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.

The coupling of a quantum emitter to the modes of a silica toroid is presented. A fiber taper is used to manipulate and transfer a preselected diamond nanocrystal onto the toroid. Optical coupling of few nitrogen vacancy (NV) color centers contained inside the nanocrystal to the resonator modes is demonstrated by detecting the fluorescence via a tapered optical fiber coupler. A clear antibunching in the photon correlation measurement is observed indicating emission from only six NV centers residing inside the nanocrystal. The latter is confirmed by a photoluminescence spectrum at liquid helium temperature resolving individual zero phonon lines.

Tapered optical fibers offer easy access to the evanescent field of their guided modes which is ideal for sensing applications. We introduce a soft-landing technique utilizing a linear Paul trap to select and place a single microparticle on the surface of a tapered optical fiber. This approach allows on-demand functionalization of fragile nanophotonic components with arbitrary particles, e.g., for advanced nanosensors.

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