacturing an optical fiber coupler used in optical fiber communication, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In optical fiber communication, light emitted from a light source or light propagating in an optical fiber is branched, merged,
The technique of demultiplexing or multiplexing is very important. here,
The expressions “branch” and “merge” mean that a plurality of lights are divided or superimposed and flow in a specific direction regardless of the wavelength of the light. Also, the expressions of demultiplexing and multiplexing are used when treating a plurality of lights of different wavelengths, and demultiplexing is used when extracting light of a specific wavelength from a light beam in which light of a plurality of wavelengths exists.
The multiplexing is used to combine lights of a plurality of wavelengths into one light beam. The techniques of branching, merging, demultiplexing, and multiplexing are not limited to optical fiber communication, but in optical fiber communication, it is desirable to process light propagating in an optical fiber as far as possible without leaving it outside. ing. That is, once the light propagating in the optical fiber goes out, it is necessary to use an optical system such as a lens to make the light enter the optical fiber again, and a coupling loss occurs at this time. In addition, since light is usually reflected on the surface of various optical systems, unnecessary light returns in the opposite direction, thereby destabilizing the operation state of the light source used for communication, for example, a laser diode. Or

[0003] From these viewpoints, there is an optical fiber coupler as an element for branching, merging, demultiplexing, and multiplexing light so that the light in the optical fiber is not emitted outside the fiber as much as possible. There are various types of optical fiber couplers,
The most mass-produced is a fusion-stretched optical fiber coupler. As shown in FIG. 13, in this fusion drawn optical fiber coupler, two optical fibers 1, 1 are attached to each other, and then heated and fused by an appropriate heat source, for example, a combustion gas burner 2 such as hydrogen. , And further stretched by pulling in the longitudinal direction. As a result, the core of the fiber in the stretched portion 3 is thinned, and the light that has propagated in the core before stretching greatly leaks to the cladding side. As a result, electromagnetic coupling occurs between the propagation modes of the two cores, thereby acting as a coupler. Depending on the type of fiber used,
There are various couplers such as single mode fiber couplers, multimode fiber couplers, and polarization maintaining fiber couplers.Single mode fibers are the mainstream in current optical fiber communications, so even optical fiber couplers Single mode fiber couplers have become mainstream.

[0004]

However, such a fusion-stretched optical fiber coupler has the following problems.

That is, a set of optical fiber couplers can be manufactured with good reproducibility while receiving light from the end of the coupler and monitoring the state of light at the output end. If you try to create them side by side, the feedback of the monitored data will be 1
The other couplers are, so to speak, made blind, since they can only be done for pairs of couplers. As shown in FIG. 14, even if a plurality of fiber pairs 3 are simultaneously heated and fused and drawn by a large burner 4, the degree of coupling of the manufactured couplers is very large. The reason for this is that it is difficult to make all the heating conditions uniform since the fusion-stretched portions of the respective couplers are separated.

The present invention has been made in view of the above circumstances, and has as its object to provide an optical fiber coupler capable of simultaneously manufacturing a plurality of couplers having uniform characteristics with good reproducibility, and a method of manufacturing the same.

[0007]

According to a first aspect of the present invention , a plurality of sets of a waveguide having a core and a cladding are provided, and a plurality of sets of waveguides having a core and a cladding are provided with a refractive index higher than the refractive index of the cladding. An extended portion is formed in a part of the multi-core fiber disposed in the glass having a low refractive index, and each of the above-described sets of waveguides is formed.
An optical fiber coupler characterized in that optical coupling is performed between the cores . In the second invention, a plurality of cores are
A plurality of waveguides housed in a cladding,
Multi-core glass placed in a glass with a lower refractive index
An extension is formed in a part of the fiber, and the core of each waveguide
An optical fiber coupler characterized by performing optical coupling between
is there.

[0008] In the method for manufacturing an optical fiber coupler according to the first aspect of the present invention, a waveguide mother having a core and a clad is provided.
A plurality of sets of a plurality of members are formed on a glass base material having a refractive index lower than the refractive index of the clad.
Each is inserted into the through hole, and then the glass preform is heated to integrate the waveguide preform and the glass preform, and further drawn to form a multi-core fiber, and then a part of the multi-core fiber is heated and drawn. Manufacturing methods are preferred. Second
The method for manufacturing the optical fiber coupler of the invention of
The waveguide base material whose core is contained in one clad,
A plurality of gases having a refractive index lower than that of the cladding;
Insert each into a plurality of through holes formed in the lath base material,
Next, the glass base material is heated to form a waveguide base material and a glass base material.
Into a multi-core fiber.
And then heat drawing a part of the multi-core fiber.
Is preferred.

The structures of the above waveguides may be all the same, or the structure of a pair of waveguides may be different from each other.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of an optical fiber coupler according to the present invention.
Is a plurality of waveguides 13 having a core 11 and a cladding 12.
(In this example, two pairs)
, Four sets), a multi-core fiber 15 disposed in a supporting glass body 14 made of glass having a refractive index lower than the refractive index of the cladding 12, and a stretched portion 16 is formed.

The waveguide 13 is, like an optical fiber,
For example, a core 11 made of quartz to which germanium oxide is added and having a high refractive index, and a clad 12 made of quartz surrounding the core 11
It is provided with. The plurality of waveguides 13 are arranged such that two arranged in contact with each other constitute one set, and four sets are arranged in the glass base material 14 at intervals.

The supporting glass body 14 is made of fluorine or boron-added quartz and has a refractive index of the cladding 1.
2 is set lower than quartz.

FIG. 2 shows a refractive index distribution between reference numerals A and B shown in FIG. 1. As shown in FIG. 2, a clad 12 made of quartz is provided in a supporting glass body 14 having a low refractive index. A waveguide 13 composed of a core 11 having a higher refractive index than that is arranged.

In the extending portion 16, the two waveguides 13 of each set are narrowed and approach each other so that optical coupling occurs between the respective cores. Accordingly, one optical fiber coupler (2 × 2
In this optical fiber coupler 10, four 2 × 2 type couplers 17 are provided by four sets of waveguides.
Are formed.

As shown in FIG. 3, the optical fiber coupler 10 has optical connectors (connectors) 18 attached to both end surfaces thereof.
The end face of each waveguide 13 of the optical fiber coupler and the end face of the optical fiber 19 are abutted and connected. With this configuration, a total of four optical fibers 19 connected to both ends of each of the two waveguides 13 in each set are denoted by reference numerals P1 to P4 in the 2 × 2 type coupler 17 shown in FIG. Port. Then, when light enters one of these ports (for example, P1), two ports on the opposite side (P1
The optical power is obtained from (3, P4).

This optical fiber coupler 10 includes a plurality of sets of a plurality of waveguides 13 in one supporting glass body 14.
By arranging several sets and forming an extension 16 in a part thereof , optical coupling is caused between the cores of the waveguides 13 of each set to form a coupler, and a plurality of couplers are assembled.
The overall shape can be made smaller than when a plurality of couplers are separately arranged. In addition, since the diameter of the stretched portion is larger than that of a normal fusion-stretched optical fiber coupler, it is stable against external forces, and since the entire stretched portion (coupler portion) is embedded in glass with a low refractive index, Even if foreign matter comes into contact with the coupler from outside, the optical characteristics are not changed and the coupler is mechanically and optically stable.

Next, a method for manufacturing an optical fiber coupler according to the present invention will be described.

[0019] FIGS. 5 to 8 are views showing an example of the present invention, in the manufacturing method according to this embodiment, first, as shown in FIG. 5 consists of a low refractive index glass, inserted in the waveguide preform 22
First , a cylindrical glass base material 21 having eight through holes 20 for insertion and a waveguide base material 22 having a core 11 and a clad 12 are formed. Next, the waveguide base materials 22 are inserted into the through holes 20 of the glass base material 21, respectively.

Next, the aggregate of the glass preform 21 and the waveguide preform 22 is placed in a heating path and heated to about 1800 ° C. to collapse the gap between the through hole 20 and the waveguide preform 22 (collapse). As shown in FIG. 6, a glass preform 21 and eight waveguide preforms 22 are provided.
To produce a multi-core fiber preform 23 in which is integrated.

Next, as shown in FIG. 7, the multi-core fiber preform 23 is attached to a drawing furnace,
In step 4, the fiber is drawn out into a fiber shape while being locally heated, and a multi-core fiber 25 having the same cross-sectional shape as the multi-core fiber preform 23 shown in FIG. 6 is produced. The manufactured multi-core fiber 25 is wound on a winding bobbin (not shown).

Next, the manufactured multi-core fiber 25
Is cut into an appropriate length, and the center of the cut fiber is pulled in the length direction while being heated by a heating means such as an oxyhydrogen burner 26 as shown in FIG. By this operation, the optical fiber coupler 1 shown in FIG.
0 is created.

In this heating and drawing operation, the optical fibers 19 are placed at both ends of the waveguide 13 in the multi-core fiber 25.
Are connected to each other, light is incident on one optical fiber on one side, and a waveguide connected to this optical fiber and two optical fibers connected on opposite sides (outgoing sides) of both the paired waveguides. It is desirable to monitor the intensity of the emitted light from the fiber 19, determine the degree of coupling from the intensity of the emitted light from the two exit-side optical fibers, and adjust the amount of stretching so as to obtain an appropriate degree of coupling.

Here, the degree of coupling in the optical fiber coupler means that, in the 2 × 2 type coupler 17 having the configuration shown in FIG. 4, light having a specific intensity is applied to the port P1 (the intensity is defined as P1).
And the light emitted from the ports P3 and P4 on the emission side (the intensities thereof are assumed to be P3 and P4, respectively) is obtained by the following equation (1).

[0025]

(Equation 1)

The excess loss in this coupler is obtained by the following equation (2).

[0027]

(Equation 2)

According to the above manufacturing method, when a plurality of couplers are manufactured, the heating conditions for the individual couplers can be easily adjusted, so that a plurality of optical fiber couplers having the same characteristics can be manufactured simultaneously with good reproducibility. Can be.

FIG. 9 is a view showing another example of the method of the present invention. In the manufacturing method according to this example, a glass base material 21 having four through holes 20 formed therein and two cores 11 in a clad 12 are provided. Twin-core fiber base material (waveguide
The base material 27 is used to insert the twin core fiber base material 27 into each through hole 20 of the glass base material 21. The twin-core fiber 27 is made of germanium oxide-doped quartz.
It comprises a core 11 and a clad 12 made of quartz surrounding the core.

Next, this assembly is placed in a heating furnace, and the glass preform 21 and the four twin-core fiber preforms 27 are integrated into a multi-core fiber preform. Next, the multi-core fiber preform is drawn to produce a multi-core fiber. Next, the obtained multi-core fiber is cut into a desired length, and a part thereof is drawn while being heated to form a drawn part.

By this stretching, the four twin-core fibers are thinned, and the cores approach each other, and each twin-core fiber functions as a 2 × 2 coupler.

In the optical fiber coupler manufactured according to this embodiment, similarly to the optical fiber coupler shown in FIG. 1, an optical fiber 19 is connected to a twin core fiber portion on both end surfaces of the coupler by bringing the respective cores into contact with each other. As shown in FIG. 3, it can be used as an aggregate of optical fiber couplers provided with four 2 × 2 type couplers.

In the manufacturing method according to this example, similarly to the previous example, an effect that a plurality of optical fiber couplers having uniform characteristics can be simultaneously manufactured with good reproducibility is obtained.
Since the number of through holes formed in the glass base material 21 can be reduced, the production can be simplified, and the gap between the cores in the twin-core fiber can be set small, so that the effect of reducing the amount of stretching can be obtained. .

In each of the above examples, four sets of two waveguides are arranged to constitute the optical fiber coupler. However, the arrangement of the waveguides is not limited to this, and three or more waveguides are arranged. May be set as one set, and a plurality of sets of waveguides other than four sets may be used.

Experimental Example An optical fiber coupler was manufactured based on the method of the present invention.

As a low refractive index glass base material, a diameter of 40 m
Fluorine-added quartz glass cylinder with a length of 220 mm and a length of 220 mm was facilitated. Next, eight through holes were formed in the glass cylinder as shown in FIG. The diameter of these through holes was 1.8 mm, the gap between a pair of holes was 0.15 mm, and the distance from the center of the hole to the center of the glass preform was 13.35 mm.

On the other hand, a waveguide base material having an outer diameter of 1.67 mm made of a core material made of germanium oxide-added quartz glass and a surrounding clad material made of quartz was prepared and cut into a length of 220 mm. It was inserted into each through hole.

Next, the composite of the glass base material and the waveguide base material was placed in a heating furnace and heated to 1850 ° C. to crush the gap between the through hole and the waveguide base material and integrated them.

Next, the obtained integrated preform was placed in a heating furnace for drawing, and a multi-core fiber shown in FIG. 6 was produced.
The outer diameter of the multi-core fiber was 3 mm, and the parameters of one waveguide were as shown in Table 1.

[0040]

[Table 1]

Next, the obtained multi-core fiber was
The optical fiber was cut to a length of 0 mm, and eight optical fibers were connected to both ends using dedicated connectors. Then, one fiber was selected from an arbitrary set of fibers at one end, and measurement light was incident thereon. The center of the multi-core fiber was heated with an oxyhydrogen burner while monitoring the output light of the two fibers on the emission side corresponding to this, and the heated portion was stretched. FIG. 10 shows the relationship between the amount of stretching and the degree of coupling of the monitored coupler.

The stretching was completed under the stretching amount conditions (stretch length 16 mm) giving the peak in FIG. 10, and an optical fiber coupler having the same configuration as that shown in FIG. 1 was obtained.

FIG. 11 shows the results of measuring the wavelength dependence of the coupling degree for the four sets of the obtained optical fiber couplers.
It was shown to. This optical fiber coupler has four couplers (2 ×
The type-2 coupler is a so-called WDM (wavelength multiplexing type) coupler, and the obtained coupler has a wavelength of 1.3 μm and a wavelength of 1.55 μm.
Wavelengths of light having different wavelengths.
As shown in FIG. 11, the optical coupling characteristics of the four sets of couplers are fairly uniform, and as shown in Table 2, the insertion loss,
The wavelength and the degree of separation were all satisfactory results.

[0044]

[Table 2]

Next, as another example, a coupler was manufactured in which the wavelength dependence of the degree of coupling was suppressed. In this example, a multi-core fiber having a structure in which two fibers (fiber and fiber) having the structural parameters shown in Table 3 form one set and four sets are embedded in a supporting glass body.

[0046]

[Table 3]

Using this multi-core fiber, an optical fiber coupler was produced in the same manner as in the previous example. The relationship between the coupling degree of the four optical fiber couplers and the wavelength dependence was measured, and the results are shown in FIG.

As shown in FIG. 12, four couplers (2 × 2 type couplers) included in the obtained optical fiber coupler are:
It is a so-called WIC type (wavelength independent) coupler, and its characteristics are well-aligned. In particular, near the wavelength of 1.55 μm, light incident from one end is split into almost 50%: 50%. You can see that.

As a basic condition for producing a multi-core fiber, the core pitch of the multi-core fiber is desirably equal to or larger than the outer diameter of a generally used optical fiber.

The distance L between each fiber group of the multi-core fiber, that is, a pair of fiber groups forming a coupler by stretching, and the adjacent fiber group, the refractive index of the cladding of each fiber, and the entire multi-core fiber are represented by The difference ΔS (%) from the refractive index of the supporting low refractive index region must be such that substantially no electromagnetic wave coupling occurs between the couplers even when the couplers are stretched to form them. In an experimental study, it is sufficient that the relationship represented by the following equation 3 is satisfied after the multi-core fiber is drawn.

[0051]

(Equation 3)

It has been found that, to this extent, electromagnetic coupling between adjacent couplers, so-called crosstalk, does not substantially cause a problem.

[0053]

As described above, according to the present invention,
When manufacturing a plurality of couplers, the heating conditions for the individual couplers can be easily adjusted, so that a plurality of optical couplers having uniform characteristics can be simultaneously manufactured with good reproducibility. In addition, since a plurality of drawn couplers can be manufactured in one supporting glass, compared with a case where individual couplers are separately connected,
The overall size can be reduced. In addition, since the shape of the fusion-stretched portion is thicker than that of a normal fusion-stretched optical fiber coupler, it is mechanically and optically stable against external force.
Furthermore, since the fused and stretched portion of each coupler can be embedded in a supporting glass body with a low refractive index, even if foreign matter comes into contact with the coupler from the outside, the optical and transmission characteristics do not change and extremely stable. Excellent coupler is obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of an optical fiber coupler of the present invention.

FIG. 2 is a graph showing a refractive index distribution between symbols A and B in FIG.

FIG. 3 is a schematic plan view showing a connection state of the optical fiber coupler of FIG.

FIG. 4 is a schematic diagram showing the operation of one coupler in FIG. 3;

FIG. 5 is a view for explaining an example of a method for manufacturing an optical fiber coupler according to the present invention, and is a perspective view of a step of inserting a waveguide base material into a glass base material.

FIG. 6 is a perspective view showing a step of integrating a glass base material and a waveguide base material.

FIG. 7 is a schematic side view showing a step of drawing an integrated base material.

FIG. 8 is a perspective view showing a step of drawing a multi-core fiber.

FIG. 9 is a view for explaining another example of the method of manufacturing an optical fiber coupler according to the present invention, and is a perspective view of a step of inserting a twin-core fiber preform into a glass preform.

FIG. 10 is a graph showing the relationship between the coupling degree and the extension length in the optical fiber coupler according to the present invention.

FIG. 11 is a graph showing an example of the wavelength dependence of the coupling degree in the optical fiber coupler according to the present invention.

FIG. 12 is a graph showing another example of the wavelength dependence of the coupling degree in the optical fiber coupler according to the present invention.

FIG. 13 is a side view for explaining an example of a conventional optical coupler manufacturing method.

FIG. 14 is a perspective view for explaining another example of the conventional optical coupler manufacturing method.

[Explanation of symbols]

 Reference Signs List 10 optical fiber coupler 11 core 12 clad 13 waveguide 14 supporting glass body 15 multi-core fiber 16 extending portion 17 coupler 20 through-hole 21 glass base material 22 waveguide base material 23 multi-core fiber base material 25 multi-core fiber 27 twin-core fiber base material

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-154006 (JP, A) JP-A-63-129307 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/28-6/293

Claims (4)

(57) [Claims] Claims: 1. A plurality of waveguides having a core and a cladding
Ranaru sets of a plurality of sets, it forms a stretched portion in a part of the multi-core fiber which is arranged in a glass of lower refractive index than the refractive index of the cladding, light between the cores of the each set of waveguide An optical fiber coupler for performing coupling. 2. A plurality of cores are housed in one clad.
Multiple waveguides, lower than the refractive index of the cladding
Part of a multi-core fiber placed in a refractive index glass
The optical coupling between the cores of each waveguide
An optical fiber coupler characterized by performing. 3. A composite of a waveguide base material having a core and a clad.
A plurality of sets, a plurality of sets, in a plurality of through holes formed in a glass base material having a refractive index lower than the refractive index of the cladding
And then heat the glass preform to guide
A method of manufacturing an optical fiber coupler, comprising: integrating a road preform and a glass preform; further forming a multi-core fiber by drawing; and heating and drawing a part of the multi-core fiber. (4) Multiple cores in one clad
A plurality of waveguide preforms, the refractive index of the cladding
Multiple through-holes formed in glass base material with low refractive index
And then heating and guiding the glass preform
Wave base material and glass base material are integrated,
Forming a multi-core fiber, and then forming the multi-core fiber
An optical fiber cable characterized in that a part of the fiber is heated and stretched.
Plastic manufacturing method.