Distributed optical fiber sensing based on coherence-length gated microwave photonics interferometry

This paper reports a highly sensitive distributed optical fiber sensing technique based on resolving the optical interference information in the microwave frequency domain. This technique uses a microwave intensity modulated coherent light through cascaded weak reflectors along a single mode fiber (SMF). The microwave is used to resolve the location of each reflector along the SMF. The coherence length of the optical carrier performs as the time domain gate and segments the optical interference between reflectors in the time domain. Within the coherence length, a small optical path difference change between two reflectors produces a change in the amplitude of the corresponding time domain pulses. The sensitivity of sub-με for distributed strain sensing has been demonstrated.