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