Nonlinear interactions in coupled microlasers

Abstract

Nonlinear interactions in coupled microlasers are theoretically investigated. For the description of the lasing properties of such systems the Steady-State Ab-Initio Lasing theory is used. A computational framework for solving the resulting equations has been developed on top of the finite element library ngsolve so that arbitrarily shaped two dimensional cavities can be modelled numerically. In particular, we investigate the lasing behavior of two evanescently coupled microdisks, a so-called photonic molecule. The dependence of the lasing behavior on the coupling strength, which can be modified by varying the intercavity spacing of the disks, is compared to measurements of real devices, which are fabricated from quantum cascade lasers at the Institute for Photonics of TU-Vienna. A good qualitative agreement with the experimental results is observed. A special emphasis is put on a specific pumping scheme where the disks of the photonic molecule are pumped sequentially to full pump strength. Although the overall pump of our laser system is continuously increased, we observe an intensity drop in the laser output which can even lead to the shutdown of the laser. To explain this effect investigations are carried out for an equivalent 1D system. Thereby we show that the intensity drop is directly related to the occurrence of an exceptional point, which result connects our findings to a similar effect found in PT-symmetric systems.