Measurement of Total and Longitudinal Nonlinear Phase Shift as Well as Longitudinal Dispersion for a Fiber-Optic Link Using a Digital Coherent Transceiver

This paper presents novel techniques to measure the total and longitudinal nonlinear phase shifts, as well as longitudinal net dispersion with a dual-polarization digital coherent transceiver in a multi-span fiber optic system. We show, with additional information of span lengths and fiber core effective areas, that the longitudinal launched power profile can be estimated. The measurement is based on cross-phase modulation between two orthogonally polarized subcarriers acting as the pump and the probe, which are generated from the same coherent transmitter. With proper waveform design in the transmitter and signal processing in the receiver, we demonstrate the feasibility of measuring the accumulated nonlinear phase shift caused by the optical signal in the fiber link between the transmitter and the receiver. Profiles of launched optical power along fiber spans can also be measured based on the differential time walk-off between the pump and the probe, and net chromatic dispersion of each fiber span along the fiber link can be estimated from this measurement. We show that digital pre-compensation on pump pulses in the transmitter and digital post-compensation on the received probe pulses are essential to ensure the accuracy of the power profile measurement.