Photon-Counting Optical Time Domain Reflectometer Using Superconducting Nanowire Single Photon Detector Based on Time to Digital Converter

High-resolution photon-counting optical time-domain reflectometry (PC-OTDR) is crucial for the development of fiber-optic sensing and network diagnostics, allowing accurate fault location and long-haul performance optimization. A major step forward for OTDR is reported by combining a superconducting nanowire single-photon detector (SNSPD) with a low-cost FPGA-based time-to-digital converter (TDC) to perform high-resolution measurements over 150 km of fiber. The SNSPD has 63% efficiency at 1550 nm and 25 ps timing jitter in free running, and the FPGA-TDC system provides high time precession 17.0 ± 1.3 ps with high data acquisition data rates The experimental data exhibit a 22.87 dB dynamic range with 7.5 cm (25 km) and 1.6 m (100 km) spatial resolution, which reflects the high-fidelity fiber characterization capability of the system. This work lays the groundwork for future developments in real-time signal processing and automatic failure detection in fiber networks, enhancing optical sensing applications.