Whispering gallery mode spectra of channel waveguide coupled microspheres

Evanescent coupling of light from glass channel waveguides into the whispering gallery modes of glass microspheres of radius 15 ?m and 100 ?m is studied experimentally at wavelengths near 1550 nm. Fitting the positions, widths and heights of resonances in the experimental spectra to the characteristic equation for microsphere modes and to universal coupled microresonator theory, we establish sphere radius and index, identify mode numbers, and determine losses. The results provide detailed information for the design of optical devices incorporating microsphere resonators in planar lightwave circuits.