BIFURCATION IN 20-GHZ GAIN-SWITCHED 1.55-MU-M MQW LASERS AND ITS CONTROL BY CW INJECTION SEEDING

A gain-switched laser operating at a 20-GHz repetition rate exhibited chaos and period-doubling depending on the bias condition, which was t he first observation for 1.55 mu m strain-compensated InGaAlAs-InGaAsP multiple-quantum-well (MQW) lasers, Unlike the case previously report ed for bulk lasers, the irregular behavior was set over wide bias curr ent conditions for the MQW laser. We show that the instability is attr ibutable to a small gain compression factor of the MQW laser and a hig h-repetition frequency of the gain-switching operation. Further, we re port that the irregular behavior can be successfully suppressed by see ding the laser with external coherent-light injection. The numerical s imulations of a set of rate equations using parameters extracted from small-signal modulation characteristics were carried out in order to c larify the conditions for the stabilization of the gain-switching oper ation, The scenario behind the inhibition of irregular behavior was du e to the enhanced damping phenomena of a nonlinear oscillator induced by the injection seeding light. The influence of the alpha parameter o n the optical pulse distortion under the external seeding and the para metric dependence for a single-period operation were investigated base d on numerical simulation.