Stabilised 10 GHz rationally mode-locked erbium fibre laser and its use in a 40 Gbit/s RZ data transmission system over 240 km of standard fibre

Mode-locked fibre lasers are a promising pulse source for use in high-speed data communication systems. Optical pulses at high repetition rates can be achieved by mode-locking the laser cavity at a rational harmonic of the fundamental mode-locking frequency. Using this technique, optical pulse streams at very high rates can be obtained by using longer laser cavities and slower optoelectronic components. A 10 GHz rationally mode-locked laser is presented, which is the fastest stabilised rationally mode-locked laser reported. The pulse source produces stable soliton-like pulses, with a full-width half-maximum pulse width of 5 ps and a back-to-back receiver sensitivity of -19.7 dBm for a bit error rate (BER) of 10^-9. Using optical time division multiplexing, a 40 Gbit/s data stream is generated from the 10 GHz optical pulse source with a back-to-back receiver sensitivity of -18.9 dBm. This 40 Gbit/s transmitter is used for transmitting data over 240 km of dispersion-managed fibre. This incurs a sensitivity penalty of only 0.4 dB for a BER of 10^-9