Design and analysis of chemically etched and biconically tapered fiber for chemical sensing application

Abstract

Evanescent field (EF) based sensor has been of great importance in chemical and gas sensing application. Chemical sensing using evanescent wave sensor occurs due to EF absorption, scattering or both. In this paper, the phenomenon of EF scattering for sensing is critically analyzed by modeling of (i) chemically etched fiber and (ii) tapered fiber using COMSOL. Based on the modeling, the tapered fiber is predicted to have better sensitivity to the external medium than the chemically etched fiber. Finally the tapered fiber is fabricated and tested for different concentration of sucrose and glucose solution. An effect of mode coupling is evident in the response indicated by a reversal of the spectrum after the cutoff frequency of single mode fiber.