Design and Fabrication of Lossy Mode Resonance Based U-Shaped Fiber Optic Refractometer Utilizing Dual Sensing Phenomenon

Abstract

The present work for the first time, provides a detailed analysis of U-shaped lossy mode resonance (U-LMR) fiber optic refractometer which is based on dual sensing phenomena. Theoretical and experimental studies on the sensitivities of U-LMR based fiber optic refractometer have been carried out utilizing different surrounding medium refractive indices (SRI). Also, the effect of bend diameter on the sensitivity has been investigated in detail by fabricating and analyzing zinc oxide (ZnO) coated U-shaped fiber optic probes of various bend diameters. Experimental sensitivities of the proposed U-LMR fiber optic refractometer were characterized in terms of wavelength shift, absorbance and full-width at half-maximum (FWHM) changes with respect to the SRI. With ZnO coated U-shaped fiber optic probe of bend diameter of 1.5 mm, we achieved six fold increase in the LMR sensitivity compared to the straight LMR probe. Also, in terms of the absorbance, our proposed probe was found to be four times sensitive compared to the uncoated U-shaped probe. In addition to this, for the probe diameter of 2.1 mm, sensitivity obtained by monitoring a new parameter, viz. FWHM change, is $\sim$ 900 nm/RIU which is at least 3 times better than the straight LMR probe.