Figure of Merit of All-Dielectric Waveguide Structures for Absorption Overtone Spectroscopy

The figure of merit is proposed for all-dielectric waveguides for absorption overtone spectroscopy as the measure of probing efficiency of molecular overtones. It is defined as the power in the evanescent tail over the total power carried by the guided mode. The figure of merit was calculated for the proposed waveguide structures and then compared. We address each waveguide structure in probing overtones. We show that the figure of merit can be substantially increased due to the downscaling of the physical dimensions of the waveguide and microfiber. Such a configuration enables integration possibilities for ultrasensitive devices harnessing evanescent excitation of molecular overtones on miniature and portable chips.