Transceiver Noise Characterization Based on Perturbations

In this paper, we discuss a new technique for measuring transceiver noise, skew, and for the detection of uncompensated transceiver impairments. The method introduces frequency domain notch or notches at the transmitter, which allows for the estimation of the Signal-to-Noise and Distortion Ratio at different stages over the transmission chain. The proposed technique requires the detection of the signal spectrum using either: a modem receiver, an Optical Spectrum Analyzer (OSA), an oscilloscope, or an Electrical Spectrum Analyzer (ESA), depending on the stage where the spectrum is measured and requiring minimal processing of the received signal. Our analysis is focused on Ciena's WaveLogic Ai commercial transceiver and a 95 Gbaud DAC. We demonstrate that symmetrically placed frequency domain notches can be used to mitigate the influence of crosstalk on the Signal-to-Noise and Distortion Ratio estimates. Finally, we show how a single notch spectrum can be used to detect and compensate for impairments, and we perform skew estimation as an example.