Whispering gallery mode microsphere resonator integrated inside a microstructured optical fiber

A compact, robust scheme for reliable in-fiber broadband excitation of whispering gallery mode (WGM) resonances into a microspherical resonator is demonstrated. A polymer microsphere (10 m) is encapsulated in the hollow channel of a collapsed-core, microstructured optical fiber, in direct contact with the suspended core. Such configuration allows efficient and reproducible excitation of the in-MOF-microsphere resonator that is characterized by two launch/collection schemes: core-input/scattering-output, and sphere-input/core-output. The latter allows an extra-fiber excitation of the microsphere WGMs. Numerically calculated WGM spectra are in agreement with experiments. Q factors in the range 103 - 104 are typically measured.