Applications of Broadband Polarization-Insensitive Fiber Optical Parametric Amplifiers

Abstract

This thesis explores a major challenge in the development of fiber optical parametric amplifiers (FOPAs) in optical communication systems: the mitigation of stimulated Brillouin scattering (SBS). The research focuses on pump phase modulation as an effective SBS suppression technique for FOPAs, particularly in the amplification of QAM signals within state-of-the-art polarization-insensitive FOPA architectures. Both single-polarization and polarization-insensitive FOPAs are studied to evaluate the impact of pump phase modulation on signal degradation, as an induced phase noise, which negatively affects signal OSNR and pathways to minimize this impact. A numerical and experimental study was conducted to evaluate the required optical signal-to-noise ratio (OSNR) and the performance of various phase modulation schemes on the impact of pump phase modulation on QAM signals. The key findings reveal that the pump phase modulation-induced signal phase noise is proportional to the pump bandwidth and the effect of pump phase modulation on signals is more complex in polarization-insensitive FOPAs compared to single-polarization FOPAs. It can be minimized by optimizing pump phase modulation by using a higher number of sine tones with smaller spacing between them, which results in a denser, bandwidth efficient pump spectrum, allowing for effective SBS mitigation while keeping the total pump bandwidth narrow. Nearly complete cancellation of this impact is possible by employing features of polarization diversity schemes. The key results provide the optimization enabled a new record in long-haul transmission experiments, where polarization-insensitive FOPAs were used as in-line amplifiers. In these experiments, a data transmission at distance of 539 km below BER of 0.02 was achieved for a 200G PDM-16-QAM signal, maintaining a net FOPA gain of 25 dB.