A scatterer-assisted whispering-gallery-mode microprobe

A fiber-based whispering-gallery-mode (WGM) microprobe, combining both the high optical field enhancement of the WGMs and the compact structure of the optical fiber, is highly desired for sensing and imaging. Here we report a WGM microsphere resonator coupled to a single-mode fiber interfaced by a graded-index lens. By scattering a focused laser beam through a nano-scatterer, with the help of a two-step focusing technique as well as Purcell effects, the efficient far-field coupling of WGMs with an efficiency as high as 16.8% has been demonstrated in our system. With the feature of both input and output of the probe light propagating along the same fiber, such a scatterer-assisted WGM microprobe will serve as a convenient tool for sensing/imaging applications.