An Efficient Integrated Two-Color Source for Heralded Single Photons
  We present a pulsed and integrated, highly non-degenerate parametric downconversion (PDC) source of heralded single photons at telecom wavelengths, paired with heralding photons around 800 nm. The active PDC section is combined with a passive, integrated wavelength division demultiplexer on-chip, which allows for the spatial separation of signal and idler photons with efficiencies of more than 96.5 %, as well as with multi-band reflection and anti-reflection coatings which facilitate low incoupling losses and a pump suppression at the output of the device of more than 99 %. Our device is capable of preparing single photons with efficiencies of 60 % with a coincidences-to-accidentals ratio exceeding 7400. Likewise it shows practically no significant background noise compared to continuous wave realizations. For low pump powers, we measure a conditioned second-order correlation function of g^(2)(0)=0.0038, which proves almost pure single photon generation. In addition, our source can feature a high brightness of <n_pulse>=0.24 generated photon pairs per pump pulse at pump power levels below 100 uW. The high quality of the pulsed PDC process in conjunction with the integration of highly efficient passive elements makes our device a promising candidate for future quantum networking applications, where an efficient miniaturization plays a crucial role. 
Stephan Krapick, Harald Herrmann, Viktor Quiring, Benjamin Brecht,   Hubertus Suche and Christine Silberhorn
quant-ph physics.optics