An alignment-free fiber-coupled microsphere resonator for gas sensing applications

In this paper we report on the assembly of a robust sensor system consisting of a polystyrene microsphere resonator attached to an optical fiber taper. Since the sphere is only supported by the micrometer-sized fiber no further alignment is necessary. This results in a thermally and mechanically well isolated optical resonator system with quality factors as high as 6×105. The narrow resonances of whispering gallery modes supported by the polystyrene resonators shift with temperature at a rate of 3.8 GHz/K. Thus, a sensitive thermometer is established which allows to detect the surrounding gas via its characteristic thermal conductivity.