Experimental Studies of the Development of Nanoparticle Based optical Fiber Humidity Sensor with Linear Response Over a Large Dynamic Range

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The present thesis work is focused on the development of optical fiber relative humidity sensor with linear response over a widest possible dynamic range with an optimum sensitivity through a simple optical fiber sensor configuration. A comprehensive experimental study is carried out employing three schemes, namely, evanescent-wave (EW) absorption employing Zinc oxide (ZnO) as well as Titanium dioxide (TiO2) nanoparticle immobilized nanostructured sensing fiber cladding, direct guided mode exhaustive attenuation employing ZnO nanoparticle immobilized microstructured sensing fiber core, and Localized Surface Plasmon Resonance (LSPR) employing in-house scaled metal (gold) as well as metaldielectric (silver-TiO2) nanoparticles film in order to fulfill the objective. Response of all the proposed sensors was optimized against all possible influential compositional parameters such as chemical composition, reaction parameters, thickness etc. A wide linear dynamic range of 4-96%RH is observed with a sensitivity of 0.0012/%RH for the sensor employing evanescent wave absorption scheme with ZnO nanoparticles immobilized sol-gel sensing fiber cladding. Thus, a widest possible linear dynamic range is achieved, nevertheless, the sensitivity needed to be further increased. To realize this objective, a sensing configuration allowing exhaustive attenuation of entire guided mode was employed using ZnO nanoparticles (that corresponds to the widest linear dynamic range) immobilized sol-gel microstructured fiber. Almost identical linear dynamic range (5-95%RH) is observed with a manifold (~9 times) increase in the sensitivity as compared to ZnO nanoparticle employed EW fiber sensor. The maximum linear dynamic range decreased to 24-95%RH when the ZnO nanoparticles in sol-gel sensing cladding were replaced with TiO2 nanoparticles. Nevertheless, the optimized sensitivity improved much in comparison with ZnO nanoparticles immobilized sol-gel sensing cladding RH sensor. In the last sensing scheme (metal as well as metal-dielectric nanoparticles assisted LSPR), a linear dynamic range of 6- 90%RH is observed for sensing probe with gold nanoparticle film. The observed linear sensitivity is 0.0213nm/%RH. For sensor based on silver-TiO2 nanoparticle film, the linear dynamic range decreased to 29-95%RH; nevertheless, sensitivity is improved ~2 times compared to the sensing probe with gold nanoparticle film..
Supervisor: S.K Khijwania