Designing asymmetric fiber tapers for multimode-input-enhanced dissipative sensing in microresonators

A method for designing asymmetric fiber tapers, with nonadiabatic downtapers and adiabatic uptapers, is described. Such tapered fibers allow multimode input to a whispering-gallery microresonator for the enhancement of absorption sensing. The design described here permits the degree of nonadiabaticity for various pairs of fiber modes to be chosen. In this way, an asymmetric taper can be optimized to reduce excitation of fiber modes that do not couple into the microresonator whispering-gallery mode (WGM) but only provide undesired loss. This process allows for increased sensitivity enhancement when monitoring changes in the throughput dip depth rather than in the linewidth of the WGM.