Helical Multicore Fiber-Based Vibration Sensing

Long-distance monitoring of vibrations is essential for smart infrastructure. Forward transmission distributed sensing technologies lead the way in sensing distance, albeit with an extra layer of complexity caused by synchronization for vibration positioning. A unidirectional distributed fiber-optic vibration sensing system using helical multi-core fiber is proposed and demonstrated to overcome the synchronization challenge. By exploiting the optical path difference between straight and helical cores in a single optical fiber, and employing self-referencing interferometric in-phase/quadrature (IQ) demodulation, distributed vibration positioning can be achieved without bidirectional transmission, long-distance detector synchronization, multiple wavelength channels, nor backscatter noise suppression. The proof-of-concept experimental results reveal a minimum standard positioning deviation of 28 m over 20 km of sensing fiber. The sensitivities of the straight core and helical core are 8.6 rad/με and 9.1 rad/με, respectively, with the helical structure enhancing sensitivity by 5.5%. The corresponding limit of detection are 26.4 pε/Hz1/2and 22.6 pε/Hz1/2, respectively. The combination of space-division-multiplexing and forward transmission methods can open up a new avenue for fully distributed sensing.