Abrupt taper Michelson interferometer using heterodyne for measuring refractive index

A method is proposed for measuring the refractive index (RI) of aqueous solutions using an abrupt taper Michelson interferometer and a synthetic heterodyne detection scheme. In the proposed approach, the abrupt taper Michelson interferometer is implemented with a Fabry-Perot cavity in a path-matching differential interferometer. The RI of the aqueous solution is then extracted from the phase shift of the heterodyne demodulated interferometric signal. The experimental results show that a change in the RI of 0.0001 prompts a phase shift of ~1.35° in the demodulated signal given the use of an abrupt taper Michelson interferometer with a sensing length of 20 cm.