Dynamical Analysis of Modal Coupling in Rare-Earth Whispering-Gallery-Mode Microlasers

We report on an experimental study of a laser regime in erbium-doped whispering-gallery-mode (WGM) microspheres under modal-coupling between the co- and counterpropagating modes. The evidence of modal coupling is observed in the relative intensity noise spectrum of several WGM lasers. Cross-correlation measurements are carried out in order to analyze precisely the emission regimes. It is shown that depending on the material constituting the WGM resonator, frequency-locked bidirectional emission or a self-modulated regime could be reached. The control of the laser emission regime of WGM microlasers is of great importance in the aim of applications in microwave optics or optical sensor miniaturization.