Analysis and application of nonlinear amplification effects in single-mode optical fibers

This thesis focuses on all-optical signal generation and processing through nonlinear amplification phenomena in single-mode fibers. Three different nonlinear fiber optical oscillators are investigated and experimentally demonstrated. A continuous-wave pump for fiber Raman amplifiers, developed with the goal of achieving high degree of polarization, tunability and suppression of stimulated Brillouin scattering, is presented, discussed and used to achieve nonlinear polarization attraction. A fast and widely tunable fiber optical oscillator based on stimulated Raman scattering and on broad- and narrow-band fiber optical parametric amplification, and exploiting the time-dispersion-tuning technique, is demonstrated and characterized. Each nonlinear effect dominates in a different spectral region, so that the fiber optical oscillator achieves a tuning range of 160 nm. Through the same time-dispersion-tuning method, a fast tunable optical frequency comb, based on cascaded four-wave mixing, is obtained by using a single pump, avoiding the limitations in spectral purity and frequency and phase stability given by double pump systems. Finally, the control of the state of polarization and of the degree of polarization through nonlinear polarization attraction in counter-propagating fiber Raman amplifiers in standard, randomly birefringent, single-mode fibers is studied, analyzed and characterized. The analysis, including the effects of pump depletion, nonlinear polarization rotation and orthogonal Raman gain, shows that counter-propagating fiber Raman amplifiers are effective in attracting the signal toward a predetermined state of polarization settled by the pump input state of polarization. Moreover, the importance of the role of pump depletion in achieving signal repolarization in fibers with moderately-high polarization-mode dispersion is discussed. The performances and the limits of repolarization efficiency are determined, leading to a quantitative relationship between the degree of polarization and the gain of the fiber Raman amplifier, which is then confirmed to represent an upper bound on the maximum achievable degree of polarization