Mode characteristics for gapless-coupled twin circular-side square microcavity lasers

We propose gapless-coupled twin circular-side square microcavities (TCSMs), and experimentally demonstrate the TCSM semiconductor lasers with weak mode coupling. The introduction of circular sides modifies the field distributions of the whispering-gallery modes and enables gapless coupling for the TCSMs without degrading the mode quality factors. Numerical simulation results show crossing and avoided crossing of the modes in the TCSMs with the variation of the wavelength difference and gain-loss contrast between the two cavities. By tuning the injection currents of the laser cavities, mode crossing is observed from the experimental lasing spectra of a TCSM laser. The realization of weak mode coupling in TCSM lasers indicates that the gapless-coupled deformed square microcavities provide a feasible robust coupling scheme for photonic integration. (C) 2021 Optical Society of America