Suppression of intrinsic photoluminescence in silica microtoroid resonators for hybrid NV center integration

Silica microtoroid resonators are an attractive platform for hybridly integrating solid-state single-photon emitters with on-chip photonic systems. A key challenge, however, is parasitic background photoluminescence from the resonators that spectrally overlaps with single-photon emission. Here, we show that the microtoroid photoluminescence originates from nonbridging oxygen hole-center defects generated during the laser reflow. This background photoluminescence is suppressed by controlled thermal bleaching at temperatures exceeding 600°C. Using this approach, we couple fluorescence from nitrogen-vacancy centers in nanodiamonds to silica microtoroids and collect it through optical fibers with a high signal-to-background ratio, demonstrating the potential of this hybrid interface for quantum technologies.