Spectral behaviors of evanescent-wave-coupled gain lasing from dielectric-coated cylindrical microcavities

The spectral behavior of evanescent-wave-pumped and gain-coupled lasing was investigated in a dielectric-coated optical fiber surrounded by a dye-doped liquid. As the coating thickness increases, the lasing spectrum exhibits a blue shift due to a decrease in the number of the dye molecules in the evanescent field region of the whispering gallery mode. For comparison, lasing spectra of bare fibers with different dye concentrations were also measured. A simple model for evanescent-wave gain-coupled lasing in a coated cavity is proposed to explain the observed shifting behaviour.