High Dynamic Range Externally Time-gated Photon Counting Optical Time-domain Reflectometry

TL;DR

This paper introduces an externally time-gated photon counting scheme using a high-speed optical switch to enhance the dynamic range of optical time-domain reflectometry, demonstrated through theoretical analysis, simulation, and experiments.

Contribution

It proposes a novel externally time-gated approach with a Mach-Zehnder interferometer to improve PC-OTDR dynamic range, validated by experiments at 800 nm wavelength.

Findings

Achieved 30.0 dB dynamic range over 70 meters with 50 ns gating.

Improved dynamic range by 11.0 dB compared to no gating.

Successfully detected a 0.37 dB loss event with gating.

Abstract

Single photon detector (SPD) has a maximum count rate due to its dead time, which results in that the dynamic range of photon counting optical time-domain reflectometry (PC-OTDR) de-creases with the length of monitored fiber. To further improve the dynamic range of PC-OTDR, we propose and demonstrate an externally time-gated scheme. The externally time-gated scheme is realized by using a high-speed optical switch, i.e. a Mach-Zehnder interferometer, to modulate the back-propagation optical signal, and to allow that only a certain segment of the fiber is monitored by the SPD. The feasibility of proposed scheme is first examined with theoretical analysis and simulation; then we experimentally demonstrate it with our experimental PC-OTDR testbed operating at 800 nm wavelength band. In our studies, a dynamic range of 30.0 dB is achieved in a 70 meters long PC-OTDR system with 50 ns external gates, corresponding to an improvement of 11.0 dB in dynamic range comparing with no gating operation. Furthermore, with the improved dynamic range, a successful identification of a 0.37 dB loss event is detected with 30-seconds accumulation, which could not be identified without gating operation. Our scheme paves an avenue for developing PC-OTDR systems with high dynamic range.