Multi-span transmission of WDM signals with a Mach-Zehnder polarization-insensitive fiber optical parametric amplifier

In this work, we explore the performance of a polarization-insensitive fiber optical parametric amplifier (PI-FOPA) used as an in-line amplifier in a multi-span transmission experiment. We transmit an equivalent of 24 × 35 GBaud PDM-16QAM signals with a capacity of 4.8 Tbps over 770 km, or 38 × 35 GBaud PDM-16QAM signals with a capacity of 7.6 Tbps over 231 km. The former is the record reach, and the latter is the record capacity for PI-FOPA-amplified multi-span links. These achievements have been facilitated by the employment of a Mach-Zehnder-like polarization diversity configuration for PI-FOPA, which reduces interchannel nonlinear crosstalk and optimization of a pump phase modulation waveform applied for mitigation of the stimulated Brillouin scattering. We demonstrate that the impact of pump phase modulation on amplified signals in state-of-the-art PI-FOPAs is the primary factor limiting the reach of multi-span links employing PI-FOPAs, while nonlinear crosstalk involving the pump limits the signal bandwidth employable for long reach transmission.