Comparison of photon counting and analog techniques for the measurement of photon pair generation in a PPLN waveguide

We present two independent measurements of the photon pairs production efficiency (PPPE) at 1572 nm, generated in a noncommercial periodically poled lithium-niobate waveguide fabricated in our laboratory. The first measurement, referred to as "direct" measurement, is performed at the photon-counting level (light power at the level of a few picowatts), exploiting a typical coincidence detection technique and a dedicated statistical model. In this case the measured PPPE is (4.1± 1.1) 1011 pairs/(s W). The same parameter was estimated independently by a well-established "indirect" measurement, based on a difference frequency generation experiment (typical light power level of a few microwatts). This other measurement yields (5.0±2.4) 1011 pairs/ (s W). Despite the large uncertainty of this second measurement, we observe that the two results are in good agreement even considering only the lower uncertainty value. To our knowledge, it is the first realization of a comparison between these two measurement techniques, working at so different light levels.