Advanced single photon counting instrumentation for SPADs

In order to acquire low-level optical signals with picosecond resolution, Single-Photon Avalanche Diodes (SPADs) are exploited thanks to their extreme performance. For many demanding applications, there is a growing need to operate such detectors with advanced instrumentation, specifically designed for efficiently exploiting the best performance in terms of sensitivity, timing resolution, fast-gating capabilities, etc. To this purpose we designed, tested and employed an ultra-fast pulse generator, a fast gated-counter and a wide-band delayer. The pulse generator is designed for gating SPADs with fast transition times (less than 100 ps), when it is needed to avoid unwanted photons that either precede or follow the useful signal. The gated counter acquires photons in well-defined time windows, programmable from 100 ps up to 10 ns. Finally, a wide-band delayer provides programmable delays, ranging from 25 ps up to 6.4 ns in steps of 25 ps. Such a delayer can be used to synchronize signals in many different experimental setups.