RESUMEN
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.
RESUMEN
In this Letter, we conceptually demonstrate the potential of a phase-sensitive amplifier to operate as an active detector of stochastic phase changes in fiber-based frequency dissemination systems with two orders of magnitude better sensitivity than state-of-the-art one-way systems relying on two-wavelength dissemination schemes. Theoretical and experimental analyses show that these stochastic phase changes (caused by environmental changes, e.g., due to temperature) can be detected with high sensitivity via optical phase comparison performed within the phase-sensitive amplifier. Experimental results are in close agreement with theoretical predictions showing that phase-sensitive amplifiers may find a niche application in metrology, with potential to significantly improve one-way fiber-based frequency dissemination systems.
RESUMEN
Physical unclonable functions are the physical equivalent of one-way mathematical transformations that, upon external excitation, can generate irreversible responses. Exceeding their mathematical counterparts, their inherent physical complexity renders them resilient to cloning and reverse engineering. When these features are combined with their time-invariant and deterministic operation, the necessity to store the responses (keys) in non-volatile means can be alleviated. This pivotal feature, makes them critical components for a wide range of cryptographic-authentication applications, where sensitive data storage is restricted. In this work, a physical unclonable function based on a single optical waveguide is experimentally and numerically validated. The system's responses consist of speckle-like images that stem from mode-mixing and scattering events of multiple guided transverse modes. The proposed configuration enables the system's response to be simultaneously governed by multiple physical scrambling mechanisms, thus offering a radical performance enhancement in terms of physical unclonability compared to conventional optical implementations. Additional features like physical re-configurability, render our scheme suitable for demanding authentication applications.
RESUMEN
We propose and experimentally validate a new cost-effective optical receiver-regenerator scheme for long-distance microwave-frequency standard dissemination, based on the properties of dual-wavelength injection locked Fabry-Perot (FP) lasers. The regenerator FP laser is injection locked to one of its longitudinal modes by the incoming intensity-modulated light carrying the microwave-frequency standard. The light of a local CW laser is also injected in the regenerator FP, locking it to an adjacent mode. The dual-injection locked laser reproduces the sinusoidal microwave-frequency standard on both wavelengths. The regenerated original signal is transmitted to the next node, whilst the local wavelength is fed back to the previous node for phase error extraction and link compensation. The performance of the proposed regenerator is demonstrated with Allan deviation and phase-noise measurements.