Label-Free Particle Sensing by Fiber Taper-Based Raman Spectroscopy

A fiber taper-based method for label-free Raman sensing is presented, which exploits the interaction between adsorbed specimen and the exposed evanescence tail of guided pump light. Chemical specificity and detection of microsphere specimens with diameters as small as 1 mu m are shown. To improve the sensitivity, we further propose resonator-enhanced Raman spectroscopy by taking advantage of the power build-up of a resonant mode in a cavity. Proof of concept is demonstrated by incorporating a fiber taper within a fiber ring resonator and locking a tunable laser to a circulating resonant mode. This demonstration shows a modest 40% enhancement of the Raman signal.