Distributed Raman amplifier and optical communication system

A distributed Raman amplifier for supplying a pumping light to a transmission path to Raman amplify a WDM light being propagated through the transmission path, comprising:

• a pumping light supplying section configured to supply a pumping light output from at least one pumping light source to the transmission path;
• an OSNR monitoring section configured to monitor an OSNR representing a ratio between a signal light level of each channel contained in the WDM light which has been propagated through the transmission path to be Raman amplified and thereafter is amplified by an optical amplifier in an optical repeating node connected to a signal output end of the transmission path, and a noise light level of each channel contained in the WDM light;
• a judging section configured to judge whether a monitor value of the OSNR of each channel in the OSNR monitoring section is larger or smaller than a previously set target value thereof;
• and
• a control section configured to control a driving state of the pumping light source based on the judgment result in the judging section,
• wherein the OSNR monitoring section includes:
• a first branching device configured to branch a part of the WDM light amplified by the optical amplifier in the optical repeating node;
• an optical filter configured to extract a noise component from the light branched by the first branching device;
• a first optical receiving element configured to detect the power of the noise component extracted by the optical filter;
• a second branching device configured to branch a part of the WDM light amplified by the optical amplifier in the optical repeating node, at a site different from the branching site by the first branching device;
• a demultiplexer configured to demultiplex the light branched by the second branching device to takes out each channel;
• a second optical receiving element configured to detect the power of each channel taken out by the demultiplexer;
• and
• an OSNR computation circuit configured to compute the OSNR, based on the detection results in the first and second optical receiving elements and a route loss between the optical amplifier and the demultiplexer.

An optical communication system that transmits a WDM light from an optical transmitter to a transmission path, and repeating-transmits the WDM light to an optical receiver while amplifying the WDM light by at least one optical repeating node arranged on the transmission path;

• and also, is provided with a plurality of distributed Raman amplifiers each of which supplies a pumping light to the transmission path in each repeating span to Raman amplify the WDM light being propagated through the transmission path,
• wherein each of the plurality of distributed Raman amplifiers comprises:
• a pumping light supplying section configured to supply a pumping light output from at least one pumping light source to the transmission path;
• an OSNR monitoring section configured to monitor an OSNR representing a ratio between a signal light level of each channel contained in the WDM light which has been propagated through the transmission path to be Raman amplified and thereafter is amplified by an optical amplifier in the optical repeating node, and a noise light level of each channel contained in the WDM light;
• a judging section configured to judge whether a monitor value of the OSNR of each channel in the OSNR monitoring section is larger or smaller than a previously set target value thereof;
• a control section configured to control a driving state of the pumping light source based on the judgment result in the judging section;
• and
• a span loss monitoring section configured to monitor a span loss indicating a loss in the transmission path to which the pumping light is supplied by the pumping light supplying section, and
• the optical communication system further comprising:
• a selecting section configured to select the repeating span in which the control of the pumping light source is preferentially performed from the plurality of repeating spans, based on the judging result in the judging section and the monitor result in the span loss monitoring section, which are transmitted from each distributed Raman amplifier;
• and
• a control target value computing section configured, for the repeating span selected by the selecting section, to correct a control target value of the pumping light source according to an excessive or deficient amount of the monitor value of the OSNR relative to the target value thereof at a reception end, to notify the control target value after correction to the control section of the distributed Raman amplifier corresponding to the selected repeating span.