Temperature measurements in deployed optical fiber networks using single photon optical time domain reflectometry.

We demonstrate an approach to measure average temperature changes in deployed optical fiber networks using Optical Time Domain Reflectometry, OTDR, at the single photon level. In this article we derive a model relating the change in temperature of an optical fiber to the change in time of flight of reflected photons in the fiber in the range -50 → 400 °C. A setup is constructed to validate this model utilizing a pulsed 1550 nm laser and a Superconducing Nanowire Single Photon Detector, SNSPD. With this setup we show that we can measure temperature changes with 0.08 °C accuracy over km distances and we demonstrate temperature measurements in a dark optical fiber network deployed across the Stockholm metropolitan area. This approach will enable in-situ characterization for both quantum and classical optical fiber networks.