Sensitive seismic sensors based on microwave frequency fiber interferometry in commercially deployed cables

Abstract

The use of fiber infrastructures for environmental sensing is attracting global interest, as optical fibers emerge as low cost and easily accessible platforms exhibiting a large terrestrial deployment. Moreover, optical fiber networks offer the unique advantage of providing observations of submarine areas, where the sparse existence of permanent seismic instrumentation due to cost and difficulties in deployment limits the availability of high-resolution subsea information on natural hazards in both time and space. The use of optical techniques that leverage pre-existing fiber infrastructure can efficiently provide higher resolution coverage and pave the way for the identification of the detailed structure of the Earth especially on seismogenic submarine faults. The prevailing optical technique for use in earthquake detection and structural analysis is distributed acoustic sensing (DAS) which offers high spatial resolution and sensitivity, however is limited in range (< 100 km). In this work, we present a novel technique which relies on the dissemination of a stable microwave frequency along optical fibers in a closed loop configuration, thereby forming an interferometer that is sensitive to deformation. We call the proposed technique Microwave Frequency Fiber Interferometer (MFFI) and demonstrate its sensitivity to deformation induced by moderate-to-large earthquakes from either local or regional epicenters. MFFI signals are compared to signals recorded by accelerometers of the National Observatory of Athens, Institute of Geodynamics National Seismic Network and by a commercially available DAS interrogator operating in parallel at the same location. Remarkable agreement in dynamical behavior and strain rate estimation is achieved and demonstrated. Thus, MFFI emerges as a novel technique in the field of fiber seismometers offering critical advantages with respect to implementation cost, maximum range and simplicity.

A simple algorithm for optimal design in distributed fibre-optic sensing

“…Variations of the Kangerlussuaq may be used for OED with fibre-optic sensing technologies that are not based on DAS. This includes, for instance, transmission fibre-optics systems that are characterized by a position-dependent measurement sensitivity that is controlled by local cable curvature (Marra et al 2018;Mecozzi et al 2021;Bowden et al 2022;Bogris et al 2022;Fichtner et al 2022a). High-curvature segments along the cable thereby mimic a distributed sensing system that should be optimally designed in order to maximize resolution of Earth structure or earthquake source parameters.…”

Environmental Monitoring: A Comprehensive Review on Optical Waveguide and Fiber-Based Sensors

“…The most developed method [ 180 ] is DAS (“distributed acoustic sensing”) technology. DAS uses fiber optic cables installed specifically for research purposes [ 182 ] or existing “dark” fiber of the optic networks (unused fibers that were originally installed for communication) [ 183 ]. In addition, to increase the sensitivity, optical fibers are supplemented with fiber Bragg gratings (FBG) [ 184 ].…”

Dual wavelength microwave frequency fiber interferometer system for distributed localization based on time delay estimation

“…They can be used in perimeter security, pipeline monitoring, seismic detection and other fields. In 2021~2022, Adonis Bogris and others from University of West Attica proposed a novel optical fiber sensor called microwave frequency fiber interferometer (MFFI) [1,2]. Basing on microwave photonics technology and frequency dissemination technology, the MFFI uses an intensity modulator to modulate the light and realizes fiber sensing by calculating the phase change of the light-carried microwave after transmitting in the fiber link.…”