Deployment and comparison of a low-cost high-sensitivity concentration meters using micro-optical resonators

Micro-optical resonators have been introduced as sensors in many applications for a wide number of variable types of stimuli due to their very high resolution, high sensitivity and high quality factor. In this paper a novel micro-optical sensor was designed and tested as a concentration meter for chemical composition of a solution. The micro-optical resonator used is based on whispering gallery mode (WGM). This phenomenon appears when a tapered single mode laser carrying micro-optical fiber is evanescently coupled with a polymeric or silica micro-optical resonator. The presented sensor shows the change in concentration by experiencing a change in its morphology due to the varied viscosity of its environment. The variation of concentrations or fluid contents results in a change between the radii of the micro-optical resonator. With varied chemical composition and concentration in the tested sample varied infinitesimally small morphological changes are detected. The change in the resonators shape is read as a WGM shift in the resonance transmission spectrum which is interpreted using a technique called cross-correlation which compares the output across time to display the shift which is later translated into distinct concentration levels. The proposed exceptionally low cost sensors were able to detect change at very high resolutions allowing better sensitivity along with wider range of variation. Experimental work for detection of ranges of concentrations of variable type of contaminants is presented.