Coexisting periodic attractors in injection-locked diode lasers

We present experimental evidence of coexisting periodic attractors in a semiconductor laser subject to external optical injection. The coexisting attractors appear after the semiconductor laser has undergone a Hopf bifurcation from the locked steady state. We consider the single-mode rate equations and derive a third-order differential equation for the phase of the laser field. We then analyse the bifurcation diagram of the time-periodic states in terms of the frequency detuning and the injection rate and show the existence of multiple periodic attractors.