JP2902800B2 - Optical fiber for optical coupler - 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 suitable for producing an optical coupler for branching, merging, demultiplexing, and multiplexing an optical signal in the field of optical communication and optical sensing. is there.

[0002]

2. Description of the Related Art An optical fiber coupler is very important as an element for splitting, merging, demultiplexing and multiplexing light in optical fiber communication. As shown in FIG. 10, the optical fiber coupler 1 abuts two optical fibers 2, 2 and heats the portion by heating or discharging with an oxyhydrogen burner.
Further, it is stretched in the axial direction of the fiber and is fused and stretched.
The cores of the fibers are made thinner and closer to each other to cause optical coupling between the fibers. An advantage of this method is that the state of coupling between the fibers can be monitored during manufacturing, that is, during fusion and drawing, whereby the characteristics of the coupler can be controlled with high accuracy.

[0003]

However, the disadvantages are as follows.

[0004] Usually, an optical fiber is provided with a coating called a primary coating. However, in order to fabricate a fusion drawn fiber coupler, it is necessary to remove this coating, and a fine fiber is attached with high precision. However, although the characteristics of the final coupler can be satisfied, it takes time and effort to produce the coupler, and the operation requires skill.

[0005] In addition, since the outer shape of the coupler is reduced to about several tens of μm in the stretched portion, it is necessary to pay close attention to handling and reinforcement in terms of mechanical strength.

As a method of compensating for these drawbacks, a method of forming a plurality of cores in one clad in advance, stretching this multi-core fiber to cause optical coupling between both cores, and manufacturing an optical coupler. Is also considered.

However, a problem with this method is that even if a coupler can be manufactured, it is necessary to connect both ends of the coupler.
In particular, when the optical fiber is a single mode fiber, a large insertion loss will be caused by itself if the core is not connected with an accuracy of about 1 to 2 [mu] m or less as a guideline. That is, as shown in FIG. 11, an optical fiber is connected to both ends of an optical coupler 8 having an extending portion 7 formed at the center of a twin-core fiber 6 surrounded by a clad 5 in a state where two cores 4 are arranged in parallel. In order to connect, fusion connection or mechanical connection is required, but the former fusion connection is almost impossible because the dimensions of the end face of the optical coupler and the end face of the optical fiber to be connected do not match. . On the other hand, in the latter method of mechanical connection, since there is no reference for the position of the core on the end face of the optical coupler, it is difficult to position the fiber (axis alignment).

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide an optical fiber for an optical coupler capable of forming a guide hole on an end face thereof for easy connection with another optical component by a simple chemical treatment. I have.

[0009]

The object of the present invention is to provide a multi-core fiber having a plurality of cores in a common clad, in which a chemical reaction occurs at a position separated from the core by a predetermined distance and in parallel with the core compared to other parts. The problem is solved by providing the eluting region made of a material that is easy to use.

It is also possible to provide two cores and two eluting regions, and adjust the positional relationship between the cores and the eluting regions so that the cores have polarization maintaining characteristics. .

[0011]

The optical fiber for an optical coupler can be formed by heating a part of the optical fiber, stretching the fiber, reducing the diameter of the fiber, and bringing the cores closer to each other to cause optical coupling between the cores. . In addition, the fiber is provided with an elutable region made of a material that is more likely to cause a chemical reaction than the other part in parallel with the core at a position separated from the core by a predetermined distance, so that the end face of the fiber is immersed in an acid aqueous solution, By eroding the eluting region, a guide hole is formed along the eluting region, so that connection with the end face of another optical component having a guide pin fitted into the guide hole is facilitated. Furthermore, this fiber has two cores and two eluting regions, and by adjusting the positional relationship between them, the eluting region can be used as a stress applying region and the core can have polarization maintaining characteristics. 2. Compared to producing a polarization maintaining optical coupler by fusing and stretching two single-core polarization maintaining fibers, the process of aligning the polarization axis during the production of the coupler can be omitted, resulting in good polarization characteristics. Thus, a polarization maintaining optical coupler having excellent characteristics such as the above can be manufactured.

[0012]

1 shows an optical fiber for an optical coupler according to the present invention.
1 shows an embodiment (hereinafter abbreviated as a fiber). The fiber 10 comprises two cores 11, 11 arranged in the horizontal direction, two elutable regions 12, 12 arranged in the vertical direction, and a cladding 13 surrounding them.
It consists of The core 11 is made of a material obtained by adding GeO ₂ for increasing the refractive index to quartz glass. The cladding 13 is made of pure quartz glass.

The eluting region 12 is made of a material which is more susceptible to a chemical reaction than the core 11 and the clad 13, that is, an acid, an alkali, an erosive salt, a chlorine gas or a fluorine gas, preferably a strong acid aqueous solution such as hydrochloric acid or sulfuric acid. Made of eroded material. As such a material, in particular, B ₂ O ₃
Added quartz glass is desirable.

An example of a method of manufacturing the fiber 10 will be described. First, four holes are formed in a transparent base material made of pure silica glass by mechanical processing along the length direction, and a core is formed in these holes. It is manufactured by inserting and integrating the base material and the base material in the dissolvable region, heating and melting the obtained base material, and spinning to an appropriate thickness.

FIG. 2 shows a state in which a guide hole 14 is formed by eroding the elutable region by performing an appropriate chemical treatment such as an acid treatment on both ends of the fiber 10. Further, FIG. 3 shows that an extended portion 15 is formed at the center of
1 shows an optical coupler 16 in which optical coupling has occurred between 1 and 11. When the guide hole 14 is formed by performing an acid treatment, the core 11 may be slightly eroded. Therefore, it is preferable that the core end surface be covered with a non-erodible material such as a synthetic resin adhesive.

FIG. 4 shows a connector 18 suitably used for connecting the optical coupler 16 to the optical fibers 17 and 17. The connector 18 has a cylindrical connector main body 19, two optical fibers 17, 17 fixed in the main body, and two guides fixed in the main body with the tips protruding from the connection end face. Pin 20,
20. The relative positions of the guide pin 20 and the optical fiber 17 on the end face of the connector 18 are set to correspond to the positions of the guide hole 14 and the core 11 on the connection end face of the optical coupler 16. When the connector 18 is connected to the optical coupler 16, the two guide pins 20 of the connector 18 are connected to the optical coupler 16.
In the two guide holes 14. As a result, the end faces of the core 14 of the connection end face of the optical coupler 16 and the core 21 of the optical fiber 17 of the connector 18 are brought into close contact, and the optical coupler 16 and the optical fibers 17 are connected.

The fiber 10 is cut into an appropriate length, and the center is heated by an oxyhydrogen burner or electric discharge.
Each core 1 is stretched by applying a pulling force in the longitudinal direction to reduce the fiber diameter and to bring the cores closer to each other.
An optical coupler can be formed by causing optical coupling between the light emitting elements 1 and 11. In addition, the fiber 10 is provided with an elutable region 12 made of a material that is more susceptible to a chemical reaction than the other part and is separated from the core 11 by a predetermined distance and parallel to the core 11, so that the end face of the fiber is immersed in an aqueous acid solution. By immersing and eroding the elutable region 12, a guide hole 14 is formed along the elutable region 12, so that the guide hole 1 is formed.
This facilitates connection with the end face of another optical component having the guide pin 20 fitted into the optical component 4.

FIG. 6 shows another embodiment of the fiber according to the present invention.
In the figure, the core is composed of two cores 11 arranged in the longitudinal direction, two stress applying regions 23 located outside thereof, and a clad 13 surrounding these.

The stress applying region 23 is made of quartz glass to which B ₂ O ₃ is added. Since the quartz glass to which B ₂ O ₃ is added has a very large coefficient of thermal expansion as compared with the pure quartz glass, the two cores 11 and 11 and the stress applying regions 23 on both outer sides thereof like the fiber 22 are shown. , 23
Are arranged in a straight line, so-called PANDA
An anisotropic strain similar to that of the type fiber is generated. For this purpose, the stress application region 23 has a larger amount of added B ₂ O ₃ than that of the eluting region 12 according to the previous embodiment, and is 17 mol.
% Is desirable.

The stress applying region 23 is formed by the core 11 and the cladding 1 similarly to the eluting region 12 according to the previous example.
3 is more susceptible to a chemical reaction than the material No. 3, and is immersed in an aqueous solution of a strong acid such as hydrochloric acid or sulfuric acid.
Only erosion occurs, forming guide holes.

The fiber 22 is cut into an appropriate length, and the central portion thereof is heated and stretched so that the respective cores 11 and
By causing optical coupling between the optical couplers 11, a polarization maintaining optical coupler having polarization maintaining characteristics can be manufactured. Further, by forming a guide hole in the connection end face in the same manner as in the previous embodiment, it is possible to easily and accurately connect to another optical component having a guide pin fitted into the guide hole. In addition, due to the above configuration, the fiber 22 has a polarization axis alignment at the time of manufacturing the coupler, which is different from a case where two single-core polarization maintaining fibers are fused and drawn to manufacture a polarization maintaining optical coupler. Can be omitted, and an excellent polarization-maintaining optical coupler can be manufactured, such as obtaining good polarization characteristics.

(Experimental Example) Four holes were formed in a pure quartz glass cylinder having a diameter of 40 mm along a longitudinal direction by machining, and a core preform cylinder made of quartz glass having GeO ₂ added therein in an amount of 5 mol% was formed. A column of the eluting region made of quartz glass containing 10 mol% of B ₂ O ₃ was put therein, heated and integrated into a fiber preform, and the fiber preform was spun into an outer diameter of 1200 μm in a drawing furnace. A fiber similar to that shown in FIG. 1 was produced. The obtained fiber has a diameter of two cores of about 8.5 μm and a core interval of 125 μm.
m, the diameter of the two eluting regions is 100 μm, the interval between the eluting regions is 800 μm, and the cladding outer diameter (fiber diameter) is 12 μm.
It was 00 μm.

The obtained fiber was cut off by 50 mm and polished lightly to remove burrs on both ends. This polishing is not an essential step as long as the fiber cutting state is good. Next, after applying and curing an ultraviolet curable resin around the core end surfaces at both ends of the cut fiber, the fiber was immersed in a 10% hydrochloric acid solution (temperature: 45 ° C.) for 100 hours.
The leaching region was eroded to form a guide hole having a depth of about 250 μm. Next, the resin on the end face was removed, and connectors 18 shown in FIG. 4 were attached to both ends. The connector connection was performed by joining the vicinity of the end face with an epoxy-based adhesive. However, in order to make the connector detachable, it may be mechanically pressed, for example, by sandwiching with a leaf spring. In this case, in order to prevent Fresnel reflection on the end face, it is preferable to insert matching oil or matching jelly having a refractive index close to that of glass. Next, as shown in FIG.
And stretched by pulling in the longitudinal direction. The stretch length was about 12 mm. The characteristics of the resulting optical coupler are shown in FIG. The obtained optical coupler was a so-called WDM-type coupler, and had characteristics capable of demultiplexing and multiplexing light having wavelengths of 1.3 μm and 1.55 μm.

Next, a fiber having polarization maintaining characteristics shown in FIG. 6 was manufactured. Four holes are formed in a line on a straight line in the same pure quartz preform as the previous fiber, and the core preform and the stress-applied area preform are inserted and integrated into a preform, spun and spun to an outer diameter of 1200 μm. A fiber was made. As a material for the stress application region, quartz glass to which 17 mol% of B ₂ O ₃ was added was used. The stress applying region has a diameter of 250 μm,
The interval between the stress applying regions was set to be very close to 80 μm. The distance between the cores was also 80 μm. The obtained fiber was cut off by about 50 mm, and a fiber with a connector was connected to both ends in the same manner as described above. However, a so-called PANDA type polarization maintaining fiber was used as the fiber of the connector. A PANDA type fiber has a core at the center of a circular cladding, and has a stress applying portion on both sides of the core. An anisotropic refractive index is generated. As a result, the degeneracy of the two fundamental modes propagating in the single mode fiber can be resolved and the difference in the propagation constant between the modes can be increased, so that the polarization direction of the light incident on the input end of the fiber is slightly changed. It has such characteristics that it does not change even if the fiber is bent or the like.

A fiber having a connector to which a PANDA fiber was attached was drawn by heating in the same manner as described above to prepare a coupler. The characteristics of the obtained coupler are shown in FIG. Here, the measured polarization direction is the direction connecting the center of the stress applying part.
(Usually conventionally referred to as the X direction). In any case, the production of the coupler is very simple, and the procedure of heating, fusing, and stretching after aligning the polarization axes of two PANDA-type fibers, as in the production of a conventional polarization type optical fiber coupler, is described. Without stepping on, the yield was greatly improved.

[0026]

As described above, according to the present invention,
Since the positional relationship of the fibers forming the optical coupler is fixed in advance, it is easy to manufacture the coupler by heating and drawing, and the elution area is chemically treated to form a guide hole in the end face of the fiber, so that the optical coupler is formed. Low-loss connection to the lead fiber at both ends is possible. Further, since the polarization maintaining characteristic can be obtained by appropriately setting the glass composition and the disposition position of the elution region, a polarization maintaining fiber coupler can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an optical fiber for an optical coupler according to an embodiment of the present invention.

FIG. 2 is a side view showing a state in which a guide hole is formed in an end face of the fiber of FIG. 1;

FIG. 3 is a perspective view showing an optical coupler formed using the fiber shown in FIG.

FIG. 4 is a perspective view showing a connector suitable for connection with the optical coupler shown in FIG. 3;

5 is a side sectional view showing a connection structure between the optical coupler shown in FIG. 3 and the connector shown in FIG. 5;

FIG. 6 is a cross-sectional view of a fiber showing another embodiment of the optical fiber for an optical coupler of the present invention.

FIG. 7 is a schematic side view for explaining a method of manufacturing an optical coupler using the fiber of the present invention.

FIG. 8 is a graph illustrating a first example of characteristics of an optical coupler manufactured using the fiber of the present invention.

FIG. 9 is a graph showing a second example of the characteristics of the optical coupler manufactured using the fiber of the present invention.

FIG. 10 is a perspective view showing an example of a conventional optical coupler.

FIG. 11 is a perspective view showing another example of the conventional optical coupler.

[Explanation of symbols]

 10, 22 fiber (optical fiber for optical coupler) 11 core 12 eluting area 13 clad 14 guide hole 15 extension 16 optical coupler 17 optical fiber 18 connector (other optical parts) 23 stress applying area

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-268507 (JP, A) JP-A-64-2401 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 6/28 G02B 6/16

Claims (2)

(57) [Claims] An optical fiber used to form an optical coupler between cores by forming an extended portion in a part of a multi-core fiber having a plurality of cores in a common clad. An optical fiber for an optical coupler, wherein an eluting region made of a material that is more susceptible to a chemical reaction than other portions is provided at a position separated from the core by a predetermined distance in parallel with the core. 2. The core has two eluting regions and two eluting regions. By adjusting the positional relationship between the core and the eluting region, the eluting region becomes a stress applying region, and the core has polarization maintaining characteristics. The optical fiber for an optical coupler according to claim 1.