Predictable single photon source with variable photon flux

Abstract

This paper describes a method that allows us to realise an SI traceable single-photon source (SPS) based on a silicon vacancy centre in nanodiamond, which is optically excited by a pulsed laser.

Our method takes advantage of a very sensitive analog-mode photodetector comprising of a low-noise 3×3 mm silicon photodiode in conjunction with a custom made switched integrator amplifier. At the excitation rate of 70 MHz, the source delivers a photon flux large enough to be measured by the low optical flux detector. The directly measured photon flux constitutes an absolute reference. A measurement of the SPS’s absolute optical power with this detector eliminates the need for a precise knowledge of the SPS characteristics.

By changing the pump laser repetition rate, the photon flux of the SPS can be tuned in a controlled way. This gives us a direct way of linking conventional optical power levels, measurable with specifically designed analog-mode detectors, down to low photon flux levels needed for single-photon detectors.

The advantage of our method of changing the pump laser repetition rate is that it does not require precise knowledge of the source efficiency, as long as it remains the same for all the used pump frequencies. The source is calibrated by the analog-mode detector and can then be used at the reduced repetition rate for detector responsivity characterizations at the few-photon level.