Optimized Tapered Optical Fiber for Ethanol (C $_{\bf 2}$ H $_{\bf 5}$ OH) Concentration Sensing

An optimized study of biconical tapered multi-mode plastic optical fiber sensor for concentration sensing of ethanol (C₂H₅OH) is presented. The sensitivity is enhanced through V-number matching as well as by optimizing the taper radius and taper length. The ray-tracing method is used to analyze the evanescent wave penetration depth (EWPD). The theoretical analysis and experimental results are used to optimize the taper ratio and taper length for the achievement of high EWPD and high sensitivity. The analysis indicates that the sensitivity of tapered fiber sensor can be improved by decreasing the taper ratio with simultaneous increase in the taper length. The highest sensitivity of 1.527 mV/% is achieved from the tapered fiber with a taper ratio of 0.27 and taper length of 8 cm. The proposed parametric optimized tapered fiber sensor can detect the change in concentration of C₂H₅OH as small as 6.55 × 10^-3.