Development of special optical fibers for evanescent-wave chemical sensing

The paper summarizes results achieved in the Institute of Radio Engineering and Electronics in the field of investigation and fabrication of novel fib er-optic structures for evanescent-wave chemical sensing. Several approache s for increasing the evanescent-wave sensitivity of multimode silica optica l fibers to gaseous and liquid chemicals are shown. These approaches make u se of the decrease of the core diameter in sectorial and capillary sectoria l fibers, modification of trajectories of optical rays in the cores of inve rted-graded-index fibers, tailoring of the refractive index of porous layer s applied on silica cores, an output mode filter preventing the detection o f rays propagating at low axial angles or fibers bent in single or multiple turns.