Temporal Localized Structures in Mode-Locked Vertical External-Cavity Surface-Emitting Lasers

The possibility of using optical Localized States (LSs) in resonators to code and process information bits has attracted a great deal of attention in the last twenty years [1]. LSs are stable solutions of dissipative systems characterized by a correlation range much shorter than the size of the hosting system. Temporal LSs (TLSs) have been recently reported in passively mode-locked (PML) semiconductor lasers [2]. It was shown that for cavity round-trip τ larger than the gain recovery τ
_g
and for large modulation of the losses induced by the absorber, several pulsating states with different number of pulses coexist for the same parameter values. In this multistable regime mode-locked pulses become localized, i.e. they can be addressed individually [3]. This was implemented in an electrically-pumped broad-area Vertical-Cavity Surface-Emitting Laser (VCSEL) coupled to a resonant semiconductor saturable absorber mirror (SESAM). VCSEL far-field transverse profile was imaged onto the SESAM in a self-collimating scheme for achieving stable mode-locking regime [4]. Though this peculiar scheme allowed efficient saturation of the SESAM, it also induced global coupling of the VCSEL's transverse section.