CHARACTERIZING WHISPERING-GALLERY MODES IN MICROSPHERES BY DIRECT OBSERVATION OF THE OPTICAL STANDING-WAVE PATTERN IN THE NEAR-FIELD

We demonstrated the use of a near-field probe to map the evanescent fi eld of an optical standing wave in a fused-silica whispering-gallery m ode microresonator. The periodicity of the observed standing wave allo ws us to estimate accurately the radial mode number of the whispering- gallery mode resonance that is being excited. We find that the use of a fiber half-coupler to excite these resonances in fused-silica micros pheres results in only the lowest radial mode numbers' being strongly excited, as predicted. (C) 1996 Optical Society of America