Optical time-domain reflectometry (OTDR) has been widely employed for optical cable monitoring and management. However, constrained by the trade-off between the detection bandwidth and sensitivity of linear detectors, it is difficult for conventional OTDR systems to achieve long sensing range and high spatial resolution simultaneously. Photon-counting OTDR (PC-OTDR) combines the characteristics of single-photon detectors and time-correlated single photon counting technology, has the potential to realize high spatial resolution measurement over long sensing range. In this work, the impact of PC-OTDR system parameters on spatial resolution and sensing range are analyzed: the light pulses are optimized by considering both the fiber dispersion and the time jitter of the single photon detection in the system; the signal-to-noise ratio is analyzed considering all the noises in the system, including the dark counts of the SPD, the photon counting fluctuation due to the Poisson distribution and the coherent Rayleigh noise. Accordingly, a PC-OTDR system with a spatial resolution of 10 cm and a sensing range of 100 km is demonstrated. Moreover, the spatial resolution of 10 cm is further verified over an 81.7 km fiber link that includes deployed fibers of 30.9 km. Thes results demonstrate that PC-OTDRs have strong capacity on long-distance high-resolution distributed sensing, which has great potential on optical link management and remote sensing over long-distance underground/submarine fiber cables, quantum communication networks, and energy transmission pipe networks.

The work was published on Photonics Research (https://www.researching.cn/Articles/OJ24f089f670377e31) at 26 April 2026 with the title of Photon-counting optical time-domain reflectometry with centimeter-level spatial resolution over fibers of 100 km. Xizi Sun from the Beijing Academy of Quantum Information Sciences is the first author of this paper. Prof. Wei Zhang is the corresponding author of this paper.