JPH04268513A - Optical fiber for optical coupler - Google Patents

Abstract

PURPOSE:To easily connect an optical coupler and other optical components to properly set the composition and position of an eluting area, to provide polarization holding characteristics, and to facilitate the manufacture of a polarization holding fiber coupler by forming a guiding hole by etching the eluting area. CONSTITUTION:This optical fiber is an optical fiber used for manufacturing the optical coupler by generating an optical coupling between cores 11 in a common clad 13 by forming a drawing part at a part of the multi-core fiber 10 having the cores 11 in the common clad 13, and the elution area 12 made of a material which reacts chemically more easily than other parts is provided on a position with a specific distance from the core 11 in parallel to the relevant core 1.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention relates to an optical fiber suitable for producing optical couplers for branching, merging, demultiplexing, and multiplexing optical signals in the optical communication and optical sensing fields. be.

0002

2. Description of the Related Art Optical fiber couplers are very important in optical fiber communications as elements for branching, merging, demultiplexing, and multiplexing light. This optical fiber coupler 1 is made by splicing two optical fibers 2, 2 together as shown in FIG.
Further, the fiber is stretched in the axial direction and fused/stretched part 3 2
The cores of the main fibers are narrowed and brought closer together to create optical coupling between these fibers. An advantage of this method is that the bonding state between the fibers can be monitored during manufacturing, ie, during fusing and stretching, and thereby the characteristics of the coupler can be controlled with precision.

0003

[Problems to be Solved by the Invention] However, the following drawbacks can be cited.

[0004] Normally, optical fibers are coated with a coating called a primary coating, but in order to create a fusion-stretched fiber coupler, this coating must be removed, and thin fibers must be added with precision. Although the characteristics of the final coupler are satisfactory, manufacturing is time-consuming and requires skill.

[0005] Moreover, since the outer diameter of the coupler becomes thinner at the stretched portion to about several tens of micrometers, great care must be taken in handling and reinforcing the coupler in terms of mechanical strength.

[0006] As a method of compensating for these drawbacks, a method of fabricating an optical coupler involves forming a plurality of cores in advance in one cladding, and stretching this multi-core fiber to generate optical coupling between both cores. is also being considered.

However, the problem with this method is that even if the coupler can be fabricated, it is necessary to connect both ends of the coupler. In particular, when the optical fiber is a single mode fiber, unless splicing is performed with an accuracy of less than 1 to 2 μm of core axis misalignment, this alone will result in a large insertion loss. That is, as shown in FIG. 11, optical fibers are connected to both ends of an optical coupler 8, which has an extended portion 7 formed in the center of a twin-core fiber 6 in which two cores 4, 4 are arranged in parallel and surrounded by a cladding 5. To connect, either fusion splicing or mechanical connection is required, but the former fusion splicing 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 mechanical connection method, there is no reference for the position of the core on the end face of the optical coupler, making it difficult to position the fiber (axis alignment).

The present invention has been made in view of the above circumstances, and aims to provide an optical fiber for an optical coupler that can form a guide hole in its end face to facilitate connection with other optical components through a simple chemical treatment. There is.

[0009]

[Means for Solving the Problem] This problem is solved by producing a multi-core fiber having a plurality of cores in a common cladding, in which a chemical reaction occurs in a position parallel to the core and a predetermined distance from the core, compared to other parts. This problem can be solved by providing a dissolvable region made of a material that is easy to dissolve.

[0010] It is also possible to have two cores and two eluting regions, and by adjusting their positional relationship, the eluting regions can be used as stress applying regions, and the core can have polarization-maintaining properties. .

[0011]

[Operation] This optical fiber for optical couplers can be partially heated and stretched to reduce the fiber diameter and bring the cores closer together, thereby creating optical coupling between each core and forming an optical coupler. . In addition, this fiber has an elutable region made of a material that is more likely to cause a chemical reaction than other parts, parallel to the core, at a predetermined distance from the core. By eroding the eluting region, a guide hole is formed along the eluting region, so that connection with the end surface of another optical component having a guide pin fitted into the guide hole is facilitated. Additionally, this fiber has two core and two eluable regions.
By adjusting the positional relationship between the two single-core polarization-maintaining fibers, the eluting region can be used as a stress-applying region and the core can have polarization-maintaining properties. Compared to manufacturing polarization-maintaining optical couplers by stretching them, polarization-maintaining optical couplers have superior characteristics, such as omitting the process of aligning polarization axes during coupler manufacturing and obtaining good polarization characteristics. Optical couplers can be manufactured.

0012

Embodiment FIG. 1 shows an embodiment of an optical fiber for an optical coupler (hereinafter abbreviated as fiber) according to the present invention. This fiber 10 has two cores 11, 11 arranged in the horizontal direction in this figure, and two cores 11 arranged in the vertical direction.
two elutable regions 12, 12 and a cladding 1 surrounding them
It consists of 3. The core 11 is made of quartz glass doped with GeO2 to increase the refractive index. Further, the cladding 13 is made of pure silica glass.

The elutable region 12 is made of materials that are more susceptible to chemical reactions than the core 11 and the cladding 13, such as acids, alkalis, corrosive salts, chlorine gas, fluorine gas, and preferably strong acid aqueous solutions such as hydrochloric acid and sulfuric acid. Consists of erodible materials. Such materials include B2O in particular.
3-doped quartz glass is preferred.

To explain one example of the manufacturing method of this fiber 10, first, four holes are formed along the length direction in a transparent base material made of pure silica glass by mechanical processing, and a core is inserted into these holes. It is manufactured by inserting and integrating the base material and the elutable region base material, heating and melting the obtained base material, and spinning it into an appropriate thickness.

FIG. 2 shows a state in which guide holes 14 are formed by performing appropriate chemical treatment such as acid treatment on both ends of the fiber 10 to erode the elutable region. Furthermore, FIG. 3 shows that a stretched portion 15 is formed in the center of this fiber 10, and a core 11
, 11 shows an optical coupler 16 that causes optical coupling between the two. When acid treatment is performed to form the guide hole 14, there is a risk that the core 11 will be slightly eroded, so it is desirable to cover the end face of the core with a non-erodible material such as a synthetic resin adhesive.

FIG. 4 shows a connector 18 which is suitably used for connecting the optical coupler 16 and the optical fibers 17, 17. This connector 18 includes a cylindrical connector main body 19, two optical fibers 17, 17 fixed within the main body, and two guides fixed within the main body with their tips protruding from the connection end surface. pin 20,
20. The relative positions of the guide pin 20 and the optical fiber 17 on the end surface of the connector 18 are set to correspond to the positions of the guide hole 14 and the core 11 on the connection end surface of the optical coupler 16. When connecting this connector 18 to the optical coupler 16, connect the two guide pins 20, 20 of the connector 18 to the optical coupler 16.
It fits into the two guide holes 14, 14 of. As a result, the core 14 of the connection end surface of the optical coupler 16 and each end surface of 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, 17 are connected.

This fiber 10 is cut into an appropriate length, the central part of which is heated by an oxyhydrogen burner or an electrical discharge, and stretched by applying a tensile force in the longitudinal direction to reduce the fiber diameter and bring the cores closer together. By making each core 11
, 11 to form an optical coupler. In addition, this fiber 10 is provided with an elutable region 12 made of a material that is more likely to cause a chemical reaction than other parts, 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 acid aqueous solution. By dipping and eroding the eluting region 12, a guide hole 14 along the eluting region 12 is formed.
This facilitates connection with the end face of another optical component having the guide pin 20 fitted therein.

FIG. 6 shows another embodiment of the fiber according to the invention, in which the fiber 22 is
In this figure, it consists of two cores 11, 11 arranged in the vertical direction, two stress applying regions 23, 23 located outside the cores, and a cladding 13 surrounding these.

The stress applying region 23 is made of quartz glass doped with B2O3. Silica glass doped with B2O3 has a much larger coefficient of thermal expansion than pure silica glass, so it is
two cores 11, 11 and stress applying regions 23 on both outer sides thereof
, 23 in a straight line, the so-called PA
Generates anisotropic strain similar to NDA type fiber. For this purpose, the stress applying region 23 has an added amount of B2O3.
larger than in the case of the dissolution area 12 according to the previous example;
It is desirable that the content be about 17 mol%.

[0020] Also, this stress application region 23, like the elution region 12 in the previous example, is located between the core 11 and the cladding 1.
The stress-applying area 23 is more likely to cause a chemical reaction than the material No. 3, and can be immersed in a strong acid aqueous solution such as hydrochloric acid or sulfuric acid.
Only the guide hole is eroded and a guide hole is formed.

This fiber 22 is cut into an appropriate length, heated and stretched at its center to form each core 11, 1.
A polarization-maintaining optical coupler having polarization-maintaining characteristics can be manufactured by causing optical coupling between the two. Further, by forming a guide hole in the connection end surface in the same manner as in the previous embodiment, connection with other optical components having guide pins that fit into the guide hole can be easily and accurately performed. Furthermore, because the fiber 22 has the above structure, the polarization axis can be adjusted during the manufacture of the coupler, compared to manufacturing a polarization maintaining optical coupler by fusing and drawing two single-core polarization maintaining fibers. This process can be omitted, and an excellent polarization-maintaining optical coupler can be manufactured with good polarization characteristics.

(Experimental example) Four holes were formed along the longitudinal direction in a pure quartz glass cylinder with a diameter of 40 mm by machining, and a core base material cylinder made of quartz glass to which 5 mol% of GeO2 was added and B2O3 were placed in the holes. 10
A eluting region base material cylinder made of quartz glass doped with mol% was placed, heated and integrated to form a fiber base material, and this fiber base material was further spun in a drawing furnace to an outer diameter of 1200 μm to form the one shown in Figure 1. A fiber similar to that was fabricated. The obtained fiber had two core diameters of approximately 8.5 μm, a core spacing of 125 μm, and a diameter of two eluting regions of 100 μm.
The interval between the elutable regions was 800 μm, and the cladding outer diameter (fiber diameter) was 1200 μm.

[0023] Cut 50 mm from the obtained fiber,
I sanded it lightly to remove the burrs on both ends. This polishing is not an essential step if the fiber cutting condition is good. Next, after applying an ultraviolet curable resin around the core end faces at both ends of the cut fiber and curing it, the fiber was
It was immersed in a hydrochloric acid solution (temperature: 45° C.) for 100 hours. As a result, the elutable region was eroded and a guide hole with a depth of about 250 μm was formed. Next, the resin on the end faces was removed, and connectors 18 shown in FIG. 4 were attached to both ends. The connector connection is
Although this was done by joining near the end faces with epoxy adhesive, it is also possible to mechanically press the parts, such as by clamping them with leaf springs, in order to make them detachable. At this time, it is a good idea to insert matching oil or matching jelly that has a refractive index close to that of the glass to prevent Fresnel reflections on the end faces. Next, as shown in FIG. 7, the fiber with connectors attached to both ends was heated with an oxyhydrogen burner 24 and stretched in the longitudinal direction. The stretched length was about 12 mm. The characteristics of the resulting optical coupler are shown in FIG. The obtained optical coupler is a so-called WDM
It was a type coupler, and had the characteristic of being able to separate and combine light with wavelengths of 1.3 μm and 1.55 μm.

Next, a fiber having polarization maintaining characteristics shown in FIG. 6 was fabricated. Four holes are formed in a straight line in the same pure quartz base material as the previous fiber, and the core base material and the stress-applying region base material are inserted and integrated to form the base material, and the fiber is spun to form a fiber with an outer diameter of 1200 μm. A fiber was fabricated. As the material of the stress applying region, quartz glass to which 17 mol% of B2O3 was added was used. The stress applying region had a diameter of 250 μm, and the distance between the core and the stress applying region was 80 μm, which was quite close. Further, the distance between cores was also set to 80 μm. The obtained fiber was cut to a length of about 50 mm, and fibers with connectors were connected to both ends in the same manner as in the previous method. However, a so-called PANDA polarization maintaining fiber was used as the connector fiber. PANDA type fiber has a core in the center of a circular cladding and stress applying parts on both sides of the core, and uses the large difference in thermal expansion coefficient between the glass in the stress applying part and the clad glass to Generates an anisotropic refractive index. As a result, the degeneracy of the two fundamental modes propagating through the single mode fiber is resolved, and the difference in propagation constant between the modes can be increased, so the polarization direction of the light incident on the input end of the fiber can be slightly changed. It has a characteristic that it does not change even if the fiber is bent.

A coupler was prepared by heating and stretching a PANDA fiber with a connector attached thereto in the same manner as described above. The characteristics of the obtained coupler are shown in FIG. The direction of the polarized waves measured here is the direction connecting the centers of the stress applying parts (
(usually, conventionally called the X direction). In any case, manufacturing a coupler is very simple, and as with conventional polarization type optical fiber couplers, the steps of aligning the polarization axes of two PANDA fibers, heating, fusing, and stretching are required. There was no need to step on it, and the yield was significantly improved.

[0026]

[Effects of the Invention] As explained above, according to the present invention,
Since the positional relationship of the fibers that form the optical coupler is fixed in advance, it is easy to manufacture the coupler by heating and stretching, and by chemically treating the elutable region and forming a guide hole on the fiber end face, the optical coupler can be easily manufactured. Low-loss connections to lead fibers at both ends are possible. In addition, since polarization maintaining characteristics can be obtained by appropriately setting the glass composition and arrangement position of the elutable region, it has become possible to easily produce a polarization maintaining type fiber coupler.

[Brief explanation of the drawing]

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 guide holes are formed in the end face of the fiber in FIG. 1;

3 is a perspective view showing an optical coupler formed using the fiber shown in FIG. 1. 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.

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 showing a first example of the 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 an 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 a conventional optical coupler.

[Explanation of symbols]

10, 22 Fiber (optical fiber for optical coupler)
11 Core 12 Elution region 13 Clad 14 Guide hole 15 Stretching section 16 Optical coupler 17 Optical fiber 18 Connector (other optical parts) 23 Stress applying region

Claims (2)

[Claims] 1. An optical fiber used to produce an optical coupler by forming a stretched portion in a part of a multi-core fiber having a plurality of cores in a common cladding to cause optical coupling between the cores. An optical fiber for an optical coupler, characterized in that an elutable region made of a material that is more likely to cause a chemical reaction than other parts is provided parallel to the core at a position separated from the core by a predetermined distance. [Claim 2] It is characterized by having two cores and two eluting regions, and by adjusting the positional relationship of each, the eluting regions are made into stress applying regions, and the core has polarization maintaining characteristics. The optical fiber for an optical coupler according to claim 1.