Towards Practical Implementation of Phase-Sensitive Amplifier Based Transmission Systems

Licentiate thesis, 2013

All commercially available optical amplifiers are so-called phase-insensitive amplifiers (PIAs) which degrade the signal-to-noise ratio (SNR) through the amplification process. This kind of amplifier has a quantum limited noise figure (NF) of 3 dB. Another category of amplifiers are phase-sensitive amplifiers (PSAs) which in theory are capable of noiseless amplification, i.e. amplification with a 0 dB NF. Successful implementation of PSAs in transmission systems would lead to significant performance improvements compared to using conventional PIAs. However, the implementation is challenging and no system with wavelength division multiplexing (WDM) compatibility has previously been demonstrated over a significant transmission distance. This thesis is dedicated to realizing and investigating the properties of PSA-amplified transmission links utilizing fiber optical parametric amplifiers (FOPA) and the so-called copier-PSA scheme. One of the main challenges on the way towards realization is to recover and amplify a weak phase-modulated wave with high fidelity. To handle this, a hybrid injection locking (IL)/Erbium-doped fiber amplifier (EDFA)-based pump recovery system was designed and thoroughly investigated experimentally. Other challenges include continuous phase-locking of several waves and high-precision wave tuning. A single-span PSA-amplified transmission link with WDM compatibility was demonstrated over 80 km of fiber. The link performance was compared against a conventional EDFA-based link for operation both in the linear and nonlinear transmission regime. The PSA-amplified system is shown to have capability to mitigate nonlinear distortions due to the Kerr effect and outperform the EDFA-amplified link in both regimes.