Light power control system, light power control node apparatus, and method of controlling light power

A light power control system is used in a network in which a control signal is transmitted to instruct setting of a wavelength path. The light power control system is provided with a light amplifier control section configured to carry out a constant output control to a light amplifier which amplifies a light signal transmitted from a node to another node, when said node in said network receives the control signal; and a variable optical attenuator control section configured to adjust an attenuation quantity of a variable optical attenuator to attenuate a light power of the light signal on any of wavelength paths, when said node receives the control signal and moreover the light signal is transmitted on said any of wavelength paths of said node. It becomes possible to receive the data right in a receiving end by a simple unit when there is a change of the number of wavelength paths.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/JP2010/069511 filed Nov. 2, 2010, claiming priority based on Japanese Patent Application No. 2009-254135 filed Nov. 5, 2009, the contents of all of which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention is related to a light power control in a node to which a wavelength path is set, in a photonic network.

BACKGROUND ART

In a photonic network, a light amplifier is an important device to elongate a transmission distance of a light signal. In the photonic network, the WDM (Wavelength Division Multiplexing) transmission using a plurality of wavelengths is general for the transmission of a large amount of data in the network. In case of the WDM transmission, the light amplifier amplifies the light signal of the plurality of wavelengths. Here, it is thought of that the light power of the light signal which is supplied to the light amplifier changes due to increase or decrease of the number of wavelength paths on the network. For example, when the number of wavelength paths for the light signal which is supplied to the light amplifier is decreased, the light power of the light signal which is supplied to the light amplifier decreases. In this case, it is necessary to decrease the light power of the light signal which is outputted from the light amplifier, according to the supplied light signal.

CITATION LIST

SUMMARY OF THE INVENTION

In the light amplifier described in Patent Literature 1, there are an ALC (Automatic Level Control) mode and an AGC (Automatic Gain Control) mode. In the ALC mode, data of increase or decrease of the number of wavelength paths is received from a control signal on the network, and the output signal of the light amplifier is increased or decreased based on the data. However, a time of about hundreds msec is required to increase or decrease in light power of the output signal of the light amplifier. When the number of wavelength paths for the light signal which is supplied to the light amplifier is decreased, there is not a change in the light power of the light signal which is outputted from the light amplifier for the time of hundreds msec. Therefore, the light power per one wavelength path has increased temporarily and as the result of this, there is a possibility that the data can not be received correctly in a receiving end of the wavelength path.

In the AGC mode, when the light power of the light signal supplied to the light amplifier changes, the light power of an output signal of the light amplifier changes so that a constant gain is kept, by adjusting the power of excitation light according to the change. The output signal of the light amplifier can be changed faster in the AGC mode than in the ALC mode. However, generally, because the light amplifiers are connected in a multi-stage configuration, there is a possibility that the time which can not receive data right in the receiving end of the wavelength path has becomes long. Also, the cost is high in the AGC mode.

It is demanded that data can be received right in the receiving end by use of a simple technique, even when there is the increase or decrease of the number of wavelength paths.

The light power control system according to an aspect of the present invention is used in a network in which a control signal is transmitted to instruct setting of a wavelength path, and is provided with a light amplifier control section configured to carry out a constant output control to a light amplifier which amplifies a light signal transmitted from a node to another node, when the node in the network receives the control signal; and a variable optical attenuator control section configured to adjust an attenuation quantity of a variable optical attenuator to attenuate a light power of the light signal on any of wavelength paths, when the node receives the control signal and moreover the light signal is transmitted on any of wavelength paths of the node.

The light power control node apparatus according to an aspect of the present invention is used in a node of a network in which a control signal is transmitted to instruct setting of a wavelength path, and is provided with a light amplifier control section configured to carry out a constant output control to a light amplifier which amplifies a light signal transmitted to another node by the node, when the node receives the control signal; and a variable optical attenuator control section configured to adjust an attenuation quantity of a variable optical attenuator to attenuate a light power of the light signal on any of wavelength paths, when the node receives the control signal and moreover the light signal is transmitted on any of wavelength paths of the node.

A method of controlling a light power in an aspect of the present invention includes carrying out a constant output control to a light amplifier which amplifies a light signal transmitted to another node by a node, when the node of the network receives the control signal; and adjusting an attenuation quantity of a variable optical attenuator to attenuate a light power of the light signal on any of wavelength paths, when the node receives the control signal and moreover the light signal is transmitted on the any of wavelength paths of the node.

According to the present invention, by a simple technique, data can be received right in the receiving end when the number of wavelength paths increases or decreases.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, referring to the attached drawings, the exemplary embodiments of the present invention will be described in detail. First, a configuration example of the first exemplary embodiment will be described.FIG. 1shows a network to which a light power control system of the present exemplary embodiment is applied. Wavelength paths are optionally set among plurality of nodes1-1to1-3in the network1-6. A control signal1-4is transmitted to instruct the setting of the wavelength paths on the network1-6. For example, the control signal is a signal to instruct the setting of a new wavelength path or a signal to instruct the removal of the wavelength path. When a new wavelength path1-5is set, a path setting control signal is transmitted on the route where the new wavelength path is set. When the wavelength path is removed, a path removal control signal is transmitted on the route where the wavelength path is removed.

FIG. 2shows a block diagram of the light power control node apparatus which is provided in the node1(i.e. an optional node of the nodes1-1to1-3inFIG. 1). Such a light power control system and such a light power control node apparatus can be applied to an optional node in the network1-6. The node1is provided with an ADD/DROP section101which carries out ADD/DROP of a data signal, a light amplifier102which amplifies a light signal, a wavelength demultiplexing section103which demultiplexes a multiplexed signal in units of wavelengths, VOAs (Variable Optical Attenuators)104, each of which can control an attenuation quantity of the light signal for every wavelength, receiving sections105, each of which receives a light signal of the wavelength, transmitting sections106, each of which transmits a light signal with a wavelength, a wavelength multiplexing section107which multiplexes light signals from the transmitting sections106, a control signal ADD/DROP section111which carries out ADD/DROP of the control signal, a wavelength path managing section112which manages data of the wavelength paths, and a control section113which processes the control signal. The control section113is provided with a light amplifier control section113-1and a VOA control section113-2, and is connected with the VOA104and the light amplifier102by control lines so as to control them. InFIG. 2, the light amplifier102is single, but a configuration may be adopted in which two light amplifiers are provided on the front and back sides of the ADD/DROP section101.

An operation example in the first exemplary embodiment will be described.FIG. 3is a flow chart showing an operation of the light power control node apparatus when the node1receives a path setting (path removal) control signal. The control section113receives the path setting (path removal) control signal through the control signal ADD/DROP section111(S1110). After the reception of the control signal, the light amplifier control section113-1sends out the control signal to the light amplifier102to control the output of the light amplifier102(S1120) to be constant. There is no change in the output power of the light amplifier102even when the power of a light signal supplied to the light amplifier102changes because the constant output control is carried out to the light amplifier102. Next, the control section113refers to the wavelength path managing section112to confirm whether or not its own node is using a wavelength path, that is, whether or not the wavelength path on which a light signal of a wavelength is transmitted is in a use state (S1130). When the wavelength path is not being used (S1130/No), the operation ends just as it is (S1131). When the light signal on the wavelength path is received (S1130/Yes), the VOA control section113-2sends out the control signal to the VOA104connected with the receiving section105which receives the light signal on the wavelength path, to control the value of the VOA104, i.e. the attenuation quantity of the VOA104(S1140).

Here, when receiving the path setting control signal, the control section113decreases the value of the VOA104. That is, the control section113decreases the attenuation quantity of the light signal by the VOA104. By such an operation, when a light signal is transmitted on any of wavelength paths in a node on the network, the attenuation quantity of the light power of the light signal by the variable optical attenuator (VOA) in any of the wavelength paths can be adjusted. Because the light signal supplied to the light amplifier102increases but the output is constant when a wavelength path is set newly, a signal amplification factor per a wavelength is decreased. Therefore, the receiving section can receive a signal in an optimal light power even when the wavelength path is set newly by increasing the attenuation quantity of the VOA104in advance.

On the other hand, when receiving the path removal control signal, the control section113decreases the attenuation quantity of the VOA104. Because the light signal supplied to the light amplifier102decreases when the wavelength path is removed but the output is to be constant, the signal amplification factor per a wavelength increases. Therefore, the receiving section105can receive the light signal in an optimal light power even when the wavelength path is removed by decreasing the attenuation quantity of the VOA104in advance. The rate of increase or decrease of the attenuation quantity of the VOA104is calculated based on the signal amplification factor per one wavelength. When a plurality of wavelength paths are set or removed at a same time, the rate of increase or decrease of the attenuation quantities of the VOAs104is calculated based on the number of remaining wavelength paths. Also, the initial values of the attenuation quantity of the VOA104are set in consideration of the minimum light reception power and the maximum light reception power of the receiving section.

As described above, in the first exemplary embodiment, by carrying out a constant output control to the light amplifier102when receiving the path setting (removal) control signal and controlling the attenuation quantity of the VOA104, the light signal can be received in an optimal light power by the receiving end of the originally set wavelength path. Therefore, the data can be received right by the receiving end. Especially, when many wavelength paths are set (removed) at a same time, because it would be difficult that the light amplifier102itself deals a large change of the supplied light signal, it is effective to adjust the attenuation quantity of the VOA104while carrying out the constant output control to the light amplifier102based on the path setting (removal) control signal.

In a second exemplary embodiment, the light power control when a fault such as a fiber break and a node failure occurs on the network will be described. A configuration example of the second exemplary embodiment will be described. In the network of the present exemplary embodiment, when the fault occurs on an operation wavelength path, a spare wavelength path is set to the operation wavelength path. Another light signal of the wavelength path is transmitted on the spare wavelength path before the fault occurs. When the fault occurs, the control signal is transmitted onto the spare wavelength path to notify the fault.

FIG. 4shows a network diagram of the second exemplary embodiment. The network2-7is provided with a plurality of nodes2-1to2-3. The spare wavelength path2-5is used when a fault occurs in the operation wavelength path. A low priority wavelength path2-6is used to flow data when the fault does not occur on the operation wavelength path. However, when the fault occurs, the low priority wavelength path2-6is stopped because the spare wavelength path2-5is used for data transmission. A fault notice signal2-4is transmitted on the spare wavelength path2-5when the fault occurs on the operation wavelength path.

FIG. 5is block diagram showing a node2(an optional node in the nodes2-1to2-3inFIG. 4) in the second exemplary embodiment. The difference from the configuration shown inFIG. 2is in that a monitoring section208is provided between the ADD/DROP section101and the wavelength multiplexing section103. A control section213and the monitoring section208are connected by a control line. The monitoring section208monitors the number of wavelength paths used in the node. Because a DROP section of the ADD/DROP section101shown inFIG. 5has a configuration like an optical coupler, the number of wavelengths which are used in the transmission line can be confirmed by the monitoring section208.

An operation example of the second exemplary embodiment will be described. In the present exemplary embodiment, the variable optical attenuator (VOA) control section213-2increases the attenuation quantity of the variable optical attenuator (VOA)104to attenuate the light power of a light signal on a different wavelength path, when a node receives a control signal and moreover its own node receives a light signal on another wavelength path or a light signal of another wavelength path passes on its own node. As described below, in the present exemplary embodiment, when the number of wavelengths monitored currently by the monitoring section208increases compared with the number of wavelengths monitored previously, the VOA control section213-2decreases the attenuation quantity of the VOA104according to the increase.

FIG. 6is a flow chart showing an operation of the light amplifier102when each of the nodes2-1to2-3receives a fault notice signal. The control section213receives the fault notice signal through the control signal ADD/DROP section111(S2110). The fault notice signal is generated every operation wavelength path which receives then influence of the fault. For example, when10operation wavelength paths fail at the same time,10fault notice signals are generated.

After the reception of the fault notice signal, whether its own node transmits a light signal on a low priority wavelength path of the same wavelength as a spare wavelength path or a low priority wavelength path with the same wavelength as the spare wavelength path passes on its own node is confirmed (S2120). Specifically, it confirms that the control section213refers to the wavelength path managing section212, to confirm whether the light signal is transmitted on the low priority wavelength path with the same wavelength as the spare wavelength path or the low priority wavelength path with the same wavelength as the spare wavelength path passes on its own node. The wavelength of the spare wavelength path is written in the fault notice signal.

When its own node does not transmit a light signal on the low priority wavelength path with the same wavelength as the spare wavelength path, or the low priority wavelength path with the same wavelength as the spare wavelength path does not pass on it own node (S2120/No), the operation ends (S2121). When its node transmits a light signal on the low priority wavelength path or the low priority wavelength path passes on its own node (S2120/Yes), the control section213confirms whether or not the light amplifier102is under the constant output control (S2130).

When the light amplifier102is under the constant output control (S2130/Yes), the operation ends (S2131). When the light amplifier102is not under the constant output control (S2130/No), the light amplifier control section213-1instructs the monitoring section208to monitor the number of wavelengths and record the number of monitored wavelengths as a record wavelength number (S2140). The control section213-1transmits a control signal to the light amplifier102so as to carry out the constant output control, after recording the record wavelength number (S2150).

When a fault has occurred, the transmission on the low priority wavelength path is stopped and data newly flows through a spare wavelength path. Therefore, a light signal supplied to the light amplifier102decreases and then increases immediately. Therefore, the light amplifier102is subjected to the constant output control if its own node transmits a light signal on the low priority wavelength path and the low priority wavelength path passes on its own node, when receiving the fault notice signal.

FIG. 7is a flow chart showing an operation of the light power control node apparatus when the constant output control to the light amplifier102is cancelled. After the control section213receives all the fault notice signals, the control section213receives data of the number of monitored wavelengths from the monitoring section208periodically (S2210). After that, the control section213confirms whether or not the number of wavelengths recorded when the light amplifier102is subjected to the constant output control is coincident with the number of monitored wavelengths (S2220). When being coincident (S2220/Yes), the control section213-1transmits the control signal to the light amplifier102to cancel the constant output control to the light amplifier102(S2230). When being not coincident (S2220/No), the control section213repeats monitoring the wavelength number (S2210).

The fact that the number of wavelengths recorded when the constant output control to the light amplifier102is carried out is coincident with the number of monitored wavelengths, indicates that data on the spare wavelength path flows through the route in which the flow of the low priority wavelength path is stopped. Therefore, the constant output control to the light amplifier102is cancelled.

FIG. 8is a flow chart showing an operation of the VOA104when each of the nodes2-1to2-3receives the fault notice signal. This operation is carried out in parallel with the operation ofFIG. 6. The control section213receives the fault notice signals through the control signal ADD/DROP section111(S2310). After the reception of the fault notice signals, the control section213confirms whether or not its own node receives a light signal on the low priority wavelength path with the same wavelength as the spare wavelength path or the low priority wavelength path with the same wavelength as the spare wavelength path passes on its own node (S2320). Specifically, the control section213confirms by referring to the wavelength path managing section212, in the same way as a case ofFIG. 6.

When its own node does not receive the light signal the low priority wavelength path with the same wavelength as the spare wavelength path or the low priority wavelength path with the same wavelength as the spare wavelength path does not pass on its own node (S2320/No), the operation ends (S2321). When its own node receives the low priority wavelength path with the same wavelength as the spare wavelength path or the low priority wavelength path with the same wavelength as the spare wavelength path passes on its own node (S2320/Yes), the control section213confirms whether or not its own node receives the light signal on the wavelength path (S2330). Here, the control section213confirms by referring to the wavelength path managing section212.

When its own node does not receive a signal on the wavelength path (S2330/No), the operation ends (S2331). When its own node receives the light signal on the wavelength path (S2330/Yes), the VOA control section213-2transmits the control signal to the VOA104connected with the receiving section105which receives the light signal on the wavelength path, so as to decrease the attenuation quantify of the VOA104(S2340). This decrease of the VOA104is for the purpose to deal with to the increase of the signal amplifier factor per a wavelength path through the stop of the low priority wavelength path.

FIG. 9is a flow chart showing the operation of returning the value of the VOA104to the initial value. This operation is carried out in parallel with the operation ofFIG. 7. After the control section213receives all the fault notice signals, the control section213periodically receives data of the number of wavelengths which are monitored by the monitoring section208(S2410). After the reception, the control section213compares the received number of wavelengths with the number of wavelengths monitored previously, to confirm whether or not the number of wavelengths monitored currently increases (S2420).

When the number of wavelengths has increased (S2420/Yes), the control section213increases the attenuation quantity of the VOA104connected with the receiving section105which receives the light signal on the wavelength path based on the increased number of wavelengths (S2430). Supposing that the attenuation quantity of the VOA104should be increased by 3 dB to the increase of one wave, it is increased by 6 (=3×2) dB in case of the increase of 2 wavelengths, and by 9 (=3×3) dB in case of the increase of 3 wavelengths. This increase of the attenuation quantity of the VOA104is the purpose to deal with the decrease of the signal amplifier factor per one wavelength path when the low priority wavelength path is stopped and data flows through the spare wavelength path newly.

When the number of wavelengths monitored currently is not increased as the result of comparison of the number of wavelengths monitored currently and the number of wavelengths monitored previously (S2420/No), and after the increase of the attenuation quantity of the VOA104(S2430), the control section213confirms whether or not the attenuation quantity of the VOA104is coincident with an initial value (S2440). If being coincident (S2440/Yes), the operation ends (S2450). If being not coincident (S2440/No), the control section213repeats the monitoring of the number of wavelengths (S2410).

As described above, in the second exemplary embodiment, the change of the signal supplied to the light amplifier102becomes sharp when the transmission on the low priority wavelength path is stopped due to a fault occurrence and the data is transmitted on the spare wavelength path. The light amplifier102is subjected to the constant output control while the change of the signal is sharp, so that the data can be received right by a receiving end of the wavelength path, by adjusting the attenuation quantity of the VOA. Especially, when the transmission on a large amount of low priority wavelength paths is stopped and the transmission on a large amount of spare wavelength paths is carried out, it is thought of that it would be more difficult to deal with the great change of the light signal by the operation of the light amplifier102itself. Therefore, it would be effective that the light amplifier102is subjected to the constant output control based on the fault notice signals so as to control the attenuation quantities of the VOAs.

In a third exemplary embodiment, the light power control when faults such as a fiber break and a node fault occur on the network, like the second exemplary embodiment will be described. Here, while one light amplifier is provided in the node in the second exemplary embodiment, two light amplifiers are provided in the node in the third exemplary embodiment. In the present exemplary embodiment, as described below, the node in the network has a 2-stage configuration of an upstream light amplifier (light pre-amplifier)309which amplifies and outputs a light signal from an upstream node, and a downstream light amplifier (light post-amplifier)302which amplifies the light signal from the upstream light amplifier309and outputs the amplified light signal to a downstream node. The light amplifier control section313-1of the control section313controls the light amplifiers at a same time such that these light amplifiers are in the same control mode. The other operation of the control section313such as the operation of the VOA control section313-2is same as in the second exemplary embodiment.

The configuration example of the third exemplary embodiment will be described. The configuration of the network is same as shown inFIG. 4in the second exemplary embodiment.FIG. 10shows a block diagram of the node3in the third exemplary embodiment. The difference from the configuration ofFIG. 5is in that the two light amplifiers exist such as the light pre-amplifier309and the light post-amplifier302. The light pre-amplifier309is arranged in front of the ADD/DROP section101and the light post-amplifier302is arranged behind the ADD/DROP section101.

Because the two light amplifiers operate at a same time as one amplifier, the third exemplary embodiment operates in the same way as the operation example in the second exemplary embodiment. It is possible to control the light powers even in case of the two light amplifiers.

The present invention has been described with reference to the above exemplary embodiments but the present invention is not limited to the exemplary embodiments. Various modifications can be carried out to the exemplary embodiments. For example, the above exemplary embodiments can be combined with each other.

This application claims a priority based on Japanese Patent Application No. JP 2009-254135 filed on Nov. 5, 2009. The disclosure thereof is incorporated herein by reference.