Study of extra wide coherent optical combs generated by a QW-based integrated passively mode-locked ring laser

We present an investigation of an InP quantum-well-based integrated extended cavity passively mode-locked laser which shows extra broad frequency comb generation. The ring laser was characterized in frequency and time domains for a range of the current levels injected in the semiconductor optical amplifier. The study showed an increase of the bandwidth to over 40 nm at the -20  dB level. The coherence between the longitudinal modes in the wide comb is demonstrated by the characterization of a spectrally filtered signal in time and RF domains. The relative time delay across the optical comb was measured.