JP2572978B2 - Connection method of multi-core optical fiber - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fusion splicing method of a tapered multi-core optical fiber, and more particularly, to a connection length of a single mode multi-core optical fiber, and a cutting length at the time of tapping the optical fiber. The purpose of the present invention is to realize a simple and reliable connection with low loss while suppressing the influence of the variation.

[Prior Art] Conventionally, when connecting a tapered multi-core optical fiber, the optical fiber is abutted against an abutment plate to determine the interval between the end faces of the optical fiber before electric discharge, and thereafter, the electric fiber is determined while heating by electric discharge. A certain amount of feed was performed, and fusion splicing was performed.

[Problems to be Solved by the Invention] However, it is difficult to trim a multi-core tape optical fiber to a fixed length. For this reason, the end face interval of each optical fiber varies.

At the time of fusion splicing, as shown in FIG.
Of the optical fiber 12 is sent by a certain amount L. The feeding amount is adjusted to the one having the largest end face interval. Therefore those end spacing is narrow (for example, # 5 fiber) are often pushing amount Q _5, as in the FIG. 5, the diameter d of the connecting portion 14 becomes thicker, there is a possibility that the connection loss increases.

FIG. 6 is a graph showing the relationship between the pushing amount Q and the loss increase. It can be seen that as the pushing amount increases, core distortion occurs and connection loss increases.

In the case of a five-fiber tape type optical fiber, for example, as shown in FIG. 4, if the spacing between the end faces is wide and the spacing between the other four faces is the same, the pushing amount of these four leads increases,
The average splice loss of the five cores increases.

[Another conventional problem] Conventionally, in connection of a single-core optical fiber, an optical fiber is connected by a first step of connection without alignment and a second step of pulling the optical fiber while the optical fiber is at a high temperature. 7a on connection
A method of easily forming a low-loss connection by forming a tapered portion 16 as shown in the figure has been proposed (see Japanese Patent Application No. 60-239985).

However, the method of selecting the taper ratio d / D of the tapered portion 16 was based on data in the case where the pushing amount at the time of fusion splicing was optimal.

For this reason, it is difficult to make the cut lengths of the ends of the optical fiber constant like a multi-core optical fiber.If the end faces of each core are different and a uniform pushing amount cannot be obtained, connect them with low loss. Is difficult.

As a result, in the case of batch connection of multi-core optical fiber tape,
It has been difficult to connect all the optical fibers in the tape with low loss. Normally, the quality of the connection is judged by the connection loss measurement work using OTDR etc. following the connection work.In the case of tape batch connection, if the loss is large even with one core, the batch connection work is redone, but low-loss connection If it is required, it is difficult for all the optical fibers in the tape to satisfy the required value for the above-mentioned reason in the conventional method, and it is necessary to repeat the collective connection many times to realize the required value. However, it has been difficult to reduce the connection work time.

[Means for Solving the Problems] The present inventors have found the following phenomenon.

After all the fiber cores of the multi-core optical fiber are fusion-spliced at the same time, the connection is heated at a high temperature and pulled as described above.

Then, as shown in FIG. 7a, there is a tapered portion 16, but not all optical fibers are the same.

Since there is variation in the cutting length of the optical fiber and the amount of indentation is different due to this, even if multiple cores are simultaneously pulled by the same length, for example, as shown in FIG. As shown in FIG. 7c, the case where da = D can be performed in some cases.

However, if d / D falls within a certain range, it is possible to suppress the influence of the above-mentioned variation in the pushing amount and to connect with low loss.

The present invention is based on a new perception of the above natural phenomena.

[Experimental example] For a single-core single-mode optical fiber,
52 μm, 98 μm, 116 μm (variation is 116−52 = 64 μm
Then, the connection was heated and pulled to form a tapered portion 16.

FIG. 1 shows the relationship between the taper ratio d / D and the connection loss at that time.

When the tapered portion 16 is formed in the connection portion so that the taper ratio is 1.18 to 0.95, it can be seen that connection can be performed with a connection loss of 0.1 dB or less without being affected by the variation in the pushing amount of 64 μm.

The above description is for a single-core optical fiber. As shown in FIG. 2, a three-core optical fiber having a variation in end face spacing is sent by L, and the pushing amounts Q ₁ , Q ₂ , and Q ₃ are respectively set. , 52 μm, 98 μm, and 116 μm.

Therefore, when actually connecting the multi-core optical fiber, the outer diameter d of the tapered portion 16 is set so that the taper ratio is kept within the above range.
Is measured, the connection can be made with low loss.

Note that instead of measuring the outer diameter d of the tapered portion 16, a simpler method may be used to determine the pulling time.

FIG. 3 shows that when a constant tensile force is applied to the connecting portion after the connection at each of the above-mentioned pushing amounts (the optical fiber is stopped while applying the tensile force), the obtained taper ratio and the time for applying the tensile force are shown. The relationship is shown below.

 From this, the pulling time can be determined.

The method of determining the pulling time to be applied to the connection portion after the connection includes: (1) a method of setting all the cores of the multi-core optical fiber to a certain connection loss standard value or less, and (2) a method of setting the multi-core optical fiber. And minimizing the overall average splice loss.

For the above (1), the connection loss is, for example, 0.1 dB.
The upper limit and the lower limit of the taper ratio for suppressing the following are (d / D) max = 1.18 and (d / D) min = 0.95, respectively, and are shown in FIG.

Therefore, even if the indentation amount is fusion spliced under the condition that it varies from 52 μm to 116 μm, then the tensile force is 60 to 80 ms.
If applied for a certain period of time between ec, the taper ratio is 1.18 to 0.95
Can be formed at the connection portion, and the connection can be made to 0.1 dB or less.

Further, the method for minimizing the average connection loss in (2) is realized since the taper ratio for obtaining the minimum connection loss is 1.10 for any pushing amount from FIG. The tension time is determined by the weighted average of the optimal tension times for each core wire.

For example, the number of cores of the multi-core optical fiber is n, and the pushing amount Q ₁
The core has _one m, core wire ₂ m of Q _2, the core wire of Q ₃ is m ₃ present (n =
m ₁ + m ₂ + m ₃ ), and based on the empirical results shown in FIG. 3, the tensile time for realizing the taper ratio of 1.10 is shown for each of Q ₁ , Q ₂ , and Q ₃ .
by obtaining the _{t 1, t 2, t 3} , the optimum tensile time topt can be determined by _{topt = (m 1 t 1 +} m 2 t 2 + m 3 t 3) / n.

The simplest numerical example is a three-core optical fiber as shown in FIG. 2, and when the pushing amount is 52 μm, 98 μm, and 116 μm, the time corresponding to the respective taper ratio 1.1 is 96 m.
Since sec, 68 msec, and 40 msec, top = (96 + 68 + 40) / 3 = 68 msec.

[Effects of the Invention] At the time of fusion splicing of a multi-core optical fiber tape, it is unavoidable that the cut length of each optical fiber varies, and the feeding amount is simultaneously fed based on the maximum end face interval. The feed amount of each optical fiber is the same, and the one with a narrow end face spacing has a large push-in amount, the outer diameter of the connection part becomes large, the connection loss increases, and as a result, all the fibers in the multi-core optical fiber tape It is very difficult to connect optical fibers with low loss, and for this purpose it is necessary to repeat the connection work many times until the cut lengths are aligned. By applying a tension for a suitable pulling time after fusion splicing, low loss is achieved for all the optical fibers in the multi-core optical fiber tape, regardless of the amount of pushing in and out. Connection becomes almost possible.

The limited numerical value of 0.95 to 1.18 of the taper ratio d / D is
Variations in end-face spacing were obtained from multi-fiber optical fiber connection experiments within 64 μm. However, in actual use of optical fibers (including multi-core optical fibers), variations in end-face spacing are usually within 64 μm. Since it is not so difficult to fit in this range, if it is within this numerical range, it is possible in most cases to perform fusion splicing within a loss that is practically allowable, and it is possible to shorten the connection work . In particular, in the collective connection of multi-core optical fiber tapes, low-loss connection of all optical fibers can be performed almost once, and the connection work can be shortened.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a taper ratio and a connection loss. FIG. 2 is an explanatory diagram of the simplest connection of a three-core optical fiber. FIG. FIG. 4 is an explanatory view of a conventional multi-core optical fiber connection, FIG. 5 is an explanatory view of a state in which the outer diameter of a connection portion is large, FIG. FIG. 7 is a diagram showing the relationship between the pushing amount and the connection loss, FIG. 7a, FIG. 7b, and FIG. 7c are explanatory diagrams of different states of the tapered portion 16; 10: Multi-core optical fiber 12: Optical fiber, 14: Connection part 16: Tapered part

Continuation of the front page (56) References JP-A-57-135909 (JP, A) JP-A-58-21217 (JP, A) JP-A-61-117508 (JP, A) JP-A-61-120106 (JP) , A) JP-A-55-130508 (JP, A)

Claims (1)

(57) [Claims] 1. A plurality of single-core optical fibers are previously fusion-spliced at different push-in amounts, and then each connected portion is heated to a high temperature to form a tapered portion. The relationship between the time and the ratio d / D of the fiber outer diameter d of each tapered portion and the fiber outer diameter D of the non-connecting portion is determined, and from the relationship, the taper ratio d / D is determined for all the optical fibers. A suitable pulling time of 0.95 to 1.18 is determined, and a plurality of optical fibers of the two multi-core optical fibers to be connected are simultaneously fed by an equal length, and the ends of the respective optical fibers are respectively butted and pressed. After the fusion splicing, the connecting portion of each optical fiber is kept at a high temperature, and both ends thereof are simultaneously pulled by the suitable pulling time to form a taper at the connecting portion of each optical fiber. Characterized in that a connection method of a multi-core optical fiber.