JP2005115133A - Method for repairing submarine optical cable and cable determination method for repair - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for repairing a submarine optical cable and a cable determination method for repair capable of facilitating the repair of submarine optical cables which comprises a plurality of dispersion managed fiber (DMF) cables of housing positive dispersion fibers and negative dispersion fibers serially connected. <P>SOLUTION: The prescribed number of cables for repair which have the number of lines in accordance with the number of times of the marine optical cables and the lengths determined by taking the distribution of the submarine optical cables in water into consideration are prepared beforehand (S1-S5). The DMF cable which has a failure in the submarine optical cable is substituted with the cable having an appropriate length among the cables for repair prepared beforehand (S8-S9). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for repairing a submarine optical cable and a method for determining the number and lengths of repair cables used for repairing a submarine optical cable.

  In order to realize high-speed optical transmission by optical fiber communication, it is necessary to manage the accumulated chromatic dispersion of the optical fiber transmission line within a predetermined value (see, for example, Patent Document 1). For example, within one relay span, an optical fiber having a large diameter with positive dispersion is arranged on the signal light input side, an optical fiber with negative dispersion is arranged on the signal output side, and the absolute value of cumulative chromatic dispersion for each span A configuration in which a dispersion compensating fiber to be reduced is arranged is known (see, for example, Patent Documents 1 and 2).

  FIG. 2 shows an example of a dispersion map of such an optical fiber transmission line. The horizontal axis indicates transmission distance, and the vertical axis indicates cumulative chromatic dispersion. A positive dispersion fiber and a negative dispersion fiber are arranged in one relay span, and a dispersion compensating fiber is arranged for each predetermined number of relay spans. In addition, a dispersion compensating fiber (pre-dispersion compensating fiber) that imparts predetermined wavelength dispersion in advance is arranged in the transmitting terminal device so that the accumulated chromatic dispersion is within a predetermined value as the entire optical transmission line. In the receiving terminal device, a dispersion compensating fiber (post dispersion compensating fiber) that finally sets the accumulated chromatic dispersion to zero or a value close to zero is arranged.

  In the dispersion map shown in FIG. 2, since the absolute value of the cumulative chromatic dispersion of the negative dispersion fiber in each relay span is larger than the cumulative chromatic dispersion positive dispersion of the positive dispersion fiber, a positive dispersion fiber is used as the dispersion compensation fiber. In the case of wavelength division multiplexing transmission, the difference between accumulated chromatic dispersion wavelengths can be reduced by setting the dispersion slopes of the positive dispersion fiber and the negative dispersion fiber in each relay span to have opposite slopes.

  In such an optical cable used for an optical transmission system in which chromatic dispersion is managed, so-called DMF (Dispersion managed fiber) cable, each optical fiber line has two types of chromatic dispersion values having opposite signs as described above. Optical fibers, that is, a positive dispersion fiber and a negative dispersion fiber, which are serially connected in the propagation direction of the signal light. On the signal input side, a large-diameter optical fiber is used to reduce the nonlinear effect.

  In optical fiber communication, in particular, long-distance optical fiber communication between oceans, one optical fiber line is used for one-way communication. FIG. 3 shows a combination example of a pair of optical fibers accommodated in a DMF cable used for long-distance transmission. An optical fiber line 10 for transmitting signal light from west (W) to east (E) is composed of a positive dispersion fiber 10a and a negative dispersion fiber 10b, and transmits signal light from east (E) to west (W). The optical fiber line 12 is made up of a positive dispersion fiber 12a and a negative dispersion fiber 12b. As shown in FIG. 3, the positive dispersion fiber 10a and the negative dispersion fiber 12b, and the positive dispersion fiber 12a and the negative dispersion fiber 10b are juxtaposed in the cable in relation to the signal transmission direction. For example, the chromatic dispersion of the positive dispersion fibers 10a and 12a is approximately 20 ps / nm / km, and the chromatic dispersion of the negative dispersion fibers 10b and 12b is approximately −40 to −60 ps / nm / km. In order to facilitate management and maintenance, the same type of optical fiber is used for the positive dispersion fibers 10a and 12a, and the same type of optical fiber is also used for the negative dispersion fibers 10b and 12b. That is, the DMF cable is composed of two types of optical fibers.

  Since the DMF cable is composed of two types of optical fibers whose chromatic dispersion and dispersion slope are greatly different from each other, it is difficult to repair at the time of cable failure. For example, when there is a cable breakage or the like when used in a submarine optical cable, for repair, the optical fiber in the cable is cut about 1 km on both sides around the breakpoint, and the water depth of 2 Insert an optical fiber 5 times longer. If there is a failure in one of the optical fiber lines 10 and 12, a repair optical fiber is inserted into the faulty one for repair, and if there is a failure in both, the repair optical fiber is inserted into both for repair.

  Conventionally, the optical fiber used for interruption is an optical fiber having a small chromatic dispersion in the signal wavelength band, specifically, a non-zero dispersion fiber having a chromatic dispersion value of about ± 3 ps / nm / km in the 1550 nm band. The chromatic dispersion of the positive dispersion fibers 10a and 12a, about 20 ps / nm / km, and the chromatic dispersion of the negative dispersion fibers 10b and 12b, about -40 to -60 ps / nm / km, about 10%. This is because the dispersion map does not change greatly because only the chromatic dispersion value is provided.

Patent Document 3 describes a method of repairing an optical fiber having an absolute value of a chromatic dispersion value smaller than the absolute value of each chromatic dispersion of a positive dispersion fiber and a negative dispersion fiber arranged in an optical repeater section. ing.
JP 2000-261377 A Japanese Patent Laid-Open No. 2001-094510 JP 2001-228336 A

  In contrast to the breakage of the optical fiber in the middle of the DMF cable, the conventional method of cutting the DMF cable and inserting a new optical fiber inevitably changes the dispersion map of the optical fiber transmission line. Depending on the newly inserted optical fiber, it is also necessary to change or adjust the compensation amount of the dispersion compensating fiber at the optical transmitting terminal station and / or the optical receiving terminal station.

  It is necessary to store the optical fiber used for repair more than the required length, which also contributes to maintenance costs.

  It is an object of the present invention to provide a method for repairing a submarine optical cable that can be repaired more easily and requires a small number of repair cables to be prepared in advance, and a method for determining a repair cable therefor.

  The submarine optical cable repair method according to the present invention repairs a submarine optical cable including a serially connected positive dispersion fiber and a plurality of DMF cables containing negative dispersion fibers, and the plurality of DMF cables connected in series. A method is characterized in that a faulty DMF cable of the submarine optical cable is replaced with a repair cable prepared in advance.

  As a result, repair can be performed without significant fluctuations in the dispersion map.

  A method for determining a repair cable according to the present invention is a submarine optical cable composed of serially connected positive dispersion fibers and a plurality of DMF cables that accommodate negative dispersion fibers, wherein the plurality of DMF cables are serially connected. This is a method for determining a repair cable to be used for repairing a submarine optical cable. Calculate the required number of repairs from the cable length of the submarine optical cable. The number of repair cables corresponding to the number of repairs is determined. A cumulative distribution obtained by accumulating the water depth distribution of the submarine optical cable from the deeper side toward the shallower side is calculated in increments of a predetermined depth. The length of each repair cable is set to a predetermined multiple of the water depth corresponding to each dividing line when the cumulative value of the cumulative distribution is equally divided by the number equal to the number of the repair cables.

  As a result, the required number of repair cables having the required length can be determined.

  According to the present invention, submarine optical cables using DMF cables can be repaired without significant fluctuations in the dispersion map. In addition, it is possible to easily determine the necessary number of repair cables having the required length.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a flowchart of an embodiment of the present invention. In this embodiment, the water depth is evaluated in units of 1000 m. FIG. 2 shows an example of laying a submarine optical cable. In the example shown in FIG. 2, it is assumed that the length of a portion with a depth of 1000 m is 500 km, the length of a portion with a depth of 2000 m is 2000 km, and the length of a portion with a depth of 4000 m is 1500 km with respect to a submarine optical cable with a total length of 4000 km.

  The present embodiment will be described with reference to the example shown in FIG. First, the number of repairs is determined from the system length (S1). In the submarine optical cable system design, the cable is repaired once every 1000 km. In the example shown in FIG. 2, since the system length is 4000 km, the number of repairs is four.

  From the number of repairs determined in step S1, the number X of cables used for repair is determined (S2). In the example shown in FIG. 2, since the number of repairs is four, four DMF cables are prepared for repair. However, the length of each repair cable is determined as follows.

  The ratio Z of the deep sea portion of the submarine optical cable is calculated as a percentage in increments of 1000 m (S3). In the example shown in FIG. 2, the length of the portion having a water depth of 1000 m is 500 km, and the ratio to the total length (4000 km) is 500/4000, that is, 12.6%. The length of the portion having a water depth of 2000 m is 2000 km, and the ratio to the total length (4000 km) is 2000/4000, that is, 50.0%. The length of the portion having a water depth of 4000 m is 1500 km, and the ratio to the total length (4000 km) is 1500/4000, that is, 37.5%.

  The ratio Z obtained in step S3 is accumulated from a deep part to a shallow part to obtain a cumulative distribution with respect to the water depth (S4). The cumulative distribution for the example shown in FIG. 2 is shown in FIG. The horizontal axis in FIG. 3 indicates the water depth, and the vertical axis indicates the cumulative value. At a water depth of 4000 m, the cumulative value is 37.5%, when the water depth is 2000 m, the cumulative value is 87.5%, and when the water depth is 1000 m, the cumulative value is 100%.

  The cumulative value of the cumulative distribution is equally divided by X, and a repair cable having a length corresponding to 2.5 times the water depth for the cumulative value 0 and the water depth for each dividing line is prepared (S5). This repair cable is also a DMF cable similar to the DMF cable originally used as an optical submarine cable.

  In the example illustrated in FIG. 3, the water depths 4000 m, 4000 m, 2000 m, and 2000 m corresponding to the cumulative values of the cumulative distribution are determined for 0%, 25%, 50%, and 75%, respectively. It is said that a cable having a length of 2.5 times the water depth is required for repairing the submarine optical cable, so each length is multiplied by 2.5. As a result, two 10 km repair cables and two 5 km repair cables are prepared. The 10 km repair cable can handle repairs at any depth of 1000 m, 2000 m, and 4000 m, and the 5 km repair cable can support repairs at any depth of 1000 m and 2000 m. Therefore, two repairs are possible for the deepest part (water depth of 4000 m), and four repairs are possible for water depths of 1000 m and 2000 m.

  When a problem requiring repair is found in the installed submarine optical cable (S6), it is confirmed whether there is a stock of available repair cables (S7). If no repair cable is available, give up.

  When there is an available repair cable (S7), a repair cable to be used for repair is determined (S8). In the present embodiment, there are repair cables having different lengths, and the longest repair cable can cope with any depth of water. Therefore, when there is a repair cable having a different length corresponding to the depth of repair, the shortest repair cable is selected.

  Then, the DMF cable having a defect is entirely replaced with a repair cable (S9). That is, in this embodiment, a new optical fiber is not inserted in the middle of a defective DMF cable.

  In this embodiment, when the same type of optical fiber is used for the DMF cable to be removed and the repaired DMF cable to be inserted, the chromatic dispersion and the dispersion slope are different based on the difference in the cable length. However, compared to the method of inserting a new optical fiber at the cut position, the influence on the entire dispersion map, that is, the influence on the transmission of signal light is small.

  By adjusting the chromatic dispersion and dispersion slope of each repair cable in advance so that they will be the same values used from the beginning for submarine optical cables, the chromatic dispersion and dispersion slope will not change even if the cable is replaced in units of cables. You can However, for this purpose, the optical fiber accommodated in the repair cable must be different from the optical fiber accommodated in the DMF cable originally used for the submarine optical cable, or the chromatic dispersion and dispersion slope can be adjusted. It is necessary to insert an optical element for this purpose into the repair cable.

  The probability per unit length of occurrence of a fault that requires repair to the submarine cable is considered to be equal in any part in the deep sea part where the water depth is 1000 m or more. This is because in the deep sea, cables are not damaged due to human acts (fishing activities, etc.), and it is considered that most of the damage is caused by slight defects during manufacturing. . The probability of such a defect occurring is the same for any part of the entire submarine cable. Assuming that the probability of occurrence of defects is uniform, when a cable for repair is prepared in advance, a cable with a length corresponding to the depth is generated in order from the deepest part of the water as in the present invention. By preparing in consideration of the probability, the number of cables to be prepared is minimized, and the length of the cable is not short at the time of repair.

  The optical fiber accommodated in the repair cable is most suitable that the chromatic dispersion and the dispersion slope are almost zero, unlike the laid DMF cable. By using such an optical fiber, the chromatic dispersion and dispersion slope of the entire system hardly change before and after the repair. This eliminates the need for adjustment on the transmission side and reception side (change of cumulative dispersion compensation).

  Further, an optical fiber having substantially the same chromatic dispersion and dispersion slope as the installed DMF cable may be used for the repair cable. In this case, the chromatic dispersion and the dispersion slope of the entire system change before and after the repair. If the repair is repeated, the influence of this change cannot be ignored, and finally adjustment on the transmission side and reception side (change of cumulative dispersion compensation) is required.

  Although the invention has been described with reference to specific illustrative embodiments, various modifications and alterations may be made to the above-described embodiments without departing from the scope of the invention as defined in the claims. This is obvious to an engineer in the field to which the present invention belongs, and such changes and modifications are also included in the technical scope of the present invention.

It is a flowchart of one Example of this invention. This is an example of laying a submarine optical cable. It is a cumulative distribution with respect to the water depth of the submarine optical cable shown in FIG. It is an example of a dispersion | distribution map of the optical transmission system which uses a DMF cable. It is a schematic diagram which shows the structure of a DMF cable.

Explanation of symbols

10, 12: Optical fiber lines 10a, 12a: Positive dispersion fibers 10b, 12b: Negative dispersion fibers

Claims (7)

A method of repairing a submarine optical cable comprising a plurality of DMF cables that accommodates serially connected positive dispersion fibers and negative dispersion fibers, wherein the plurality of DMF cables are serially connected,
Replace the faulty DMF cable of the submarine optical cable with a repair cable prepared in advance (S9).
A submarine optical cable repair method characterized by the above. The length of a repair cable that replaces the faulty DMF cable is equal to or longer than a length corresponding to 2.5 times the water depth of the faulty DMF cable (S5). Repair method of submarine optical cable as described. Prepare a predetermined number of repair cables each having a length corresponding to the number of the submarine optical cables, each having a length determined in consideration of the distribution of the submarine optical cables in water (S1-S5),
As a repair cable to replace the faulty DMF cable, a repair DMF cable having a length corresponding to a predetermined multiple of the water depth of the faulty DMF cable is selected from the predetermined number of repair cables. (S8)
The method of repairing a submarine optical cable according to claim 1. The submarine optical cable repair method according to claim 3, wherein the predetermined multiple is 2.5 times. A submarine optical cable comprising a plurality of DMF cables that accommodates serially connected positive dispersion fibers and negative dispersion fibers, and a repair cable used for repairing the submarine optical cables to which the plurality of DMF cables are serially connected. A method of determining,
Calculate the required number of repairs from the cable length of the submarine optical cable (S1)
Determine the number of repair cables according to the number of repairs (S2),
A cumulative distribution obtained by accumulating the water depth distribution of the submarine optical cable from the deeper side to the shallower side is calculated in steps of a predetermined depth (S3, S4),
The length of each repair cable is set to a predetermined multiple of the water depth corresponding to each dividing line when the cumulative value of the cumulative distribution is equally divided by the number equal to the number of the repair cables (S5). )
A method for determining a repair cable. 5. The method for determining a repair cable according to claim 4, wherein the predetermined multiple is 2.5. The step of calculating the cumulative distribution includes
Calculate the water depth distribution of the submarine optical cable in increments of a predetermined depth (S3),
The cumulative distribution from the deep part to the shallow part of the water depth distribution is calculated (S4).
The method according to claim 5 or 6, further comprising steps.

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