Mode - locked fiber ring lasers with semiconductor optical amplifiers for repetition rates between 10 and 160 GHz

This thesis is on the development of high-speed pulsed lasers at wavelengths around 1.55 m for applications in the fiber optic communications field. The realization of future optical transmission systems and signal processing circuits will require such optical pulse sources, capable of producing picosecond pulses with a low timing jitter at repetition rates of tens or even hundreds of Gigahertz. Furthermore, versatile lasers that can operate at different wavelengths and repetition rates will be highly welcome in the broadband test and measurement field. The lasers developed in this thesis generate wavelength-tunable and nearly chirpfree pulses of picosecond and subpicosecond width at 10 to 160-GHz repetition rates. A novel scheme is proposed for this purpose, employing a Mach-Zehnder interferometer with integrated Semiconductor Optical Amplifiers (MZI-SOA) as an optically controlled modulator in actively mode-locked fiber ring lasers. As a major benefit of the optical modulation scheme, these lasers are synchronized to an optical external clock. The timing jitter, which is an indicator for the quality of the synchronization, is small over very wide offset frequency ranges, and the jitter in excess to the external clock is low. Three key results should be particularly emphasized. First, a peak power of 3 W is obtained for 1.6 ps pulses at 10 GHz. This is the highest peak power from a laser in the 1.55 m range yet published at 10 GHz or above without amplification after the laser. Second, 740 fs wide pulses are generated, which to date is the shortest pulse width achieved with fiber ring lasers at 10 GHz or above without nonlinear compression. Third, wavelength tunability over more than 15 nm is demonstrated at 80 GHz. This is among the highest reported repetition rates at which wavelength tunability of any laser is reported. SOAs play a key role in the lasers of this thesis. A significant high-speed response of the SOA gain and phase is essential to operate the lasers at high repetition rates. Optical modulation of the SOA gain is demonstrated in pump-probe experiments at record rates of more than 270 GHz. The first measurements of the timedependence of the SOA phase at GHz-repetition rates are reported, and high phase shifts of more than at 10 GHz and at 40 GHz are observed in 1.5-mm long