Response of a fiber-optic Fabry-Pérot interferometer to refractive index and absorption changes: modeling and experiments

This paper describes how the refractive index and the absorption of investigated substances change the spectrum of the optical radiation at the output of the fiber-optic Fabry-Pérot interferometer. The modeling of the operation of the interferometer takes into account not only the spectra of the refractive index and the absorption of the medium that is inside the cavity, but also spectra of the refractive indices of the core and the cladding of the optical fiber connected to the interferometer cavity and the parameters of the mirrors forming the cavity. The physical phenomena related to the beam diffraction inside the cavity (i.e. the beam divergence, the curvature of the wavefront, and the phase shift caused by the Gouy effect) are taken into account, too. The spectra obtained from simulations were compared to the spectra registered during measurements. The preliminary results indicate that the fiber-optic Fabry-Pérot interferometer can measure both the refractive index and the absorption of investigated substances with high accuracy.