High‐Resolution Time‐Correlated Single‐Photon Counting Using Electro‐Optic Sampling

A simple, practical method based on electro‐optic gating is experimentally shown to improve the temporal resolution of single‐photon detection by more than 16 times. Delay times between ultrafast single photons and a reference clock are stretched by a desired programmable sampling gate factor, allowing reconstruction of delay histograms with ≈0.001 photons per pulse to within 60 ps. By transferring the bandwidth of RF electronics to single‐photon counting, complex single‐photon signals with large time‐bandwidth products > 2000 are temporally stretched up so that they can be resolved by slow detectors, irrespective of the quality of the detector instrument response function. This method is also applied to biphotons, in order to reconstruct the 2D histogram of joint detection delays with 15 times better resolution. The phenomenon of nonlocal dispersion, which is not resolvable directly with the slow detectors, is then observable to within the 98 ps level. The proof‐of‐concept demonstration uses off‐the‐shelf commercial fiber‐integrated LiNbO3 modulators and RF electronics, and the method is readily integrable on‐chip and to speeds >100 GHz, offering a practical solution to ultrafast time‐correlated single‐photon counting beyond the research laboratory. A technique for high temporal resolution time‐correlated single‐photon counting is demonstrated using off‐the‐shelf components. Using slow detectors with an instrument response function spanning more than 1 ns, single‐photon waveforms are resolved to within 60 ps. The technique is extended to biphoton waveforms which are resolved to within 98 ps, allowing observation of nonlocal dispersion cancellation.