Refractive Index Measurement Resolution of the Core-Cladding Intermode Fiber Optic Interferometer with Spectral Interrogation

In this paper the intermodal fiber optic interferometer with the standard SMF-28 single-mode optical fiber which acts as a sensing element is considered. The calculation of the refractive index measurement resolution was performed using the Cramer-Rao relation. For that the sensitivities of the cladding mode propagation constants to the refractive index of surrounded media and the calculation of the cladding mode attenuation coefficients were carried out using numerical simulation. It has been found that the resolution increases for higher order modes and has a monotonic increasing character with increasing length of the sensitive section for the range up to several meters.