Contents I. Introduction
Strong effort is currently focused on optical transmission at 40 Gb/s and beyond for next-generation telecommunication networks. New devices are needed to achieve high-speed signal-processing function in the optical domain and specific characterization has to be developed jointly in order to meet as far as possible the advanced specifications by performing low-cost and easy measurements. Clock recovery is one of the expected all-optical functions to take place in the regenerator for retiming, in switches or cross connects for packets or streams synchronizing, or in time division multiplexer and demultiplexer [1]–[4]. Particularly, optical retiming, reshaping, and reamplification (3R) regeneration along the line path is attractive to combat hard impairments well above 40 Gb/s when nonlinear, dispersion, and crosstalk effects become too difficult to manage in long-haul systems [2], [5], [6]. Besides actively mode-locked fiber or semiconductor lasers, and phase-locked loop solutions, self-pulsating (SP) lasers are of particular interest. Among several proposed structures, multimode passively mode-locked lasers have shown interesting results at 40 GHz [7]–[9]. Such lasers exhibit potential performance to provide a robust recovered clock at low jitter and high frequency in a range of low intensity and with polarization insensitivity to the injected optical signal [8]. Clock extinction ratio is an important matter in each function as it directly reacts on output signal integrity. However, as explained below, it is of particular concern in optimizing multimode SP-laser design and it requests a phase-amplitude characterization method specifically adapted.
