JP2003177270A - Method for splicing optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber splicing method with low connection loss. <P>SOLUTION: Between optical fibers having different MFD diameters, there is inserted a mode field conversion bridge optical fiber having an intermediate MFD diameter relative to the MFD diameters of those optical fibers. As a result, the difference of the MFD diameters becomes small between those optical fibers as one part and the mode field conversion bridge optical fiber as the other part; hence, the connection loss is reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for connecting optical fibers.

[0002]

2. Description of the Related Art In recent years, the information capacity has increased with the rapid spread of the Internet and the like, and the demand for larger capacity of information transmission media has increased. The most promising technology that supports large capacity is wavelength division multiplexing (hereinafter “WD”).
M ”. ) Transmission method. Since the WDM system can transmit a plurality of signal lights with one optical fiber, it is possible to increase the transmission capacity by about 100 times.

For this reason, introduction into a long-distance, large-capacity transmission line such as an optical submarine cable system connecting continents is being advanced, and it is at the stage of practical application.

In WDM transmission, chromatic dispersion and non-linear effects on the transmission line are the main causes of limiting the transmission capacity and transmission distance. In order to suppress this non-linear effect, it is effective to increase the effective area (Aeff).

Therefore, a single mode optical fiber in which Aeff is expanded (hereinafter referred to as "Aeff expanded SMF").
A hybrid large-capacity WDM transmission line, which is a combination of optical fibers with compensation for dispersion and dispersion slope, has been receiving attention. Generally, the Aeff expanded SMF has a refractive index distribution as shown in FIG. 8, and the dispersion / dispersion slope compensating optical fiber has a refractive index distribution as shown in FIG. Aef
Fluorine is added to the cladding of both the f-enlarged SMF, dispersion, and dispersion slope compensation optical fibers.

FIG. 8 is a diagram showing the refractive index distribution of the Aeff enlarged SMF, in which the horizontal axis represents the radial position and the vertical axis represents the refractive index. FIG. 9 is a diagram showing the refractive index distribution of the dispersion and dispersion slope compensating optical fiber, where the horizontal axis represents the radial position and the vertical axis represents the refractive index.

Fluorine is added to the cladding of both the Aeff expanded SMF, dispersion and dispersion slope compensation optical fibers. In a transmission line using such an optical fiber,
It is necessary to connect the Aeff expansion SMF to an optical fiber that compensates for dispersion and dispersion slope, and these connections are performed by fusion splicing using a fusion splicer.

[0008]

However, since the MFD diameters of the two optical fibers are greatly different from each other, there arises a problem that the connection loss increases when the direct connection is performed by the above method. For example, when the Aeff expanded SMF is directly connected to the dispersion / dispersion slope compensating optical fiber, there is a problem that a connection loss of about 1.0 dB occurs.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an optical fiber connecting method with less connection loss.

[0010]

In order to achieve the above object, an optical fiber splicing method of the present invention is a method of fusion splicing optical fibers having different MFD diameters with respect to the MFD diameters of both optical fibers. A mode field conversion bridge optical fiber having an intermediate MFD diameter is inserted and fusion spliced.

In addition to the above structure, in the optical fiber connecting method of the present invention, it is preferable to use a mode field conversion bridge optical fiber to which fluorine is added from the core center to the cladding.

In addition to the above structure, the optical fiber connecting method of the present invention is a mode-field conversion bridge optical fiber, wherein the composition includes at least germanium oxide and fluorine from the center of the core to the cladding, and the relative refractive index difference of the center core is It is preferable to use one having a content of 0.6% or more and 0.8% or less.

In addition to the above configuration, the optical fiber connecting method of the present invention is such that one of the both optical fibers is an MFD.
It is preferable to use a fiber having a diameter of 5 μm or more and 7 μm or less and a fiber having an MFD diameter of 11 μm or more and 13 μm or less as the other optical fiber.

According to the present invention, by inserting a mode field conversion bridge optical fiber having an intermediate MFD diameter with respect to the MFD diameters of both optical fibers between the optical fibers having different MFD diameters, both optical fibers are inserted. Since the difference in MFD diameter between the optical fiber and the mode-field conversion bridge optical fiber becomes small, the connection loss decreases.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a diagram showing the relationship between the bridge optical fiber mode field diameter and the connection loss for explaining the optical fiber connection method of the present invention, in which the horizontal axis represents the bridge optical fiber mode field diameter, and the vertical axis represents the vertical axis. The axis shows splice loss.

The figure shows an optical fiber having an MFD diameter of 5 μm, an optical fiber having an MFD diameter of 13 μm, and an MFD diameter of 7 μm.
It is a result showing the relationship between the MFD diameter of the bridge optical fiber and the electric field distribution mismatch loss in the connection between the optical fiber of m and the optical fiber having the MFD diameter of 11 μm.

In the figure, A is a dispersion having a MFD diameter of 5 μm, a dispersion slope compensating optical fiber, and an MFD diameter of 13 μm.
3 is a calculation result showing the connection loss between the Aeff expanded SMF and the mode field conversion bridge optical fiber of FIG. Also, B
Is a calculation result showing the connection loss between the dispersion and dispersion slope compensating optical fiber having the MFD diameter of 7 μm, the Aeff expanded SMF having the MFD diameter of 11 μm, and the mode field conversion bridge optical fiber.

From the calculation result of A, it is preferable that the MFD diameter is 7 μm or more and 9 μm or less in order to reduce the electric field distribution mismatch loss in the connection of optical fibers having a large difference in MFD diameter. The range of the value of the MFD diameter is a value that can be sufficiently controlled in industrial production.
The present invention pays attention to this point, and the MFD diameter is 5 μm or more and 7 μm or more.
When connecting the following dispersion / dispersion slope compensating optical fiber and the Aeff expanded SMF having an MFD diameter of 11 μm or more and 13 μm or less, it is necessary to insert an optical fiber having an MFD diameter of 7 μm or more and 9 μm or less in the middle of the both optical fibers. It has a feature. As a result, the optical fiber can be connected with a small connection loss.

FIG. 2 is a diagram showing the relationship between the connection time and the connection loss in the connection between the dispersion-dispersion-compensated optical fiber and the mode-field conversion bridge optical fiber, where the horizontal axis indicates the connection time and the vertical axis. Indicates connection loss.

(A) and (b) Two types of bridge optical fibers were examined. (A) is one in which fluorine is added from the core center to the cladding, and (b) is one in which no fluorine is added.

FIG. 3 is a diagram showing the refractive index distribution of an optical fiber to which fluorine is added, where the horizontal axis indicates the radial position,
The vertical axis represents the refractive index.

In the figure, the value of the relative refractive index difference (Δn2) of the first cladding 2 is lower than the value of the relative refractive index difference (Δn1) of the center core 1, and the relative refractive index difference (Δn2) of the first cladding 2 is smaller. ) Value of the second cladding 3 relative to the relative refractive index difference (Δ
n3) is high and the relative refractive index difference (Δn
The value of the relative refractive index difference (Δn4) of the third cladding is lower than the value of 3), and the relative refractive index difference of the fourth cladding 5 is the relative refractive index difference (Δn1, Δn3) of the center core 1 and the second cladding 3.
Is lower than the value of relative refractive index (Δn2, Δn4) of the first cladding 2 and the third cladding 4, and the value of relative refractive index difference (Δn2) of the first cladding 2 is smaller than that of the third cladding 4. A quadruple clad structure type refraction that is higher than the relative refractive index difference (Δn4) and the relative refractive index difference (Δn3) of the second cladding 3 is lower than the relative refractive index difference (Δn1) of the center core. It has a rate distribution.

Fluorine is added to the first clad 2 and the third clad 4.

FIG. 4 is a diagram showing the refractive index distribution of an optical fiber to which fluorine is not added, where the horizontal axis shows the radial position and the vertical axis shows the refractive index.

In the figure, the value of the relative refractive index difference (Δn6) of the first cladding 7 is lower than the value of the relative refractive index difference (Δn5) of the center core 6, and the relative refractive index (Δ
n7) is lower than the relative refractive index difference (Δn5) of the center core 6, and the relative refractive index difference (Δn6) of the first cladding 7 is
Triple clad structure in which the relative refractive index difference of the third cladding 9 is lower than that of the center core 6, the first cladding 7 and the second cladding 8 (Δn5, Δn6, Δn7). It has a refractive index profile of the mold.

Here, it can be seen from FIG. 2 that the bridge optical fiber (α) containing fluorine has a lower connection loss than the bridge optical fiber (β) containing no fluorine. In the dispersion and dispersion slope compensating optical fiber, since fluorine is added at a high concentration, the germanium in the core is easily diffused during fusion of the optical fiber.

Therefore, by adding a lower concentration of fluorine to the bridge optical fiber than in the dispersion / dispersion slope compensating optical fiber, the softening temperature of the glass is lowered and the heating amount required for fusion is reduced. As a result, by selecting the fusion-bonding conditions for diffusing the germanium of the dispersion / dispersion slope compensating optical fiber while suppressing the diffusion of germanium of the bridge optical fiber, the difference between the MFD diameters of the two optical fibers can be reduced and the connection loss can be reduced. Can be lowered. Focusing on this point, the present invention is characterized in that an optical fiber doped with an appropriate amount of fluorine is connected as a bridge optical fiber from the core center to the cladding.

FIG. 5 is a diagram showing the relationship between the relative refractive index difference of the optical fiber and the connection loss in the connection between the Aeff magnifying optical fiber and the fluorine-doped mode field conversion bridge optical fiber. The refractive index difference is shown, and the vertical axis shows the connection loss.

The experimental value is the minimum connection loss value when the optical fibers having different relative refractive index differences and the Aeff magnifying optical fiber are connected. In order to reduce the connection loss to 0.2 dB or less, it is preferable to set the relative refractive index difference of the mode field conversion bridge optical fiber to 0.5% or more and 0.88% or less.

FIG. 6 is a diagram showing the relationship between the relative refractive index difference of the optical fiber and the connection loss in the connection between the dispersion and dispersion slope compensating optical fiber and the fluorine-doped mode field conversion bridge optical fiber. The horizontal axis indicates the relative refractive index difference, and the vertical axis indicates the connection loss.

In order to reduce the splice loss to 0.2 dB or less, it is preferable to set the relative refractive index difference of the mode field conversion bridge optical fiber to 0.6% or more and 0.8% or less.

Here, the connection loss between the mode-field conversion bridge optical fiber and the Aeff expansion SMF, dispersion, dispersion slope compensation optical fiber is set to 0.2 dB or less, respectively, because the Aeff expansion SMF, dispersion, dispersion slope compensation optical fiber. There is only one connection every 40 to 50 km, and the total connection loss is 0.4 dB (Aeff expansion S
MF and dispersion, the sum of the connection loss of the dispersion slope compensation optical fiber and the mode field conversion bridge optical fiber) or less, the increase in loss on the WDM transmission line is 0.0.
This is because there is no problem because it becomes 1 dB / km or less.

The present invention pays attention to this point, and the MFD diameter is 7.
A mode field conversion bridge optical fiber having a diameter of 0 μm or more and 9.0 μm or less, fluorine added from the core center to the cladding, and a relative refractive index difference of the center core of the optical fiber of 0.6% or more and 0.8% or less is connected. It is characterized by doing. As a result, the optical fiber can be connected with a small connection loss.

[0035]

Example 1 Example 1 At both ends of a bridge optical fiber,
Aeff expanded SMF and MF with MFD diameter of 11.9 μm
A dispersion / dispersion slope compensating optical fiber having a D diameter of 6.5 μm was connected.

The relative refractive index difference (Δ
n1) is 0.71%, and the relative refractive index difference (Δ
n2) is −0.03%, and the relative refractive index (Δ
n3) is 0.14%, and the relative refractive index difference (Δ
n4) is -0.07%. The amount of fluorine added is dispersed,
Less than the dispersion slope compensation optical fiber. Also, M
The FD diameter is 8.5 μm.

The relative refractive index difference (Δn5) of the center core 1 shown in FIG. 4 is 0.71%, the relative refractive index difference (Δn6) of the first cladding 7 is 0.05%, and the relative refractive index of the second cladding 8 is The difference (Δn7) is 0.15%. The MFD diameter is 8.
It is 35 μm.

The characteristics shown in FIG. 2 are obtained by using an optical fiber connected by a general fusion splicer. As the connection condition, the discharge power of the optical fiber containing fluorine 240
mA, Fluorine-free optical fiber discharge power 350 mA, Optical fiber push-in amount 10 μ during fusion
m, fusing pre-discharge time 0.5 s, end face spacing 10 μm are the same. Under the above connection conditions, the minimum connection loss was 0.15 dB when fluorine was added and 0.55 dB when fluorine was not added.

(Embodiment 2) FIG. 7 is a diagram showing the refractive index distribution of the optical fiber at the point a shown in FIG. 5, where the horizontal axis represents the radial position and the vertical axis represents the refractive index.

The relative refractive index difference (Δn8) of the first cladding 11 is larger than the relative refractive index difference (Δn8) of the center core 10 shown in FIG.
9) is low, the value of the relative refractive index difference of the second cladding 12 is lower than the value of the relative refractive index difference (Δn8) of the center core 10, and the value of the relative refractive index difference (Δn9) of the first cladding 11 is small. It exhibits a higher W-shaped refractive index distribution, the relative refractive index difference (Δn8) of the center core at point a is 0.35%, and the relative refractive index difference (Δn9) of the first cladding 11 is −0.03. %.
The MFD diameter is 9.2 μm. The conditions for fusion splicing with the Aeff expanded SMF are: discharge power 300 mA, discharge time 5
s, the amount of pushing of the optical fiber at the time of fusion, 10 μm, the pre-discharge time for fusion, 0.5 s, the end face spacing was 10 μm, and the minimum connection loss was 0.29 dB.

(Example 3) The relative refractive index distribution of the optical fiber at the point b is the same as the refractive index distribution at the point a,
The refractive index difference (Δn8) of the center core 10 is 0.71%,
The relative refractive index difference (Δn9) of the first cladding 11 is −0.07.
%. The MFD diameter is 8.5 μm. The fusion splicing condition with the Aeff expansion SMF is as follows: discharge power 300 mA, discharge time 10 s, optical fiber pushing amount 10 μm during fusion,
Fusing pre-discharge time is 0.5 s, end face spacing is 10 μm,
The minimum connection loss was 0.16 dB.

The refractive index distribution of the optical fiber at point c is a
Has the same refractive index distribution as the center core 1
The relative refractive index difference (Δn8) of 0 is 1.2%, and the first cladding 1
The relative refractive index difference (Δn9) of 1 is −0.03%. MF
The D diameter is 7 μm. The fusion splicing condition with the Aeff expanded optical fiber is as follows: discharge power 200 mA, discharge time 15 s,
The pushing amount of the optical fiber at the time of fusing was 10 μm, the fusing pre-discharge time was 0.5 s, the end face spacing was 10 μm, and the minimum connection loss was 0.52 dB.

(Embodiment 4) In FIG. 6, points d, e,
The refractive index distribution of the optical fiber at point f is shown in FIG.
It has the same refractive index distribution as the points a, b, and c in FIG.
Dispersion at point d, fusion splicing with dispersion slope compensating optical fiber: discharge power 330 mA, discharge time 0.75
s, the amount of pushing of the optical fiber at the time of fusion, 10 μm, the pre-discharge time for fusion, 0.5 s, the end face spacing was 10 μm, and the minimum connection loss was 0.95 dB.

(Embodiment 5) At point e, the dispersion and dispersion slope compensation optical fiber are fused and spliced under the following conditions: discharge power 240 mA, discharge time 2 s, optical fiber pushing amount 10 μm during fusion, fusion pre-discharge time. 0.5 s, end face spacing 1
It was 0 μm, and the minimum connection loss was 0.15 dB.

At the point f, the conditions for fusion splicing with the dispersion and dispersion slope compensating optical fiber are as follows: discharge power 300 mA, discharge time 5 s, optical fiber pushing amount 10 μm during fusion,
Fusing pre-discharge time is 0.5 s, end face spacing is 10 μm,
The minimum connection loss was 2.2 dB.

As described above, the bridge optical fiber having the MFD diameter of 8.5 μm was used and the Ae having the MFD diameter of 11.9 μm was used.
It was possible to connect the ff expanded SMF and the dispersion / dispersion slope compensating optical fiber with the MFD diameter of 6.5 μm with a low loss of 0.31 dB.

[0047]

In summary, according to the present invention, it is possible to provide a method of connecting optical fibers with a small connection loss.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a bridge optical fiber mode field diameter and a connection loss for explaining an optical fiber connection method of the present invention.

FIG. 2 is a diagram showing a relationship between a connection time and a connection loss in a connection between an optical fiber whose dispersion and dispersion slope are compensated and a mode field conversion bridge optical fiber.

FIG. 3 is a diagram showing a refractive index distribution of an optical fiber doped with fluorine.

FIG. 4 is a diagram showing a refractive index distribution of an optical fiber to which fluorine is not added.

FIG. 5 is a diagram showing a relationship between a relative refractive index difference of an optical fiber and a connection loss in connecting an Aeff magnifying optical fiber and a fluorine-doped mode field conversion bridge optical fiber.

FIG. 6 is a diagram showing the relationship between the relative refractive index difference of an optical fiber and the difference in connection loss thereof in the connection between a dispersion / dispersion slope compensation optical fiber and a fluorine-doped mode field conversion bridge optical fiber.

7 is a diagram showing a refractive index distribution of the optical fiber at point a shown in FIG.

FIG. 8 is a diagram showing a refractive index distribution of an Aeff enlarged SMF.

FIG. 9 is a diagram showing a refractive index distribution of a dispersion and dispersion slope compensation optical fiber.

[Explanation of symbols]

1, 6, 10 center core 2, 7, 11 1st clad 3, 8, 12 2nd clad 4, 9 Third clad 5 4th clad

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tomoyuki Nishio             1-6-1, Otemachi, Chiyoda-ku, Tokyo             Standing Wire Co., Ltd. (72) Inventor Takahiro Yamazaki             1-6-1, Otemachi, Chiyoda-ku, Tokyo             Standing Wire Co., Ltd. F term (reference) 2H036 MA11                 2H050 AB05Z AB10Z AC14 AC38                       AD01 AD16

Claims (4)

[Claims] 1. A method for fusion splicing optical fibers having different MFD diameters, wherein a mode field conversion bridge optical fiber having an intermediate MFD diameter with respect to the MFD diameters of both optical fibers is inserted and fusion spliced. An optical fiber connection method characterized by the above. 2. The method for connecting optical fibers according to claim 1, wherein the mode-field conversion bridge optical fiber is one in which fluorine is added from the core center to the cladding. 3. The mode-field conversion bridge optical fiber according to claim 1, wherein the composition includes at least germanium oxide and fluorine from the core center to the cladding, and the center core has a relative refractive index difference of 0.6% or more and 0.8% or less. The optical fiber connecting method according to claim 1, wherein a certain one is used. 4. The optical fiber having an MFD diameter of 5 μm or more and 7 μm or less is used as one of the optical fibers, and the optical fiber having an MFD diameter of 11 μm or more and 13 μm or less is used as the other optical fiber. Optical fiber connection method described in.