Microsphere resonator integrated inside a microstructured optical fiber

Here we report on a novel in-fiber microresonator coupler, which combines a microstructured optical fiber (MOF) and a polystyrene microsphere (PM), embedded into one of its empty capillaries. The MOF consists of a germanium-doped silica core (~2.5 m), suspended within three hollow channels with a maximum dimension of ~11 m. The microsphere has a diameter of 10.4 m and a refractive index n=1.59 at 589 nm. After selection of a single PM from a glass micropipette and its controllable infiltration inside the fiber capillary with the help of a liquid solvent, the microsphere is placed inside the MOF, in contact with the core, ~3 cm from the fiber endface. The operation of the coupler when radiation is guided along the fiber has been investigated under two different launch/collection schemes, i.e. in the core-input/sphere-output (C/S) and the sphere-input/core-output (C/S) mode.