JP2013141159A - Wavelength multiplexed optical transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To avoid degradation in transmission characteristics of a normal signal when a transmission line fault occurs in a wavelength multiplexed optical transmission system.SOLUTION: A wavelength multiplexed optical transmission system comprises optical terminal devices 200, 300 and 400 which transmit and receive wavelength multiplexed signals in plural wavelength bands and an optical branch and insertion device 100. The optical branch and insertion device 100 includes: an optical branch unit 110 which branches input light from the optical terminal device 200; an optical branch unit 130 which branches input light from the optical terminal device 300; an optical power monitor unit 140 which monitors the optical power of light branched by the optical branch unit 130; and an optical path selection unit 120 which, when the optical power monitored by the optical power monitor unit 140 is smaller than a predetermined value, selects input light from the optical branch unit 110 in place of the input light from the optical branch unit 130 for the light to be output to the optical terminal device 400. The optical terminal device 300 includes an optical power adjustment unit 310 which adjusts the optical power to be transmitted to the optical terminal device 400 to a constant level.

Description

The present invention relates to a wavelength division multiplexing optical transmission system, and more particularly to an OADM (Optical Add / Drop Multiplexer) wavelength division multiplexing transmission system.

FIG. 13 is a diagram illustrating a configuration of a general OADM wavelength division multiplexing optical transmission system. In FIG. 13, the wavelength division multiplexing transmission system includes optical terminal devices 20 and 40 connected to the optical add / drop multiplexer 10 via trunk lines 50 and 70 serving as system trunk lines, and a branch line 60 serving as a branch line. The optical add / drop device 30 is connected to the optical add / drop device 10. Generally, the trunk lines 50 and 70 and the branch line 60 are provided with optical repeaters (not shown).

Here, there is a technique described in Patent Document 1 as an example of a countermeasure against a transmission path failure in an OADM wavelength division multiplexing transmission system. In the description of Patent Document 1, an optical add / drop device detects a transmission path failure between a branch station and an optical add / drop device by monitoring signal light input from the branch station to the optical add / drop device. Switch the optical path in the insertion device. Thereby, it is possible to prevent the deterioration of the transmission characteristics when a failure occurs in the branch line.

International Publication No. 2004/088893

However, the transmission path failure is not limited to the branch line, but can also occur in the transmission-side trunk line (transmission-side trunk line 50 shown in FIG. 13) that connects the optical terminal equipment on the transmission side and the optical add / drop multiplexer. In this case, only the signal in the wavelength band transmitted from the branch line is transmitted to the receiving trunk line (receiving trunk line 70 shown in FIG. 13). Therefore, the total power of light output from the optical add / drop device is reduced. Here, in general, an optical amplifier such as an EDFA (Erbium-Doped Optical Fiber Amplifier) in a receiving-side trunk line repeater or the like is controlled with constant pumping light, and the output optical power is reduced even when the input optical power is lowered. It becomes almost constant. Therefore, if the optical power is amplified so that the total power of the wavelength multiplexed light becomes constant by a repeater of the receiving trunk line connecting the receiving optical terminal device and the optical add / drop multiplexer, the normal wavelength band is Amplified excessively. As a result, the optical power in the normal wavelength band is excessively increased and is easily affected by the nonlinear effect, and the transmission characteristics are deteriorated.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a wavelength division multiplexing optical transmission system capable of preventing deterioration of transmission characteristics of normal optical signals even when a transmission line failure occurs in either a transmission side trunk line or a branch line. Is to provide.

According to the present invention, a first optical terminal device that transmits wavelength multiplexed optical signals in a plurality of wavelength bands;
A second optical terminal device that transmits and receives a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals transmitted by the first optical terminal device;
A third optical terminal device that receives a wavelength-multiplexed optical signal transmitted by the second optical terminal device;
An optical add / drop multiplexer connected to the first to third optical terminal devices via an optical transmission line;
The optical add / drop device includes:
A first optical branching unit that branches input light from the first optical terminal device and outputs the branched light to the second optical terminal device;
A second optical branching unit for branching input light from the second optical terminal device;
An optical power monitor for monitoring the optical power of the light branched by the second optical branch;
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, the first light is output as the light output to the third optical terminal device instead of the input light from the second optical branching unit. An optical path selection unit that selects input light from the branch unit,
The second optical terminal device is:
There is provided a wavelength division multiplexing optical transmission system including an optical power adjustment unit that adjusts the optical power of a wavelength division multiplexed optical signal transmitted to the third optical terminal device to be constant.

According to the present invention, even when a transmission line failure occurs in either the transmission-side trunk line or the branch line, it is possible to suppress power fluctuations of normal signals and prevent transmission characteristic deterioration due to nonlinear effects.

It is a figure which shows the structure of the OADM wavelength division multiplexing optical transmission system of the 1st Embodiment of this invention. It is a figure which shows the structure of the optical add / drop device in the OADM wavelength division multiplexing optical transmission system of the 2nd Embodiment of this invention. It is a figure which shows the structure of the optical terminal station apparatus of a branch station in the OADM wavelength multiplexing optical transmission system of the 2nd Embodiment of this invention. It is a sequence diagram which shows the operation | movement at the normal time in the OADM wavelength multiplexing optical transmission system of the 2nd Embodiment of this invention. It is a figure which shows the flow of the optical signal at the time of normal in the OADM wavelength division multiplexing transmission system of the 2nd Embodiment of this invention. It is a sequence diagram which shows the operation | movement when a failure generate | occur | produces in the transmission side trunk line in the OADM wavelength division multiplexing optical transmission system of the 2nd Embodiment of this invention. It is a figure which shows the flow of the optical signal when a failure generate | occur | produces in the transmission side trunk line in the OADM wavelength division multiplexing optical transmission system of the 2nd Embodiment of this invention. FIG. 10 is a sequence diagram illustrating an operation when a failure occurs in a branch line in the OADM wavelength division multiplexing optical transmission system according to the second exemplary embodiment of the present invention. It is a figure which shows the flow of the optical signal when the failure generate | occur | produces in the branch line in the OADM wavelength division multiplexing optical transmission system of the 2nd Embodiment of this invention. It is a figure which shows the structure of the optical add / drop apparatus in the OADM wavelength multiplexing optical transmission system of the 3rd Embodiment of this invention. It is a figure which shows the structure of the optical add / drop device in the OADM wavelength division multiplexing optical transmission system of the 4th Embodiment of this invention. It is a figure which shows the structure of the optical terminal device of a branch station in the OADM wavelength division multiplexing optical transmission system of the 5th Embodiment of this invention. It is a figure which shows the structure of a general OADM wavelength division multiplexing optical transmission system.

(First embodiment)
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a wavelength division multiplexing optical transmission system according to the first embodiment. The wavelength division multiplexing optical transmission system of FIG. 1 transmits an optical terminal device 200 that transmits wavelength multiplexed optical signals in a plurality of wavelength bands, and a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals that the optical terminal device 200 transmits. Are connected to the optical terminal devices 300, 300, and 400 through optical transmission lines. The optical add / drop multiplexer 100 includes an optical add / drop unit 110 that branches input light from the optical terminal device 200 and outputs the branched light to the optical terminal device 300, and the optical terminal device 300. The optical branching unit 130 for branching the input light, the optical power monitoring unit 140 for monitoring the optical power of the light branched by the optical branching unit 130, and the optical power monitored by the optical power monitoring unit 140 is smaller than a predetermined value Optical terminal equipment 4 The light output to 0 includes an optical path selection unit 120 that selects input light from the optical branching unit 110 instead of input light from the optical branching unit 130, and the optical terminal device 300 is an optical terminal device 400. The wavelength multiplexing optical transmission system includes an optical power adjustment unit 310 that adjusts the optical power of the wavelength multiplexing optical signal to be transmitted to a constant.

According to this embodiment, even if a transmission line failure occurs in either the transmission trunk line 500 or the branch line 600, the power of the optical signal in the normal wavelength band is kept constant, and the transmission characteristics are deteriorated due to the nonlinear effect. Can be prevented.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. The present embodiment differs from the configuration of FIG. 1 in the configuration of the optical add / drop multiplexer 100 and the optical terminal device 300. FIG. 2 is a diagram illustrating a configuration of the optical add / drop multiplexer 100 according to the present embodiment. 2, the optical add / drop multiplexer 100 includes an optical add / drop unit 110, an optical path switching unit 121, an optical path control unit 122, an optical add / drop unit 130, and an optical power monitor unit 140. Here, the optical path switching unit 121 and the optical path control unit 122 illustrated in FIG. 2 correspond to the optical path selection unit 120 in FIG. 1. The optical branching unit 110 branches light input from the transmission-side trunk line 500 to the optical path switching unit 121 and the branch line 600. The optical branching unit 130 branches an optical signal input from the branch line 600 to the optical path switching unit 121 and the optical power monitoring unit 140. The light input to the optical power monitor unit 140 is converted into an electrical signal, and the converted electrical signal is input to the optical path control unit 122. The optical path control unit 122 controls the optical path switching unit 121 to switch the light output to the reception-side trunk line 700 between the light from the optical branching unit 110 and the light from the optical branching unit 130. In this embodiment, the trunk lines 500 and 700 and the branch line 600 in FIG. 1 include optical repeaters (not shown), and the optical repeaters include optical amplifiers such as EDFAs.

FIG. 3 is a diagram illustrating a configuration of the optical terminal device 300 according to the present embodiment. The optical terminal device 300 includes an optical amplifying unit 311, an optical branching unit 320, a variable filter 312, an optical coupling unit 330, an optical demultiplexing unit 341, and a plurality of optical receiving nodes 342-1 to 342-n. The optical receiver 340 includes an optical multiplexer 351 and an optical transmitter 350 having a plurality of optical transmission nodes 352-1 to 352-n. Here, the optical amplification unit 311 and the variable filter 312 shown in FIG. 3 correspond to the optical power adjustment unit 310 in FIG. The optical amplifying unit 311 amplifies light input from the branch line 600. The optical branching unit 320 branches the light input from the optical amplification unit 311, one to the variable filter 312 and the other to the optical demultiplexing unit 341. The variable filter 312 transmits a limited wavelength band of the light from the optical branching unit 320 while limiting the band (transmission wavelength band) to one of the optical coupling units 330. The wavelength demultiplexing unit 341 separates a specific wavelength band in the light from the optical branching unit 320 (separated wavelength band), and demultiplexes each wavelength unit of WDM (Wavelength Division Multiplex) communication. Each of the optical reception nodes 342-1 to 342-n receives the optical signals of the respective wavelengths that have been demultiplexed. Each of the optical transmission nodes 352-1 to 352-n transmits an optical signal having a wavelength corresponding to the wavelength of the optical signal received by the optical reception nodes 342-1 to 342-n. The wavelength combining unit 351 combines the optical signals having a plurality of wavelengths transmitted from the respective optical transmission nodes 352-1 to 352-n, and outputs them to one of the optical coupling units 330. The light coupled by the optical coupling unit 330 is output to the branch line 600. Here, it is assumed that the variable filter is a device capable of arbitrarily setting light blocking / transmission with high resolution in response to LCOS (Liquid Cystal On Silicon) technology used in liquid crystal televisions or the like. If there is something that satisfies the equivalent performance, it can be replaced.

Next, the operation of the wavelength division multiplexing optical transmission system according to this embodiment will be described. FIG. 4 is a sequence diagram illustrating an operation in a normal time when no transmission path failure occurs. FIG. 5 is a diagram showing the flow of signals in each wavelength band during normal operation together with the configuration of the present embodiment. Here, in the wavelength division multiplexing optical transmission system, the transmitting trunk station and the receiving trunk station are stations installed at the end of the trunk line, and the branch station is a station installed at the end of the branch line. Explained. In this embodiment, the wavelength division multiplexing optical transmission system is a transmission / reception bidirectional communication, and the transmission-side trunk station and the reception-side trunk station have transmission / reception functions. However, since the uplink system and the downlink system in bidirectional communication are target configurations, the present embodiment will be described on the assumption that the transmission-side trunk station is the transmission side and the reception-side trunk station is the reception side. The optical terminal device 200 of the transmission-side trunk station will be described by taking as an example a case where wavelength multiplexed light in which optical signals of a plurality of wavelength bands a to c are combined is transmitted.

First, the optical terminal device 200 provided in the transmission-side trunk station transmits an optical signal in which the wavelength bands a to c are wavelength-multiplexed to the optical add / drop multiplexer 100 (steps S1a and S2a). The optical add / drop multiplexer 100 branches the optical signals in the wavelength bands a to c transmitted from the optical terminal device 200, and transmits the optical signals to the optical terminal device 300 included in the branch station (step S3a). Here, in the optical add / drop multiplexer 100, the optical branching unit 110 shown in FIG. 2 branches the optical signals in the wavelength bands a to c input from the transmission-side trunk line to the branch line 600.

  The optical terminal apparatus 300 outputs the optical signal input from the branch line to the branch line 600 with the total optical power being fixed by the optical amplifying unit 311 and the variable filter 312 shown in FIG. Here, the optical amplifying unit 311 amplifies and outputs the optical signal input from the branch line to the optical terminal device 300 so that the total optical power becomes a constant value (step S4a).

  Further, the variable filter 312 limits the band of the optical signal input from the optical branching unit 320, thereby reducing the power of the separation wavelength band a to a predetermined value or less, and at the same time, the total optical output of the wavelength bands other than the separation wavelength band a. The power is made constant (step S5a).

The optical terminal station 300 outputs an optical signal to the optical add / drop multiplexer 100 (step S6a). At this time, since the optical signal is normally input to the optical add / drop multiplexer 100, the optical power monitor 140 detects a predetermined optical power (step S7a). At this time, the optical path control unit 122 determines that the branch line is normal and transmits a normal determination signal to the optical path switching unit 121. Receiving the normality determination signal, the optical path switching unit 121 connects the branch line 600 to the receiving trunk line 700 (step S8a).

  The optical add / drop multiplexer 100 outputs an optical signal to the optical terminal device 400 of the receiving trunk station (step S9a). At this time, the optical terminal apparatus 400 receives optical signals in the wavelength bands a to c (S12a). In addition, the optical terminal device 200 again outputs an optical signal in which the wavelength bands a to c are wavelength-multiplexed to the optical add / drop multiplexer 100 (step S10a). Since the optical add / drop multiplexer 100 connects the branch line 600 to the receiving trunk line 700, the optical add / drop multiplexer 100 outputs an optical signal to the optical terminal apparatus 300 of the branch station (step S11a).

  Next, the operation when a transmission failure occurs in the transmission-side trunk line 500 in the wavelength division multiplexing transmission system according to the present embodiment will be described. FIG. 6 is a sequence diagram showing an operation when a transmission failure occurs in the transmission-side trunk line 500. FIG. 7 is a diagram showing a signal flow in each wavelength band when a transmission failure occurs in the transmission-side trunk line 500 together with the configuration of the present embodiment.

The optical terminal device 200 provided in the transmission-side trunk station transmits an optical signal in which the wavelength bands a to c are wavelength-multiplexed to the optical add / drop multiplexer 100 (step S1b). However, an optical signal to be input to the optical add / drop multiplexer 100 from the transmission side trunk line 500 is not input because the transmission failure blocks the optical signal transmitted through the transmission side trunk line 500 (step S2b). Therefore, the optical add / drop multiplexer 100 cannot output an optical signal to the optical terminal device 300.

  Since no optical signal is input to the optical terminal device 300, no optical signal is input to the optical amplifying unit 311 illustrated in FIG. When no optical signal is input to the optical amplifying unit 311, the optical amplifying unit 311 loses a target to be optically amplified, so that the optical power for outputting so that the total optical power becomes a constant value is insufficient. At this time, the optical amplifying unit 311 compensates for the shortage of optical power by emitting ASE (Amplified Spontaneous Emission) light (step S4b).

  Then, the variable filter 312 limits the band of the optical signal input from the optical branching unit 320, thereby reducing the power of the separation wavelength band a to a predetermined value or less, and at the same time, the total optical output of the wavelength bands other than the separation wavelength band a. The power is made constant (step S5b). Since the band-limited light is combined with the optical signal of the separation wavelength band a in the optical coupling unit 330, the total power of the light output from the optical terminal device 300 to the branch line 600 is the same level as in normal time. Can be adjusted.

  The optical terminal apparatus 300 outputs an optical signal to the optical add / drop multiplexer 100 (step S6b). At this time, since the same level of optical power as that in the normal state is input to the optical add / drop multiplexer 100, the optical power monitor unit 140 detects a predetermined optical power (step S7b). At this time, the optical path control unit 122 determines that the branch line is normal and transmits a normal determination signal to the optical path switching unit 121. Receiving the normality determination signal, the optical path switching unit 121 connects the branch line 600 to the receiving trunk line 700 (step S8a).

  The optical add / drop multiplexer 100 outputs an optical signal to the optical terminal device 400 of the receiving trunk station (step S9b). At this time, the optical terminal device 400 cannot receive the transmission wavelength bands b and c because it is not a normal optical signal, but the separated wavelength band a is normally transmitted without being influenced by the nonlinear effect. Since it is an optical signal, it can be received (step S12b). Since a transmission failure has occurred in the transmitting trunk line 500, the optical signal transmitted from the optical end device 200 is not yet input to the optical add / drop multiplexer 100 (step S10b).

  Next, an operation when a transmission failure occurs in the branch line 600 in the wavelength division multiplexing transmission system according to the present embodiment will be described. FIG. 8 is a sequence diagram showing an operation when a transmission failure occurs in the branch line 600. FIG. 9 is a diagram showing a signal flow in each wavelength band when a transmission failure occurs in the branch line 600 together with the configuration of the present embodiment. The optical terminal device 200 included in the transmission-side trunk station transmits an optical signal in which the wavelength bands a to c are wavelength-multiplexed to the optical add / drop multiplexer 100 (steps S1a and S2a).

  The optical add / drop multiplexer 100 branches the optical signals in the wavelength bands a to c transmitted from the optical terminal device 200 and transmits the optical signals to the optical terminal device 300 included in the branch station. However, since the transmission failure blocks the optical signal transmitted through the branch line 600, the signal light to be input from the branch line 600 to the optical terminal device 300 is not input (step S3c).

Therefore, since no optical signal is input to the optical terminal device 300, no optical signal is input to the optical amplifying unit 311 shown in FIG. As described above, when an optical signal is not input to the optical amplifying unit 311, the optical amplifying unit 311 emits ASE light (step S4c). The variable filter 312 limits the band of the optical signal input from the optical branching unit 320 so that the power of the separation wavelength band a is equal to or lower than a predetermined value, and at the same time, the total optical output of wavelength bands other than the separation wavelength band a. The power is made constant (step S5c).

  The optical terminal station 300 outputs an optical signal to the optical add / drop multiplexer 100. However, since the transmission failure blocks the optical signal transmitted through the branch line 600, the signal light to be input from the branch line 600 to the optical add / drop multiplexer 100 is not input (step S6c). At this time, since the optical signal is not normally input to the optical add / drop multiplexer 100, the optical power monitor unit 140 does not detect the predetermined optical power (step S7c). At this time, the optical path control unit 122 determines that a failure has occurred in the branch line, and transmits a failure determination signal to the optical path switching unit 121. Receiving the failure determination signal, the optical path switching unit 121 connects the transmission-side trunk line 500 to the reception-side trunk line 700 (step S8c).

  The optical edge device 200 again transmits the optical signal in which the wavelength bands a to c are wavelength-multiplexed to the optical add / drop device 100 (step S10c). Since the optical add / drop multiplexer 100 connects the transmitting trunk line 500 to the receiving trunk line 700, the optical add / drop multiplexer 100 outputs an optical signal to the optical terminal apparatus 400 of the receiving trunk station. (Step S11c). In this case, the optical terminal device 400 cannot receive the separated wavelength band a because it is not a normal optical signal, but the transmitted wavelength bands b and c are normally transmitted without being affected by the nonlinear effect. Since it is an optical signal, it can be received (step S12c).

  As described above, according to the present embodiment, as in the first embodiment, even if a transmission path failure occurs in either the transmission-side trunk line 500 or the branch line 600, the optical signal in the normal wavelength band It is possible to obtain an effect of keeping power constant and preventing deterioration of transmission characteristics due to a nonlinear effect. When a transmission line failure occurs in the transmission-side trunk line 500, the optical terminal device 300 provided in the branch station outputs the total optical power at a constant level. When a transmission line failure occurs in the branch line 600, This is because the optical add / drop multiplexer 100 outputs the optical signal from the transmission-side trunk line 500 to the reception-side trunk line 700, so that a signal in a normal wavelength band can be transmitted without being excessively amplified.

  In the variable filter 312, the wavelength range of the filter may be set according to the channel group to be transmitted instead of the channel unit. Since all the extracted ASE light can be efficiently used as light for compensating for the shortage of optical power, power loss can be reduced as compared with a method of cutting out ASE light in channel units.

(Third embodiment)
Next, a third embodiment of the present invention will be described. The present embodiment is different from the second embodiment in the configuration of the optical add / drop multiplexer 100. Hereinafter, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 10 is a diagram illustrating a configuration of the optical add / drop multiplexer 100a according to the present embodiment. In FIG. 10, an optical switch 123 corresponds to the optical path switching unit 121 in FIG. The optical path control unit 122 outputs a normal determination signal or a failure determination signal to the optical switch 123. When receiving the normality determination signal, the optical switch 123 physically connects the branch line 600 to the receiving trunk line 700, and physically separates the transmitting trunk line 500 and the receiving trunk line 700. Further, when receiving the failure determination signal, the optical switch 123 physically connects the transmission-side trunk line 500 to the reception-side trunk line 700 and physically divides it into the branch line 600 and the reception-side trunk line 700.

  As described above, the optical path can be switched using the optical switch. According to the present embodiment, as in the first and second embodiments, the power of an optical signal in a normal wavelength band can be increased regardless of whether a transmission path failure occurs in either the transmission-side trunk line 500 or the branch line 600. It is possible to obtain an effect of keeping constant and preventing deterioration of transmission characteristics due to a nonlinear effect.

(Fourth embodiment)
Next, a fourth embodiment of the present invention will be described. The present embodiment is different from the second embodiment in the configuration of the optical add / drop multiplexer 100. Hereinafter, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 11 is a diagram illustrating a configuration of the optical add / drop multiplexer 100b according to the present embodiment. In FIG. 11, two variable optical attenuators 124 and 125 and an optical coupling unit 126 correspond to the optical path switching unit 121 in FIG. The variable optical attenuator 124 is arranged between the optical branching unit 110 and the optical coupling unit 126, and the variable optical attenuator 125 is arranged between the optical branching unit 130 and the optical coupling unit 126.

  The optical path control unit 122 outputs a signal for controlling the attenuation amount to the variable optical attenuators 124 and 125. When the branch line 600 is connected to the reception-side trunk line 700, the optical path control unit 122 sends a control signal that minimizes the amount of attenuation to the variable optical attenuator 124 and a control signal that maximizes the amount of attenuation to the variable optical attenuator. It outputs to 125. When the transmission side trunk line 500 is connected to the reception side trunk line 700, the optical path control unit 122 supplies the control signal that minimizes the attenuation to the variable optical attenuator 125 and the control signal that maximizes the attenuation to the variable light. Output to the attenuator 124.

  As described above, the optical path can be switched using the two variable optical attenuators and the optical coupling unit. According to the present embodiment, as in the first to third embodiments, the power of an optical signal in a normal wavelength band is kept constant regardless of whether a transmission path failure occurs in either the transmission-side trunk line 500 or the branch line 600. Thus, an effect of preventing deterioration of transmission characteristics due to a nonlinear effect can be obtained.

(Fifth embodiment)
Next, a fifth embodiment of the present invention will be described. The present embodiment is different from the second embodiment in the configuration of the optical terminal device 300 provided in the branch station. Hereinafter, the same components as those in the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

FIG. 12 is a diagram illustrating a configuration of the optical terminal device 300a according to the present embodiment. In FIG. 12, an optical amplification unit 311, a variable filter 312, and a filter control unit 313 correspond to the optical power adjustment unit 310 in FIG. The filter control unit 313 acquires the wavelength band information and the optical power information received by the optical reception unit 340, determines the band of the variable filter 312 from the acquired information, and outputs a signal for controlling the band to the variable filter 312. To do. The variable filter 312 band-limits the optical signal input from the optical branching unit 320 according to the signal from the filter control unit 313, thereby reducing the power of the separation wavelength band a to a predetermined value or less, and at the same time, the separation wavelength band a. Keep the total optical output power in the other wavelength bands constant.

  As described above, according to the present embodiment, as in the first to fourth embodiments, even if a transmission path failure occurs in either the transmission-side trunk line 500 or the branch line 600, the light in the normal wavelength band It is possible to obtain the effect of keeping the signal power constant and preventing the deterioration of the transmission characteristics due to the nonlinear effect. Furthermore, in order to acquire the wavelength band information and the optical power information received by the optical receiving unit 340 and determine the band of the variable filter 312 from the acquired information, the variable filter 312 has changed in the used wavelength band in the system. In this case, it is possible to limit the bandwidth appropriately.

  The embodiments described above are examples of the present invention, and various configurations other than those shown in the embodiments can be taken in the present invention.

(Other expressions of the embodiment)
Some or all of the embodiments described above can be described as in the following supplementary notes, but are not limited thereto.

(Appendix)
(Appendix 1)
A first optical terminal device that transmits wavelength-multiplexed optical signals in a plurality of wavelength bands;
A second optical terminal device that transmits and receives a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals transmitted by the first optical terminal device;
A third optical terminal device that receives a wavelength-multiplexed optical signal transmitted by the second optical terminal device;
An optical add / drop multiplexer connected to the first to third optical terminal devices via an optical transmission line;
The optical add / drop device includes:
A first optical branching unit that branches input light from the first optical terminal device and outputs the branched light to the second optical terminal device;
A second optical branching unit for branching input light from the second optical terminal device;
An optical power monitor for monitoring the optical power of the light branched by the second optical branch;
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, the first light is output as the light output to the third optical terminal device instead of the input light from the second optical branching unit. An optical path selection unit that selects input light from the branch unit,
The second optical terminal device is:
A wavelength division multiplexing optical transmission system, comprising: an optical power adjustment section that adjusts the optical power of a wavelength division multiplexed optical signal to be transmitted to the third optical terminal device to be constant.
(Appendix 2)
The optical path selector is
When the optical power monitored by the optical power monitor unit is smaller than a predetermined value, an optical path control unit that outputs a fault determination signal;
Light that switches light output to the third optical terminal device from input light from the second optical branching unit to input light from the first optical branching unit when the fault determination signal is input The wavelength division multiplexing optical transmission system according to appendix 1, further comprising: a path switching unit.
(Appendix 3)
The second optical terminal device is:
An optical amplifying unit for amplifying light input from the optical branching device or emitting ASE light to output light of constant power to the optical branching unit;
An optical branching unit for branching the light input from the optical amplification unit;
An optical receiver that demultiplexes and receives an optical signal in a predetermined wavelength band of the light input from the optical branching unit;
Of the light input from the optical branching unit, the power of the light in the predetermined wavelength band is a predetermined value or less, a variable filter that makes the optical power of the wavelength band excluding the predetermined wavelength band constant,
An optical transmitter that multiplexes and transmits an optical signal having the same wavelength as the optical signal received by the optical receiver;
The wavelength division multiplexing optical transmission system according to appendix 1, further comprising: an optical coupling unit that multiplexes the input from the variable filter and the input from the optical transmission unit and outputs the multiplexed signal to the optical add / drop multiplexer. .
(Appendix 4)
The wavelength division multiplexing optical transmission system according to appendix 2, wherein the optical path switching unit is an optical switch having a function of physically switching a connection combination of input and output.
(Appendix 5)
The optical path switching unit is
A first optical variable attenuator that attenuates light input from the first optical branching unit;
A second optical variable attenuator for attenuating light input from the second optical branching unit;
A second optical coupling unit that couples light input from the first and second optical variable attenuators and outputs the coupled light to the output of the optical add / drop device;
The optical path controller is
When the optical power monitored by the optical power monitor unit is equal to or greater than a predetermined value, a control signal for maximizing the attenuation is output to the first optical variable attenuator, and a control signal for minimizing the attenuation is transmitted to the first optical attenuator. 2 to the optical variable attenuator
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, a control signal for maximizing the attenuation is output to the second optical variable attenuator, and the control signal for minimizing the attenuation is the first signal. The wavelength division multiplexing optical transmission system as set forth in appendix 2, wherein the output is output to a single optical variable attenuator.
(Appendix 6)
The wavelength according to appendix 3, wherein the second optical terminal device includes a filter control unit that outputs a predetermined control signal to the variable filter according to the wavelength and optical power of the optical receiving unit. Multiplex optical transmission system.
(Appendix 7)
A first optical terminal device that transmits wavelength-multiplexed optical signals in a plurality of wavelength bands;
A second optical terminal device that transmits and receives a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals transmitted by the first optical terminal device;
A third optical terminal device that receives a wavelength-multiplexed optical signal transmitted by the second optical terminal device;
An optical transmission method in a wavelength division multiplexing optical transmission system comprising the first to third optical terminal devices and an optical add / drop multiplexer connected via an optical transmission line,
The optical add / drop device includes:
Branching the input light from the first optical terminal device and outputting it to the second optical terminal device;
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, the light output to the third optical terminal device is replaced with the input light from the second optical branching unit. Select the input light from the branch,
The second optical terminal device is:
An optical transmission method characterized in that the optical power of a wavelength division multiplexed optical signal transmitted to the third optical terminal device is adjusted to be constant.

DESCRIPTION OF SYMBOLS 100 Optical add / drop multiplexer 200, 300, 400 Optical terminal station 500 Transmission side trunk line 600 Branch line 700 Reception side trunk line 110 First optical branching unit 120 Optical path selection unit 130 Second optical branching unit 140 Optical power monitor Unit 310 optical power adjustment unit 121 optical path switching unit 122 optical path control unit 311 optical amplification unit 312 variable filter 320 optical branching unit 330 optical coupling unit 340 optical reception unit 350 optical transmission unit 341 optical demultiplexing unit 351 optical multiplexing unit 342 light Receiving node 352 Optical transmitting node 123 Optical switch 124 First variable optical attenuating unit 125 Second variable optical attenuating unit 313 Filter control unit 10 Optical add / drop multiplexers 20, 30, and 40 Optical terminal device 50 Transmitting trunk line 60 Branch Line 70 Receiver trunk line

Claims (7)

A first optical terminal device that transmits wavelength-multiplexed optical signals in a plurality of wavelength bands;
A second optical terminal device that transmits and receives a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals transmitted by the first optical terminal device;
A third optical terminal device that receives a wavelength-multiplexed optical signal transmitted by the second optical terminal device;
An optical add / drop multiplexer connected to the first to third optical terminal devices via an optical transmission line;
The optical add / drop device includes:
A first optical branching unit that branches input light from the first optical terminal device and outputs the branched light to the second optical terminal device;
A second optical branching unit for branching input light from the second optical terminal device;
An optical power monitor for monitoring the optical power of the light branched by the second optical branch;
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, the first light is output as the light output to the third optical terminal device instead of the input light from the second optical branching unit. An optical path selection unit that selects input light from the branch unit,
The second optical terminal device is:
A wavelength division multiplexing optical transmission system, comprising: an optical power adjustment section that adjusts the optical power of a wavelength division multiplexed optical signal to be transmitted to the third optical terminal device to be constant. The optical path selector is
When the optical power monitored by the optical power monitor unit is smaller than a predetermined value, an optical path control unit that outputs a fault determination signal;
Light that switches light output to the third optical terminal device from input light from the second optical branching unit to input light from the first optical branching unit when the fault determination signal is input The wavelength division multiplexing optical transmission system according to claim 1, further comprising a path switching unit. The second optical terminal device is:
An optical amplifying unit for amplifying light input from the optical branching device or emitting ASE light to output light of constant power to the optical branching unit;
An optical branching unit for branching the light input from the optical amplification unit;
An optical receiver that demultiplexes and receives an optical signal in a predetermined wavelength band of the light input from the optical branching unit;
Of the light input from the optical branching unit, the power of the light in the predetermined wavelength band is a predetermined value or less, a variable filter that makes the optical power of the wavelength band excluding the predetermined wavelength band constant,
An optical transmitter that multiplexes and transmits an optical signal having the same wavelength as the optical signal received by the optical receiver;
2. The wavelength division multiplexing optical transmission according to claim 1, further comprising: an optical coupling unit that multiplexes an input from the variable filter and an input from the optical transmission unit and outputs the multiplexed signal to the optical add / drop device. system.   The wavelength division multiplexing optical transmission system according to claim 2, wherein the optical path switching unit is an optical switch having a function of physically switching a connection combination of input and output. The optical path switching unit is
A first optical variable attenuator that attenuates light input from the first optical branching unit;
A second optical variable attenuator for attenuating light input from the second optical branching unit;
A second optical coupling unit that couples light input from the first and second optical variable attenuators and outputs the coupled light to the output of the optical add / drop device;
The optical path controller is
When the optical power monitored by the optical power monitor unit is equal to or greater than a predetermined value, a control signal for maximizing the attenuation is output to the first optical variable attenuator, and a control signal for minimizing the attenuation is transmitted to the first optical attenuator. 2 to the optical variable attenuator
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, a control signal for maximizing the attenuation is output to the second optical variable attenuator, and the control signal for minimizing the attenuation is the first signal. 3. The wavelength division multiplexing optical transmission system according to claim 2, wherein the wavelength division multiplexing optical transmission system outputs the signal to one optical variable attenuator.   The said 2nd optical terminal apparatus contains the filter control part which outputs a predetermined control signal to the said variable filter according to the wavelength and optical power of the said optical receiving part, The Claim 3 characterized by the above-mentioned. Wavelength multiplexing optical transmission system. A first optical terminal device that transmits wavelength-multiplexed optical signals in a plurality of wavelength bands;
A second optical terminal device that transmits and receives a predetermined wavelength multiplexed optical signal among the wavelength multiplexed optical signals transmitted by the first optical terminal device;
A third optical terminal device that receives a wavelength-multiplexed optical signal transmitted by the second optical terminal device;
An optical transmission method in a wavelength division multiplexing optical transmission system comprising the first to third optical terminal devices and an optical add / drop multiplexer connected via an optical transmission line,
The optical add / drop device includes:
Branching the light input from the first optical terminal device and outputting it to the second optical terminal device;
When the optical power monitored by the optical power monitoring unit is smaller than a predetermined value, the light output to the third optical terminal device is replaced with the input light from the second optical branching unit. Select the input light from the branch,
The second optical terminal device is:
An optical transmission method characterized in that the optical power of a wavelength division multiplexed optical signal transmitted to the third optical terminal device is adjusted to be constant.

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