Coupling of ultrathin tapered fibers with high-Q microsphere resonators at cryogenic temperatures and observation of phase-shift transition from undercoupling to overcoupling

摘要

We cooled ultrathin tapered fibers to cryogenic temperatures and controllablycoupled them with high-Q microsphere resonators at a wavelength close to theoptical transition of diamond nitrogen vacancy centers. The 310-nm-diametertapered fibers were stably nanopositioned close to the microspheres with apositioning stability of approximately 10 nm over a temperature range of 7-28K. A cavity-induced phase shift was observed in this temperature range,demonstrating a discrete transition from undercoupling to overcoupling.