Highly accurate refractive index sensor based on Fourier-transformed phase acquisition in fiber-optic interferometer

High precision refractive index (RI) measurement was achieved by utilizing the phase term of a Fourier-transformed interference signal. With a fiber-optic Fabry-Perot RI sensor, it was verified that the proposed method had high resolving performance in RI determination compared with the conventional wavelength tracing method. Even with a tiny variation in liquid RI, the Fourier-transformed phase shift showed high accuracy as much as 0.99995 of R square value.