Joint OSNR and CD monitoring in digital coherent receiver using long short-term memory neural network

To enable the high quality-of-service of reliable and dynamic optical networks, it is essential to implement optical performance monitoring (OPM) for fiber optical transmission link. Being directly related to the quality of optical signal, optical signal-to-noise ratio (OSNR) and chromatic dispersion (CD) have become the most vital parameters to be monitored during OPM implementation. However, most existing simultaneous OSNR and CD monitoring schemes still suffer from high implementation complexity and low accuracy. Here, we demonstrate a joint OSNR and CD monitoring scheme for the digital coherent receiver, enabled by the long short-term memory neural network (LSTM-NN). LSTM-NN is able to identify the mapping from the received data to corresponding OSNR and CD values simultaneously, without manual feature pre-engineering. We carry out an experimental verification for optical signals with variable modulation formats and baud-rates. The mean absolute errors (MAEs) of simultaneous OSNR and CD monitoring are below 0.12 dB and 1.09 ps/nm, respectively, when both OSNR and CD are at the range from 15 to 30 dB and 1360 to 2040 ps/nm for 5/10 Gbaud PDM-16QAM/64QAM optical signals.