In-fibre whispering gallery mode resonators: From isolated microspheres to coupled systems

We review here on a new, integrated in-fiber microresonator coupler, which is a combination of a microstructured optical fiber (MOF) and a microsphere; the last is encapsulated into the capillaries of the MOF. The light guided into the MOF core excites WGMs inside the encapsulated microsphere, manifested in out-scattering or transmission mode. Microspheres being made of polystyrene or BaTiO₃ glass, have been infiltrated inside silica and germanosilicate core MOFs and their spectral response was measured. The operation of this composite light coupler has leaded to Q-factors greater than 3.5×10³ for a single microsphere. Results related to the infiltration of several polystyrenes microspheres and the formation of coupled cavities inside a single MOF capillary and their spectral scattering characterisation will be shown. Finally, the tuning of the WGM spectrum of a BaTiO₃ glass microsphere infiltrated inside a MOF by exploiting photorefractivity will be presented.