EVANESCENT-ABSORPTION COEFFICIENT FOR DIFFUSE SOURCE ILLUMINATION - UNIFORM-FIBER AND TAPERED-FIBER SENSORS

A comparative study of evanescent-wave fiber-optic absorption sensors based on uniform and tapered fibers has been carried out. The expressi ons for an effective evanescent-absorption coefficient have been deriv ed for diffused or Lambertian source illumination. It has been shown t hat the sensitivity of sensors depends on the numerical aperture of th e fiber, the taper ratio, and the refractive index of the absorbing fl uid. The higher the sensitivity the smaller the range of functional re fractive indices of the fluid. In the case of taper, which fiber (with a low or high numerical aperture) has maximum sensitivity depends on the refractive index of the fluid.