JP2003075676A - Fusion splicing method for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber fusion splicing method for preventing a mode field diameter in a fusion splicing part from greatly expanding locally by heating of the fusion splicing and that efficiently reduces connection loss through implementation of TEC by the heat treatment. SOLUTION: In this optical fiber splicing method, two types of optical fibers 1a, 1b having a different mode field diameter are abutted on each other at the end faces for fusion splicing, and then heat treatment is performed so that the mode field diameters are coincided with each other at the connecting faces. In this case, fusion splicing is carried out using a resistance heating unit 12 while the heat treatment is performed with a burner 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber fusion splicing method for fusion splicing two kinds of optical fibers having different mode field diameters.

[0002]

2. Description of the Related Art In recent years, development of a hybrid optical fiber in which a high-performance optical fiber such as an optical fiber for wavelength division multiplexing transmission or an optical fiber for Raman amplification is combined with an ordinary single-mode optical fiber has been advanced. In the development of this optical fiber, not only the improvement of the characteristics of the optical fiber itself but also the connection technology between the optical fibers is an important factor. Generally, the optical fiber loss is 0.15 dB / km
However, in the case of long-distance installation such as undersea optical cable,
Connections are made between many optical fibers. If the loss in one optical fiber connection is, for example, 0.15 dB, the optical fiber loss is equivalent to 1 km. Since there is a certain limit to reducing the loss of the optical fiber itself, it is desired to reduce the connection loss of the optical fiber as much as possible.

The mode field diameter of an optical fiber (hereinafter,
In the connection between the above-mentioned high-performance optical fibers having different core diameters) and a normal single-mode optical fiber, it is difficult to obtain a practical connection loss only by fusion splicing by arc discharge. For this reason, the fusion spliced portion is heat-treated to form a smooth shape by tapering so that the core diameters of the spliced portion match (Thermal Expanded Core, hereinafter referred to as TEC).
Is known (for example, Japanese Patent No. 261850).
No. 0 publication).

FIG. 5 is a diagram showing an example of performing heat treatment after the above-described fusion splicing. FIG. 5 (A) is a diagram showing a state where optical fibers having different core diameters are opposed to each other for fusion splicing, and FIG. 5 (B) is a diagram showing a state where they are fusion spliced by arc discharge. C) is a diagram showing a state in which TEC is performed by heat treatment with a micro torch. 1a, 1 in the figure
Reference numeral b is an optical fiber, 2 is a cladding portion, 3a and 3b are core portions, 4 is a fusion splicing portion, 5 is a discharge electrode, and 6 is a micro torch.

Optical fibers 1a and 1b fusion-spliced together
Have the same outer diameter as the cladding portion 2, but have different core diameters and relative refractive index differences between the core portions 3a and 3b. Optical fiber 1
As shown in FIG. 5A, the connection end faces of a and 1b are arranged to face each other, and then the connection end faces are melted and fused by arc discharge as shown in FIG. 5B. When the fusion splicing is simply performed, the core portion 3 of the optical fiber 1a is formed at the fusion splicing portion 4.
Due to the difference in core diameter between the core diameter 3a and the core diameter 3b of the optical fiber 1b, the connection becomes discontinuous and the connection loss increases. In order to improve this, the vicinity of the fusion splicing part 4 is heated by a micro torch 6 or a ring heater using combustion gas to perform TEC treatment. This heating is performed by the optical fibers 1a and 1b.
Although it does not melt itself, it is carried out at a temperature and time at which the dopant agent for increasing the refractive index, which is added to the core portions 3a and 3b, diffuses to the cladding portion side.

By the heating shown in FIG. 5C, the core diameter of the core portion 3b of the optical fiber 1b having a small core diameter and a large relative refractive index difference is expanded in a taper shape so that the core portion 3a of the optical fiber 1a and the core portion 3a thereof are not connected. It reduces the continuous state and reduces the connection loss.
When performing fusion splicing between such heterogeneous optical fibers, by performing the above-mentioned TEC process, the optical fiber having a small core diameter can be gradually brought closer to the core diameter of the other optical fiber, and the connection loss can be reduced. Has been revealed. Further, it is known that such TEC treatment by heating is effective for expanding the core diameter of the fusion spliced portion and reducing the splice loss due to eccentricity or the like even when splicing optical fibers of the same kind. .

However, as shown in FIG. 6, due to heat generated by arc discharge during fusion splicing, the dopant added to the core portions 3a and 3b is largely diffused in the vicinity of the fusion splicing portion, and the core diameter is partially reduced. And the guided mode of light disappears, resulting in a large loss. In such cases,
Even if the TEC process is performed, the loss may not be easily reduced. Therefore, reduce the discharge current of the arc discharge or shorten the discharge time to suppress the local expansion of the core diameter due to the arc discharge, and reduce the connection loss in the subsequent heat treatment. I've been trying. However, with these methods, the strength of the fusion-spliced portion is reduced, and it is difficult to contribute to practical use.

It is also known that the fusion splicing is performed by a ribbon-shaped filament heater instead of the arc discharge (see Japanese Patent No. 3073520). This filament heater has an open loop shape and is formed to remove the optical fiber from the loop opening. It is said that the fusion temperature can be easily adjusted by fusion-splicing using a filament heater, and it is also disclosed that heat treatment after fusion is performed to remove surface damage and the like that may occur during the connection work. There is. However, it is merely disclosed that the fusion splicing of the optical fibers is performed by the filament heater, and whether or not the fusion splicing between the different kinds of optical fibers having different core diameters and the subsequent TEC treatment and the problem of increasing the loss are unclear. It remains.

[0009]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and by heating at the time of fusion splicing,
An object of the present invention is to provide an optical fiber fusion splicing method capable of efficiently reducing splice loss by performing TEC by heat treatment without locally greatly increasing the mode field diameter.

[0010]

According to the optical fiber fusion splicing method of the present invention, the end faces of two types of optical fibers having different mode field diameters are butted against each other for fusion splicing, and then the mode field diameters of the splicing surfaces are matched. The optical fiber fusion splicing method is performed by heat treatment so that the fusion splicing is performed by using a resistance heater and the heat treatment is performed by using a burner.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. FIG. 1 (A) is a diagram showing a pair of optical fibers having different mode field diameters for performing fusion splicing, and FIG. 1 (B).
Is a process drawing of fusion splicing, and FIG. 1C is a diagram showing an outline of work contents corresponding to the process drawing. In the figure, 1a and 1b are optical fibers, 2 is a glass fiber part (clad part), 3
a and 3b are core parts, 4 is a fusion splicing part, 7 is a fiber coating, 8a and 8b are holding clamps, 9 is a scratching blade, 11 is a fusion bonding clamp, 12 is a resistance heating heater, 13 is a burner, 14 is a A protection member is shown.

The fusion splicing method of the present invention is shown in FIG.
It is applied to fusion splice a pair of optical fibers 1a and 1b having different mode field diameters (hereinafter referred to as core diameters) as shown in (A). A pair of optical fibers 1a and 1b
As described in the section of the prior art, the clad portion 2 has the same outer diameter, but the core portions 3a and 3b have different core diameters. The fiber coatings 7 may have the same outer diameter or different outer diameters. Below, the optical fibers 1a and 1b
The fusion splicing method will be described with reference to the process diagram of FIG. 1 (B) and the work schematic diagram of FIG. 1 (C).

First, in step S1, the optical fibers 1a and 1b are
The fiber coating 7 on the tip portion of is removed by a predetermined length including a margin for cutting the end face to expose the glass fiber portion 2 (clad portion). This fiber coating removal can be performed using a conventional coating removal device.

Then, in order to obtain a connection end face suitable for fusion splicing in the step S2, the end faces of the optical fibers 1a and 1b are cut. The end face cut of the optical fiber is, for example,
As shown in FIG. 1C, there is a method in which both sides to be cut are held by holding clamps 8a and 8b, and a tension is applied to the optical fiber, and the optical fiber is scratched and cut by a scratching blade 9. When cutting the end faces of the optical fibers 1a and 1b, it is necessary that the exposed surface of the glass fiber portion 2 is not scratched and that the cut surface is cut so as to be perpendicular to the optical fiber axis. .

When the exposed surface of the glass fiber portion 2 is scratched, stress is concentrated on the scratched portion and the glass fiber portion 2 is easily broken. Therefore, the tip of the glass fiber part 2 on the side to be discarded after cutting may be directly held by the holding clamp 8b, but the part on the opposite side is the part of the fiber coating 7 so as not to be scratched by the clamp. Is preferably held by a holding clamp 8a. There is also a method of cutting the end portion of the optical fiber by pressing a damaged portion with a damaged blade with a pressing pillow, but in this case also, it is preferable to clamp the fiber coating portion.

If the cut surfaces of the optical fibers 1a and 1b are inclined with respect to the plane perpendicular to the optical fiber axis, the transmission loss at the time of fusion splicing becomes large, and the loss is improved even if the TEC treatment is performed later. I can't plan enough. Optical fiber 1
The relationship between the inclination angle of the cut surfaces of a and 1b and the connection loss is shown in FIG. 4 described later. In addition, it is preferable that the cut surface has an inclination angle of less than 1 °.

In the next step S3, the optical fibers 1a and 1b are
Are set in a fusion machine (for example, FFS2000 manufactured by Vytran). Normally, the glass fiber portion 2 of the optical fibers 1a and 1b is placed on the V-groove clamp base and the fiber coating portion is separately clamped. However, in the high-strength connection in which the exposed length of the glass fiber portion 2 is shortened, the portion of the fiber coating 7 is provided. Are directly clamped and set by the fusion-bonding clamp 11 using a V groove base. Then, in step S4, the optical fibers 1a and 1b are aligned. This alignment is performed by the outer diameter of the glass fiber portion 2 of the optical fiber and the core portions 3a, 3
b is performed with a microscope camera (not shown), and the end face spacing is adjusted. Further, in the next step S5, the optical fiber 1
The end faces of a and 1b are observed with a microscope camera, and the inclination angle, chipping or burrs on the end faces, and the presence or absence of dust adhesion are inspected.

In the next step S6, fusion splicing is performed. In the present invention, this fusion splicing is performed using a resistance heater. 2A and 2B are views showing an example of fusion splicing by a resistance heater, FIG. 2A is a perspective view, and FIG. 2B is a current-voltage characteristic diagram of the resistance heater. In the figure, 12 is a resistance heating heater, 15 is a heater power source, and 16 is a power adjusting device. The resistance heater 12 can be formed of an electric resistance material such as tungsten, molybdenum, or tantalum. The shape of the resistance heater 12 is preferably U-shaped so that the ribbon resistance wire can be opened at a part of the loop and the optical fiber can be inserted and removed through the opening.

Specifically, the resistance heater 12 is made of a tungsten resistance wire having a thickness of 0.05 mm and a width of 0.6 mm, and a U-shaped portion 12a having an arc of a radius of 0.4 mm and a depth of 1.0 mm. To do. Voltage of this resistance heater 12-
The current characteristics show non-linearity as shown in FIG.
A heating amount is adjusted by an electric power adjusting device 16 connected to the heater power supply 15. The electric power of the heater is 20 W, and the glass end faces melted by heating for about 5 seconds can be fusion-bonded by pushing the glass end faces to each other. The resistance heater 12 can easily adjust the heating amount and can be easily managed. In addition, the resistance heater 12 is not easily affected by the ambient air such as atmospheric pressure and humidity, so that stable and highly accurate fusion splicing can be performed. .

After the fusion splicing is performed, the TEC process by the burner 13 is performed in the next step S7. This TE
As shown in FIG. 3, the C treatment is carried out by moving the optical fibers 1a and 1b to the burner heating stage while holding them by the fusion clamp 11. As the combustion gas of the burner 13, oxyhydrogen gas produces a too strong flame, and it is preferable to use propane gas and oxygen gas. The heating temperature can be easily adjusted by changing the flow rate of propane gas,
It can also be adjusted by changing the oxygen flow rate.

This TEC processing is performed by the optical fibers 1a and 1b.
The temperature at which the optical fiber softens and does not deform (about 1300 ° C. or less), and the temperature at which the dopant in the core part diffuses into the clad part (about 500 ° C.).
In the above range, it takes about 3 to 10 minutes. Moreover, the heating range in the vicinity of the fusion splicing part 4 of the optical fiber can be adjusted along the axial direction by heating in the TEC treatment, if necessary. The heating position may be adjusted by moving the optical fiber side or the burner side.

After the TEC treatment, the connection portion is inspected in step S8. The inspection contents include thick or thin appearance inspection of the connection part, dust and air bubble mixture, core part inclination,
There is misalignment. Thereafter, in step S9, a tensile force is applied to the fusion splicing part 4 to perform screening. After passing the screening, in step S10, the optical fiber 1
The a and 1b are removed from the fusion clamp 11 and recoated with a resin similar to the fiber coating for protection. Further, the fusion splicing part 4 can be protected by using a protection member 14 such as a protection tube.

FIG. 4 shows the relationship between the inclination angle θ of the cut surfaces of the optical fibers 1a and 1b and the loss after fusion splicing and TEC treatment. FIG. 4A is a diagram showing the inclination angle θ,
FIG. 4B is a diagram showing loss data. The pair of optical fibers to be fusion-spliced had a core diameter difference of 2 μm or more. As a cutter for cutting an optical fiber, a No. The inclination angle θ was measured for 20 samples for each cutter using 3 types of 1 to 3, and the average end face angle and the standard deviation were obtained. For loss measurement,
The inclination angle θ is not measured for each sample, and the cutter N
o. (The average tilt angle has been obtained in advance) and the loss after fusion and T
The loss after EC was measured. Figure 1 shows the connection loss measurement.
The fusion splicing method was performed after the fusion splicing by the resistance heater 12 and after the TEC was performed by the burner 13, and the average value was obtained. The heating time of TEC is
All were performed in 200 seconds.

As a result, as shown in FIG. In the case of 1 (average tilt angle θ = 1.28 °), the loss after fusion splicing was 0.75 to 0.9 dB, and after performing TEC was 0.1 dB. Cutter No. In the case of 2 and 3 (average inclination angle θ = 0.29 °, 0.49 °), the loss after fusion splicing was 0.7 to 0.8 dB, and after TEC was 0.08 dB, Cutter No. Compared to No. 1, both the loss after fusion splicing and the loss after performing TEC were reduced. Also, the standard deviation of the loss is small. This is considered to be because the inclination angle θ of the cut surface is small and the variation is small, so that the radiation loss due to the angular irregularity is reduced. From these results, the inclination angle θ of the cut surface is 1
It is preferably cut to less than °.

In addition to this, for comparison, a cutter N is used.
o. The optical fiber cut in 1 was fusion spliced by conventional arc discharge. The loss after fusion splicing is 1.10 to 1.
It was 14 dB. After this, do the same with the burner TE
C was performed, and the TEC time was doubled for 400 seconds. However, the loss after the TEC was 0.12 dB, and the TEC time was increased, but the loss could not be reduced as compared with the case of fusion splicing with a resistance heater.

This is because in the fusion splicing by arc discharge,
Since the connection end face portion is locally heated, it is considered that the change due to the expansion of the core diameter is rapid and the change rate in the length direction is large. When TEC is performed by burner heating, the rate of change of the core diameter itself is alleviated, but it takes a lot of time, and there is a limit in reducing connection loss. On the other hand, in fusion splicing using a resistance heater, since a relatively wide range is heated more slowly than fusion splicing using arc discharge, bending of the core part can be suppressed, and the change in core diameter in the longitudinal direction can be suppressed. The rate is also considered small. As a result, TEC by burner
In the treatment, it is considered that the rate of change in core diameter can be easily reduced and the heating time can be shortened.

Although the present invention has been described above with respect to fusion splicing between optical fibers of different types having different core diameters, splicing loss due to eccentricity of the core portion, etc. even when splicing between optical fibers of the same type having the same core diameter. It can be applied to perform the TEC process when is large. Further, although the burner is used for the TEC treatment, the heating amount of the resistance heater can be reduced to perform the TEC treatment subsequent to the fusion splicing.

[0028]

As is apparent from the above description, according to the present invention, the local diffusion of the dopant in the splicing portion at the time of fusion splicing is relaxed, and the mode field diameters of different optical fibers are smoothly matched. The TEC process can be performed as described above. As a result, it is possible to reduce the connection loss by heat treatment in a short time.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention.

FIG. 2 is a diagram illustrating fusion splicing using a resistance heater.

FIG. 3 is a diagram illustrating TEC processing by burner heating.

FIG. 4 is a diagram showing data on a relationship between a tilt angle of a connection end face of an optical fiber and a connection loss.

FIG. 5 is a diagram showing a conventional fusion splicing method.

FIG. 6 is a diagram for explaining a problem at the time of conventional fusion splicing by arc discharge.

[Explanation of symbols]

1a, 1b ... Optical fiber, 2 ... Glass fiber part (cladding part), 3a, 3b ... Core part, 4 ... Fusion splicing part, 5 ...
Discharge electrode, 6 ... Micro torch, 7 ... Fiber coating, 8
a, 8b ... Holding clamp, 9 ... Scratch blade, 11 ... Fusion clamp, 12 ... Resistance heating heater, 13 ... Burner, 14
… Protective material.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoyuki Hattori             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works (72) Inventor Motonobu Nakamura             Sumitomoden 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa             Ki Industry Co., Ltd. Yokohama Works F-term (reference) 2H036 MA12 MA13 MA17

Claims (5)

[Claims] 1. An optical fiber fusion splicing method in which end faces of two types of optical fibers having different mode field diameters are butted against each other and fusion-spliced, and then heat treatment is performed so as to match the mode field diameters of the spliced portions. An optical fiber fusion splicing method, wherein the fusion splicing is performed using a resistance heater and the heat treatment is performed using a burner. 2. The optical fiber fusion splicing method according to claim 1, wherein the resistance heating heater is formed by bending a ribbon resistance wire into a U-shape. 3. The optical fiber fusion splicing method according to claim 2, wherein the resistance heater is made of tungsten. 4. The optical fiber fusion splicing method according to claim 1, wherein the inclination angle of the end face of the optical fiber is 1 ° or less. 5. The optical fiber fusion splicing method according to claim 1, wherein the fusion splicing is performed by clamping a coating portion of the optical fiber.