Spectral cleaning and output modal transformations in whispering-gallery-mode microresonators

A systematic study on the effects of microtaper fiber diameters on the spectral characteristics of a whispering-gallery-mode (WGM) micro-bottle resonator (MBR) is presented. Progressively cleaner and simpler spectra of the MBR were observed when the utilized microtaper fiber waist diameter ( D t ) was increased from 2µm to 10µm. The maximum transmission depth at resonance varies with different microtaper fiber utilized from ~20 dB ( D t = 2µm) to ~4 dB ( D t = 10µm). The loaded Q-factors were observed to be unaffected by the increase of D t with values of > 10 6 being measured in all cases. Mode transformation of MBR was also experimentally investigated and compared to a microdisc FDTD simulation by studying near-field images of the output beam on the waist of the microtaper fibers. For the first time, experimental observation of mode transformation from LP 01 to LP 11 across scanned WGM resonances is being reported.