Collective modes in coupled semiconductor disk lasers in the case of whispering-gallery modes

Samples of coupled semiconductor disk laser based on quantum-dimensional GaInAsSb/AlGaAsSb nanoheterostructures (emission wavelength of $\lambda\approx$ 2.28 $\mu$m) operating in the whispering-gallery modes are fabricated and studied. The emission spectra and directivity patterns are studied for laser systems of two types, i.e., coupled disk lasers with a bridge between resonators and those without it. It is found that both types of these lasers generate collective modes with an intermodal difference twice as small as that for a single disk laser. It is suggested that this effect is caused by the propagation of radiation from one disk laser to the other.