Photon-counting optical time-domain reflectometry (PC-OTDR) offers high sensitivity and spatial resolution for long-distance fiber measurements. InGaAs/InP single-photon avalanche diodes (SPADs) provide a mature, compact, and cost-effective detector solution, but their long dead time causes nonlinear distortion. Here, we propose a scheme combining gated detection with dynamic power control to maintain a consistent detector operating point across the fiber. We further optimize the operating parameters to balance signal-to-noise ratio (SNR) and inter-gate continuity. Measurements over a 20 km fiber demonstrate effective distortion suppression and a uniform SNR averaging 11.77 dB. Loss and reflection measurements, compared with a commercial OTDR, confirm the scheme’s accuracy and robustness. The scheme also supports probe pulse peak powers comparable to those of commercial OTDRs, potentially extending the dynamic range to 24.4 dB in theory. This work improves the practicality of SPAD-based PC-OTDR for long-distance fiber testing and sensing.

This work was published in Journal of Lightwave Technology on October 15, 2026 (https://ieeexplore.ieee.org/document/11663403). The first author is Ph.D. student Zhechun Ding, and the corresponding authors are Dr. Xizi Sun (BAQIS) and Prof. Wei Zhang.