  We present the detailed characterization of the phase dynamics of a telecom
hybrid III-V-on-silicon passively mode-locked laser with a ring cavity. We
explore the various regimes of operation as a function of gain current and
saturable absorber bias voltage. We use a stepped-heterodyne measurement to
quantify the spectral chirp and reconstruct the pulse envelop. With this
technique we are able to identify regimes of near-transform-limited operation
and we assess the degradation of mode-locking in the comb phase relationship
when saturable absorber bias voltage is changed. Finally, we present a
preliminary study of the phase-locking in hybrid mode-locked operation and
demonstrate transform-limited pulses.
