Coherent Pulse Interactions in Mode-Locked Semiconductor Lasers

Passive mode-locking (PML) is a well established technique to obtain short optical pulses with high repetition rates. A pulsating laser can operate in the harmonic mode-locked <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\text{HML}_{N})$</tex> regime, where the laser cavity supports a train of several equidistant pulses within one round-trip. However, even in this ordered state, each pulse possesses its own phase within the cavity round-trip. In the long cavity limit the situation becomes even more intricate as pulses become temporal localized structures that can be configured in arbitrary patterns in terms of relative positions and phases, cf. orange and blue arrows in Fig. 1. Note that these quantities are not necessarily independent as the pulses have several possibilities to interact with each other via carriers dynamics and/or their coherent overlapping due to e.g., optical feedback or tails interactions.