  We demonstrate a photon-counting optical time-domain reflectometry with 42.19
dB dynamic range using an ultra-low noise up-conversion single photon detector.
By employing the long wave pump technique and a volume Bragg grating, we reduce
the noise of our up-conversion single photon detector, and achieve a noise
equivalent power of -139.7 dBm/sqrt(Hz). We perform the OTDR experiments using
a fiber of length 216.95 km, and show that our system can identify defects
along the entire fiber length with a distance resolution better than 10 cm in a
measurement time of 13 minutes.
