Generation of a 20 GHz train of subpicosecond pulses with a stabilized optical-frequency-comb generator

With a modulator-based 10 GHz optical-frequency-comb generator at 1.55 microm, we report a 20 GHz repetitive train of optical pulses as short as 450 fs. The timing stability of the 20 GHz pulses, in addition to the phase for optical-comb modes, shows a strong dependence on the relative frequency detuning between the comb generator's cavity and the seed cw laser. With a new and simple scheme, the comb generator's cavity resonance was locked to a narrow-linewidth seed laser within an estimated optical-frequency range < or = 6 MHz, enabling high-fidelity 20 GHz subpicosecond pulses and stable optical-frequency-comb generation for indefinite periods.