Excitation of Whispering Gallery Modes in Silica Capillary Using SMF-MMF Joint With Lateral Offset

Whispering gallery modes (WGMs) have been effectively excited in a silica tube by employing a single-mode-fiber/multimode-fiber (SMF/MMF) joint with the lateral offset to enhance the evanescent field over the tapered MMF region. Experimental results indicate that thanks to the lateral offset at the SMF-MMF joint, the taper diameter is about one order of magnitude larger than that of a standard fiber taper coupler. The WGMs in the silica capillary have been theoretically analyzed by using the eigen equation to deal with WGMs in cylindrical microresonators. Our proposed WGM excitation scheme is more robust than the conventional WGM systems based on fiber tapers of a few micrometers in diameter, which is anticipated to serve as micro-fluidic-channel for biological and chemical sensing applications.