JP3726745B2 - Optical fiber connection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical fiber connection method.
[0002]
[Prior art]
In recent years, with the rapid spread of the Internet and the like, the information capacity has increased, and the demand for an increase in capacity for information transmission media has increased. The most promising technology for increasing capacity is the wavelength division multiplexing (hereinafter referred to as “WDM”) transmission method. Since the WDM system can transmit a plurality of signal lights with one optical fiber, the transmission capacity can be increased about 100 times.
[0003]
For this reason, it has been introduced into a long-distance large-capacity transmission line such as an optical submarine cable system connecting continents.
[0004]
In WDM transmission, chromatic dispersion and nonlinear effects in the transmission path are the main causes of limiting transmission capacity and transmission distance. In order to suppress this nonlinear effect, it is effective to increase the effective area (Aeff).
[0005]
Accordingly, a hybrid large-capacity WDM transmission line that combines a single-mode optical fiber with an expanded Aeff (hereinafter referred to as “Aeff expanded SMF”) and an optical fiber with compensated dispersion and dispersion slope is drawing attention. In general, 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. Both Aeff expanded SMF, dispersion, and dispersion slope compensating optical fibers have fluorine added to the cladding.
[0006]
FIG. 8 is a diagram showing the refractive index distribution of the Aeff-enlarged SMF, where the horizontal axis indicates the radial position and the vertical axis indicates the refractive index. FIG. 9 is a diagram showing the refractive index distribution of the dispersion / dispersion slope compensating optical fiber, where the horizontal axis indicates the radial position and the vertical axis indicates the refractive index.
[0007]
Both the Aeff expanded SMF, dispersion, and dispersion slope compensating optical fibers have fluorine added to the cladding. In such a transmission line using an optical fiber, it is necessary to connect the Aeff-enlarged SMF and the optical fiber compensated for dispersion and dispersion slope, and these connections are made by fusion splicing using a fusion machine.
[0008]
[Problems to be solved by the invention]
However, since the MFD diameters of the two optical fibers are greatly different, there is a problem that the connection loss increases when the direct connection is made by the above method. For example, there is a problem that a connection loss of about 1.0 dB occurs when an Aeff expanded SMF and a dispersion / dispersion slope compensating optical fiber are directly connected.
[0009]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and provide an optical fiber connection method with low connection loss.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the optical fiber connecting method of the present invention includes a fusion and dispersion slope compensating fiber having an MFD diameter of 5 μm to 7 μm and an Aeff expanded SMF fiber having an MFD diameter of 11 μm to 13 μm. The method comprises a center core, a first clad and a second clad, and (refractive index difference of center core)> (relative refractive index difference of second cladding)> (refractive index difference of first cladding). A mode field having a refractive index distribution, an MFD diameter of 7 μm or more and 9 μm or less, fluorine added from the core center to the cladding, and a relative refractive index difference of the center core of 0.6% or more and 0.8% or less. A conversion bridge optical fiber is inserted between the dispersion / dispersion slope compensating fiber and the Aeff expansion SMF fiber to be fusion-spliced.
[0014]
According to the present invention, a mode field conversion bridge optical fiber having an intermediate MFD diameter with respect to the MFD diameters of both optical fibers is inserted between optical fibers having different MFD diameters. Since the difference in the MFD diameter with the conversion bridge optical fiber is reduced, the connection loss is reduced.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0016]
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 according to the present invention. The horizontal axis shows a bridge optical fiber mode field diameter, and the vertical axis shows a connection. Indicates loss.
[0017]
This figure shows the MFD diameter and electric field distribution of a bridge optical fiber when connecting an optical fiber with an MFD diameter of 5 μm, an optical fiber with an MFD diameter of 13 μm, and an optical fiber with an MFD diameter of 7 μm and an optical fiber with an MFD diameter of 11 μm. It is the result which showed the relationship with a mismatch loss.
[0018]
In the figure, A is a calculation result showing a connection loss between a dispersion / dispersion slope compensating optical fiber having an MFD diameter of 5 μm, an Aeff expanded SMF having an MFD diameter of 13 μm, and a mode field conversion bridge optical fiber. B is a calculation result showing a connection loss between a dispersion / dispersion slope compensating optical fiber having an MFD diameter of 7 μm, an Aeff expanded SMF having an MFD diameter of 11 μm, and a mode field conversion bridge optical fiber.
[0019]
From the calculation result of A, it is preferable to set the MFD diameter to 7 μm or more and 9 μm or less in order to reduce the electric field distribution mismatch loss in the connection between optical fibers having a large difference in MFD diameter. The range of the value of the MFD diameter is a sufficiently controllable value for industrial production. The present invention pays attention to this point, and in the connection between a dispersion / dispersion slope compensating optical fiber having an MFD diameter of 5 μm or more and 7 μm or less and an Aeff expanded SMF having an MFD diameter of 11 μm or more and 13 μm or less, the MFD diameter is intermediate between both optical fibers. It is characterized by inserting and connecting an optical fiber of 7 μm or more and 9 μm or less. As a result, the optical fiber can be connected with a small connection loss.
[0020]
FIG. 2 is a diagram showing the relationship between connection time and connection loss in connection between an optical fiber compensated for dispersion and dispersion slope and a mode field conversion bridge optical fiber. The horizontal axis shows the connection time, and the vertical axis shows the connection loss. Indicates.
[0021]
(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 fluorine is not added.
[0022]
FIG. 3 is a diagram showing a refractive index distribution of an optical fiber to which fluorine is added. The horizontal axis indicates the radial position, and the vertical axis indicates the refractive index.
[0023]
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 value of the relative refractive index difference (Δn2) of the first cladding 2 is shown. The relative refractive index difference (Δn3) of the second cladding 3 is higher than that of the second cladding 3, and the relative refractive index difference (Δn4) of the third cladding 3 is lower than the relative refractive index difference (Δn3) of the second cladding 3. The relative refractive index difference of the fourth cladding 5 is lower than the relative refractive index difference (Δn1, Δn3) of the center core 1 and the second cladding 3, and the relative refractive index of the first cladding 2 and the third cladding 4 (Δn2). , Δn4), the relative refractive index difference (Δn2) of the first cladding 2 is higher than the relative refractive index difference (Δn4) of the third cladding 4, and the relative refractive index of the second cladding 3 is higher. Quadruple clad structure type in which the value of the difference (Δn3) is lower than the value of the relative refractive index difference (Δn1) of the center core The refractive index distribution is exhibited.
[0024]
Fluorine is added to the first cladding 2 and the third cladding 4.
[0025]
FIG. 4 is a diagram showing the refractive index distribution of an optical fiber to which fluorine is not added, the horizontal axis shows the position in the radial direction, and the vertical axis shows the refractive index.
[0026]
In the figure, the relative refractive index difference (Δn6) of the first cladding 7 is lower than the relative refractive index difference (Δn5) of the center core 6, and the relative refractive index (Δn7) of the second cladding 8 is It is lower than the value of the relative refractive index difference (Δn5) of the center core 6 and higher than the value of the relative refractive index difference (Δn6) of the first cladding 7, and the relative refractive index difference of the third cladding 9 is the center core 6, The refractive index distribution of the triple clad structure type is lower than the value of the relative refractive index difference (Δn5, Δn6, Δn7) between the first cladding 7 and the second cladding 8.
[0027]
Here, it can be seen from FIG. 2 that the bridge optical fiber (α) to which fluorine is added has a lower connection loss than the bridge optical fiber (β) to which fluorine is not added. In the dispersion and dispersion slope compensating optical fiber, since fluorine is added at a high concentration, the germanium of the core is easily diffused when the optical fiber is fused.
[0028]
Therefore, by adding lower concentration of fluorine to the bridge optical fiber than that of the dispersion / dispersion slope compensating optical fiber, the softening temperature of the glass is lowered, and the heating amount necessary for fusion is reduced. As a result, by suppressing the diffusion of germanium in the bridge optical fiber and selecting the fusion conditions for diffusing germanium in the dispersion and dispersion slope compensation optical fiber, the difference in MFD diameter between the two optical fibers is reduced, and the connection loss is reduced. Can be reduced. The present invention pays attention to this point, and is characterized in that an optical fiber to which an appropriate amount of fluorine is added from the core center to the cladding is connected as a bridge optical fiber.
[0029]
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 expanding optical fiber and the mode-field conversion bridge optical fiber doped with fluorine, and the horizontal axis represents the relative refractive index difference. The vertical axis represents the connection loss.
[0030]
The experimental value is a minimum connection loss value when an optical fiber having a different relative refractive index difference and an Aeff expansion optical fiber are connected. In order to reduce the connection loss to 0.2 dB or less, the relative refractive index difference of the mode field conversion bridge optical fiber is preferably set to 0.5% or more and 0.88% or less.
[0031]
FIG. 6 is a diagram showing the relationship between the relative refractive index difference and the connection loss of the optical fiber in the connection between the dispersion / dispersion slope compensating optical fiber and the mode-field conversion bridge optical fiber doped with fluorine. Indicates the relative refractive index difference, and the vertical axis indicates the connection loss.
[0032]
In order to reduce the connection loss to 0.2 dB or less, the relative refractive index difference of the mode field conversion bridge optical fiber is preferably set to 0.6% or more and 0.8% or less.
[0033]
Here, the connection loss between the mode field conversion bridge optical fiber and the Aeff-enhanced SMF, dispersion, and dispersion slope compensation optical fiber is 0.2 dB or less, respectively. When the total connection loss is less than 0.4 dB (the sum of the connection loss between the Aeff-enhanced SMF and dispersion / dispersion slope compensation optical fiber and the mode field conversion bridge optical fiber) in one place at 40 to 50 km, WDM transmission This is because the increase in loss on the road is 0.01 dB / km or less, and there is no problem.
[0034]
The present invention pays attention to this point, the MFD diameter is 7.0 μm or more and 9.0 μm or less, fluorine is added from the core center to the cladding, and the relative refractive index difference of the center core of the optical fiber is 0.6% or more and 0 It is characterized by connecting a mode-field conversion bridge optical fiber which is .8% or less. As a result, the optical fiber can be connected with a small connection loss.
[0035]
【Example】
(Example 1)
An Aeff expanded SMF with an MFD diameter of 11.9 μm and a dispersion / dispersion slope compensating optical fiber with an MFD diameter of 6.5 μm were connected to both ends of the bridge optical fiber.
[0036]
The relative refractive index difference (Δn1) of the center core shown in FIG. 3 is 0.71%, the relative refractive index difference (Δn2) of the first cladding 2 is −0.03%, and the relative refractive index (Δn3) of the second cladding 3 is. Is 0.14%, and the relative refractive index difference (Δn4) of the third cladding 4 is −0.07%. The amount of fluorine added is small compared to the dispersion and dispersion slope compensating optical fiber. The MFD diameter is 8.5 μm.
[0037]
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 difference (Δn7) of the second cladding 8 is. ) Is 0.15%. The MFD diameter is 8.35 μm.
[0038]
The characteristics shown in FIG. 2 are obtained by using an optical fiber connected by a general fusion machine. As the connection conditions, the discharge power of the optical fiber added with fluorine is 240 mA, the discharge power of the optical fiber not added with fluorine is 350 mA, the optical fiber pushing amount at the time of fusion is 10 μm, the fusion predischarge time is 0.5 s, and the end face interval. 10 μm is 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.
[0039]
(Example 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 shows the position in the radial direction and the vertical axis shows the refractive index.
[0040]
The relative refractive index difference (Δn9) of the first cladding 11 is lower than the relative refractive index difference (Δn8) of the center core 10 shown in FIG. It exhibits a W-type refractive index distribution that is lower than the value of the relative refractive index difference (Δn8) and higher than the value of the relative refractive index difference (Δn9) of the first cladding 11, and the relative refractive index of the center core at point a The difference (Δn8) 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 fusion splicing conditions with the Aeff expansion SMF are: discharge power 300 mA, discharge time 5 s, optical fiber indentation amount 10 μm at the time of fusion, fusion pre-discharge time 0.5 s, end face spacing 10 μm, and minimum connection loss 0 .29 dB.
[0041]
(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%, and the relative refractive index difference (Δn9) of the first cladding 11 is. ) Is -0.07%. The MFD diameter is 8.5 μm. The fusion splicing conditions with the Aeff expansion SMF are: discharge power of 300 mA, discharge time of 10 s, optical fiber indentation amount of 10 μm at the time of fusion, fusion pre-discharge time of 0.5 s, end face spacing of 10 μm, and minimum connection loss of 0.16 dB. Met.
[0042]
The refractive index distribution of the optical fiber at the point c is the same as the refractive index distribution at the point a, the relative refractive index difference (Δn8) of the center core 10 is 1.2%, and the relative refractive index difference of the first cladding 11 (Δn9). ) Is -0.03%. The MFD diameter is 7 μm. The fusion splicing conditions with the Aeff expansion optical fiber are: discharge power 200 mA, discharge time 15 s, optical fiber indentation amount 10 μm at the time of fusion, fusion pre-discharge time 0.5 s, end face interval 10 μm, and minimum connection loss 0 It was 0.52 dB.
[0043]
(Example 4)
In FIG. 6, the refractive index distributions of the optical fibers at points d, e, and f are the same refractive index distributions as points a, b, and c in FIG. 5, respectively. The fusion splicing conditions with the dispersion and dispersion slope compensating optical fiber at point d are: discharge power 330 mA, discharge time 0.75 s, optical fiber indentation amount 10 μm during fusion, fusion pre-discharge time 0.5 s, and end face spacing 10 μm. The minimum connection loss was 0.95 dB.
[0044]
(Example 5)
At point e, the fusion and splicing conditions with the dispersion and dispersion slope compensating optical fiber are: discharge power 240 mA, discharge time 2 s, optical fiber indentation amount 10 μm during fusion, fusion pre-discharge time 0.5 s, and end face spacing 10 μm. The minimum connection loss was 0.15 dB.
[0045]
The fusion splicing conditions with the dispersion and dispersion slope compensating optical fiber at point f are: discharge power 300 mA, discharge time 5 s, optical fiber indentation amount 10 μm at the time of fusion, fusion pre-discharge time 0.5 s, and end face spacing 10 μm. The minimum connection loss was 2.2 dB.
[0046]
As described above, using a bridge optical fiber having an MFD diameter of 8.5 μm, the connection between the Aeff expanded SMF having an MFD diameter of 11.9 μm and the dispersion and dispersion slope compensating optical fiber having an MFD diameter of 6.5 μm is as low as 0.31 dB. Could connect to loss.
[0047]
【The invention's effect】
In short, according to the present invention, it is possible to provide an optical fiber connection method with less connection loss.
[Brief description of the 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 connection time and connection loss in connection between an optical fiber compensated for dispersion and dispersion slope and a mode field conversion bridge optical fiber.
FIG. 3 is a diagram showing a refractive index distribution of an optical fiber to which fluorine is added.
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 the connection between an Aeff expanding optical fiber and a mode-field conversion bridge optical fiber doped with fluorine.
FIG. 6 is a diagram showing a relationship between a difference in relative refractive index and a connection loss of an optical fiber in connection between a dispersion / dispersion slope compensating optical fiber and a mode field conversion bridge optical fiber doped with fluorine.
7 is a diagram showing a refractive index distribution of an optical fiber at a point a shown in FIG.
FIG. 8 is a diagram showing a refractive index distribution of Aeff expanded SMF.
FIG. 9 is a diagram showing a refractive index distribution of a dispersion / dispersion slope compensating optical fiber.
[Explanation of symbols]
1, 6, 10 Center cores 2, 7, 11 First cladding 3, 8, 12 Second cladding 4, 9 Third cladding 5 Fourth cladding

Claims (1)

In a method in which a dispersion, dispersion slope compensating fiber having an MFD diameter of 5 μm or more and 7 μm or less and an Aeff expanded SMF fiber having an MFD diameter of 11 μm or more and 13 μm or less are fusion-bonded, the center core includes a first cladding and a second cladding. (The relative refractive index difference of the center core)> (the relative refractive index difference of the second cladding)> (the relative refractive index difference of the first cladding), and the MFD diameter is 7 μm or more and 9 μm or less. A mode field conversion bridge optical fiber in which fluorine is added from the center to the cladding and the relative refractive index difference of the center core is 0.6% or more and 0.8% or less is used as the dispersion, dispersion slope compensation fiber, and the Aeff expanded SMF. A method for connecting optical fibers, characterized by being inserted and fused-bonded between fibers.

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