JP2007049486A - Optical transmission system and upgrade method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system capable of dealing with a higher transmission speed and capable of suppressing cost increase at the time of upgrade as much as possible.
An optical transmission system includes an optical transmission line and a transmitting station and a receiving station at both ends thereof, and transmits a signal having a plurality of wavelengths transmitted from the transmitting station to the receiving station. In the optical transmission system, the optical transmission path 20 includes a plurality of optical fibers 201 to 203 and repeaters 211 to 212 that connect the plurality of optical fibers 201 to 203. Dispersion compensators 103 and 303 are arranged only at 30, and no dispersion compensator is arranged in the optical transmission line 20.
[Selection] Figure 1

Description

  The present invention relates to an optical transmission system and an upgrade method thereof.

With the arrival of an advanced information society, optical transmission systems for realizing long-distance and large-capacity optical communication have been put into practical use. In this optical transmission system, a long distance in which the distance between the transmitting station and the receiving station exceeds 200 km is desired. When realizing such a long-distance optical transmission system, a repeater is provided in an optical transmission path between a transmitting station and a receiving station (see, for example, Patent Document 1 below).
Japanese Patent Laid-Open No. 11-204866

  In the optical transmission system described above, a single mode optical fiber having a dispersion of about 17 ps / nm / km is used as the optical transmission line. In such a single mode optical fiber, when the transmission speed is 10 Gbit / s, the influence of fiber dispersion becomes significant. At 10 Gbit / s, the limit value of cumulative dispersion (dispersion tolerance) for good transmission drops to approximately 1000 ps / nm, so even if a signal source with good chirp characteristics is provided at the transmission station, the transmission station and the reception The distance to the station is about 80 km.

  Therefore, when the distance between the transmitting station and the receiving station is longer, for example, about 200 km, a non-zero dispersion-shifted fiber having a moderately low dispersion or a dispersion compensator is provided in a repeater provided in the optical transmission line. Can be used.

  However, when a dispersion compensator is provided for each repeater, it is necessary to newly install a dispersion compensator when the dispersion compensator is not provided for each repeater in an existing optical transmission line. Furthermore, it is necessary to add an optical amplifier to compensate for the insertion loss of the dispersion compensator, leading to an increase in cost.

  In addition, when the transmission speed is upgraded to 40 Gbit / s, the dispersion tolerance decreases to 50 to 100 ps / nm. Therefore, even when a non-zero dispersion shifted fiber having a moderately low dispersion is used, transmission of about several kilometers is possible. It becomes a limit. Accordingly, it is necessary to compensate for each repeater with dispersion compensation.

  Therefore, an object of the present invention is to provide an optical transmission system that can cope with a higher transmission speed and that can suppress an increase in cost at the time of upgrade as much as possible, and an upgrade method thereof.

  An optical transmission system according to the present invention is an optical transmission system that includes a transmission station and a reception station at both ends of an optical transmission line, and transmits a signal having a plurality of wavelengths transmitted from the transmission station to the reception station, The optical transmission path is composed of a plurality of optical fibers and a repeater connecting the plurality of optical fibers, and a dispersion compensator is disposed only in at least one of the transmitting station and the receiving station. A dispersion compensator is not arranged.

  According to the present invention, since the dispersion compensator is arranged only in at least one of the transmitting station and the receiving station, the upgrade can be performed only by changing the transmitting station and the receiving station without changing the optical transmission path.

  In the optical transmission system according to the present invention, it is also preferable to disperse dispersion compensators in both the transmitting station and the receiving station. Since dispersion compensators are arranged at the transmitting station and the receiving station, dispersion compensation can be performed at both the transmitting station and the receiving station.

  In the optical transmission system according to the present invention, it is also preferable that the insertion loss of the dispersion compensator is 3 dB or less. Since the insertion loss of the dispersion compensator is 3 dB or less, an optical transmission system can be configured without adding an amplifier.

  In the optical transmission system according to the present invention, the dispersion compensator is preferably a dispersion compensating fiber. Since dispersion compensation is performed using a dispersion compensation fiber, dispersion compensation including a dispersion slope can be performed.

  In the optical transmission system according to the present invention, it is also preferable that the dispersion compensator has a variable compensation amount. Since the dispersion compensator is variable in compensation amount, it is possible to perform optimum dispersion compensation according to the state of the optical transmission line.

  In the optical transmission system according to the present invention, it is also preferable to adjust the compensation amount of the dispersion compensator according to the signal format. When the state of chromatic dispersion varies depending on the signal format, adjustment according to the chromatic dispersion is possible by adjusting the compensation amount according to the signal format.

  In the optical transmission system according to the present invention, it is also preferable that the dispersion value of the optical fiber at the used wavelength is 3 to 5 ps / nm / km. Since the dispersion value of the optical fiber at the used wavelength is 3 to 5 ps / nm / km, it is possible to suppress deterioration due to four-wave mixing and to avoid exceeding the dispersion tolerance.

  An upgrade method according to the present invention includes an optical transmission line and a transmission station and a reception station at both ends thereof, and transmits signals of an optical transmission system that transmits a signal having a plurality of wavelengths transmitted from the transmission station to the reception station. An upgrade method for increasing the transmission speed, comprising a compensator arrangement step in which a dispersion compensator is inserted and arranged only in at least one of a transmission station and a reception station, and no dispersion compensator is arranged in the optical transmission line It is characterized by.

  According to the present invention, since the dispersion compensator is not disposed in the optical transmission line, but is disposed only in the transmission station and the reception station, the optical transmission line system can be upgraded more easily.

  In the upgrade method according to the present invention, in the compensator arranging step, the dispersion compensator is arranged on the optical transmission line side with respect to the multiplexer arranged in the transmitting station, and the demultiplexing arranged in the receiving station. It is also preferable to arrange it on the optical transmission line side of the device. Since the dispersion compensator is disposed closer to the optical transmission line than the multiplexer and the demultiplexer, it is possible to perform dispersion compensation for a plurality of wavelengths collectively.

  Further, in the upgrade method according to the present invention, the optical transmission path is composed of a plurality of optical fibers and a repeater that connects the plurality of optical fibers, and is vacant in a portion through which signals in the transmitting station and the receiving station pass. When a coupler and a duplexer having a vacant coupler or port are arranged, a transmitter and a receiver that are faster than the transmitters and receivers already arranged in the transmitting station and the receiving station are transmitted. It is also preferable to provide a transceiver connection step for connecting to a coupler or a port arranged in the station and the receiving station, respectively. Since the transmitter and the receiver are connected to the coupler and the duplexer having a vacant coupler or port, the transmitter and the receiver can be added and upgraded without stopping the optical transmission system. .

  In the upgrade method according to the present invention, the signal bit rate is 9.8 to 12.6 Gbit / s generated using an external modulator before the transmitter / receiver connection step. It is also preferable that the dispersion value is 1000 ps / nm or less.

  In the upgrade method according to the present invention, it is also preferable that after the transmitter / receiver connection step, the signal bit rate is 9.8 to 12.6 Gbit / s and is generated using a direct modulation drive laser.

  According to the present invention, since the dispersion compensator is arranged only in at least one of the transmitting station and the receiving station, the upgrade can be performed only by changing the transmitting station and the receiving station without changing the optical transmission path.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown for illustration only. Subsequently, embodiments of the present invention will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals, and redundant description is omitted.

  A configuration of an optical transmission system according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of the optical transmission system 1. The optical transmission system 1 includes an optical transmission line 20 and a transmitting station 10 and a receiving station 30 provided at both ends thereof.

  The optical transmission line 20 includes optical fibers 201, 202, 203 and repeaters 211, 212. Each of the optical fibers 201, 202, and 203 is a non-zero dispersion shifted optical fiber (NZDSF: Non-Zero Dispersion Shifted Fiber) having a length of 80 km.

  When the dispersion values of the optical fibers 201, 202, and 203 are less than 3 ps / nm / km, deterioration due to four-wave mixing becomes significant. If the dispersion value of the optical fibers 201, 202, and 203 is larger than 5 ps / nm / km, the dispersion tolerance is exceeded in the 80 km, 3 span optical transmission line as in this embodiment. Therefore, it is preferable that the dispersion value at the used wavelength of the optical fibers 201, 202, and 203 is 3 to 5 ps / nm / km.

  The repeater 211 is a repeater that connects the optical fiber 201 and the optical fiber 202, and the repeater 212 is a repeater that connects the optical fiber 202 and the optical fiber 202. When used in the C or L band, the repeaters 211 and 212 are optical fiber amplifiers (EDFA: Erbium Doped Fiber Amplifier) using an optical fiber in which an Er element is added to the optical waveguide region as an optical amplification medium.

  Next, the transmission station 10 will be described. The transmitting station 10 is connected to the optical fiber 201 of the optical transmission line 20. The transmitting station 10 includes a WDM (WDM: Wavelength Division Multiplexing) transmitter 101, a multiplexer 102, a dispersion compensator 103, and a repeater 104. The WDM transmitter 101 is a wavelength division multiplexing optical transmitter that generates signal light having a predetermined wavelength by a semiconductor laser element.

  The multiplexer 102 combines the signal light output from the WDM transmitter 101 and outputs it to the dispersion compensator 103. In the present embodiment, the dispersion compensator 103 compensates the chromatic dispersion of the optical transmission line 20 in cooperation with the dispersion compensator 303 described later. The chromatic dispersion of the dispersion compensator 103 is formed so as to have a different sign from the chromatic dispersion of the optical transmission line 20. The repeater 104 is a repeater that connects the dispersion compensator 103 and the optical fiber 201.

  As the dispersion compensator 103, a dispersion compensating fiber having a fixed dispersion value such as a dispersion compensating fiber is preferably used. Further, those having variable dispersion values such as FBG (Fiber Bragg Grating), etalon, VIPA (Virtually Imaged Phased Array) are also preferably used. The insertion loss of the dispersion compensator 103 is preferably 3 dB or less. When the insertion loss is within this range, it is not necessary to add an amplifier due to the installation of the dispersion compensator 103. For example, when a dispersion compensation fiber is used as the dispersion compensator 103, assuming that the figure of merit (FOM) is 300 ps / nm / dB and the fusion loss is 0.5 dB / point, the dispersion compensation range is up to 600 ps / nm. In addition, when an etalon variable dispersion compensator is used as the dispersion compensator 103, there are some which can be adjusted within a range of ± 1700 ps / nm with an insertion loss of 3 dB or less, and thus, for example, a non-zero dispersion of 4 ps / nm / km If a dispersion-shifted optical fiber is used, transmission over 400 km becomes possible.

  Subsequently, the receiving station 30 will be described. The receiving station 30 is connected to the optical fiber 203 of the optical transmission line 20. The receiving station 30 includes a WDM receiver 301, a duplexer 302, a dispersion compensator 303, and a repeater 304. The repeater 304 is a repeater that connects the dispersion compensator 303 and the optical fiber 203. The repeater 304 outputs the signal light output from the optical fiber 203 to the dispersion compensator 303.

  The dispersion compensator 303 compensates for the chromatic dispersion of the optical transmission line 20 in cooperation with the dispersion compensator 103 described above. The chromatic dispersion of the dispersion compensator 303 is formed so as to have a different sign from the chromatic dispersion of the optical transmission line 20. As the dispersion compensator 303, like the dispersion compensator 103 described above, a dispersion compensation fiber having a fixed dispersion value is preferably used. Further, those having variable dispersion values such as FBG, etalon, and VIPA are also preferably used. The signal light that has been dispersion-compensated by the dispersion compensator 303 is output to the demultiplexer 302.

  The demultiplexer 302 demultiplexes the signal light output from the dispersion compensator 303 and outputs it to the WDM receiver 301. The WDM receiver 301 is a wavelength division multiplexing type optical receiver that receives signal light of a predetermined wavelength transmitted through the optical transmission line 20 by a photodiode and performs photoelectric conversion.

  When the dispersion compensators 103 and 303 are installed in the transmitting station 10 and the receiving station 30 as in this embodiment, the dispersion compensation state is as shown in FIG. As shown in FIG. 2, dispersion by the dispersion compensator 103 and the dispersion compensator 303 is performed so that the accumulated dispersion becomes near zero after transmission through the optical transmission line 20 including optical fibers 201, 202, 203 and repeaters 211, 212. Adjust the compensation rate. This is because if the dispersion compensation is performed in the transmitting station 10 and the receiving station 30 instead of in the optical transmission line 20 as in the present embodiment, the accumulated dispersion immediately after the transmitting station 10 and immediately before the receiving station 30 is large, and performance degradation due to nonlinearity is likely to occur. This is to minimize the influence.

  In addition, when the dispersion compensators 103 and 303 having variable dispersion values are used, it is possible to cope with a case where the signal format of the signal light is changed (for example, from the solid line to the broken line in FIG. 2). Change). In this case, the dispersion compensation amount needs to be adjusted so that the sum of the dispersion compensation amounts for transmission and reception becomes substantially constant while monitoring the quality of the received signal. In order to realize this, a control mechanism (not shown) for simultaneously changing the dispersion compensation amounts of the dispersion compensators 103 and 303 is introduced.

  Next, an optical transmission system upgrade method according to an embodiment of the present invention will be described with reference to FIG. FIG. 3 is a diagram for explaining a procedure for upgrading the optical transmission system 2. FIG. 3A shows a state before the upgrade. FIG. 3B shows the state of the compensator placement step and the transceiver connection step during the upgrade. FIG. 3C shows a state after the upgrade.

  As shown in FIG. 3A, the optical transmission system 2 includes an optical transmission path 20, and a transmission station 15 and a reception station 35 provided at both ends thereof. Since the optical transmission line 20 has already been described, description thereof is omitted here. The accumulated dispersion value of the optical transmission line 20 is 1000 ps / nm or less.

  The transmission station 15 is connected to the optical fiber 201 of the optical transmission line 20. The transmission station 15 includes a WDM transmitter 151, a multiplexer 152, and a repeater 154. The WDM transmitter 151 is a wavelength division multiplexing optical transmitter that generates signal light of a predetermined wavelength by a semiconductor laser element, and has a bit rate of 10 Gbit / s. The signal source uses an external modulator.

  The multiplexer 152 multiplexes the signal light output from the WDM transmitter 151 and outputs it to the repeater 154. The multiplexer 152 has ports for 10 channels, and the WDM transmitter 151 uses 5 channels. The repeater 104 is a repeater that connects the multiplexer 152 and the optical fiber 201.

  The receiving station 35 is connected to the optical fiber 203 of the optical transmission line 20. The receiving station 35 includes a WDM receiver 351, a duplexer 352, and a repeater 354. The repeater 354 is a repeater that connects the duplexer 352 and the optical fiber 203. The repeater 354 outputs the signal light output from the optical fiber 203 to the demultiplexer 352.

  The demultiplexer 352 demultiplexes the signal light output from the repeater 354 and outputs it to the WDM receiver 351. The duplexer 352 has ports for 10 channels, and the WDM transmitter 351 uses 5 channels. The WDM receiver 351 is a wavelength division multiplexing optical receiver that receives signal light of a predetermined wavelength transmitted through the optical transmission line 20 by a photodiode and performs photoelectric conversion.

  Subsequently, as shown in FIG. 3B, a WDM transmitter 155 and a dispersion compensator 153 are arranged in the transmitting station 15, and a WDM receiver 355 and a dispersion compensator 353 are arranged in the receiving station 35, respectively. More specifically, the bit rate of the WDM transmitter 155 and the WDM receiver 355 is 40 Gbit / s. The WDM transmitter 155 is connected to an available port of the multiplexer 152. The WDM receiver 355 is connected to an available port of the duplexer 352.

  The dispersion compensator 153 and the dispersion compensator 353 have the same configuration as the dispersion compensator 103 and the dispersion compensator 303 described with reference to FIG. The dispersion compensator 153 is inserted and disposed closer to the optical transmission line 20 than the multiplexer 152. The dispersion compensator 353 is inserted and disposed closer to the optical transmission line 20 than the duplexer 352.

  Subsequently, as illustrated in FIG. 3C, the transmitter 151 is removed from the transmission station 15, and the receiver 351 is deleted from the reception station 35. Therefore, the upgrade from the transmitter 151 and the receiver 351 having a bit rate of 10 Gbit / s to the transmitter 155 and the receiver 355 having a 40 Gbit / s is completed. In addition, when there is an overlap in the wavelength of the higher-speed transmitter / receiver upgraded with the existing transmitter / receiver, the existing transmitter / receiver having the target wavelength is replaced with a higher-speed transmitter / receiver.

  In FIG. 3, only one stage of the multiplexer 152 and the branching filter 352 is used, but these may be configured in a multistage configuration. An example is shown in FIG. FIG. 4 is a diagram illustrating a duplexer in the receiving station 35. In the example shown in FIG. 4, a duplexer 356 and a duplexer 357 are used in two stages. The duplexer 356 is an 8-channel wideband duplexer. The duplexer 357 is a 4-channel wideband duplexer. With such a configuration, for example, when there are finally 32 channels but only 4 channels are used at the beginning of construction, this can be dealt with by combining one duplexer 356 and one duplexer 357. When it is necessary to increase the number of channels thereafter, it is possible to increase the number of channels (A portion in FIG. 4) as appropriate by connecting the demultiplexer 357 to an empty port of the demultiplexer 356.

  Next, a different aspect of the optical transmission system upgrade method will be described with reference to FIG. FIG. 5 is a diagram for explaining a procedure for upgrading the optical transmission system 3. FIG. 5A shows a state before the upgrade. FIG. 5B shows the state of the compensator placement step and the transceiver connection step during the upgrade. FIG. 5C shows a state after the upgrade.

  As shown in FIG. 5A, the optical transmission system 3 includes an optical transmission line 20, and a transmission station 18 and a reception station 38 provided at both ends thereof. Since the optical transmission line 20 has already been described, description thereof is omitted here.

  The transmission station 18 is connected to the optical fiber 201 of the optical transmission line 20. The transmission station 18 includes a WDM transmitter 181, a multiplexer 182, a coupler 183, and a repeater 184. The WDM transmitter 181 is a wavelength division multiplexing optical transmitter that generates signal light of a predetermined wavelength by a semiconductor laser element, and has a bit rate of 10 Gbit / s. The signal source uses an external modulator.

  The multiplexer 182 multiplexes the signal light output from the WDM transmitter 181 and outputs it to the coupler 183. The coupler 183 is an optical element that couples light incident from two optical fibers into one optical fiber. In the case of FIG. 5A, one system is in an empty state. The repeater 184 is a repeater that connects the coupler 183 and the optical fiber 201.

  The receiving station 38 is connected to the optical fiber 203 of the optical transmission line 20. The receiving station 38 includes a WDM receiver 381, a duplexer 382, a coupler 383, and a repeater 384. The repeater 384 is a repeater that connects the coupler 383 and the optical fiber 203. The repeater 384 outputs the signal light output from the optical fiber 203 to the coupler 383.

  The coupler 383 is an optical element that splits the light incident from one optical fiber into two optical fibers. In the case of FIG. 5A, one system is vacant.

  The demultiplexer 382 demultiplexes the signal light output from the coupler 383 and outputs it to the WDM receiver 381. The WDM receiver 381 is a wavelength division multiplexing type optical receiver that receives signal light of a predetermined wavelength transmitted through the optical transmission line 20 by a photodiode and performs photoelectric conversion.

  Subsequently, as shown in FIG. 5B, the WDM transmitter 185, the multiplexer 186, and the dispersion compensator 187 are provided in the transmitting station 18, and the WDM receiver 385, the demultiplexer 386, and the dispersion are provided in the receiving station 38. Each compensator 387 is arranged. More specifically, the bit rate of the WDM transmitter 185 and the WDM receiver 385 is 40 Gbit / s.

  A multiplexer 186 is connected to the WDM transmitter 185 and further connected to a dispersion compensator 187. The dispersion compensator 187 is connected to the coupler 183. Further, a demultiplexer 386 is connected to the WDM receiver 385, and further connected to a dispersion compensator 387. The dispersion compensator 387 is connected to the coupler 383.

  The dispersion compensator 187 and the dispersion compensator 387 have the same configuration as the dispersion compensator 103 and the dispersion compensator 303 described with reference to FIG. The dispersion compensator 187 is inserted and arranged closer to the optical transmission line 20 than the multiplexer 186. The dispersion compensator 387 is inserted and disposed closer to the optical transmission line 20 than the demultiplexer 386.

  Subsequently, as shown in FIG. 5C, the transmitter 181 is removed from the transmission station 18, and the receiver 381 is deleted from the reception station 38. Therefore, the upgrade from the transmitter 181 and the receiver 381 having a bit rate of 10 Gbit / s to the transmitter 185 and the receiver 385 having a 40 Gbit / s is completed. In addition, if there is an overlap in the wavelength of the higher-speed transmitter / receiver that is upgraded with the existing transmitter / receiver, the existing transmitter / receiver having the target wavelength is stopped or replaced with a higher-speed transmitter / receiver. To do.

  According to the upgrade method described with reference to FIG. 5, the transmitter 185 and the receiver 385 can be connected without stopping the transmitter 181 and the receiver 381, so that the existing low-speed system is not stopped. Upgrade to a high-speed system is possible. Further, since the signal light transmitted from the transmitter 185 is distorted by the dispersion compensator 187, the influence of the signal light transmitted from the transmitter 181 can be reduced, such as cross-phase modulation and four-wave mixing. Can be reduced.

  The upgrade method described above is generated using an external modulator with a signal bit rate of 9.8 to 12.6 Gbit / s before the transmitter / receiver connection step. The case where the dispersion value is 1000 ps / nm or less is exemplified. On the other hand, after the transmitter / receiver connection step, the upgrade method described above can be applied even when the signal bit rate is 9.8 to 12.6 Gbit / s and is generated using a direct modulation drive laser. .

It is a figure which shows the structure of the optical transmission system which concerns on this embodiment. It is a figure for demonstrating the effect | action of the dispersion compensator shown in FIG. It is a figure for demonstrating the upgrade method of the optical transmission system which concerns on this embodiment. It is a figure for demonstrating the upgrade method of the optical transmission system which concerns on this embodiment. It is a figure for demonstrating the upgrade method of the optical transmission system which concerns on this embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Optical transmission system, 10 ... Transmitting station, 20 ... Optical transmission line, 30 ... Receiving station, 101 ... WDM transmitter, 102 ... Multiplexer, 103 ... Dispersion compensator, 104 ... Repeater, 201, 202, 203 DESCRIPTION OF SYMBOLS ... Optical fiber, 211, 212 ... Repeater, 301 ... WDM receiver, 302 ... Demultiplexer, 303 ... Dispersion compensator, 304 ... Repeater.

Claims (12)

An optical transmission system comprising a transmission station and a reception station at both ends of an optical transmission line, and transmitting a signal having a plurality of wavelengths transmitted from the transmission station to the reception station,
The optical transmission line is composed of a plurality of optical fibers and a repeater connecting the plurality of optical fibers,
An optical transmission system, wherein a dispersion compensator is disposed only in at least one of the transmitting station and the receiving station, and no dispersion compensator is disposed in the optical transmission path. The optical transmission system according to claim 1, wherein the dispersion compensator is arranged in both the transmitting station and the receiving station. The optical transmission system according to claim 1 or 2, wherein an insertion loss of the dispersion compensator is 3 dB or less. The optical transmission system according to claim 1, wherein the dispersion compensator is a dispersion compensating fiber. The optical transmission system according to claim 1, wherein the dispersion compensator has a variable amount of compensation. 6. The optical transmission system according to claim 5, wherein a compensation amount of the dispersion compensator is adjusted according to a signal format of the signal. The optical transmission system according to claim 1, wherein a dispersion value of the optical fiber at a used wavelength is 3 to 5 ps / nm / km. Increasing the speed at which the signal is transmitted in an optical transmission system having a transmission station and a receiving station at both ends of the optical transmission line and transmitting to the receiving station a signal having a plurality of wavelengths transmitted from the transmitting station Upgrade method for
An upgrade method, comprising: a compensator arranging step in which a dispersion compensator is inserted and arranged only in at least one of the transmitting station and the receiving station, and no dispersion compensator is arranged in the optical transmission line. In the compensator arranging step, the dispersion compensator is arranged on the optical transmission line side with respect to the multiplexer arranged in the transmitting station, and the optical compensator is arranged more than the demultiplexer arranged in the receiving station. The upgrade method according to claim 8, wherein the upgrade method is arranged on a transmission line side. The optical transmission line is composed of a plurality of optical fibers and a repeater connecting the plurality of optical fibers,
A coupler and a duplexer having a vacant coupler or port in a portion where the signal in the transmitting station and the receiving station passes are arranged,
A transmitter and a receiver that are faster than the transmitter and receiver that are already arranged in the transmitting station and the receiving station are connected to the coupler or the port that are arranged in the transmitting station and the receiving station, respectively. The upgrade method according to claim 8, further comprising a transceiver connection step. Before the transceiver connection step, the signal is generated using an external modulator at a bit rate of 9.8 to 12.6 Gbit / s, and the accumulated dispersion value of the optical transmission line is 1000 ps / nm. The upgrade method according to claim 8, wherein the upgrade method is as follows. 11. The method according to claim 8, wherein after the transceiver connection step, the signal is generated using a direct modulation drive laser at a bit rate of 9.8 to 12.6 Gbit / s. The upgrade method according to claim 1.

Images