Phase-Sensitive Fiber Optic Parametric Amplifier and Their Applications in Optical Communications

Doktorsavhandling, 2012

This thesis deals with experimental and theoretical aspects of the phase-sensitive fiber optic parametric amplifier (FOPA) and their applications. FOPAs can be oper- ated as both phase-insensitive and phase-sensitive amplifiers (PSAs), with the latter requiring phase-locked input waves, which, until recently, has limited their practi- cal use. Based on the realization that a phase-insensitive FOPA, called the copier, can generate the phase-locked waves required, several applications of a copier-PSA configuration are proposed and demonstrated. These include phase excursion ampli- fication, ultra-low noise amplification, and, by using the copier for carrier recovery, black-box all-optical phase- and amplitude regeneration. A large part of this thesis deals with characterization of the PSA. The copier-PSA configuration is useful in this regard, since, by modulating the signal in between the copier and PSA, the phase-response of the PSA can be studied. The output signal was investigated both in terms of amplitude and phase, using a coherent receiver. Finally, methods to suppress stimulated Brillouin scattering (SBS) in HNLFs are investigated. Without suppression, SBS will severely limit the available pump power for parametric amplification. The most common way to suppress the SBS is to increase the spectral width of the pump, but this is undesirable in many ap- plications, including phase-sensitive amplification. Therefore, the application of a strain gradient to the fibers to decrease the SBS is studied. However, such a gradi- ent also introduces an undesired dispersion variation, and this trade-off is evaluated as well. A cascade of HNLFs with strain gradients, separated by low-loss and low- dispersion isolators is proposed and evaluated, with a large increase in the SBS threshold demonstrated.