Sensor platform based on packaged whispering-gallery-resonators

Monitoring and controlling processes in industry, healthcare and environment encourage the demand and development of ultrasensitive sensors to detect physical and chemical analytes with very low concentrations. Optical methods based on resonant microstructures, that present high sensitivity, precision, selectivity, sensor lifetime and unit cost, are one of the most promising detection techniques. A fundamental limitation of optical microresonators is the realization of a reliable packaging approach that includes their readout element, e.g., tapered fibers. In this paper, the sensing response of packaged glass bottle microresonators have been demonstrated. Bottle-shaped structures support optical modes called whispering gallery modes along their curvature profile having a quality factor of 2.6x10(6) at 1550 nm in air. Two simple and robust packages fabricated by 3D printing and glass structuring methods were proposed for temperature and refractive index experiments. A temperature sensitivity of 9.9 pm/K in the range from 17.1 degrees C to 22.5 degrees C was obtained with a taper-coupled bottle system assembled into a plastic package. A similar value has been found when a bottle structure was mounted on a thermally-stable glass base and subjected to temperature changes from 18.6 degrees C to 26.3 degrees C. Both values were theoretically corroborated. For refractive index measurements, the fiber taper has been partially encapsulated employing a low refractive index glue. This provides a free-vibration package solution. Preliminary results show a refractive index sensitivity of 13 nm/RIU under a constant temperature of 22 degrees C. The proposed fiber-coupled bottle package enables new possibilities for the development of practical WGM-based sensors.