Long-Distance OFDR With High Spatial Resolution Based on Time Division Multiplexing

In this study, a long-distance optical frequency domain reflectometry (OFDR) with high spatial resolution based on time division multiplexing is proposed and experimentally demonstrated. Distributed strain sensing with high spatial resolution over long sensing range can be realized by reconfiguring the system layout in a time-division-multiplexed manner by re-routing the measurement signals for segmented processing with extra circulators and couplers only, rather than any other mechanisms for performance improvement of laser source or algorithms for nonlinear errors compensation. Through time-division-multiplexed reconfiguration, the sensing distance is no longer restricted by the path difference of the auxiliary interferometer which is commonly employed in OFDR systems for compensating laser frequency tuning nonlinearity. Compared with the traditional system layout, the proposed system allows distributed measurement with flexible spatial resolutions in each sub-sensing unit without any crosstalk among them. In experiments, distributed strain sensing with spatial resolution up to 5mm is achieved over an active sensing distance of 225m by the proposed system. Furthermore, the spatial resolution flexibility of the proposed system is further verified by successfully obtaining the strain information with 2 mm spatial resolution at the end of a 235-m-long fiber.