PT-symmetry in mutually coupled semiconductor lasers with a non-zero time delay

Abstract

Existence of PT symmetric regime in a system of two semiconductor lasers coupled face to face is being reported. The coupling involves the field of one laser coupled to the field of the other with a time delay. We investigate the occurrence of PT symmetry and PT transition for non-zero, but small delay times. Eigen values are obtained theoretically for the field transformation matrix formulated using normalized Lang–Kobayashi rate equations. We show that for certain delay times, the system exhibits PT symmetry and a PT transition to broken PT symmetry as the detuning frequency and coupling strength are varied. A control on the coupling coefficient and frequency detuning between the lasers is shown to be an efficient mechanism towards fine control of the PT symmetry in coupled lasers.