Whispering-gallery mode resonator sensors based on liquid droplets
Authors: Zullo R., Giorgini A., Avino S., Malara P., De Natale P., Gagliardi G.
Autors Affiliation: Consiglio Nazionale Delle Ricerche, Istituto Nazionale di Ottica (INO), Comprensorio A. Olivetti, via Campi Flegrei 34, Pozzuoli (Naples), 80078, Italy; Consiglio Nazionale Delle Ricerche, Istituto Nazionale di Ottica (INO), Largo E. Fermi 6, Firenze, 50125, Italy
Abstract: We present a simple and effective set-up to exploit the enhancement of passive optical cavities that are directly made from a liquid droplet. The optical resonances, corresponding to the so-called whispering-gallery modes (WGMs), are excited by a focused free-space beam edge-coupling scheme. Very narrow resonances are observed, both in the visible and near-infrared spectral regions, with quality (Q) factors ranging from 105 to 107 and beyond. Different methods for interrogation via frequency locking of a laser source to the WGM are shown. Locking of a diode laser to the equatorial modes of a liquid droplet resonator is demonstrated at 1560 nm and 663 nm. This approach makes high-performance optical sensing directly feasible in liquid samples with a number of advantages in view of their application for detection and quantification of bio-molecules.
KeyWords: Drops; Infrared devices; Laser resonators; Liquids; Locks (fasteners); Optical resonators; Quantum optics; Resonators, Cavity photons; Detection and quantifications; Laser frequency; Liquid droplets; Narrow resonances; Optical resonance; Visible and near infrared; Whispering gallery mode resonator; Whispering gallery modesDOI: 10.1117/12.2230623Connecting to view paper tab on IsiWeb: Click here