Optical Transmission Systems Based on Phase-Sensitive Amplifiers

Doktorsavhandling, 2015

The capacity and reach of today's long-haul fiber optical communication systems is limited by amplifier noise and fiber nonlinearities. Conventional, phase-insensitive amplifiers (PIAs), have a quantum limited noise figure (NF) of 3 dB at high gain, meaning that with a shot-noise limited input signal the signal-to-noise ratio (SNR) is degraded by at least 3 dB. Phase-sensitive amplifiers (PSAs), have a quantum limited NF of 0 dB, meaning that a shot-noise limited input signal can be amplified without degrading the SNR. The capability of PSAs to provide noiseless amplification makes them interesting for transmission system applications. The objective of this thesis has been to experimentally realize transmission systems based on two-mode PSAs and explore their properties, both experimentally and numerically. We present the first demonstrations of multi-channel compatible and modulation format independent single-span and multi-span PSA-amplifield transmission systems. In addition to demonstrating a performance benefit due to reduced amplifier noise we also show that two-mode PSA-amplified transmission systems can mitigate distortions originating from fiber nonlinearities, such as selfphase modulation (SPM) and nonlinear phase noise (NLPN). In particular, we demonstrate PSA-amplified transmission of 10 GBd quadrature phase-shift keying (QPSK) and 16-ary quadrature amplitude modulation (16QAM) signals over 105 km single-span transmission systems showing significant performance improvements, in terms of sensitivity, compared to conventional PIA-amplified transmission systems. In the case of 16QAM transmission the improved sensitivity allows for 12 dB larger span loss. We also demonstrate PSA-amplified multi-span transmission of a 10 GBd QPSK signal achieving a maximum reach of 3465 km, a threefold reach improvement compared to the maximum reach of 1050 km that was obtained using in-line PIAs at optimal launch power.