JP2007060680A - Method for repairing transmission section, and optical communications system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent affecting a dispersion value at an optical receiving station, when a transmission line with an adjusted dispersion value is cut within a repeater section of the transmission line and the line is repaired by insertion. <P>SOLUTION: The transmission line comprises a positive dispersion fiber and a negative dispersion fiber. By adopting an intermediate diameter of each mode field diameter of the positive and negative dispersion fibers as optical fiber for inserting in the transmission line, the loss can be made minimum. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  Conventionally, in a long-distance optical transmission system, an optical signal is converted into an electric signal, and transmission is performed using an optical regenerative repeater that performs retiming, reshaping, and regenerating. However, at present, optical amplifiers have been put into practical use, and optical amplification repeater transmission systems using optical amplifiers as linear repeaters are being studied.

  By replacing the optical regenerative repeater with an optical amplifying repeater, the number of parts in the repeater can be greatly reduced, ensuring reliability and a significant cost reduction.

  Also, as one of the methods to realize large capacity optical transmission systems, attention is focused on wavelength division multiplexing (WDM) optical transmission systems that multiplex and transmit optical signals having two or more different wavelengths on one transmission line. Yes.

  In a wavelength division multiplexing optical amplifying and repeating transmission system that combines a wavelength division multiplexing optical transmission system and an optical amplifying and repeating transmission system, it is possible to amplify optical signals having two or more different wavelengths together using an optical amplifier. , Large capacity and long distance transmission can be realized with simple configuration (economical).

  A configuration example of a wavelength division multiplexing optical amplifying and repeating transmission system is shown in FIG.

  The WDM transmission optical system in FIG. 1 includes, for example, an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission line 3 that connects these transmission and reception stations, and an intermediate part of the optical transmission line 3. And a plurality of optical amplifiers 4 arranged at a required interval.

  The optical transmission station 1 includes a plurality of optical transmitters (E / O) 1A that respectively output a plurality of optical signals having different wavelengths, a multiplexer 1B that wavelength-multiplexes the plurality of optical signals, and the multiplexer 1B. And a postamplifier 1C that amplifies the WDM signal light to a required level and outputs it to the optical transmission line 3.

  The optical transmission path 3 has a plurality of relay sections connecting the optical transmission station 1 and the optical reception station 2 respectively.

  The optical amplifier 4 provided in the transmission path optically amplifies the wavelength multiplexed light and transmits it to the optical receiving station.

  The optical receiving station 2 divides the output light from the preamplifier 2C into a plurality of optical signals according to the wavelength, and a preamplifier 2C that amplifies the WDM signal light of each wavelength band transmitted through the optical transmission path to a required level. A duplexer 2B and a plurality of optical receivers (O / E) 2A for receiving and processing a plurality of optical signals, respectively.

  FIG. 2 shows an example of transmission path repair when a failure occurs in the optical transmission path 3 in the relay section between two optical amplifiers 4 when the transmission system having such a configuration is used in an optical submarine cable system.

  In FIG. 2, the same members as those in FIG.

  After removing the flooded cable, when connecting both cut cables, it will be longer than the existing cable length for connection on board.

  This removed cable length and inserted cable length are determined depending on the water depth.

  As the insertion cable, the same type of fiber cable 3 as the fiber cable used as the optical transmission line 3 was used.

  A plurality of transmission sections divided by an optical amplifier between an optical transmission station and an optical reception station may use several types of fibers having different dispersion codes for each transmission section.

  In this case, the cable inserted for repairing the transmission line uses both transmission lines with different dispersion values used in each transmission section, adjusts the length of the transmission line with two different dispersion values, and distributes the entire insertion cable. By making the value almost zero, the deviation of cumulative dispersion from the initial introduction of the transmission system was reduced.

  For example, non-zero dispersion shifted fiber (NZ-DSF) with a chromatic dispersion of -2 ps / nm / km with respect to the transmitted optical signal wavelength is used in 9 transmission sections, and the transmitted optical signal wavelength is If a 1.3 mm single mode fiber (SMF) with a chromatic dispersion of +18 ps / nm / km is used as one transmission line, the ratio of the NZ-DSF and SMF cable length is By inserting a cable that is adjusted to 9: 1 and the dispersion value of the cable is almost zero, the deviation of accumulated dispersion from the initial introduction of the transmission system due to the inserted cable is reduced.

  In addition, submarine optical cable systems can be broadly divided into three types: landing, shallow sea and deep sea.

  Fig. 3 shows a diagram defining each section.

  In FIG. 3, the same members as those in FIG.

  The landing section is the relay section from the optical transmitter station 1 to the first optical amplifier 4-1, and the relay section from the optical receiver station 2 to the first optical amplifier 4-17. The shallow sea section has a water depth of about 1000 m. The following are the relay sections where the optical amplifiers 4-2 to 4-6 are arranged and the relay sections where the 4-16 to 4-17 are arranged. -15 is the relay section where it is placed.

  The frequency of repair in each section is different. The deeper the water, the less frequent the repair, and the longer the cable to be inserted.

  Conventionally, the same type of fiber is used in the shallow and deep sea sections and in the landing section.

  In long-distance and large-capacity wavelength division multiplexing transmission systems, the application of fibers with a large average mode field diameter and small cumulative chromatic dispersion difference between wavelengths is promising in order to reduce nonlinear effects.

  The optical fiber used for the transmission line includes a positive dispersion fiber (+ D fiber) having a positive dispersion value with respect to the optical signal wavelength to be transmitted with a large mode field diameter in the first half of the transmission line in the relay section, and a transmission line. In the latter half, a negative dispersion fiber (-D fiber) having a negative dispersion value with respect to the transmitted optical signal wavelength is used to compensate for the chromatic dispersion and the chromatic dispersion slope of the first half of the fiber with a small mode field diameter.

  FIG. 4 shows a configuration example of a wavelength division multiplexing transmission system using positive dispersion and negative dispersion.

  The same members as those in FIG.

  The WDM transmission optical system in FIG. 4 includes, for example, an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission path 3 that connects these optical transmission and reception stations, and an intermediate part of the optical transmission path 3. And a plurality of optical amplifiers 4 arranged at a required interval.

  The configurations of the optical transmitting station 1 and the optical receiving station 2 are the same as those in FIG.

  The optical transmission line 3 has a plurality of relay sections that connect the optical transmission station 1, the optical amplifiers 4, and the optical reception station 2, respectively.

  For each repeater section, a 1.3 μm zero-dispersion SMF3a with a positive chromatic dispersion value and a positive dispersion slope is used for the first half (transmission side) for the WDM signal light wavelength band. A hybrid transmission line using a dispersion compensating fiber 3b having a dispersion slope in the latter half is applied.

  In this example, the average chromatic dispersion of the section of the hybrid transmission line of the positive dispersion fiber 3a and the negative dispersion fiber 3b is set to about -2 ps / nm / km, and the accumulated chromatic dispersion is set to the section of only the positive dispersion fiber 3a (a ) And (b).

  Figure 5 shows examples of dispersion maps when using NZ-DSF as the transmission path of the wavelength division multiplexing transmission system and when using positive dispersion and negative dispersion fibers.

  The characteristics in the figure are characteristics when optical signal channels are multiplexed at intervals of 50 GHz and optical signals of 34 waves are multiplexed.

  The characteristics marked with Δ, ■, ○ in the figure are the cases where NZ-DSF is used as the transmission line, ○ indicates channel 1, ■ indicates channel 17, and Δ indicates channel 34.

  Further, the characteristics without marks indicate the case where positive dispersion and negative dispersion fibers are used as the transmission line as shown in FIG.

The transmission line using positive dispersion and negative dispersion fibers has a smaller average dispersion slope, so that the accumulated dispersion after transmission is reduced, and transmission waveform distortion can be reduced.
Japanese Patent Laid-Open No. 11-084168 JP 09-181705 A JP-A-11-038230 JP 09-033744 A

When repairing a + D / -D fiber transmission line, the following problems arise.
(1) Transmission waveform distortion due to dispersion management and changes in cumulative dispersion: Table 1 shows the chromatic dispersion values of positive dispersion fiber, negative dispersion fiber, and the conventional transmission line NZ-DSF.

正分散および負分散ファイバの単位長さ当たりの波長分散量の絶対値が, ともに数十ps/nm/kmであり, 従来の伝送路であるNZ-DSFよりも1桁以上大きい。

The absolute values of chromatic dispersion per unit length of positive dispersion and negative dispersion fibers are both tens of ps / nm / km, which is one order of magnitude higher than the conventional transmission line NZ-DSF.

Therefore, in a transmission system using positive dispersion and negative dispersion fibers, when the transmission path is repaired using the transmission path that constitutes the system as in the past, the dispersion management of the system is greatly disrupted. Later, the accumulated dispersion also changes greatly, and the waveform distortion increases and the transmission characteristics deteriorate.
(2) Increase in splice loss: Table 2 shows the mode field diameters of positive dispersion fiber, negative dispersion fiber, NZ-DSF and SMF.

従来の伝送システムで用いられているNZ-DSFとSMFのモードフィールド径の差に比べ, 正分散および負分散ファイバのモードフィールド径の差が大きいため,伝送路ファイバの接続損も大きくなる。修理頻度が多い場合および中継区間が短い場合にこの影響は顕著になる。
(3) 負分散ファイバにおける非線形効果の過剰な増加：波長分散による影響を正分散と負分散ファイバの組み合わせにより低減する場合，中継区間の前半において障害が発生すると，挿入ケーブルを構成する負分散ファイバにおいて生じる非線形効果による波形歪みが伝送特性に大きく影響する。

Compared to the difference in mode field diameter between NZ-DSF and SMF used in conventional transmission systems, the difference in mode field diameter between positive dispersion and negative dispersion fibers is large, so the connection loss of transmission line fibers also increases. This effect becomes significant when the repair frequency is high and when the relay section is short.
(3) Excessive increase in nonlinear effect in negative dispersion fiber: When the influence of chromatic dispersion is reduced by the combination of positive dispersion and negative dispersion fiber, if a failure occurs in the first half of the relay section, the negative dispersion fiber that constitutes the insertion cable Waveform distortion due to non-linear effects generated in the process greatly affects transmission characteristics.

  An optical communication system according to a first aspect of the present invention is an optical communication system for submarine communication in which optical communication terminal stations are divided into a plurality of transmission sections. The optical communication system is divided into a shallow sea section and a deep sea section as water depth for repairing the transmission path. The transmission path of the transmission section arranged in the section includes a first optical fiber having a positive chromatic dispersion with respect to the light wavelength for transmission, and a second light having a negative chromatic dispersion for the light wavelength for transmission. The transmission path of the transmission section, which is composed of fiber and arranged in the shallow water section as the water depth for repairing the transmission path, has an absolute value of chromatic dispersion per unit length with respect to the optical wavelength for transmission, the first optical fiber or The third optical fiber is smaller than the absolute value of dispersion per unit length of the second optical fiber.

  An optical communication system according to a second aspect of the present invention is an optical communication system in which an optical communication terminal station is divided into a plurality of transmission sections, wherein the transmission section generates a loss in a dispersion compensator, a gain equalizer, or an optical add / drop multiplexer. A first optical fiber having a chromatic dispersion positive with respect to an optical wavelength for transmission, wherein the transmission path is divided into a transmission section having a unit and a transmission section not having the unit; The second optical fiber having a negative chromatic dispersion with respect to the optical wavelength for performing the transmission, and the transmission path of the transmission section having the unit is the absolute value of the chromatic dispersion per unit length for the optical wavelength for performing the transmission However, the third optical fiber is smaller than the absolute value of dispersion per unit length of the first optical fiber or the second optical fiber.

  An optical communication system light according to a third aspect of the present invention is an optical communication system in which communication terminal stations are divided into a plurality of transmission sections, wherein the transmission section generates a loss in a dispersion compensator, a gain equalizer, or an optical add / drop multiplexer A first optical fiber having a chromatic dispersion positive with respect to an optical wavelength for transmission, wherein the transmission path is divided into a transmission section having a unit and a transmission section not having the unit; The second optical fiber having a negative chromatic dispersion with respect to the optical wavelength for performing the transmission, and the transmission path of the transmission section having the unit is the absolute value of the chromatic dispersion per unit length for the optical wavelength for performing the transmission However, the third optical fiber is smaller than the absolute value of dispersion per unit length of the first optical fiber or the second optical fiber.

  The transmission path is composed of a positive dispersion fiber and a negative dispersion fiber, and an optical fiber having an absolute value of dispersion smaller than that of the positive dispersion fiber and the negative dispersion fiber is used as an optical fiber for the transmission path. In the transmission path in which the dispersion value is adjusted in the relay section, when the transmission path is cut and the transmission path is interrupted, the dispersion value at the optical receiving station can be prevented from being affected, Since only one type of optical fiber is inserted for repair, there is no need to consider directionality when preparing cables for repairing the uplink and downlink, improving work efficiency.

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

  As a first embodiment, a wavelength division multiplexing optical signal band transmitted as a fiber for repairing a transmission line in a wavelength division multiplexing transmission system using positive dispersion and negative dispersion fibers with respect to a wavelength division multiplexed optical wavelength to be transmitted as shown in FIG. Figure shows an example of one relay section using NZ-DSF, which has a zero dispersion value on the long wavelength side or short wavelength side adjacent to each other, and has a smaller absolute dispersion value than the positive dispersion fiber and the negative dispersion fiber. Shown in 6.

  Here, the optical signal wavelength to be transmitted is transmitted from a plurality of channels (for example, 32 channels) from an optical transmission station between 1.530 μm and 1.610 μm.

  With respect to this optical signal wavelength, each optical fiber constituting the transmission line has a dispersion value as shown in Table 1.

  FIG. 6 (a) shows a case where a failure has occurred in the positive dispersion fiber 3a at the front of the relay section of the hybrid transmission path composed of the positive dispersion fiber 3a and the negative dispersion fiber 3b.

  The signal light amplified to a predetermined level in the optical amplifier 4 is transmitted through the positive dispersion fiber 3a1 in front of the positive dispersion fiber 3a divided due to the failure, and then passes through the NZ-DSF 3c inserted for repair. .

  Thereafter, the light is transmitted through the positive dispersion fiber 3a2 and the negative dispersion fiber 3b at the rear of the positive dispersion fiber 3a that has been divided due to a failure, and then enters the next optical amplifier 4.

  FIG. 6B shows a case where a failure occurs near the boundary between the positive dispersion fiber 3a and the negative dispersion fiber 3b in the relay section of the hybrid transmission line composed of the positive dispersion fiber 3a and the negative dispersion fiber 3b.

  The signal light amplified to a predetermined level in the optical amplifier 4 is transmitted through the positive dispersion fiber 3a, and then passes through the NZ-DSF 3c inserted for repair.

  Then, after transmitting through the negative dispersion fiber 3b, it enters the next optical amplifier 4.

  FIG. 6 (c) shows a case where a failure occurs in the negative dispersion fiber 3b at the rear of the relay section of the hybrid transmission path composed of the positive dispersion fiber 3a and the negative dispersion fiber 3b.

  The signal light amplified to a predetermined level in the optical amplifier 4 is transmitted through the positive dispersion fiber 3a, and then passes through the negative dispersion fiber 3b1 at the front of the negative dispersion fiber 3b divided due to the failure.

  After that, the NZ-DSF 3c inserted for repair and the negative dispersion fiber 3b2 at the rear of the negative dispersion fiber 3b divided for failure are transmitted, and then incident on the next optical amplifier 4.

In the case of transmission line repair, it is necessary to consider any of the cases shown in FIGS. 6 (a), (b) and (c). However, in any case by using the present invention as described above, the following ( Effects such as A), (B) and (C) occur.
(A) NZ-DSF3c has a small absolute value of chromatic dispersion per unit length (~ 2ps / nm / km), so the dispersion management of the system does not collapse greatly, and the change in cumulative dispersion is also small. The impact on the can be reduced.
(B) The mode field diameter of NZ-DSF 3c is exactly halfway between positive dispersion fibers 3a, 3a1 and 3a2 and negative dispersion fibers 3b, 3b1 and 3b2.

For this reason, the connection loss does not become excessively large regardless of which fiber in the hybrid transmission line section composed of the positive dispersion fiber 3a and the negative dispersion fiber 3b is connected, and the design is easy because it is almost the same. Further, excessive deterioration due to the nonlinear effect that occurs when the negative dispersion fiber 3b is used in the front part (transmission station side) of the hybrid transmission line section is small.
(C) Since the spare fiber needs only one type of fiber, there is no need to consider the directionality when preparing cables for repairing the uplink and downlink, improving work efficiency.

  In this embodiment, a zero dispersion value is present on the adjacent long wavelength or short wavelength side of the wavelength band of the optical signal wavelength to be transmitted, and the absolute value of the amount of dispersion per unit length with respect to the transmitted optical signal wavelength is a positive dispersion fiber. The NZ-DSF, which is smaller than the negative dispersion fiber, is used for explanation, but the fiber for repairing the optical fiber whose absolute value of dispersion per unit length for the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber. Can be used as

  As an example, a dispersion shifted fiber (dispersion shifted fiber DSF) in which the transmission signal wavelength and the zero dispersion wavelength coincide with each other can be used.

  Here, DSF is considered to have better transmission characteristics when NZ-DSF is applied, considering the non-linear effect between transmission signal light wavelengths.

  A second embodiment is shown in FIG.

  The WDM transmission optical system in FIG. 7 includes an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission line 5 that connects the transmission and reception stations and the optical amplifier 4 in the first section from these stations. And an optical transmission line 3 connecting the other sections, and a plurality of optical amplifiers 4 arranged in the optical transmission line 3 at a predetermined interval.

  The configurations of the optical transmitting station 1 and the optical receiving station 2 are the same as those in FIG.

  Here, a plurality of channels (for example, 32 channels) are transmitted between 1.530 μm and 1.610 μm of the optical signal wavelength transmitted by the optical transmission station 1.

  The NZ-DSF is applied to the relay section from the optical transmission station to which the optical transmission line 5 is arranged to the first optical amplifier and the relay section from the optical reception station to the first optical amplifier.

  In addition, for other repeater sections, 1.3 μm zero dispersion SMF3a with a positive chromatic dispersion value and a positive dispersion slope for the wavelength band of WDM signal light is used as the optical transmission line 3 (front side). The hybrid transmission line using the dispersion compensating fiber 3b with negative chromatic dispersion value and negative dispersion slope at the rear and the 1.3μm zero-dispersion SMF3a only transmission line to compensate for the dispersion of the mixed transmission line are applied. .

  The signal light transmitted from the transmitting station 1 is transmitted through the NZ-DSF, which is the optical transmission line 5, in the first section, and then a mixed transmission line of a plurality of 1.3 μm zero dispersion SMF 3a and dispersion compensating fiber 3b and its A transmission line of only 1.3 μm zero dispersion SMF3a that compensates for the dispersion of the hybrid transmission line is transmitted.

  Then, in the last section, the NZ-DSF that is the optical transmission line 5 is transmitted and incident on the receiving station.

  The hybrid transmission line of 1.3 μm zero-dispersion SMF3a and dispersion-compensating fiber 3b has better transmission characteristics than NZ-DSF for long-distance transmission.

  However, because two types of fibers with large chromatic dispersion per unit length and different mode field diameters are used, if the fiber is removed or inserted when a failure occurs, a transmission system for dispersion management or section loss The impact on is great.

  As a result, the degradation of transmission characteristics is greater than that of NZ-DSF.

  Therefore, chromatic dispersion per unit length is present in the relay section from the optical transmitter station where the failure is likely to occur to the first optical amplifier 4 and in the relay section from the optical receiver station to the first optical amplifier 4. Apply NZ-DSF, which is an optical transmission line 5 with a small value.

  The optical transmission line 5 NZ-DSF has a small absolute value of the amount of chromatic dispersion per unit length, so when a failure occurs, even if the fiber is removed or inserted, the dispersion management of the system is greatly disrupted. In addition, since the change in the accumulated dispersion is small, the influence on the transmission characteristics can be reduced.

  In addition, since the optical transmission line 5 does not use multiple types of fibers, excessive connection loss does not occur during repair.

  The positive dispersion fiber, negative dispersion fiber, and NZ-DSF here can use the fibers shown in Table 1.

  Similarly to the first embodiment, if the absolute value of the amount of dispersion per unit length with respect to the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber, the first section is used instead of the NZ-DSF. And can be used for the last section.

  A third embodiment is shown in FIG.

  The WDM transmission optical system shown in Fig. 8 is an optical transmission line that connects an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission / reception station, and optical amplifiers 4 arranged at a depth of 1000 m or less. 5 and an optical transmission line 3 for connecting optical amplifiers 4 arranged at a water depth of 1000 m or more at a required interval.

  The configurations of the optical transmitting station 1 and the optical receiving station 2 are the same as in FIG. 1, and transmission is performed using the wavelength in the second embodiment.

  The NZ-DSF is applied to the section where the optical transmission path 5 is placed at a depth of 1000 m or less.

  For other relay sections with a depth of 1000 m or more, the first half is 1.3 μm zero-dispersion SMF3a, which has a positive chromatic dispersion value and a positive dispersion slope, as the optical transmission line 3 for the wavelength band of WDM signal light. (Transmission side) Hybrid transmission line using dispersion compensating fiber 3b with negative chromatic dispersion value and negative dispersion slope in the latter half, and transmission line of 1.3μm zero dispersion SMF3a only to compensate the dispersion of the hybrid transmission line Applies.

  The signal light transmitted from the transmission station 1 is transmitted through the NZ-DSF, which is the optical transmission line 5, in a plurality of relay sections having the optical amplifier 4 arranged at a water depth of 1000 m or less.

  Then, in the relay section having the optical amplifier 4 arranged at a water depth of 1000 m or more, a 1.3 μm zero dispersion SMF3a for compensating for the mixed transmission line of a plurality of 1.3 μm zero dispersion SMF3a and dispersion compensating fiber 3b and the dispersion of the hybrid transmission line Only transmit the transmission path.

  Thereafter, the NZ-DSF, which is the optical transmission line 5, is transmitted through a plurality of repeater sections having the optical amplifier 4 arranged again at a water depth of 1000 m or less, and is incident on the receiving station.

  The hybrid transmission line of 1.3 μm zero-dispersion SMF3a and dispersion-compensating fiber 3b has better transmission characteristics than NZ-DSF.

  However, because two types of fibers with large chromatic dispersion per unit length and different mode field diameters are used, if the fiber is removed or inserted when a failure occurs, a transmission system for dispersion management or section loss The impact on is great.

  As a result, the degradation of transmission characteristics is greater than that of NZ-DSF.

  Therefore, the NZ-DSF, which is an optical transmission line 5 with a small chromatic dispersion value per unit length, is applied to the repeater section having the optical amplifier 4 arranged at a water depth of 1000 m or less where failure is likely to occur.

  The optical transmission line 5 NZ-DSF has a small absolute value of the amount of chromatic dispersion per unit length, so when a failure occurs, even if the fiber is removed or inserted, the dispersion management of the system is greatly disrupted. In addition, since the change in the accumulated dispersion is small, the influence on the transmission characteristics can be reduced.

  In addition, since the optical transmission line 5 does not use multiple types of fibers, excessive connection loss does not occur during repair.

  The positive dispersion fiber, negative dispersion fiber, and NZ-DSF here can use the fibers shown in Table 1.

  Similarly to the first embodiment, if the absolute value of the dispersion amount per unit length with respect to the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber, the water depth can be used instead of the NZ-DSF. Can be used for sections below 1000m.

  In Fig. 8, the transmission section is less than 1000m in depth, but it exists only on the optical transmitting station side 1 and the optical receiving station side 2, but the transmission section with a depth of 1000m or less is partly in the central part between the terminal stations. In some cases, it is possible to use an optical fiber whose absolute value of the amount of dispersion per unit length with respect to the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber.

  A fourth embodiment is shown in FIGS. 9, 10 and 11. FIG.

  In the WDM transmission system shown in FIG. 4, a gain equalizer 6 that equalizes the gain of an optical amplifier, a dispersion compensator 7 that compensates for chromatic dispersion, or a light that branches the signal light of the main line and inserts the signal light into the main line A configuration example of a transmission system having a relay section including the add / drop device 8 will be shown, and in particular, the vicinity of a section having those devices will be shown.

  The signal light transmitted from the transmitting station is amplified by the optical amplifier 4 at predetermined intervals, and the mixed transmission line of 1.3 μm zero dispersion SMF3a and dispersion compensating fiber 3b and the dispersion of the mixed transmission line are compensated for 1.3 μm After transmitting the transmission line of only zero dispersion SMF3a, it transmits the relay section including gain equalization device 6, dispersion compensation device 7 or optical add / drop device 8, and then again 1.3μm zero dispersion SMF3a and dispersion compensation fiber 3b The transmission line of only 1.3 μm zero dispersion SMF3a that compensates for the dispersion of the hybrid transmission line and the dispersion of the hybrid transmission line is transmitted to the receiving station.

  In the relay section including these devices, the NZ-DSF which is the optical transmission line 5 is arranged at both ends connected to the optical amplifier 4, and each device is arranged in the center.

  Since these devices generate losses, the length of the optical fiber in the section including these devices is shorter than in other relay sections.

  When a 1.3 μm zero-dispersion SMF3a and dispersion-compensating fiber 3b hybrid transmission line is applied to the section including these devices, the effect on the transmission characteristics decreases as the length of the hybrid transmission line decreases. The advantage of applying the hybrid transmission line of 1.3 μm zero dispersion SMF3a and dispersion compensating fiber 3b to the included section is very small.

  On the other hand, only the necessity of controlling the average dispersion by adjusting the length ratio of the hybrid transmission line, and the disadvantages of dispersion management deviation and excessive connection loss at the time of transmission line repair are emphasized.

  Therefore, by applying the NZ-DSF, which is the optical transmission line 5, as the fiber used in the section including these devices, excessive deterioration of the transmission characteristics during transmission line repair can be suppressed, and the transmission system design can be facilitated.

  The positive dispersion fiber, negative dispersion fiber, and NZ-DSF here can use the fibers shown in Table 1.

  Similarly to the first embodiment, if the absolute value of the amount of dispersion per unit length with respect to the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber, use it instead of the NZ-DSF. Can do.

  A fifth embodiment is shown in FIGS. 12 (a) to 12 (d). An example in which the NZ-DSF, which is the optical transmission line 5, is applied as the fiber of the input / output unit of the spare optical amplifier 4 ′, gain equalization device 6 ′, dispersion compensation device 7 ′, and optical add / drop device 8 ′ is shown. .

  The NZ-DSF optical transmission line 5 has a small absolute value of chromatic dispersion per unit length, so even if it is used as an extra length, the dispersion management of the system does not collapse significantly, and the change in accumulated dispersion is small. The influence on transmission characteristics can be reduced.

  Further, the mode field diameter of the NZ-DSF which is the optical transmission line 5 is just between the positive dispersion fiber 3a and the negative dispersion fiber 3b. For this reason, the connection loss does not become excessively large regardless of which fiber in the hybrid transmission line section composed of the positive dispersion fiber 3a and the negative dispersion fiber 3b is connected, and the design is easy because it is almost the same.

  Further, in the system in which the NZ-DSF is applied to both ends of the section including the gain equalization device, the dispersion compensation device, and the optical add / drop device as shown in FIGS. 9 to 11, it is unnecessary to consider excessive connection loss.

  Furthermore, excessive deterioration due to the nonlinear effect that occurs when the negative dispersion fiber 3b is used in the front part (transmission station side) of the hybrid transmission line section is reduced.

Furthermore, in order to reduce transmission characteristics degradation due to chromatic dispersion,
a) Insert a fixed or variable batch chromatic dispersion compensator at the transmitting or receiving station
b) It is effective to insert a variable dispersion compensator in the transmission section.

  The NZ-DSF here can use the fibers shown in Table 1.

  Similarly to the first embodiment, if the absolute value of the amount of dispersion per unit length with respect to the transmitted optical signal wavelength is smaller than the positive dispersion fiber and the negative dispersion fiber, use it instead of the NZ-DSF. Can do.

  As an example of the above a), FIG. 13 shows a configuration example of a wavelength division multiplexing transmission system in which devices capable of compensating dispersion collectively are inserted into a transmitting station and a receiving station.

  The WDM transmission optical system in FIG. 13 includes, for example, an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission path 3 that connects these transmission and reception stations, and an optical transmission path 3 in the middle. And a plurality of optical amplifiers 4 arranged at a required interval.

  The optical transmission station 1 includes a plurality of optical transmitters (E / O) 1A that respectively output a plurality of optical signals having different wavelengths, a multiplexer 1B that wavelength-multiplexes the plurality of optical signals, and the multiplexer 1B. An optical amplifier 1D that amplifies the WDM signal light to a predetermined level and outputs it to a collective chromatic dispersion compensator 1E, and a collective dispersion compensator 1E that compensates in advance for the accumulated chromatic dispersion that occurs in the transmission line for all wavelengths in advance. And a postamplifier 1C that amplifies the WDM signal light from the collective dispersion compensator 1E to a required level and outputs it to the optical transmission line 3.

  The optical receiving station 2 amplifies the WDM signal light of each wavelength band transmitted through the optical transmission path to a required level, and the accumulation generated in the transmission path for all wavelengths of light output from the preamplifier 2C. Batch dispersion compensator 2E that collectively compensates for chromatic dispersion, optical amplifier 2D that amplifies the output from batch dispersion compensator 2E to a predetermined level, and a plurality of optical signals corresponding to the output light from optical amplifier 2D And a plurality of optical receivers (O / E) 2A for receiving and processing a plurality of optical signals, respectively.

  The optical transmission line 3 has a plurality of relay sections that connect the optical transmission station 1, the optical amplifiers 4, and the optical reception station 2, respectively.

  For each repeater section, a 1.3 μm zero-dispersion SMF3a with a positive chromatic dispersion value and a positive dispersion slope is used for the first half (transmission side) for the WDM signal light wavelength band. A hybrid transmission line using a dispersion compensating fiber 3b having a dispersion slope in the latter half is applied.

  If a shift in accumulated chromatic dispersion occurs during transmission line repair, the accumulated chromatic dispersion can be compensated by changing the chromatic dispersion compensation amounts of the collective dispersion compensators 1E and 2E at the transmitting and receiving stations so as to compensate for the generated chromatic dispersion deviation. Deviation can be reduced and deterioration of transmission characteristics can be suppressed.

  As an example of the above-mentioned b), FIG. 14 shows a configuration example of a wavelength division multiplexing transmission system in which devices capable of compensating dispersion collectively are inserted in the transmission section.

  The WDM transmission optical system of FIG. 14 includes, for example, an optical transmission station (OS) 1, an optical reception station (OR) 2, an optical transmission path 3 that connects these transmission and reception stations, and an intermediate part of the optical transmission path 3. A plurality of optical amplifiers 4 arranged at a required interval, a variable dispersion compensator 9, and an optical transmission line 5 applied to a section in which the variable dispersion compensator is inserted.

  The configurations of the optical transmitting station 1 and the optical receiving station 2 are the same as those in FIG. 1 or a configuration in which a collective dispersion compensator is inserted in the transmitting and receiving stations as shown in FIG.

  The signal light transmitted from the optical transmission station 1 is transmitted through the optical transmission line 3 while being amplified by the optical amplifier 4 at predetermined intervals.

  In the section including the variable dispersion compensator 9, after passing through the optical transmission line 5, the optical transmission line 5 is transmitted through the variable dispersion compensator. Thereafter, the light is again transmitted through the optical transmission line 3 while being amplified by the optical amplifier 4 at predetermined intervals, passes through the section including the variable dispersion compensator 9, and is then amplified by the optical amplifier 4 at predetermined intervals. It is transmitted through the optical transmission line 3 and received by the receiving station.

  If a shift in accumulated chromatic dispersion occurs during repair of the transmission line, the shift in accumulated dispersion is reduced by changing the chromatic dispersion compensation amount of the variable dispersion compensator 9 so as to compensate for the generated chromatic dispersion shift. And deterioration of transmission characteristics can be suppressed.

  A configuration example of the variable dispersion compensator is shown in FIG.

  The variable dispersion compensator is composed of two optical switches 9A and 9B, n positive dispersion fibers 9D, n negative dispersion fibers 9E, and 2n + 1 optical attenuators (optical ATT) 9C. Composed.

  Several types of positive dispersion fiber 9D and negative dispersion fiber 9E are prepared on the step, and the loss of all ports is adjusted to be equal in advance by using the optical attenuator 9C.

  The signal light is incident on the optical switch 9A. At that time, positive dispersion occurs at the port where the positive dispersion fiber 9D is disposed for the signal light, and negative dispersion occurs at the port where the negative dispersion fiber 9E is disposed. Therefore, the ports of the optical switches 9A and 9B are selected. Thus, the dispersion compensation amount can be changed.

  Then, after transmitting through each port, it enters the optical switch 9B again to transmit the optical transmission line.

Example of wavelength multiplexing transmission system configuration Diagram showing conventional transmission line repair Definition of section names for submarine cables Configuration example of wavelength division multiplexing transmission system using positive dispersion and negative dispersion Example of dispersion map of wavelength division multiplexing transmission system Examples of transmission line repair Example of wavelength division multiplexing transmission system Example of wavelength division multiplexing transmission system Example of wavelength division multiplexing transmission system Example of wavelength division multiplexing transmission system Example of wavelength division multiplexing transmission system Configuration example of each device Example configuration of a wavelength division multiplexing transmission system when a batch chromatic dispersion compensator is inserted in the transmitter and receiver Configuration example of wavelength division multiplexing transmission system with variable chromatic dispersion compensator inserted in transmission section Configuration example of variable dispersion compensator

Explanation of symbols

1 is an optical transmission station
2 is an optical receiver station
3 is optical fiber
3a is positive dispersion fiber
3b is negative dispersion fiber
3c and 5 are NZ-DSF
4 is an optical amplifier
6 is a gain equalizer
7 is a dispersion compensator
8 is an optical branching repeater
1E and 2E are batch dispersion compensators

Claims (3)

In an optical communication system for submarine communication where optical communication terminal stations are divided into a plurality of transmission sections,
The water depth for repairing the transmission path is divided into a shallow sea section and a deep sea section, and the transmission path of the transmission section disposed in the deep sea section has a first optical fiber having positive chromatic dispersion with respect to the light wavelength to be transmitted, A second optical fiber having negative chromatic dispersion with respect to the optical wavelength for transmission;
The transmission path of the transmission section arranged in the shallow sea section has an absolute value of chromatic dispersion per unit length with respect to an optical wavelength for transmission, and the dispersion per unit length of the first optical fiber or the second optical fiber. An optical communication system, wherein a plurality of third optical fibers smaller than the absolute value are used. In an optical communication system that divides between optical communication terminal stations into a plurality of transmission sections,
The transmission section is divided into a transmission section having a loss compensator or a gain equalizer or an optical add / drop unit and a transmission section not having the unit,
The transmission path of the transmission section that does not have the unit has a first optical fiber having positive chromatic dispersion with respect to the light wavelength for transmission;
A second optical fiber having negative chromatic dispersion with respect to an optical wavelength for transmission;
The transmission path of the transmission section having the unit has an absolute value of chromatic dispersion per unit length with respect to an optical wavelength for performing the transmission, than an absolute value of dispersion per unit length of the first optical fiber or the second optical fiber. An optical communication system, characterized in that it is a small third optical fiber. In an optical communication system that divides between optical communication terminal stations into a plurality of transmission sections,
The transmission section is divided into a transmission section having a loss compensator or a gain equalizer or an optical add / drop unit and a transmission section not having the unit,
The transmission path of the transmission section that does not have the unit has a first optical fiber having positive chromatic dispersion with respect to the light wavelength for transmission;
A second optical fiber having negative chromatic dispersion with respect to an optical wavelength for transmission;
The transmission path of the transmission section having the unit has an absolute value of chromatic dispersion per unit length with respect to the optical wavelength for performing the transmission,
An optical communication system, characterized in that the third optical fiber is smaller than the absolute value of dispersion per unit length of the first optical fiber or the second optical fiber.

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