Low-temperature tapered-fiber probing of diamond nitrogen-vacancy ensembles coupled to GaP microcavities

In this work, we present a platform for testing the device performance of a cavity–emitter system, using an ensemble of emitters and a tapered optical fiber. This method provides high-contrast spectra of the cavity modes, selective detection of emitters coupled to the cavity and an estimate of the device performance in the single-emitter case. Using nitrogen-vacancy (NV) centers in diamond and a GaP optical microcavity, we are able to tune the cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a tapered fiber and measure the fiber-coupled NV spontaneous emission decay. Theoretically, we show that the fiber-coupled average Purcell factor is 2–3 times greater than that of free-space collection, although due to ensemble averaging it is still a factor of 3 less than the Purcell factor of a single, ideally placed center.