Existing fiber optic sensing technologies, such as fiber Bragg gratings (FBGs) and phase-sensitive optical time-domain reflectometry (φ-OTDR) systems, encounter significant challenges. These challenges include complex and high system cost, limited sensitivity, narrow frequency ranges constrained by factors like pulse repetition rates, and signal fading. Addressing these issues requires developing more cost-effective, highly sensitive and versatile fiber optic sensors that can operate over a broad frequency range and are simpler to fabricate.

NETL’s invention is a low-cost, acoustic emission monitoring system that utilizes multiplexed SNS fiber sensors to detect vibrations via multimode interference, offering enhanced sensitivity and a simplified fabrication process compared to traditional sensors. Light from a distributed feedback (DFB) laser is split into multiple SNS sensors, each comprising a no-core fiber (NCF) segment between two single-mode fibers (SMFs). Vibrations induce strain changes in the NCF, altering the transmitted interference pattern and resulting in measurable output power changes. A high-speed photodetector, coupled with a fast optical switch or fiber coupler, captures the variations for real-time analysis. Operating over a broad frequency range from 1 Hz to 400 kHz, this system is novel in being the first to demonstrate quasi-distributed acoustic/vibration monitoring using multiplexed SNS fiber structures, surpassing existing approaches such as FBG and distributed acoustic sensing (DAS) systems.