Optical Solitons and Frequency Comb Generation - Abstract

Panayotov, Krassimir

Polarization dynamics of mode-locked VECSELs

VCSELs exhibit interesting polarization dynamics due to the lack of strong polarization selectivity mechanism [1]. Well accepted model reproducing these intriguing polarization dynamics is the so called Spin-Flip Model or SFM [2], which takes into account the carrier spin-dynamics during transitions between conduction band and heavy hole valence band in quantum well active material. SFM also explains the peculiar polarization properties of cavity solitons in broad area VCSELs [3, 4]. Recently, a spin-flip model for a broad-area VCSEL with a saturable absorber predicted a period doubling route to spatially localized chaos of elliptically polarized cavity solitons [5]. Although many research has been devoted to polarization dynamics of VCSELs, such studies for Vertical External-Cavity Surface-Emitting Lasers (VECSELs) are lacking. VECSELs are very well-suited for mode-locked (ML) operation by utilizing saturable absorber either as a mirror in the external cavity [6] or integrated in the gain-chip [7]. To the best of our knowledge, the impact of spin-flip dynamics on light polarization emission in ML operating VECSELS has not been considered. Here, we introduce a time-delayed SFM for VECSELs with saturable absorber mirror based on extension of the Vladimirov-Turaev model for ML semiconductor lasers [8] and reveal the existence of polarization multistability of the system. First, by including the spin-flip dynamics and phase and amplitude anisotropies we demonstrate that Vladimirov-Turaev SFM reproduces the existence of polarization instabilities and polarization switching in a similar fashion as the original SFM. Time trances for parameters typical for the VECSEL configuration are presented in Fig. 1, where (a) and (b) show that the fundamental ML can actually be realized for two orthogonal linear polarizations ”X” and ”Y” and (c) demonstrates more complicated dynamics with the two linear polarizations competing.