Smoothly wavelength-tunable, harmonically mode-locked fiber ring lasers.

摘要

The development of all-optical wavelength division multiplexing (WDM) and optical time division multiplexing (OTDM) communication systems calls for wavelength-tunable high-speed optical pulse generators. While the conventional harmonically mode-locked fiber ring lasers are able to produce picosecond pulses at high bit rates, their wavelength cannot be tuned without interrupting the stable pulsing behavior of the lasers. It is the goal of this thesis to propose, study and demonstrate a new class of mode-locked fiber ring lasers, which are able to realize smooth wavelength tuning while maintaining low noise and good pulse qualities.; Two key techniques are applied in order to achieve such improvement. Dispersion tuning allows the oscillating wavelength of a mode-locked laser being changed by tuning only the modulation frequency without disturbing the mode-locking condition. An intracavity semiconductor optical amplifier (SOA) is able to suppress the intensity noise induced by supermode beating. Smooth wavelength tuning within 10 nm and 5.3-ps pulses at a 10-GHz repetition rate are demonstrated using a dispersion-tuned, harmonically mode-locked fiber ring laser with an intracavity SOA. In-depth study on SOA supermode noise (SMN) suppression shows excellent agreement between experiments and simulations.; The combination of intracavity dispersion and intracavity SOAs offers new flexibilities to tailor the laser performances. Two novel configurations incorporating a directly modulated SOA and a proper amount of dispersion are successfully demonstrated. 3.7-ps pulses at 6 GHz are achieved when the dispersion is anomalous whereas near-transform-limited pulses are obtained without external pulse compression in the normal dispersion regime.; Detailed analysis shows that the wavelength tuning range of dispersion-tuned mode-locked lasers depends not only on the gain profile of the amplifier, but also on the amount of total intracavity dispersion, the modulation parameters and the wavelength-dependent cavity loss. Multi-wavelength oscillation is possible under certain conditions, which are determined theoretically and compared with experiment.; The applications of the proposed system include low-cost commercial picosecond pulse generators, testing signal sources for WDM/OTDM components/subsystems and all-optical clock recovery. A wide bit-rate range (1.5∼2.8 Gbit/s) all-optical clock recovery system is demonstrated experimentally.