Fano resonance in a multimode tapered fiber coupled with a microspherical cavity

Fano resonance in a tapered optical fiber in contact with a high-Q microsphere is demonstrated. Multimode waves propagating in a 2.3 mu m diameter taper were coupled with a single whispering gallery mode of a 220 mu m sphere, and their coherent interaction resulted in Fano resonance. The asymmetric line shapes of the transmission spectra changed periodically with scanning of the coupling position along the taper. The observed 24 mu m period was due to modal dispersion in the tapered fiber.