Abstract

Actively mode-locked Er-doped fiber lasers operating in the rational-harmonic repetition-rate-doubling regime are attractive sources of picosecond and sub-picosecond optical pulses [1]. In this regime, the repetition rate of the pulse train is increased twofold with respect to the modulation frequency f_M. Unfortunately, in this regime, the radio-frequency (RF) spectrum of the pulse train contains an unwanted component at the modulation frequency. To the best of our knowledge, only a simple qualitative model of the rational-harmonic repetition-rate-doubling regime was reported to date [1]. According to this model, the unwanted component at f_M is attributed to pulse-to-pulse amplitude fluctuations. However, it does not explain the strong suppression of the f_M - component that was observed experimentally [2] when the frequency detuning, δ = f_M/F -n ± 1/2, was equal to zero (F is the free spectral range of the laser cavity, n is an integer). The nature of the f_M - component is not completely elucidated and ultimate limitations on the parameters of the pulse train are not determined.

© 2000 IEEE