Bistability in a two-colour semiconductor laser with dual injection

摘要

Optically injected semiconductor lasers exhibit a range of dynamical phenomonen, which for a single mode laser subjected to a single injection the bifurcations between these dynamical regions have been explained with simple rate equations [1]. Recently, motivated by potential switching applications, the dynamics of two-mode lasers including VCSELs, ring lasers and two-colour Fabry-Perot (FP) lasers have been of interest. In this work we consider theoretically and experimentally a two-colour FP laser subjected to dual injection and demonstrate a new bistable region between two locked states. Fig. 1 (a). shows the optical spectrum of the two-colour FP laser which has a 480 GHz mode spacing resulting in simultaneous oscillation of the two primary modes, ω_1 and ω_2 [2]. We have adapted the rate equations [2] to include two injected fields into the two modes, with amplitude K_(1,2) and detunings Δω_(1,2), and analyse the bifurcations using the continuation tool AUTO-07p. As we are only interested in fixed points of the system and for clarity, Fig. 1 (b). shows the saddle-node (SN) bifurcations in the K_1 - K_2 plane for Δω_2 =-18GHz. When Δω_1 =Δω_2, the SN is circular and for K_(1,2) > SN the slave is locked to the master. Thereby varying K_1 and K_2 inside the locked region allows continuous tuning between the two locked states. Decreasing Δω_1 the SN deforms and at Δω_1=-12GHz a cusp bifurcation is born and creates a triangular region where both lock states coexist giving rise to a bistability between the locked states.