A NOVEL PROBE FOR AN EVANESCENT-WAVE FIBEROPTIC ABSORPTION SENSOR

A novel, highly sensitive probe consisting of a uniform region sandwic hed between two linear tapers for an evanescent wave fibre-optic absor ption sensor is proposed. The diameter of the uniform region is chosen to be equal to the minimum allowed diameter of the taper's output end . The first taper is used to bring the angles of the rays in the input fibre close to the critical angle of the sensing region while the sec ond taper reconverts the angles into their initial values so that they can propagate in the output fibre. It has been shown that the sensiti vity of the sensor depends on the length of the uniform region of the probe, the refractive index of the fluid and the numerical aperture of the fibre. The sensitivity increases with increase in the length of t he uniform region and also with decrease in the numerical aperture of the fibre. In addition, the sensitivity of the proposed probe can be f urther increased by launching the selected rays into the input fibre.