Abstract: A theoretical analysis of the operation of a chemical sensor based on cavity-enhanced optical absorption is given for a system in which the cavity is a dielectric whispering-gallery microresonator. Continuouswave input is assumed, and the detection sensitivity is characterized in terms of an effective absorption path length. In the case of tunable singlefrequency input, it is shown that monitoring analyte-induced changes in the throughput dip depth enables detection with relative sensitivity greater than that of frequency-shift and cavity-ringdown methods. In addition, for the case of broadband input and drop-port output, an analysis applicable to microcavity-enhanced absorbance spectroscopy experiments is given
