  The generation of stable short optical pulses in mode-locked lasers is of
tremendous importance for many applications. Mode-locking is a broad concept
that encompasses different processes enabling short pulse formation. It
typically requires an intracavity mechanism that discriminates between single
and collective mode lasing, which can be complex and sometimes adds noise.
Moreover, known mode-locking schemes do not guarantee phase stability of the
carrier wave. Here we theoretically propose that injecting a detuned signal
seamlessly leads to mode-locking in fiber lasers. We show that phase-locked
pulses, akin to cavity solitons, exist in a wide range of parameters. In that
regime the laser behaves as a passive resonator due to the non-instantaneous
gain saturation.
