JP2003066246A - Method for sealing airtight sealing part of optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a method for sealing an airtight sealing part optical fiber in which light loss is reduced by removing internal stress at an airtight sealing part for deriving an optical fiber from pressure tight case. SOLUTION: A plurality of optical fibers 11 are inserted to a sleeve 13, a guide 12 is fixed to the sleeve 13, the circumference of the optical fiber 11 is sealed by airtight through the use of low-melting metal 14 and the airtight sealing part 17 is thermally treated. A thermal treatment is performed after an airtight test is performed for the airtight sealing part. The thermal treatment is performed in a thermostatic bath, etc., at 50-60 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sealing an optical fiber hermetically sealing portion when an optical fiber is introduced into a pressure-resistant housing and connected to a repeater circuit in an optical submarine repeater of an optical communication system. It is about.

[0002]

2. Description of the Related Art An optical submarine repeater is a repeater of an optical submarine cable used on the seabed in an optical communication system.
FIG. 5 is a partial sectional view showing the optical submarine repeater. In the figure, 1 is a pressure-resistant housing, 2 is a cylinder, 3 is a heat dissipation buffer, 4
Is a repeater circuit, 5 is an end plate, 6 is a field through, and 7 is a tail cable. A repeater circuit 4, which is a main component of this repeater, is surrounded by a pressure-resistant housing 1 composed of a heat radiation buffer 3, a cylinder 2 and an end face plate 5. The optical fiber in the optical submarine cable is introduced into the optical submarine repeater, passes through the tail cable 7 and the field through 6 attached to the end face plate 5, and is connected to the repeater circuit 4.

A plurality of optical fibers to be introduced into the pressure-resistant housing 1 are sealed with a low melting point metal in a fiber guide 16 mounted in the field through 6. FIG. 6 is a sectional view showing the fiber guide 16. In the figure, 11 is an optical fiber, 12 is a guide, 13 is a sleeve, 14 is a low melting point metal such as solder, 15 is a nut, and 17 is a hermetically sealed portion of the end of the sleeve 13. As shown in the figure, the optical fiber 11 is guided by the sleeve 13 along the groove around the guide 12.
Guided inside, the guide 12 fits inside the sleeve 13 into the nut 15
Is fixed by. The end portion of the sleeve 13 hermetically seals the periphery of the optical fiber 11 with the solder 14 to form a hermetically sealed portion 17. The hermetically sealed portion 17 has a function of preventing seawater from entering the relay circuit 4 in the pressure-resistant housing 1 when the cable is cut.

FIG. 7 is a process chart showing a conventional method for sealing an optical fiber hermetically sealed portion in the order of steps. First, the guide 12 having the plurality of optical fibers 11 arranged in the surrounding groove is inserted into the sleeve 13 (step S1). Then, for example, the guide 12 is fixed to the sleeve 13 with the nut 15 (step S2). After that, the protective coating of the optical fiber 11 is removed, and the metal coating on the core portion is hermetically sealed between the guide 12 and the sleeve 13 with a low melting point metal such as solder 14 (step S3).

As a conventional method for sealing the periphery of an optical fiber, Japanese Patent Application Laid-Open No. 10-186158 discloses a resin sealing method for a branch portion of an optical fiber tape cord. In this sealing method, when sealing the branch portion of the optical fiber with a resin, a heat treatment is applied to the vicinity of the branch portion of the optical fiber before the resin sealing. By this heat treatment, the internal stress is removed, and then the optical fiber is sealed with resin.

[0006]

As described above, in the method of sealing the optical fiber hermetically sealed portion shown in FIG. 7, internal stress is generated when the solder is solidified during the sealing, and this internal stress causes the optical stress. A microbend or the like occurs in the fiber to increase the optical loss. FIG. 8 is an explanatory diagram showing the cause of the internal stress generated in the hermetically sealed portion 17. 8A to 8C respectively show the periphery of the portion 17 where the optical fiber 11 is hermetically sealed with the solder 14 at the end of the sleeve 13. In the figure, the white arrow indicates the solidification direction, the black arrow indicates the heat shrinkage direction, and the solid arrow P indicates the pressure. As shown in FIG. 8A, the solder 1
When No. 4 does not solidify uniformly but solidifies from the outside to the inside, the solder 14a on the outside indicated by the diagonal lines is solid, and the solder 14b on the inside white portion is still liquid. Therefore, when the liquid solder 14b is solidified, a contracting force is generated in the arrow direction with respect to the optical fiber 11. Further, as shown in FIG. 8B, when the solder 14 is cooled to room temperature after the solidification is completed, the solder 14, the guide 12, and the sleeve 13 are thermally contracted in the arrow direction, so that internal stress is generated. Further, when an airtight test or the like is performed after the airtight sealing, pressure is applied in the arrow P direction as shown in FIG. 8C. In this way, internal stress is generated by the solidification and thermal contraction of the solder 14, the thermal contraction of the guide 12 and the sleeve 13, and the pressure load. In addition, JP-A-10
The sealing method disclosed in Japanese Patent Laid-Open No. 186158 discloses a method in which internal stress is removed by heat treatment and then resin sealing is performed, and the internal stress generated by the resin sealing remains as it is.

As described above, in any of the conventional sealing methods, there is a problem that internal stress is generated and microbends are generated in the optical fiber to increase the optical loss.

The present invention has been made in order to solve the above-mentioned problems, and eliminates the internal stress in the hermetically sealed portion for introducing the optical fiber into the pressure-resistant housing, thereby reducing the optical loss. It is an object of the present invention to obtain a method for sealing a fiber hermetically sealed portion.

[0009]

A method of sealing an optical fiber hermetically sealing portion according to the present invention seals a plurality of optical fibers to be introduced into a pressure resistant casing with a low melting point metal in a fiber guide in a feedthrough. In the method described above, after hermetically sealing the periphery of the optical fiber with the low melting point metal, heat treatment is applied to the hermetically sealed portion.

Further, the periphery of the optical fiber is hermetically sealed with the low melting point metal, an airtightness test of the hermetically sealed portion is performed, and then a heat treatment is applied to the hermetically sealed portion. is there.

The heat treatment is characterized by heating at a temperature of 50 ° C. to 60 ° C.

Further, the heat treatment is characterized by heating in a constant temperature bath.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiment 1. 1 is a cross-sectional view showing a fiber guide that has been subjected to heat treatment according to a method of sealing an optical fiber hermetically sealing portion according to a first embodiment of the present invention. This fiber guide is mounted in the field through. In the figure, 11 is an optical fiber, 12
Is a guide, 13 is a sleeve, 14 is a low melting point metal such as solder, 15 is a nut, 16 is a fiber guide, 17 is a hermetically sealed portion of the end of the sleeve 13, 18 is a band heater,
19 is a clamp. As shown in the figure, the optical fiber 1
1 is guided into a sleeve 13 along a groove around the guide 12, and the guide 12 is fixed in the sleeve 13 by a nut 15. The end of the sleeve 13 is the optical fiber 1
The periphery of 1 is hermetically sealed with solder 14 to form a hermetically sealed portion 17. In addition, the band heater 18 keeps the hermetically sealed portion 17 at 50 ° C.
The clamp 19 is a tool for fixing the fiber guide 16 by heating to -60 ° C.

FIG. 2 is a process chart showing the method of sealing the optical fiber hermetically sealing portion according to the first embodiment in the order of steps. First,
A plurality of optical fibers 11 are arranged in the groove around the guide 12 and inserted into the sleeve 13 (step S1). Then, the guide 12 is fixed to the sleeve 13 with the nut 15 (step S2). After that, the protective coating of the optical fiber 11 is removed, and the metal coating on the core portion is hermetically sealed with the solder 14 between the guide 12 and the sleeve 13 (step S3). Here, after the solder 14 is arranged between the guide 12 and the sleeve 13 around the optical fiber 11, the hermetically sealed portion 17 is heated to a temperature equal to or higher than the melting point of the solder 14, and the solder 14 arranged there is removed. Melt. At this time, the melted solder 14 is filled up to a small gap around the optical fiber 11 and then cooled to hermetically seal the inside of the fiber guide 16. After the airtight sealing work is completed, heat treatment is applied to the airtight sealing portion 17 of the fiber guide 16 taken out from the sealing device (step S4).

In the heat treatment of step S4, as shown in FIG. 1, the fiber guide 16 is fixed by a clamp 19, the band heater 18 is applied to the hermetically sealed portion 17, and only that portion is heated at 50 ° C. to 60 ° C. for 3 hours. Heat for more than an hour.

In the step S3, the following happens. In the cooling process after melting the solder 14, the solder 14
When the solidification occurs, a temperature distribution is created. For example, in FIG.
As in (a), the surrounding solder 14a is solid and the inner solder 14b is liquid. When solidification progresses further, internal stress (residual stress) is generated due to solidification contraction.
Further, as shown in FIG. 8B, even in the cooling step after all the solder 14 is solidified, internal stress is further generated due to thermal contraction of the member forming the hermetically sealed portion 17. Due to these internal stresses, compressive force and bending force are applied to the optical fiber 11 to generate microbends, and as a result, optical loss increases. In this embodiment, step S4 is performed after step S3, and this heat treatment results in solder 1
The residual stress in 4 is removed. Therefore, the compressive force and the bending force generated by the residual stress are not applied to the optical fiber 11, the microbend can be relaxed, and the optical loss can be reduced.

The temperature of the heat treatment in step S4 is the solder 14 which is a low melting point metal used for hermetically sealing.
The temperature is lower than the melting point of, for example, 50 ° C. to 60 ° C. As the solder 14, for example, a tin (Sn) -lead (Pb) alloy is used. In this alloy, Sn easily forms an alloy with iron or copper, so that it serves mainly as an adhesive, and Pb lowers the melting point and reduces the strength of the solder. increase. In this case, Sn
63% of the most common solder is used and its melting point is 1
It is 83 ° C. In the heat treatment of step S4, it is not necessary to melt the solder 14, but if it is melted, another internal stress will be generated. Therefore, heating is performed at a temperature lower than the melting point of the solder 14. If the heating temperature is low, the effect of removing the internal stress becomes weak. 50 ° C. in this embodiment
-60 degreeC is set. In this heat treatment, since only the hermetically sealed portion 17 is heated and the parts other than the hermetically sealed portion 17 are not heated, it is possible to prevent a defect due to heating from occurring in other portions, and it is possible to use extra energy for heating. Absent.

In the heat treatment shown in FIG. 1, the hermetically sealed portion 17
Only the fiber was heated at 50 ℃ -60 ℃.
The whole 6 may be heated. FIG. 3 is an explanatory diagram showing a state where heat treatment is applied to the entire fiber guide 16.
Is a constant temperature oven with a heating device. The constant temperature bath 20 is, for example, 50
The fiber guide 16 is kept at a temperature of 60 ° C to 60 ° C.
The whole is put in a constant temperature bath 20 and heated for 3 hours or more. When the entire fiber guide 16 is heat-treated, if it is heated to a temperature higher than 60 ° C., for example, near the melting point of the solder 14, the thermal contraction of the peripheral members has a great influence. Therefore, it is preferable that the temperature is as low as possible, but if the temperature is too low, the effect of the heat treatment is weakened. Therefore, the heat treatment temperature is suitably 50 ° C to 60 ° C. When heat treatment is performed with a large device such as the constant temperature bath 20,
Multiple fiber guides 16 can be heated at one time. Further, since the whole can be heated uniformly, the temperature distribution of the fiber guide is less likely to occur, and the variation in heat shrinkage during cooling can be reduced. Further, the entire pressure-resistant housing may be heat-treated, but if the temperature at which the heat-treatment is performed is too high, the parts constituting the repeater, such as LDs and circuit parts,
Further, the solder or the like fixing them may be damaged by heat. Considering this, the heat treatment temperature is 50
C. to 60.degree. C. is suitable. Further, the airtight sealing device used in step S3 has a heating function for melting the solder 14, and it can be used as it is for the heat treatment in step S4.

In the above, as the low melting point metal, Sn--
Although the solder of Pb alloy was used, it is not limited to this,
Other low melting point metals may be used. For example, pure tin (Sn) having a melting point of 232 ° C. or tin (Sn) -bismuth (Bi) alloy having a melting point of 138 ° C. may be used.

Embodiment 2. FIG. 4 is a process chart showing a method of sealing the optical fiber hermetically sealing portion 17 according to the second embodiment of the present invention in the order of steps. Similar to the first embodiment, first, a plurality of optical fibers 11 are arranged in the groove around the guide 12 and inserted into the sleeve 13 (step S1). Then, for example, the guide 12 is fixed to the sleeve 13 with the nut 15 (step S2). After that, the protective coating of the optical fiber 11 is removed, and the metal coating on the core portion is hermetically sealed with the solder 14 between the guide 12 and the sleeve 13 (step S3). Then, the airtightness test of the airtight sealing part 17 is performed (step S5). In this step, in order to inspect the airtightness of the hermetically sealed portion 17 of the fiber guide 16, a high pressure is applied to the hermetically sealed portion 17 with He or the like to perform a leak test. After this airtightness test, heat treatment is applied to the airtightly sealed portion 17 of the fiber guide 16 (step S4). In this step S4, after performing the airtightness test, the fiber guide 16 taken out from the airtightness tester is placed in the constant temperature bath 20 or the like, and the temperature is lower than the melting point of the solder 14, for example, 50 ° C to 6 ° C.
The entire fiber guide 16 is heated at a temperature of 0 ° C. The details of this heat treatment are the same as in the first embodiment, and only the hermetically sealed portion 17 may be heated using a dedicated device such as the band heater 18.

The internal stress generated in the step S3 is the same as in the first embodiment. Further step S5
By performing the airtightness test at, the following occurs. That is, in step S5, the hermetically sealed portion 17 of the fiber guide 16 is pressurized. As shown in FIG. 8C, internal stress is applied to the solder 14 of the hermetically sealed portion 17 by applying pressure. Therefore, a compressive force and a bending force are applied to the optical fiber 11 to generate microbends, resulting in an increase in optical loss. After the test, even if the pressure is removed, the internal stress (residual stress) may remain, so
As a result, the optical loss increases more than before the airtightness test. In this embodiment, step S4 is performed after step S5, and this heat treatment removes the residual stress in the solder 14. Therefore, there is no compressive force or bending force applied to the optical fiber 11 due to the residual stress, the microbend can be relaxed, and the optical loss can be reduced.

Even after the airtightness test, the internal stress caused by the airtightness test is released by the creep of the solder 14, and the light loss at the hermetically sealed portion 17 is recovered even if the airtightness test is left as it is without heat treatment. Go. However, by performing the heat treatment in step S4, the creep deformation rate of the solder 14 is increased, and the time until the internal stress of the solder 14 is released can be shortened. That is, the recovery time of light loss can be significantly shortened. Further, since the internal stress originally existing before the airtightness test can be removed, the light loss is reduced as compared with before the airtightness test.

This airtightness test is an airtightness test of the airtightly sealed part of the fiber guide 16 alone. In addition, when the airtightness test of the housing is carried out even after being incorporated in the repeater pressure resistant housing as shown in FIG. There is. Also in this case, as in the airtightness test of the fiber guide 16 alone, the airtight sealing part 1 of the fiber guide 16
Since 7 is pressurized, step S4 is performed after the airtightness test of the housing.
Process. That is, after performing the airtightness test of the casing, the pressure-resistant casing is put in the constant temperature bath 20 or the like as in the first embodiment, and the entire casing is heated at a temperature lower than the melting point of the solder 14, for example, 50 ° C. to 60 ° C. To heat. By this heat treatment, the residual stress in the solder 14 is removed and the optical fiber 1
There is no compressive force or bending force applied to 1, the microbend can be relaxed, and the optical loss can be reduced.

In the first and second embodiments, the heat treatment is applied to the fiber guide 16 alone, and the heat treatment is performed on the pressure-resistant housing after the fiber guide 16 is assembled in the pressure-resistant housing. The heat treatment is performed at 60 ° C to 60 ° C. But,
When heat-treating the fiber guide 16 alone, it may be heated at about 50 ° C. to 100 ° C., which is lower than the melting point of the solder. On the other hand, the repeater circuit in the pressure resistant housing is 60 ° C to 1
It is preferable to heat at a temperature of 50 ° C. to 60 ° C., because heating at about 00 ° C. may cause damage by heat. However, the hermetically sealed fiber guide 16 is
By heating at a temperature of 0 ° C. to 60 ° C., the internal stress generated during solidification of the solder can be removed, which is sufficiently effective. Therefore, as in the first and second embodiments, the heat treatment is performed at the same temperature in the case where the heat treatment is performed on the fiber guide 16 alone and the case where the heat treatment is performed on the pressure resistant case after being incorporated in the pressure resistant case. When heating is performed, management of heat treatment can be unified, and heat treatment can be performed together.

[0025]

As described above, according to the method of sealing the hermetically sealed optical fiber according to the present invention, a plurality of optical fibers to be introduced into the pressure-resistant housing are used as the fiber guide in the feedthrough with a low melting point metal. In the method of sealing by, after sealing the periphery of the optical fiber with the low melting point metal, by applying a heat treatment to the hermetically sealed portion,
It is possible to remove the internal stress generated when the solder is solidified,
Microbending that occurs in the optical fiber due to internal stress is relaxed, and optical loss at the hermetically sealed portion can be reduced.

Further, the periphery of the optical fiber is hermetically sealed with the low melting point metal, an airtightness test of the hermetically sealed portion is performed, and then a heat treatment is applied to the hermetically sealed portion. The internal stress generated in the hermetically sealed portion can be removed by the airtight test, the microbend occurring in the optical fiber due to the internal stress can be relaxed, and the optical loss in the hermetically sealed portion can be recovered or reduced. Moreover, the recovery time of the light loss can be shortened significantly.

Further, since the heat treatment is a treatment of heating at a temperature of 50 ° C. to 60 ° C., for example, in a constant temperature bath, internal stress generated during solidification of solder can be removed, The microbend occurring in the optical fiber due to the stress is relaxed, and the optical loss at the hermetically sealed portion can be reduced.

Furthermore, since the above heat treatment is characterized by heating in a constant temperature bath, it is possible to heat a plurality of fiber guides at the same time, and it is possible to heat the whole uniformly. The temperature distribution of the fiber guide is less likely to occur, and the variation in heat shrinkage during cooling can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a fiber guide during heat treatment according to a first embodiment of the present invention.

FIG. 2 is a process chart showing a method of sealing the optical fiber hermetically sealing portion according to the first embodiment in the order of steps.

FIG. 3 is an explanatory diagram showing a state of another heat treatment according to the first embodiment.

FIG. 4 is a process chart showing a method of sealing an optical fiber hermetically sealing portion according to a second embodiment of the present invention in the order of steps.

FIG. 5 is a partial sectional view showing an optical submarine repeater.

FIG. 6 is a cross-sectional view showing a fiber guide.

FIG. 7 is a process diagram showing a conventional method for sealing an optical fiber hermetically sealing portion in the order of steps.

FIG. 8 is an explanatory diagram showing the cause of internal stress occurring in the hermetically sealed portion.

[Explanation of symbols]

11 optical fiber 12 guide 13 sleeve 14 low melting point metal 16 fiber guide 17 airtight sealing part.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Masaharu Moriyasu             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Shoichiro Nishitani             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. (72) Inventor Naotoshi Masuda             2-3 2-3 Marunouchi, Chiyoda-ku, Tokyo             Inside Ryo Electric Co., Ltd. F-term (reference) 2H038 CA44 CA46 CA49                 5G363 AA03 BA10 CA05 CA20 CB01                 5G375 AA18 BA02 BB55 BB71 CC02                       EA08

Claims (4)

[Claims] 1. A method of sealing a plurality of optical fibers to be introduced into a pressure-resistant housing in a fiber guide in a feedthrough with a low-melting point metal after hermetically sealing the periphery of the optical fiber with the low-melting point metal. A method for sealing an optical fiber hermetically sealed portion, characterized in that a heat treatment is applied to the hermetically sealed portion. 2. A hermetically sealing the periphery of the optical fiber with the low melting point metal, and performing an airtight test of the hermetically sealed portion,
The method of sealing an optical fiber hermetically sealed portion according to claim 1, wherein heat treatment is applied to the hermetically sealed portion. 3. The method of sealing an optical fiber hermetically sealed portion according to claim 1, wherein the heat treatment is a treatment of heating at a temperature of 50 ° C. to 60 ° C. 4. The method of sealing an optical fiber hermetically sealed portion according to claim 1, wherein the heat treatment is heating in a constant temperature bath.