Control modulation technique for client independent optical performance monitoring and transport of channel overhead

A new subcarrier technique for optical performance monitoring and transport of channel overhead independent of the client data and without optoelectronic conversion in the client data path has been verified experimentally performing loop tests with PRBS bit error measurements for the example of a 10 Gb/s client channel and a 50 Mb/s control channel converted to an RF subcarrier above the client modulation spectrum. Strict correlation between the client channel the ASE noise of optical amplifiers and nonlinear distortion due to self phase modulation (SPM). An early warning function of the control channel is realised by proper choice of the modulation depth. A pronounced BER degradation in the control channel indicates a beginning degradation in the client channel. This feature enables preemptive performance management, i.e. management can take measures in good time to prevent the network from outages and maintain the quality of service. It was shown for the measurement example that the control signal together with the client signal can be transmitted error free over distances up to 1653 km. This enables transport of channel overhead or labelling for optical burst and packet networks. The overhead or label maybe protected against degradation of optical transmission by implementing a forward error correction (FEC) in the control channel. The activity of the error correction algorithm can be used as a quality measure instead of a direct BER measurement.