A fully digital MIMO-OFDM scheme for fading mitigation in Coherent Delta Phi-OTDR
13 October 2021
We introduce a Coherent-MIMO Delta Phi-OTDR based sensing technique that uses digital frequency division multiplexing of probing sequences in order to mitigate the coherent fading issue in Delta Phi-OTDR. Orthogonal Frequency Division Multiplexing (OFDM) is used to probe the optical channel on several electrical subcarriers, which responses are then combined according to specific reliability criterion to enhance the overall sensing sensitivity. This allows a decrease of the noise floor in sensing measurements on single mode fiber (SMF) and the mitigation of false alarms. Coherent MIMO-OFDM enables sensing over telecom fibers with a measured sensitivity level below 0.7n epsilon along 1.3km fiber over a mechanical bandwidth of 760Hz. Enhancements in the dynamic range for detection of mechanical excitation are presented with a gain over 18dBrad2 /Hz as compared to single-carrier probing.
