Phase locking of a two-element laser array

Abstract

The dynamics of a two-element nonlinear-coupled laser array are briefly reviewed. It is pointed out that if the pump of the laser array reduces to zero for a time period shorter than the population decay time, then the system reduces to two coupled equations for the relative intensity and relative phase. It is well-known from the Poincare-Bendixson theorem that such an autonomous system of dimension two (without detuning) cannot exhibit chaos. By creating two evanescent-coupled lasers in a Nd:YAG etalon using diode end-pumping, the coupling strength between the two laser elements in the array can be continuously varied by adjusting the position of the pumping beams. This allows the observation of the phase locking process over a wide range of coupling strength. We have found that the locking is as fast as the on-set of lasing without undergoing a transition state as along as the coupling is strong enough to ensure such locking. The instantaneous locking is also independent of the coupling strength once the coupling is strong enough to ensure phase locking. New interpretation of phase locking process for a phase locked laser array is provided.