JP3108180B2 - Optical fiber fusion splicing method - 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 fusion splicing method suitable for connecting optical fibers having different mode field diameters.

[0002]

2. Description of the Related Art FIG. 4 shows a mode field diameter (a mode field diameter means that the light intensity is 1 / e with respect to the central axis of the core).
² shows an example of an Er (Elumbum) -doped optical fiber amplifier formed by connecting optical fibers having different diameters to each other (referring to the diameter of the region attenuated to ² ). In the figure, a coupler 2 is connected to a laser diode light source 1 for optical excitation via an optical fiber, and the coupler 2 couples the excitation light of the laser diode light source 1 to an optical signal on the single mode optical fiber 3 side. Have been. Coupler 2
One end of the Er-doped optical fiber 4 is connected to the output single-mode optical fiber 3 by fusion, and the other end of the Er-doped optical fiber 4 is connected to the input single-mode optical fiber 3 of the isolator 5 by fusion. When the optical signal and the pump light are coupled and pass through the Er-doped optical fiber 4, the optical signal is amplified, and the amplified optical signal is transmitted to a desired location via the isolator 5 and the filter 6. It is led to.

The fusion splicing of the single mode optical fiber 3 and the Er-doped optical fiber 4 is performed as shown in FIG. That is, the single-mode bare optical fiber 3 exposed by peeling off the coating layer at the connection end of the optical fiber core 7, and the Er which similarly exposes the end of the optical fiber core 8 by peeling. The doped bare optical fiber 4 is opposed to the bare optical fiber 4 with a minute gap 9 therebetween. Heat energy is applied to the connection end by the discharge between the electrodes 10 and 11, and the connection end of the bare optical fibers 3 and 4 is softened. Sometimes, the bare optical fibers 3 and 4 are pushed into contact with each other while applying discharge energy, and the single mode optical fiber 3 and the Er-doped optical fiber 4 are fusion-spliced.

[0004]

However, when the single-mode optical fiber 3 and the Er-doped optical fiber 4 are fused, the mode field diameter of the single-mode optical fiber 3 is larger than that of the Er-doped optical fiber 4. Because of the large size, the fusion splicing occurs due to a so-called mismatch of mode field diameters (since the mode end diameters of the connection end faces of the single mode optical fiber 3 and the Er-doped optical fiber 4 are different, when the end faces abut each other, a portion that does not overlap occurs). There is a problem that an optical signal leaks from the portion and connection loss increases.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an optical fiber fusion splicing method capable of connecting optical fibers having different mode field diameters with a small connection loss. Is to provide.

[0006]

The present invention is configured as follows to achieve the above object. That is, in the present invention, a first optical fiber having a larger mode field diameter and a second optical fiber having a mode field diameter smaller than the first optical fiber and having a large core dopant concentration are opposed to each other. In a fusion splicing method of an optical fiber, in which discharge energy is applied to the opposing region to fusion splice a first optical fiber and a second optical fiber, the fusion splicing of the first optical fiber and the second optical fiber is performed. Later this fusion welding
Discharge energy is again applied to the continuation portion to heat the fusion spliced portion at a temperature lower than the fusion splicing temperature, and the mode field diameter on the connection end face side of the second optical fiber is more diffused than on the first optical fiber side. It is allowed by the second optical fiber mode field so as to substantially match the mode field diameter of the connection end face side to the mode field diameter of the connection end face side of the first optical fiber
The thermal diffusion of this mode field diameter is fused
Transmits an optical signal to the connected optical fiber and passes through the optical fiber.
Observation of the light intensity is performed.
When the fusion splice loss reaches the minimum peak, heat diffusion
Is characterized by stopping discharge heating .

[0007]

In the present invention having the above-described structure, when connecting the first optical fiber having the larger mode field diameter to the second optical fiber having the smaller mode field diameter, first, the first optical fiber is connected to the first optical fiber. The fiber and the second optical fiber are connected by fusion as in the conventional example. After the fusion, the fusion splicing region is heated intermittently or continuously at a temperature lower than the fusion splicing temperature for a predetermined time, so that the mode field diameter of the first optical fiber and the mode field of the second optical fiber are increased. Encourages diffusion (diameter expansion) of the diameter. In this thermal diffusion, since the core dopant concentration is larger in the smaller mode field diameter than in the larger one, the larger core dopant concentration, that is, the smaller mode field diameter promotes the diffusion of the mode field diameter more. The mode field diameter of the first optical fiber and the second
When the mode field diameter of the optical fiber substantially matches the mode field diameter ,
Observation of light intensity of optical signal through spliced optical fiber
When the fusion splice loss reaches the minimum peak , diffusion heating of the mode field diameter is stopped.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a fusion splicing method according to one embodiment of the present invention. In the figure, a first optical fiber 12 has a core diameter of 10 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 0.3%.
The second optical fiber has a core diameter of 6 μm, a cladding diameter of 125 μm, and a relative refractive index difference of 1%.
Er-doped optical fiber. In the fusion splicing of the first optical fiber 12 and the second optical fiber 13 having different mode field diameters, the connection end faces of the first optical fiber 12 and the second optical fiber 13 are as shown in FIG. As shown in FIG. In this state,
As in the case of FIG. 3, when discharge energy is applied between the connection end faces and the connection end faces of the two optical fibers 12 and 13 are softened, the connection end faces are pushed into contact with each other, so that the two optical fibers 12 and 13 are conventionally formed. Fusion splicing is performed as in the example.

What is characteristic in the present embodiment is that after this fusion splicing, heat energy is applied to the fusion splicing region so that the mode field diameter on the connection end face side of the first optical fiber 12 and the second optical fiber 13 is increased. Is diffused, so that the mode field diameters at the connection end faces of the two optical fibers 12 and 13 are made to substantially match as shown in FIG. 1B.

If the heating temperature after the fusion splicing, that is, the heating temperature for the thermal diffusion of the mode field diameter is set to the same high temperature as the heating temperature at the time of fusion, the thermal diffusion of the mode field diameter is performed too rapidly. Since the boundary between the core and the clad is disturbed and light power is radiated, transmission loss of an optical signal increases. For this reason, in this embodiment, the temperature of the thermal diffusion of the mode field diameter is set at a temperature lower than the temperature at the time of fusion splicing. When the fusion spliced part is heated intermittently or continuously after fusion splicing, the first optical fiber
The mode field diameter of 12 and the mode field diameter of the second optical fiber 13 gradually increase due to thermal diffusion. During the heat diffusion, the core dopant concentration of the second optical fiber is higher than that of the first optical fiber. Therefore, when the fusion spliced portion is heated, the second optical fiber has a second mode field diameter larger than the mode field diameter of the first optical fiber 12. The thermal diffusion of the mode field diameter of the optical fiber 13 is further promoted, and the mode field diameter of the second optical fiber 13 having the smaller diameter gradually increases to the mode field diameter of the first optical fiber 12. As the distance approaches, the connection loss gradually decreases.

FIG. 2 is a graph showing the state obtained by experiments. The horizontal axis of this graph indicates the number of discharges in which the fusion spliced part was intermittently heated by the discharge, and the vertical axis indicates the fusion splice loss. In this experiment, the first optical fiber
When the second optical fiber 13 and the second optical fiber 13 are fusion spliced, for example, an optical signal is transmitted from the first optical fiber 12 side to the second optical fiber 13 side, and the light intensity is measured with a power meter or the like. The discharge energy is repeatedly applied to the fusion spliced portion while measuring (monitoring), and the fusion splice loss at that time is calculated and shown in a graph. As can be seen from this graph, after the fusion splicing, the fusion splice loss gradually decreases as the number of discharges increases. This indicates that the mode field diameter of the second optical fiber gradually approaches the mode field diameter of the first optical fiber 12 every time the number of discharges increases. In this embodiment, the discharge voltage is set lower than the voltage at the time of fusion, and the discharge time per discharge is reduced to 7 times.
The result was that the fusion splice loss was 0.8 dB in the first discharge, but the splice loss was reduced to 0.1 dB when the discharge was repeated 15 to 20 times. was gotten. It can be seen that the mode field diameter of the first optical fiber 12 and the mode field diameter of the second optical fiber 13 substantially coincided by the 15 to 20 discharges. In this experiment, the fusion splice loss reached its minimum peak at 0.1 dB, and when the discharge was further repeated, the fusion splice loss gradually increased.

Therefore, when performing the thermal diffusion of the mode field diameter, an optical signal is transmitted between the optical fibers to be connected, the light intensity is observed while performing the thermal diffusion, and the fusion splice loss is minimized. (When the fusion splice loss changes from a decreasing trend to an increasing trend), or the data of the number of discharges (or discharge time) and the fusion splice loss is obtained in advance, and the fusion splice loss is minimized. It is desirable to stop the thermal diffusion heating when the number of discharges (or discharge time) reaches the level.

Note that the present invention is not limited to the above-described embodiment, but can adopt various embodiments. For example, in the above embodiment, the fusion splicing of a single mode optical fiber and an Er-doped optical fiber has been described as an example. However, the present invention relates to various types of optical fibers having different mode field diameters, for example, an Er-doped optical fiber. And a dispersion-shifted optical fiber. In the above embodiment, a connection example of a single-core optical fiber is shown, but the present invention is naturally applicable to fusion splicing of a multi-core optical fiber such as a tape fiber.

Further, heating conditions such as a discharge voltage (heating temperature), a discharge time, and the number of discharges for performing thermal diffusion of a mode field diameter can be appropriately changed according to the type of the optical fiber to be fused.

[0015]

[0016]

According to the present invention, after fusion splicing optical fibers having different mode field diameters, the fusion spliced portion is heated at a temperature lower than the temperature at the time of fusion splicing to reduce the mode field diameter of the optical fiber. Since the diffusion heating is used, the diffusion heating increases the mode field diameter of the first optical fiber and the second optical fiber by reducing the mode field diameter and increasing the core dopant concentration. Can be substantially matched, thereby making it possible to perform fusion splicing with a small connection loss even in optical fibers having different mode field diameters, which can greatly contribute to the development of the optical communication field. In particular, this mode
Thermal diffusion of the hard field diameter is applied to the spliced optical fiber.
Send an optical signal and observe the light intensity through the optical fiber.
Observation of this light intensity minimizes fusion splice loss.
Discharge heating of thermal diffusion is stopped at the side peak
To ensure that fusion splice loss is set to a minimum.
It has an excellent effect that it can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing one embodiment of the present invention.

FIG. 2 is a graph of experimental data showing the relationship between the number of discharges of thermal diffusion and the fusion splice loss in the example.

FIG. 3 is an explanatory view of a general optical fiber fusion splicing method.

FIG. 4 is an explanatory diagram of an Er-doped optical fiber amplifier using fusion splicing of optical fibers having different mode field diameters.

[Explanation of symbols]

 7,8 Optical fiber core 10,10 Electrode 12 First optical fiber 13 Second optical fiber

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hideyo Hiramatsu 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Nobuyuki Kagi 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (72) Inventor Kazunori Nakamura 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd. (56) References JP-A-3-130705 (JP, A) JP-A-61 -194410 (JP, A) JP-A-60-68303 (JP, A) JP-A-4-98206 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 6/24- 6/40

Claims (1)

(57) [Claims] 1. A first optical fiber having a larger mode field diameter and a second optical fiber having a smaller mode field diameter and a larger core dopant concentration than the first optical fiber. In a fusion splicing method of an optical fiber in which a first optical fiber and a second optical fiber are fusion-spliced by applying discharge energy to the opposing region, after the fusion splicing of the first optical fiber and the second optical fiber, this
Discharge energy is again applied to the fusion splicing part to heat the fusion splicing part at a temperature lower than the fusion splicing temperature, so that the mode field diameter on the connection end face side of the second optical fiber is larger than that on the first optical fiber side. Modofu so as to substantially match the mode field diameter of the connection end face side of the second optical fiber by more diffuse to the first mode field diameter of the connection end face side of the optical fiber
Field diameter, and the thermal diffusion of this mode field diameter
Transmits an optical signal to the fusion spliced optical fiber and
While observing the light intensity passing through the
When the splice loss reaches the minimum peak
A fusion splicing method of an optical fiber, wherein the discharge heating of thermal diffusion is stopped .