Photon-counting optical time-domain reflectometry with superconducting nanowire single-photon detectors

We applied superconducting nanowire single-photon detectors to photon-counting optical time-domain reflectometry (OTDR). The setup was optimized to minimize the timing jitter of the photon detections to 42 ps. Therefore, we achieved a spatial resolution of 4 mm in our OTDR system. Based on the super high spatial resolution, we observed the reflection from a small fiber coil and see the peak width spread.