Inverted-graded index fiber structures for evanescent-wave chemical sensing

The paper deals with a novel multimode fiber-optic structure, the inverted- graded index profile (IGI) fiber, and its feasibility for evanescent-wave c hemical sensing. Results of the theoretical analysis of the sensitivity of the IGI fiber to changes of the refractive index and light absorption coeff icient of its cladding are shown. Fabrication of IGI fibers doped in the co re with GeO2 or B2O3 is described. The evanescent-wave sensitivity of the p repared IGI fibers to changes of the cladding refractive index and light ab sorption coefficient is given showing its increase in comparison with refer ence fibers with cores of purr: silica and with the same polymer claddings as the IGI fibers. (C) 1998 Elsevier Science S.A. All rights reserved.