JPH04219707A - Optical fiber coupler and its manufacture - Google Patents

Abstract

PURPOSE:To provide an optical fiber and its manufacture where an optical fiber coupler used in the optical fiber communications can be manufactured in an efficient and an inexpensive manner. CONSTITUTION:An extending part 16 is formed at a part of a multicore fiber where a plurality of waveguides 13 comprised of a core 11 and a clad 12 are arranged in the glass with lower index of refraction than that of the clad 12, and thus optical coupling can be made among the respective waveguides 13. This constitution enables a plurality of couplers with uniform characteristics to be manufactured simultaneously and with good reproducibility.

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 and a method for manufacturing the same, which can efficiently and inexpensively manufacture optical fiber couplers used in optical fiber communications.

0002

[Prior Art] In optical fiber communication, light emitted from a light source and light propagating through an optical fiber are branched, combined,
Demultiplexing or multiplexing technology is very important. here,
The expressions "branching" and "merging" refer to separating multiple lights, superimposing them, and flowing them in a specific direction, regardless of the wavelength of the light. Furthermore, the expressions demultiplexing and multiplexing are used when dealing with multiple lights of different wavelengths. Waves are used to combine light of multiple wavelengths into a single light beam. Branching, merging, demultiplexing, and multiplexing techniques are not limited to optical fiber communication, but in optical fiber communication, it is desirable to process the light propagating through the optical fiber without letting it out as much as possible. ing. That is, once the light propagating within the optical fiber is taken out, it is necessary to use an optical system such as a lens in order to make the light enter the optical fiber again, and at this time a coupling loss occurs. Also, the surfaces of various optical systems usually reflect light, which causes unnecessary light to return in the opposite direction, causing light sources used in communications
For example, it may make the operating state of a laser diode unstable.

From these viewpoints, an optical fiber coupler is an element that branches, joins, demultiplexes, and multiplexes light while preventing the light in the optical fiber from exiting the fiber as much as possible. There are various types of optical fiber couplers.
The most mass-produced type is the fusion-stretched optical fiber coupler. As shown in FIG. 13, this fusion-stretched optical fiber coupler attaches two optical fibers 1, 1 to each other and then heats them with a suitable heat source, for example, a combustion gas burner 2 such as hydrogen, to fuse them. , and further stretched by pulling in the longitudinal direction. As a result, the core of the fiber in the drawn section 3 is narrowed;
The light that was propagating in the core before stretching begins to seep out to the cladding side. As a result, electromagnetic coupling occurs between the propagation modes of the two cores, which act as a coupler. There are various couplers depending on the type of fiber used, such as single mode fiber couplers, multimode fiber couplers, and polarization maintaining fiber couplers, but single mode fibers are the mainstream in current optical fiber communications. Furthermore, single-mode fiber couplers have become mainstream among optical fiber couplers.

0004

[Problems to be Solved by the Invention] However, such a fused and drawn type optical fiber coupler has the following problems.

In other words, a set of optical fiber couplers can be manufactured with good reproducibility by inputting light from the end of the coupler and monitoring the state of the light at the output end. If they are lined up and fabricated at the same time, the monitored data can only be fed back to one set of couplers, so the other couplers will be fabricated blind, so to speak. As shown in FIG. 14, even if a plurality of fiber pairs 3 are heated with a large burner 4 and fused and drawn at the same time, the degree of coupling of the manufactured couplers varies greatly. The reason for this is that since the fused and stretched portions of each coupler are separated, it is difficult to align all heating conditions.

The present invention has been made in view of the above-mentioned circumstances, and aims to provide an optical fiber coupler and a method for manufacturing the same, which can simultaneously manufacture a plurality of couplers with uniform characteristics with good reproducibility.

[0007]

[Means for Solving the Problems] The optical fiber coupler of the present invention is a multi-core fiber in which a plurality of sets of waveguides each having a core and a cladding are disposed in glass having a refractive index lower than that of the cladding. The above-mentioned problem was solved by forming an extension part in the part and optically coupling between each set of waveguides.

[0008] Furthermore, as a manufacturing method of the above-mentioned optical fiber coupler, a plurality of sets of waveguides each having a core and a cladding are arranged in a glass base material having a refractive index lower than that of the cladding, and then the glass base material is A manufacturing method is desirable in which the waveguide and the glass base material are integrated by heating, the multi-core fiber is further drawn to form a multi-core fiber, and then a part of the multi-core fiber is heated and drawn.

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

The present invention will be explained in detail below with reference to the drawings.

FIG. 1 shows an example of an optical fiber coupler according to the present invention, and this optical fiber coupler 10
is a plurality of waveguides 13 having a core 11 and a cladding 12
A multi-core fiber 1 disposed in a supporting glass body 14 made of glass having a refractive index lower than that of the cladding.
5, an extension portion 16 is formed in a part of the portion 5.

[0012] The waveguide 13, like an optical fiber,
For example, a core 11 with a high refractive index made of quartz doped with germanium oxide, and a cladding 12 made of quartz surrounding it.
It is equipped with the following. Two of the plurality of waveguides 13 are arranged in contact with each other, and four sets are arranged at intervals in the glass base material 14.

The supporting glass body 14 is made of fluorine- or boron-doped quartz, and has a refractive index equal to that of the cladding 1.
It is set lower than the quartz that makes up No. 2.

FIG. 2 shows the refractive index distribution between symbols A and B shown in FIG. 1, and as shown in this figure, a cladding 12 made of quartz and A waveguide 13 consisting of a core 11 having a higher refractive index than that is arranged.

In the extended portion 16, the two waveguides 13 of each set are narrowed and brought close to each other, so that optical coupling occurs between the respective cores. Therefore, one optical fiber coupler (2×2
In this optical fiber coupler 10, four 2×2 type couplers 17 are formed by four sets of waveguides.
is formed.

As shown in FIG. 3, this optical fiber coupler 10 has optical connectors 18 attached to both end faces, and the end faces of each waveguide 13 of the optical fiber coupler are butted against the end face of the optical fiber 19. Connect. With this configuration, a total of four optical fibers 19 connected to both ends of each set of two waveguides 13 are designated by symbols P1 to P4 in the 2×2 type coupler 17 shown in FIG. This is the port shown. When light enters one of these ports (for example, P1), the light enters the two ports on the opposite side (for example, P1).
P3, P4), the optical power is obtained.

This optical fiber coupler 10 arranges a plurality of sets of waveguides 13 in one support glass body 14 and forms an extension part 16 in a part of the waveguides 14, so that light is transmitted to each set of waveguides 13. Since the couplers are formed by coupling and the plurality of couplers are assembled, the overall shape can be made smaller than when the plurality of couplers are arranged separately. In addition, the diameter of the stretched part is larger than that of a normal fusion-stretched optical fiber coupler, so it is stable against external forces.Furthermore, the entire stretched part (coupler part) is embedded in low-refractive-index glass, so it is stable against external forces. Even if a foreign object comes into contact with the coupler from the outside, the optical characteristics do not change and the coupler is mechanically and optically stable.

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

FIGS. 5 to 8 are diagrams showing an example of the method of the present invention. In the manufacturing method according to this example, first, as shown in FIG.
a cylindrical glass base material 21 in which through holes 20 are formed;
A waveguide base material 22 having a core 11 and a cladding 12 is manufactured, and each through hole 20 of the glass base material 21 is formed.
The waveguide base material 22 is inserted inside.

Next, the assembly of the glass base material 21 and the waveguide base material 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 base material 22.
As shown in FIG. 6, a glass base material 21 and eight waveguide base materials 2
A multi-core fiber preform 23 is produced by integrating the fibers 2 and 2.

Next, as shown in FIG. 7, the multi-core fiber preform 23 is attached to a drawing furnace, and the tip of the preform is heated by the heating device 2.
4, the multi-core fiber 25 is pulled out into a fiber shape while being locally heated, thereby producing a multi-core fiber 25 having the same cross-sectional shape as the multi-core fiber preform 23 shown in FIG. The produced multi-core fiber 25 is wound onto a winding bobbin (not shown).

Next, the produced multi-core fiber 25
The fiber is cut into an appropriate length, and as shown in FIG. 8, the center of the cut fiber is heated by a heating means such as an oxyhydrogen burner 26 and pulled in the length direction to elongate the heated portion. By this operation, the optical fiber coupler 1 shown in FIG.
0 is created.

In this heating and stretching operation, optical fibers 19 are connected to both ends of the waveguide 13 in the multi-core fiber 25.
The light is input to one optical fiber on one side, and the waveguide connected to this and the two optical fibers connected to the opposite side (output side) of the paired waveguide are connected. 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 output side optical fibers, and adjust the amount of stretching so as to obtain an appropriate degree of coupling.

Here, the degree of coupling in an optical fiber coupler means that in the 2×2 type coupler 17 having the configuration shown in FIG.
is incident, and the output light from ports P3 and P4 on the output side (their intensities are P3 and P4, respectively) is calculated using the following equation 1.
It is obtained by the formula.

[0025]

[Math 1]

Further, the excess loss in this coupler can be obtained from the following equation 2.

[0027]

[Math 2]

[0028] According to the above manufacturing method, when manufacturing a plurality of couplers, the heating conditions for each coupler can be easily aligned, so that a plurality of optical fiber couplers with uniform characteristics can be manufactured simultaneously with good reproducibility. I can do it.

FIG. 9 is a diagram showing another example of the method of the present invention. In the manufacturing method according to this example, a glass preform 21 in which four through holes 20 are formed and a twin core fiber preform 27 in which two cores 11 are provided facing each other in the cladding 12 are used, and each of the glass preforms 21 is A twin core fiber preform 27 is inserted into the through hole 20. This twin-core fiber base material 27 consists of two cores 1 of quartz doped with germanium oxide.
1 and a cladding 12 made of quartz surrounding it.

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

By this stretching, the four twin-core fibers are thinned and the cores are brought closer together, so that each twin-core fiber functions as a 2×2 type coupler.

The optical fiber coupler manufactured in this example is similar to the optical fiber coupler shown in FIG. 1, in which the optical fibers 19 are connected to the twin-core fiber portions on both end faces of the coupler with their cores in contact with each other. , as shown in FIG. 3, can be used as an assembly of optical fiber couplers including four 2×2 type couplers.

The manufacturing method according to this example has the effect of simultaneously manufacturing a plurality of optical fiber couplers with uniform characteristics with good reproducibility, as in the previous example.
Since the number of through holes formed in the glass base material 21 can be reduced, manufacturing can be simplified, and since the gap between each core in the twin-core fiber can be set small, effects such as a reduction in the amount of stretching can be obtained. .

In each of the above examples, the optical fiber coupler was configured by arranging four sets of two waveguides, but the arrangement of the waveguides is not limited to this, and three or more waveguides may be arranged. may be one set, or may be a plurality of waveguide sets other than four sets.

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

[0036] As a glass base material with a low refractive index, a diameter of 40 m
A cylinder of fluorine-doped quartz glass with a length of 220 mm was prepared. Next, eight through holes were formed in this glass cylinder as shown in FIG. The diameter of these through holes is 1.8 mm,
The gap between one set of holes was 0.15 mm, and the distance from the center of the hole to the center of the glass base material was 13.35 mm.

On the other hand, an outer diameter 1 consisting of a germanium oxide-doped quartz glass core material and a quartz cladding material surrounding it.
．． A 67 mm waveguide base material was produced, cut to a length of 220 mm, and inserted into each through hole of the glass base material.

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

Next, the obtained integrated base material was placed in a heating furnace for wire drawing, and a multi-core fiber shown in FIG. 6 was produced. The outer diameter of the multicore 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 is
It was cut into a length of 0 mm, and 8 optical fibers were connected to each end using a dedicated connector. Then, one fiber was selected from among an arbitrary set of fibers at one end, and the measurement light was incident thereon. Further, while monitoring the output light of the corresponding two fibers on the output side, the center of the multi-core fiber was heated with an oxyhydrogen burner, and the heated portion was stretched. FIG. 10 shows the relationship between the amount of stretching and the monitored degree of coupler bonding.

Stretching was completed under the stretching amount conditions (stretching length 16 mm) that gave the peak ■ in FIG. 10, and an optical fiber coupler having the same structure as that shown in FIG. 1 was obtained.

FIG. 11 shows the results of measuring the wavelength dependence of the degree of coupling for the four pairs of optical fiber couplers obtained.
It was shown to. This optical fiber coupler has 4 couplers (2×
The type 2 coupler) is a so-called WDM (wavelength multiplexing type) coupler, and the obtained coupler has wavelengths of 1.3 μm and 1.5 μm.
It had the ability to separate and combine light with a wavelength of 5 μm. As shown in Figure 11, the optical coupling characteristics of the four couplers are fairly well matched, and as shown in Table 2, the insertion loss and
The wavelength and resolution were all satisfactory.

[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 (fibers ■ and fibers ■) having the structural parameters shown in Table 3 form one set, and four sets are embedded in the supporting glass body was used.

[0046]

[Table 3]

[0047] 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 and wavelength dependence of the four couplers of the obtained optical fiber coupler was measured, and the results are shown in FIG.

As shown in FIG. 12, the four couplers (2×2 type couplers) included in the obtained optical fiber coupler are so-called WIC type (wavelength independent) couplers.
Their characteristics are well matched, especially at a wavelength of 1.55 μm.
In the vicinity of , the light incident from one end is approximately 50%:50%
It can be seen that it is branched into

By the way, as a basic condition when producing a multi-core fiber, it is desirable that the pitch of the cores of the multi-core fiber be equal to or larger than the outer diameter of a generally used optical fiber.

In addition, the distance L between each fiber group of the multi-core fiber, that is, a set of fiber groups forming a coupler by drawing and the adjacent fiber group, the refractive index of the cladding of each fiber, and the entire multi-core fiber. The difference ΔS (%) from the refractive index of the supporting low refractive index region is
Even when stretched to form a coupler, it must be such that substantially no electromagnetic coupling occurs between the couplers. In experimental studies, it is sufficient to satisfy the following equation (3) after drawing the multi-core fiber.

[0051]

[Math 3]

It has been found that, at this level, electromagnetic coupling between adjacent couplers, so-called crosstalk, does not substantially pose a problem.

[0053]

[Effects of the Invention] As explained above, according to the present invention,
When producing a plurality of couplers, the heating conditions for each coupler can be easily aligned, so a plurality of optical couplers with uniform characteristics can be produced simultaneously with good reproducibility. In addition, since multiple stretched couplers can be fabricated within one support glass, compared to the case where each coupler is connected separately,
The overall size can be reduced. Furthermore, since the shape of the fused and stretched portion is thicker than that of a normal fused and stretched optical fiber coupler, it is mechanically and optically stable against external forces. Furthermore, since the fused and stretched portion of each coupler can be embedded in a supporting glass body with a low refractive index, the optical and transmission characteristics will not change even if foreign objects come into contact with the coupler from the outside, making it extremely stable. An excellent coupler can be obtained.

[Brief explanation of the drawing]

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

FIG. 2 is a graph showing the refractive index distribution between symbols A and B in FIG. 1;

FIG. 3 is a schematic plan view showing the connection state of the optical fiber coupler in FIG. 1;

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

FIG. 5 is a diagram for explaining an example of the 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 wire drawing process of the integrated base material.

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

FIG. 9 is a diagram for explaining another example of the method for 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 degree of coupling and the stretching 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 degree of coupling in the optical fiber coupler according to the present invention.

FIG. 12 is a graph showing another example of the wavelength dependence of the degree of coupling 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]

10 Optical fiber coupler 11 Core 12 Clad 13 Waveguide 14 Support glass body 15 Multi-core fiber 16 Stretched part 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

Claims (4)

[Claims] 1. A multi-core fiber in which a plurality of sets of waveguides each having a core and a cladding are disposed in glass having a refractive index lower than that of the cladding, and an extended portion is formed in a part of the multi-core fiber. An optical fiber coupler characterized by performing optical coupling between a set of waveguides. 2. A plurality of sets of waveguides each having a core and a cladding are placed in a glass base material having a refractive index lower than that of the cladding, and then the glass base material is heated to separate the waveguides and the glass base material. 1. A method for manufacturing an optical fiber coupler, comprising: integrating materials, further drawing to form a multi-core fiber, and then heating and drawing a part of the multi-core fiber. 3. The method of manufacturing an optical fiber coupler according to claim 2, wherein the structures of the waveguides are all the same. 4. The method of manufacturing an optical fiber coupler according to claim 2, wherein the structures of the two waveguides are different from each other.