Optical fiber biosensor based on multiple total internal reflections in heterodyne interferometry

Abstract

In this paper, an optical fiber biosensor based on multiple total internal reflections in heterodyne interferometry is proposed. The sensor is made of a long U-shaped multimode optical fiber which cladding is removed from the sensing portion of the fiber. With the optical fiber biosensor the phase shift difference due to the multiple total internal reflections (MTIR) effect between the P and S-polarizations is measured by using heterodyne interferometry with the optical fiber biosensor. Substituting the phase shift difference into Fresnel's equations, the refractive index for the tested medium can be calculated. The resolution of the sensor can reach 1.58×10^-6 refractive index unit (RIU). The optical fiber biosensor could be valuable for chemical, biological and biochemical sensing. It has some merits, such as, high resolution and stability, small size and real-time measurement.