Low-noise cascaded frequency conversion of 637.2 nm light to the telecommunication C-band in a single-waveguide device.

Interconnected quantum devices are the building blocks of quantum networks, where state transduction plays a central role. The frequency conversion of photons into the telecommunication C-band is decisive in taking advantage of current low-loss transmission lines. Here, we report the difference frequency conversion of 637.2 nm fluorescent light from a cluster of NV centers in diamond to tunable wavelengths between 1559.0 nm and 1564.9 nm. In order to avoid detrimental noise from spontaneous emissions, we use a two-step conversion device based on a single-pumped periodically poled lithium niobate waveguide. We observed a total external (internal) conversion efficiency of 3.0 ± 0.1 (20.5 ± 0.8) % with a noise rate of 2.4 ± 0.8 (16 ± 5) cps/GHz.