High-accuracy displacement measurements under single-photon-level signal conditions using asynchronous optical sampling with dual-wavelength combs

We experimentally demonstrated high-speed and high-accuracy displacement measurements under single-photon-level signal conditions using an ultrafast time-resolved photon-counting method employing a two-color fiber-comb-based asynchronous optical sampling (ASOPS) technique. Multi-ASOPS trigger was utilized to accumulate the photon signal, effectively suppressing the residual timing jitter between the two independent combs with a simple experimental setup. This approach enabled photon-counting cross-correlation measurement of pW signal pulses with a FWHM below 200 fs across the entire time range, whereas without this approach, the width was broadened to ~3 ps from the original 120 fs with mW signal pulses. Displacements of up to 400 mm - the pulse-to-pulse spacing of the comb - was measured by the photon-accumulated signal with µm-level accuracy. The non-ambiguity measurement range can be extended by changing the repetition frequency of the combs. This technique provides a powerful tool for high-accuracy single-photon optical ranging such as for remote sensing or biomedical imaging.