JP4115295B2 - Optical fiber connection method - Google Patents

Description

【００４０】
表１から次のことが明らかである。
融着接続部への印加張力が７８mNまでは、融着接続部の光損失は小さく、また、融着接続部のファイバ外径変動量も少なく、強度の低下は認められない。
【００４１】
【発明の効果】
以上の説明で明らかなように、本発明方法によれば、ＭＦＤが異なる異種光ファイバやＭＦＤが非常に小さい同種の光ファイバを低損失で接続することができる。これは、融着接続部を加熱して光ファイバのＭＦＤを合致させる際に、融着接続部の軸方向に７８.４mN以下の張力を印加しながら加熱処理を施すことによって得られる効果である。
【図面の簡単な説明】
【図１】本発明の接続方法の１例を示す概略図である。
【図２】本発明の接続方法において、接続状態をモニタするシステム例を示す概略図である。
【図３】実施例１の結果を示すグラフである。
【符号の説明】
１，２ 接続対象の光ファイバ
３ 融着接続部
４ 加熱手段（バーナ）
５ 張力計
６Ａ，６Ｂ ローラ
７ 重錘
８Ａ，８Ｂ 固定治具（クランプ）
９ ダミーファイバ
１０ ＯＴＤＲ
１１ 加熱手段制御部
１２ フィードバック制御部
１２Ａ 信号比較部
１２Ｂ メモリ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for connecting optical fibers, and more specifically, when two optical fibers having different mode field diameters (MFD) or two optical fibers having small MFDs are end-face connected. The present invention relates to an optical fiber connection method for connecting two optical fibers with low loss.
[0002]
[Prior art]
In recent years, in optical communication systems, the transmission capacity has increased rapidly due to the development of Wavelength Division Multiplexing (WDM) transmission systems. For optical fiber lines wired in such a system having a large transmission capacity, performances such as a reduction in nonlinear effects, a reduction in chromatic dispersion, and a reduction in chromatic dispersion slope are strongly demanded.
[0003]
In order to meet this demand, the following distributed management lines are being studied. The dispersion management line includes, for example, an end face of a single mode optical fiber (SMF, eg, 1300 nm zero dispersion optical fiber) and a dispersion compensating optical fiber (eg, Dispersion Compensating Fiber) that compensates for the dispersion and dispersion slope of the SMF. : DCF, Dispersion Slope Compensating Fiber: DSCF, Reverse Dispersion Fiber: RDF, etc.) and is about to be used for high-speed communication using, for example, light in the 1550 nm band.
[0004]
By the way, in the case of the 1300 nm zero-dispersion optical fiber which is a single mode optical fiber exemplified above, the core is made of silica doped with GeO ₂ , the clad is made of pure silica, and the MFD at a wavelength of 1550 nm is 9 ˜11 μm. In the MFD expansion type single mode optical fiber, the MFD is 11 μm or more.
[0005]
On the other hand, in the case of a dispersion compensating optical fiber having negative high dispersion characteristics, it is necessary to increase the relative refractive index difference to around 2%. For this reason, the core is formed of silica doped with, for example, GeO ₂ at a high concentration, and the cladding is formed of silica doped with fluorine. And the core diameter is about 2-3 micrometers, and is extremely small compared with the core diameter of a single mode optical fiber. The MFD at a wavelength of 1550 nm is about 5 μm. That is, the dispersion-compensating optical fiber has a smaller core diameter and MFD than the single-mode optical fiber.
[0006]
Therefore, if the end surfaces of the two optical fibers described above are simply fused and connected, even if the optical axes of the two optical fibers coincide with each other, light leakage based on the difference in MFD occurs at the connecting portion. Light loss. For example, if a single mode optical fiber having an MFD of 10 μm and a dispersion compensating optical fiber having an MFD of 5 μm are fused and joined with their optical axes aligned, the optical loss at the fusion spliced portion is 1.94 dB. It will be about.
[0007]
For the occurrence of optical loss in such a fusion spliced portion, the optical loss is usually reduced by applying a TEC method (Thermally Defused Expanded Core method) (see Patent Document 1).
In this TEC method, the fusion splicing portion is subjected to heat treatment, and the dopant in the core is diffused into the cladding to substantially expand the diameter of the core and the MFD.
[0008]
For example, when the TEC method is applied to the fusion spliced portion of a single mode optical fiber and a dispersion compensating optical fiber, the softening temperature of the dispersion compensating optical fiber clad (fluorine-doped) is as follows. ), The diffusion rate of the dopant (GeO ₂ ) in the cores of both optical fibers into the respective cladding is faster in the dispersion-compensating optical fiber than in the single-mode optical fiber. Therefore, during the heat treatment process, the core dopant of the dispersion compensating optical fiber is preferentially diffused, and the core diameter of the dispersion compensating optical fiber is substantially increased at the fusion spliced portion. Matches the core diameter of the mode optical fiber. That is, the MFD matches, and a reduction in optical loss between both optical fibers is realized.
[0009]
In this way, optical loss at the fusion splicing portion is reduced.
As for the connection of optical fibers, as described above, not only the connection of different types of optical fibers having different core diameters and MFDs, but also the same type of optical fibers can be connected to each other for length adjustment and characteristic adjustment of the entire optical line. It is also necessary to connect.
For example, the same type of dispersion compensating optical fiber having a very small MFD and therefore a very small core diameter may be connected. Also in this case, the mutual end faces of the two optical fibers are fusion-spliced using, for example, a fusion splicer.
[0010]
However, in this case, since the core diameter is very small, there is a problem that the optical loss at the fusion splicing portion becomes large even if the cores are slightly misaligned. In addition, for example, when a discharge fusion splicer is used at the time of fusion splicing, even if the discharge conditions of the discharge fusion splicer are optimized, a sufficient reduction in optical loss can be achieved at the time of connection of the recent thin wire core. Not realized.
[0011]
Therefore, even in such a connection, the TEC method is applied to the formed fusion splicing part to diffuse the dopant in the core to expand the MFD in the splicing splicing part. The generation of loss is solved.
[0012]
[Patent Document 1]
Japanese Patent No. 2804355
[Problems to be solved by the invention]
By the way, for example, when the above-mentioned dispersion management line is used for an optical submarine cable or the like, the fusion splicing portion is required to have a low loss and a high strength at the same time.
Conventionally, the following measures have been taken to increase the strength of the fusion spliced portion. In other words, prior to performing the fusion splicing, the influence of factors that deteriorate the strength of the optical fiber, such as contact with the fiber cutter, the V groove of the fusion splicer in which the optical fiber is disposed, and the fiber clamp that fixes the optical fiber is affected. In order to reduce or remove, the surface of the optical fiber is covered with a resin protective layer.
[0014]
However, when the above-mentioned resin protective layer is formed, not a little tackiness remains on the surface. For this reason, the optical fiber linearity may be lost during fusion splicing, meandering, or may not advance at the timing to advance each other, and as a result, the amount of deviation of the core is less than when a resin protective layer is not formed. It becomes very large, and the optical loss at the fusion splicing portion becomes large.
[0015]
In particular, when an optical fiber having a small MFD is to be fusion spliced with high strength, and the above-mentioned resin protective layer is formed on the optical fiber for fusion splicing, in order to reduce optical loss, It must be fusion spliced so as not to cause shaft misalignment, but in practice it is a very difficult task.
Thus, it can be said that forming a resin protective layer on the surface of the optical fiber to be connected is an effective means for increasing the strength of the fusion spliced portion, but on the other hand, when the resin protective layer is not formed. In contrast, the optical loss at the fusion spliced portion is further increased.
[0016]
Further, as the heat treatment performed after the fusion splicing, a heat treatment by discharge, hydrogen / oxygen burner flame or propane / oxygen burner flame is usually employed.
However, in the case of discharge heating, only very localized heating is realized for the fusion spliced portion, and the heating temperature is high, and after being processed in a relatively short time, it is rapidly cooled. . For this reason, the diffusion state of the dopant in the core tends to be unstable, and there is a problem that strain is accumulated in the glass of the fusion splicing portion.
[0017]
In addition, it is very difficult for discharge heating to realize optimization of the discharge conditions, and it is difficult to realize control to an appropriate heating temperature and optimization of a heating location. Therefore, when the discharge heating is repeated a plurality of times, there arises a problem that the outer diameter fluctuation (so-called constriction) occurs in the fusion spliced portion and the diameter is reduced, and at the same time the strength is lowered.
On the other hand, in the case of heating by a burner flame, it is easier to perform appropriate temperature control and it is easy to appropriately narrow down the heating location as compared to discharge heating. However, on the other hand, since the optical fiber is disposed sideways and the burner flame is blown to the softened fusion splice, it bends to the fusion splice due to the pressure of the flame and the weight of the optical fiber. Deformation may occur and optical loss may increase.
[0018]
For such a problem, a method has been proposed in which a heat treatment is applied to the fusion splice while applying axial tension to the fusion splice. However, depending on the magnitude of the applied tension, the softened fusion spliced portion may be stretched, and as in the case of repeated discharge heating, the fusion spliced portion may be constricted, and the strength of the fusion spliced portion may be reduced. And increase in the intensity variation.
[0019]
In the optical fiber in such a state, when the fusion splicing portion is bent, stress may concentrate on the optical fiber and cause a breakage accident.
The present invention reduces the optical loss by optimizing the applied tension when applying heat treatment to the fusion splice while applying tension to the fusion splice of the optical fiber. An optical fiber connection method that can be applied to connection of dissimilar optical fibers having different MFDs and to the same type of optical fiber connection having an extremely small MFD, which can realize high strength of connection parts and minimization of variation in strength. For the purpose of provision.
[0020]
[Means for Solving the Problems]
In order to achieve the above-described object, in the present invention, two optical fibers are fusion-bonded at the end faces of each other to form a fusion-bonding portion,
Arranging the fusion splicing part of the two optical fibers at the position to be heat-treated,
Gripping and fixing one of the two optical fibers with a tensiometer,
Tension of 0 to 78.4 mN is applied in the axial direction of the fusion splicing part (including cases where the applied tension is zero and 78.4 mN) , and the tension is smaller than the gripping force when gripping with the tensiometer. Is suspended from the other optical fiber by a weight that generates
Holding the pair of optical fibers closer to the fusion splicing part than the tensiometer and the weight in a loose state so as to be loosened by a fixing jig, and fixing,
There is provided an optical fiber connecting method characterized in that the heat-sealing connection portion is heated by a heating means and heat-sealed and connected so that the MFDs of the two optical fibers are matched.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, first, the end surfaces of two optical fibers to be connected are fusion-bonded to form a fusion-bonded portion. The fusion splicing may be performed using, for example, a discharge fusion splicer as in the conventional case. At this point, in the fusion splice, the MFDs of the two optical fibers do not match in most cases.
[0022]
Next, a heat treatment described later is performed on the fusion spliced portion, and the MFD matching operation of the two optical fibers is performed. The procedure will be described below with reference to FIG.
Procedure 1: First, the fusion splicing part 3 between the optical fiber 1 and the optical fiber 2 is disposed at the position of the heating means 4, and one optical fiber (the optical fiber 2 in FIG. 1) is held and fixed by the tensiometer 5.
[0023]
At this time, the gripping force with respect to the optical fiber 2 by the tension meter 5 is set to a value larger than an applied tension described later.
Procedure 2: Next, a predetermined magnitude of tension is applied in the axial direction of the fusion splicing portion 3. For example, as shown in FIG. 1, a pair of freely rotating rollers 6A and 6B are disposed on the optical fiber 1 side, and a weight 7 having a predetermined weight is suspended from the optical fiber 1 between the rollers.
[0024]
As the weight 7 at this time, a weight whose load is 78.4 mN or less is used. If a weight having a load greater than 78.4 mN is used, the fusion splicing part 3 is stretched and reduced in diameter during the heat treatment described later, and the light loss of the splicing splicing part increases rapidly.
In this way, a tension corresponding to the weight of the weight 7 is always applied in the axial direction of the fusion splicing portion 3. At this time, the gripping force of the tension meter 5 is larger than the tension by the weight 7, so that the optical fiber 2 does not come out of the tension meter 5.
[0025]
Procedure 3: Next, the optical fiber 1 and the optical fiber 2 are held and fixed by fixing jigs 8A and 8B such as clamps. The gripping state at this time is a loose state in which the optical fiber 1 and the optical fiber 2 can freely move the fixing jigs 8A and 8B.
Procedure 4: Finally, the heating means 4 is actuated to heat the fusion splice 3 and match the MFDs of the two optical fibers.
[0026]
The heating means 4 used at this time is preferably a burner flame. As described above, the control of the heating temperature is the capacity, and only the target portion can be selectively heated relatively accurately.
By this heat treatment, in the fusion splicing part 3, among the MFDs of the optical fiber 1 and the optical fiber 2, the small MFD expands in a trumpet shape and matches the large MFD. As a result, light loss can be reduced.
[0027]
In that case, if the heating temperature is constant, as the heating time elapses, the diffusion of the dopant advances and the diameter of the small MFD increases, and the optical loss at the fusion splice decreases accordingly. To go. The optical loss is minimized when the sizes of the two MFDs are completely matched.
In order to monitor this state, in the present invention, it is preferable to perform connection work under the following system.
[0028]
As shown in FIG. 2, the OTDR 10 is connected to the other end of the optical fiber 2 in FIG. 1 via, for example, a fusion-bonded dummy fiber 9. Further, the heating means (for example, the burner) 4 is connected to a heating means control section 11 that performs heating on / off, temperature control, time control, and the like.
Then, the OTDR 10 and the heating means control unit 11 are connected to a feedback control unit 12 including a signal comparison unit 12A and a memory unit 12B in which a target set value of optical loss is stored, respectively.
[0029]
In the system of FIG. 2, the inspection light from the OTDR 10 enters the dummy fiber 9 and the optical fiber 2, enters the optical fiber 1 from the optical fiber 2 via the fusion splicing unit 3, and the dummy fiber 9 and the optical fiber The return light of the fiber 2, the fusion splicing part 3, and the optical fiber 1 returns to the OTDR 9 in this order.
The OTDR 10 detects these return lights and converts them into electrical signals. Then, the light intensity of the fusion splicing unit 3, that is, the degree of optical loss is monitored every moment, and the monitor signal is input to the feedback control unit 12.
[0030]
In the feedback control unit 12, the signal comparison unit 12A compares the target set value of the optical loss stored in the memory unit 12B with the monitor signal from the OTDR 10.
If the optical loss in the fusion splicing unit 3 displayed by the monitor signal is larger than the target set value, an operation signal for continuing heating is transmitted to the heating means control unit 11 and is the same as the target set value? If it becomes lower than that, a heating end signal is sent to the heating means control section 11 to end the heating operation by the heating means 4.
[0031]
According to this system, it is possible to prevent the excess or deficiency of the heat treatment, reliably match the two MFDs, and control the processing time so that the optical loss at the fusion splicing unit 3 becomes the target set value. .
In consideration of the problem of the outer diameter fluctuation (thinning) and the strength reduction of the fusion splicing portion 3, it is preferable to set the applied tension in the procedure 2 within the range of 0 to 78.4 mN. This is because, when the applied tension is set within the above range, the occurrence of fluctuations in the outer diameter and a decrease in strength can be reliably suppressed in a state where the optical loss of the fusion spliced portion is reduced to, for example, 0.1 dB or less.
[0032]
【Example】
Example 1
The following connection work was performed in the mode shown in FIGS.
Outer diameter 125μm, MFD11.4μm, an optical fiber (single mode optical fiber) 1, the core dopant is GeO _2, an outer diameter of 125μm, MFD5.7μm, optical fiber (dispersion-compensating optical fiber) 2 is the core dopant GeO ₂ Prepared.
[0033]
These optical fibers are set in a discharge fusion splicer, and their end faces are fusion spliced under the conditions of an arc discharge voltage of 1 kV, a discharge current of 17.9 mA, a discharge time of 2.3 seconds, and an indentation amount of 11 μm. Part 3 was formed.
The optical loss of this fusion spliced portion was about 1.7 dB.
Then, the optical fiber 2 was held and fixed with a tension meter 5. The gripping force at this time was set to about 294 mN.
[0034]
Next, a weight 7 was suspended from the optical fiber 1 to apply tension to the fusion splicing portion 3. At this time, the applied tension was changed using various weights.
Subsequently, the burner 4 was operated and the fusion splicing part 3 was heated. And when the value of light loss became a target set value, the burner 4 was act | operated again and heating was stopped.
The optical loss at the fusion spliced portion 3 after heating was measured, and the result is shown in FIG. 3 as the relationship with the applied tension.
[0035]
As is apparent from FIG. 3, when the applied tension in the procedure 3 is larger than 78.4 mN, the optical loss increases rapidly.
Further, even when the tension is simply applied without applying the tension (when the applied tension is zero in FIG. 3), the optical loss is small, about 0.1 dB. This is because glass generally undergoes an elastic deformation of about 0.1% during the heat treatment, so that during the heat treatment, the optical fibers 1 and 2 are slightly contracted toward the respective fixing jigs, and are fusion-bonded. It is considered that the tension application state automatically appears in the section 3.
[0036]
Example 2
Single mode optical fiber 1 of MFD expansion type having an outer diameter of 125 μm, MFD of 12 μm, and a core dopant of GeO ₂ , an outer diameter of 125 μm, MFD of 4.9 μm, a core being highly doped silica of GeO ₂ , and a cladding being fluorine-doped silica A dispersion compensating optical fiber 2 comprising:
[0037]
The end face of each optical fiber was discharge fusion spliced under the same conditions as in Example 1 to form a fusion splice.
Next, after applying various applied tensions shown in Table 1 to the fusion spliced portion in the same procedure as in Example 1, the optical fibers 1 and 2 were fixed, and the fusion spliced portion was burner heated in each case. .
[0038]
In the system shown in FIG. 2, the optical loss of the fusion spliced portion was monitored with a laser beam having a wavelength of 1500 nm, and the heat treatment was stopped when the optical loss was minimized.
And the outer diameter of the fusion splicing part and the amount of bending deformation were measured using a laser outer diameter measuring instrument. The following results are collectively shown in Table 1.
[0039]
[Table 1]

[0040]
From Table 1, the following is clear.
Up to 78 mN of tension applied to the fusion spliced portion, the optical loss at the fusion spliced portion is small, the amount of fluctuation in the fiber outer diameter of the spliced splice is small, and no decrease in strength is observed.
[0041]
【The invention's effect】
As is clear from the above description, according to the method of the present invention, different types of optical fibers having different MFDs and the same type of optical fibers having very small MFDs can be connected with low loss. This is an effect obtained by applying a heat treatment while applying a tension of 78.4 mN or less in the axial direction of the fusion splice when heating the fusion splice to match the MFD of the optical fiber. .
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of a connection method of the present invention.
FIG. 2 is a schematic diagram showing an example of a system for monitoring a connection state in the connection method of the present invention.
3 is a graph showing the results of Example 1. FIG.
[Explanation of symbols]
1, 2 Optical fiber 3 to be connected 3 Fusion splicer 4 Heating means (burner)
5 Tension meter 6A, 6B Roller 7 Weight 8A, 8B Fixing jig (clamp)
9 Dummy fiber 10 OTDR
11 Heating means control unit 12 Feedback control unit 12A Signal comparison unit 12B Memory unit

Claims (4)

Two optical fibers are fusion spliced at the end faces of each other to form a fusion splicing part,
Arranging the fusion splicing part of the two optical fibers at a position to be heat-treated,
Gripping and fixing one of the two optical fibers with a tensiometer,
A tension of 0 to 78.4 mN is applied in the axial direction of the fusion splicing portion (including the case where the applied tension is zero and 78.4 mN) , and a tension smaller than the gripping force when gripping with the tensiometer. Is suspended from the other optical fiber by a weight that generates
Holding the pair of optical fibers closer to the fusion splicing part than the tensiometer and the weight in a loose state so as to be loosened by a fixing jig, and fixing,
A method for connecting optical fibers, characterized in that the heat-sealing connection portion is heated by a heating means, and the MFDs of the two optical fibers are matched to each other by heat-sealing. 2. The method for connecting optical fibers according to claim 1, wherein the heating means used in the heat treatment is burner means. The light is introduced from the end of one of the optical fibers while performing the heat treatment on the fusion spliced portion, and the change in light intensity when the introduced light passes through the fusion spliced portion is monitored. Or the connection method of 2 optical fibers. In either one of the two optical fibers, an OTDR is connected to the end of the one that is not fusion-bonded via a dummy fiber, and a heating means controller is connected to the heating means,
The OTDR and the heating means control unit are connected to a feedback control unit having a signal comparison unit and a memory unit in which a target optical loss setting value is stored,
The optical fiber connection method according to claim 1 or 2, wherein the OTDR detects return light from the heat fusion splicing section, and the processing time is controlled while sequentially monitoring light loss at the splicing splicing section.

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