JPS60134210A - Connecting method of multicored optical fiber - Google Patents

Abstract

PURPOSE:To enable realization of connection with high density and to perform setting of the central position with high accuracy with respect to the outside circumference of a core having just a simple circular shape and control of the hole diameter by making use of one core in connecting fibers. CONSTITUTION:A pair of plugs 10 are connected to an adapter 20. The positioning key 11 of each plug 10 is engaged with the engaging groove 21 of the adapter 20 to position circumferentially a core 30. A clad is removed from the end of a clad optical fiber 1 to expose optical fibers 2. A circular cylindrical body 2' (an optical fiber may be used as a dummy) having the max. outside diameter is disposed at the center of the many optical fibers 2 and thereafter the multicored fibers 2 are assembled by a heat shrinkable tube 40. The central dummy fiber 2' is provided at the center and the fibers 2 are provided on the outside. The top ends of the seven-cored fibers 2, 2' are assembled into a hexagonal shape by the shrinkage force acted toward the center when the tube 40 heated to shrink, by which an optical fiber bundle is formed. The core 30 is inserted into a split sleeve 22 in the stage of connecting.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of connecting multi-core optical fibers using a core.

Conventionally, in a method for connecting multi-core optical fibers, a multi-core optical fiber connector is used, which consists of a pair of plugs 7 that house cores attached to the connecting ends of multi-core optical fibers, and an adapter that connects the plugs to each other in a detachable manner. The methods used are known. In such connectors, positioning of the optical fibers is an important issue. FIG. 1 shows an example in which a large number of cores are used for positioning an optical fiber.

In the figure, 1 is a coated optical fiber, 2 is an optical fiber, 3 is a core, and 4 is a positioning hole provided at the center of one end surface of the core 3. In this method, the number of cores 3 equal to the number of cores of the optical fiber 2 is used to position the multi-core optical fiber.
However, positioning the optical fiber 2 requires inserting the optical fiber 2 one by one into the positioning hole 4 of each core 3, and then assembling the cores 3.
Although high-precision positioning is possible, ■The volume of the connector becomes large due to the use of a large number of cores, making it impossible to increase the density. ■The optical fibers are fixed to the core one by one by adhesive bonding. Therefore, there were drawbacks such as poor workability.

Next, FIG. 2 shows an example in which one core is used. In the figure, 1 is a coated optical fiber, 21d optical fiber 7, 5 is a core, and 6 is a positioning hole provided at the center of one end surface of the core 5. As shown in the enlarged view in Figure 3, positioning in the circumferential direction is The inner periphery is polygonal in order to Although such a core 5 can eliminate the above-mentioned roundness defect, since the inner periphery is polygonal, there is a drawback that precision machining of 1.0 μm or less is impossible. Furthermore, a structure similar to that shown in FIG. 2 but with a circular inner peripheral shape of the positioning hole 6 has also been proposed.

Although precision machining of the hole is easy in this circular type, there is a problem in that the optical fiber axis cannot be positioned with high precision unless all the outer diameters of the original fibers 2 are made equal. However, since the outer diameter of currently manufactured optical fibers has a distribution of 12214n to 128μm, it is not possible to connect multi-core optical fibers with low loss by simply inserting the multi-core optical fibers into the optical fiber positioning hole and assembling them together. The disadvantage was that it could not be realized.

In order to eliminate these drawbacks, the present invention provides a cylindrical body with a diameter large enough to contact all the optical fibers outside the center at the center of a large number of optical fibers, and then applies a force from the outside toward the center. , A large number of optical fibers are assembled to form an optical fiber bundle, and the optical fiber bundle is inserted into the positioning hole of the core.

At the same time as the insertion and fixing, a positioning key in the circumferential direction of the core is attached to the circumference of the plug.The purpose is to connect multi-core optical fibers. The objective is to improve the accuracy of pupil determination. The drawings will be explained in detail below.

FIGS. 4 to 8 show an embodiment of the present invention. Note that the same components as in the conventional example are represented by the same reference numerals. FIG. 4 shows an example of a connector used in the method of the present invention, which consists of a pair of plugs 10 (only one is shown in the figure) and an adapter 20 that connects the plugs 10 in a detachable manner.

Reference numeral 11 denotes a positioning key attached to the outer peripheral edge of the plug 10, which engages with the engagement groove 21 of the adapter 20 and positions the core 30 housed on the central axis of the plug 10 in the circumferential direction. It has become.

12 is a coupling nut, 13 is a cover, 14 is a spring, and 22 is a split sleeve into which the tip of the core 30 can be forcibly inserted. Note that this connecting tool is connected to the positioning key 11. The engaging groove 21° is known except for the internal structure of the core 30, so a detailed explanation will be omitted. Figure 5- is the core 3o
In the figure, 31 is a flange, 32 is a circular positioning hole (see FIG. 6), and 4o is a heat-shrinkable tube.

Next, the connection method of the present invention will be explained. The coating is removed from the end of the coated optical fiber 1 without being separated, leaving the optical fiber 2 exposed. After repeating the same operation and obtaining a large number of optical fibers 2, a cylindrical body (an optical fiber may be used as a dummy) 2' with the largest outer diameter is placed in the center of them, and then a heat shrink tube is placed. At 40, the multi-core optical fibers 2 are assembled. In the following, a case will be described in which a dummy fiber is arranged at the center of a six-core optical fiber. FIG. 6 shows the arrangement of the optical fiber 2 and the dummy fiber 2I. 2t is the dummy fiber in the center, dummy fiber 2I
is not smaller than the diameter of the other optical fibers 2. By heating the heat-shrinkable tube 40, a shrinking force is exerted from the outside toward the center, and the tips of the seven optical fibers 2.about.2' are assembled into a hexagonal shape to form an optical fiber bundle.

Next, a core 30 having the optimum positioning hole diameter for the assembled optical fiber bundle is selected. Prepare various types of cores 30 in which positioning holes 32 with inner diameters of 385 μmt are drilled in steps of 1 μIn from 367 μm, and insert optical fiber bundles sequentially from the cores 3O with the positioning holes (2) with large inner diameters. To go.

A core 30 having a hole diameter 1 μl larger than the core 30 that cannot be inserted is selected as the optimal core 30. This allows the clearance between the optical fiber bundle and the positioning hole to be 1μ.
m or less.

The optical fiber bundle is fixed to the selected core 3O with epoxy adhesive. After the adhesive has sufficiently hardened, the end faces of the core and optical fiber bundle are polished to obtain a proper mating end face, ]0a. The core 30 that has completed the above operations is stored in the plug 10.

Next, positioning in the circumferential direction is performed. A master plug (not shown) is used for this purpose. The master plug also has a structure similar to that shown in FIG. 5, with a dummy fiber in the center and 6 mm optical fibers arranged around it. An LED light source with a wavelength of 0.85 μm is connected to the first optical fiber on the circumference through a 500 m dummy fiber. 5
A 00m dummy fiber is inserted to obtain a steady mode. This master plug and the core 3 configured as described above
After connecting the plug 10 which houses the plug 10 using the adapter 20, the light coming from the first optical fiber attached to the plug 10 is monitored by optical power make. While monitoring, rotate the core 3 degrees of the plug 1o to find the position where maximum power is transmitted, and place the positioning key 1 in the circumferential direction on the circumference of the plug 10.
Attach and secure 1. Similarly, other plugs are constructed and both are connected using the adapter 20.

Next, the accuracy of mounting the positioning key 11 will be explained. The mounting radius of the positioning key 11 (radius 't from the center of the positioning core 30 is 5.0 rm. On the other hand, the radius from the center of the core of the central axis of the 6-fiber optical fiber) is 125 μm & degree. Therefore, when the positioning key 11 is fixed at one point on the fin with a radius of 5.0 mm, if the installation error is 40 μm or less, the misalignment error of the optical fiber/this central axis will be 1 μm or less. Since positioning of about 40 μm is easy, positioning in the circumferential direction can be achieved with high accuracy using the positioning key 11.

Next, we will evaluate the connector loss due to the difference in the outer diameter of the optical fiber. Here, it is necessary to consider the eccentricity of the core, but based on the manufacturing experience of graded optical fibers, the eccentricity of the core is 0.68 μm on average, and is not a major cause of connector loss, so it is excluded. Since the outer diameter standard of currently manufactured optical fibers is 122 to 128/7 m, highly accurate positioning cannot be achieved simply by inserting a seven-core optical fiber into one positioning hole 32. Furthermore, even if the central dummy fiber 2' is assembled by applying a force toward the center, if the outer diameter of the central dummy fiber 2' is smaller than the outer diameter of the other six optical cores ζ2, the optical fibers that are not in contact with the central dummy fiber 2' , F, the fluctuation range of the central axis of the optical fiber becomes large and the connector loss increases. FIG. 7 shows a state in which six optical core ingots 2 are assembled around a central dummy fiber S2' with a heat shrink tube 40. Dummy 7 eye! ! Do the diameter of 2/,
The diameter of the optical fiber cells 2 arranged on the circumference is di(i=] ~
6) The maximum deviation of the optical fiber center axis that occurs on one circumference is D
Then, equation (1) approximately holds true.

D=6do-Σ di (μm) l1li=1 The connector loss caused by the axis misalignment D in the graded optical fiber is expressed by equation (2).

,,3 L = −D (d B ) (2) where a is the diameter of the core. Table I below shows the outer diameters and core diameters of the optical cores used in the experiments. 0), the maximum deviation D can be calculated as 2.8μ'n.2,8
The connector loss caused by an 11m misalignment is (2
) is 0.17 dB.

As mentioned above, in the method of the present invention, positioning in the circumferential direction was performed by monitoring the connector loss for a single-core optical fiber. Positioning of A was performed in the circumferential direction, and variations in connector loss were investigated. The results are shown in Table H below. The minimum connector loss of the first optical fiber, S, in Table 3 is the connector loss when the first optical fiber is aligned th in the circumferential direction. The maximum connector loss of the second optical core was determined using the following method. That is, when positioning the third (1-1) optical fiber in the rotational direction, the connector loss of the first optical fiber becomes greater than when positioning the first optical fiber. The maximum value of connector loss when J was varied from 1 to 6 was defined as the maximum connector loss. The difference between the maximum and minimum connector loss is due to the maximum axis deviation in the circumferential direction, and from Table H, the average value is 19 dB.

This value corresponds to the connector loss of 0.1 calculated using the calculation described above.
It is in good agreement with 7dB. By arranging the optical fiber or the like with the largest radius at the center in this way, it is possible to reduce the axial deviation and to evaluate the maximum value of the axial deviation in the circumferential direction.

Finally, we created 6 sets connected by the method of the present invention and evaluated the connector loss using matching oil.
) and realized a low-loss connector. The results are shown in FIG.

Table - ■ - Variation of connector loss Note that the core constructed by the method of the present invention positions a large number of optical fibers point-symmetrically, so by providing a rotation mechanism in the core portion, a large number of optical fibers can be It is also possible to configure a rotary switch that connects two optical fibers.

As explained above, the present invention uses one core and does not require a large number of cores unlike the conventional connection method, so that high-density connections can be realized. In addition, since the shape of the positioning hole may be a simple circle rather than a complicated polygon, it is possible to set the center position with high accuracy and control the hole diameter with respect to the outer periphery of the core.

- It is possible to machine high-precision positioning holes. In addition, a cylindrical body with a diameter large enough to touch all optical fibers outside the center is provided at the center, and a large number of optical fibers are gathered together by applying force toward the center. Since the optical fiber is in contact with the cylindrical body at the center, the fluctuation range of the central axis of the optical fiber on the circumference can be narrowed, and therefore a low-loss connection can be realized. Furthermore, positioning in the circumferential direction is performed using a positioning key installed on the circumference of the plug, but since the setting position of the positioning key has a sufficiently large radius compared to the center axis of the optical fiber, it is possible to perform positioning in the circumferential direction with high precision. There are advantages such as the possibility of positioning.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional method for connecting multi-core optical fibers using a large number of cores, Fig. 2 is a diagram similar to Fig. 1 using a conventional single core, and Fig. An enlarged diagrammatic representation of the positioning holes in Fig. 2, and Figs. 4 to 8 show an embodiment of the present invention, and Fig. 4 shows a multi-core optical fiber to which the method of the present invention is applied. 5 is an enlarged sectional view of the core portion, FIG. 6 is a diagram diagrammatically representing the connecting end surface of the core, and FIG. 7 is a diagram for explaining another example. FIG. 8, which is similar to FIG. 8, is a connector loss distribution diagram of a connecting portion according to the method of the present invention. ■...Coated optical fiber, 2...Optical fiber, 10...
Plug, 11・Positioning key, 20・Adapter, 30
... Core, 32 ... Positioning hole, 40 ... Heat shrink tube. Patent Applicant Nippon Telegraph and Telephone Public Corporation Agent Patent Attorney Yoshi 1) Takashi Sei

Claims (2)

[Claims] (1) A multi-core optical fiber connection method in which a core is attached to the connection end of a multi-core optical fiber, the core is housed in a plug, and then the core is removably connected via an adapter. A cylindrical body with a diameter large enough to touch all the optical fibers outside the center is provided at the center of the fibers, and a uniform force is applied from the outside toward the center of the cylindrical body using a covering means such as a heat shrink tube. A method for connecting multi-core optical fibers, comprising forming an optical fiber bundle by doing so, and inserting and fixing the optical fiber bundle into a circular positioning hole provided at the center of the core. (2) A multi-core optical fiber connection method in which a core is attached to the connection end of a multi-core optical fiber, the core is housed in a plug, and then the core is removably connected via an adapter. A cylindrical body with a diameter large enough to touch all the optical fibers outside the center is provided at the center of the fibers, and a uniform force is applied from the outside toward the center of the cylindrical body using a covering means such as a heat shrink tube. An optical fiber bundle is formed by inserting and fixing the optical fiber bundle into a circular positioning hole provided at the center of the core, and at the same time positioning the core in the circumferential direction on the circumference of the plug. A method for connecting multi-core optical fibers, which is characterized in that the key can be retrieved.