D-type fiber optic sensor used as a refractometer based on total-internal reflection heterodyne interferometry

A new type of fiber optic sensor (FOS) based on total-internal reflection heterodyne interferometry (TIRHI) is proposed. It can be used as a liquid refractometer. The phase shift difference due to the TIR effects between the P- and S-polarizations is measured using heterodyne interferometry with a D-type fiber optic sensor. Substituting the phase shift difference into Fresnel’s equations, the refractive index can be calculated. It has some merits, such as, high sensitivity and stability, small size and real-time measurement.