“…with z being the longitudinal coordinate, P the photon number inside the cavity, and the phase of the electrical field. In (1) and (2), is the free-running laser frequency, is the lasing frequency in the presence of optical feedback, is the amplitude reflectivity of the external optical feedback coming from a distant reflecting point and being assumed to be such as , is the external round-trip time (with the external cavity length), is the complex electrical field defined as , and are the Langevin forces in the time domain, and is the carrier density deviation induced by the external optical feedback. As it has been previously mentioned, longitudinal variations such as those on internal optical power are taken into account through the integral terms over the cavity length L. On the other hand, it is important to stress that expressions of , , and given by (3), (4), and (5) are linked to the Wronskian that comes as a consequence of the resolution of the wave equation for the electromagnetic field [12].…”