Twin-Field Quantum Key Distribution (TF-QKD) is a promising protocol to extend the secure communication range beyond the limits of conventional QKD, provided that phase noise along the optical channels is tightly controlled. In this work, we experimentally investigate the electro-mechanical phase noise affecting optical fibers in electrical grid environments, as a preliminary step toward deploying TF-QKD over Optical Ground Wire (OPGW) networks that run together with the electricity grids. Measurements were performed in a medium and low voltage smart grid test facility, which offered an accessible and controllable environment that shares some key features with OPGW installations. We analyze phase noise under varying electrical load conditions and infer the corresponding Quantum Bit Error Rate (QBER), providing a first experimental benchmark for future quantum communication over power grid fibers.

Data routinely collected from distributed fiber-optic cables embedded in civil structures can be repurposed as measurements for structural health monitoring (SHM). However, effectiveness depends critically on fiber-structure coupling and on the ability to infer meaningful structural parameters from the recorded signals. This proof-of-concept study proposes a framework to transform fiber-optic signals, acquired by a recently developed coherent Laser Interferometry (LI) technique, into distributed structural stress fields by combining a calibrated digital twin with surrogate modeling. A finite-element (FE) model is first calibrated using fiber-derived natural frequencies and fiber-averaged strain histories under different fiber-structure coupling conditions, providing a physics-based reference for subsequent strain-to-stress inference. Based on the calibrated FE response, surrogate models are identified via a local response function approach to map fiber-averaged strain to the stress distribution along the beam. Numerical damage scenarios show sensitivity to localized stiffness loss, with the surrogate model reconstructing damage-induced stress redistributions and phase shifts from the fiber signal alone. The proposed framework highlights the potential of repurposing existing communication fiber networks to recover distributed strain and stress fields over large-scale structures when combined with appropriate digital surrogate modeling.

Optical fiber sensing on deployed cables is gaining significant interest as a means to enhance network integrity and expand environmental monitoring capabilities. To fully achieve these goals, sensing signals must coexist with data transmission. While phase and state-of-polarization analysis are promising candidates for this integration, their practical exploitation presents several challenges. Because these methods measure the integrated deformation along the entire cable, sensitivity is often limited by high environmental noise floors. Furthermore, event interpretation and localization require more sophisticated analytics than conventional distributed fiber sensing. Incorporating fiber sensing into standard network architectures also necessitates a novel telemetry management system capable of handling heterogeneous datasets, high data rates, and stringent synchronization requirements. We present progress on these aspects, based on multi-year analysis of fiber-sensing data collected in field environments. Our results confirm that integrated sensing achieves the sensitivity required to detect mid- and low-magnitude seismic events within a range of tens of kilometers from the fiber, holding the potential to support seismic monitoring services in terrestrial areas. Additionally, we demonstrate the detection and localization of anomalous vibrations and anthropogenic events and the development of an autonomous anomaly-detection tool suitable for real-time alerting. Finally, we outline the requirements for an advanced network management system designed to accommodate sensing alongside conventional telemetry, supporting the transition from proof-of-concept experiments to robust, large-scale applications.

An intercontinental metrological clock comparison between Italy and the Republic of Korea was performed by means of geodetic K-band VLBI observations. The comparison involved the hydrogen masers (H-masers) used at Medicina and Sejong radio telescopes. The same clocks were simultaneously compared by a satellite link and by high-precision optical clocks maintained at the National Metrology Institutes, KRISS in Korea and INRIM in Italy, and delivered to VLBI antennas via optical fiber. The H-masers frequency difference was estimated by extrapolating the clock rate from VLBI data using two geodetic VLBI software. This was subsequently compared with clock differences derived by satellite link and by local optical clocks. Results obtained with different approaches were in agreement at the level of 10-15 s s-1. This pilot study demonstrates that standard high-frequency (K-band) geodetic VLBI campaigns could be a viable approach to conduct intercontinental clock comparisons, now only possible via satellite links. This uncertainty can be reduced thanks to the planned installation of new-generation, broadband, high-frequency receivers on the involved telescopes. K/Q/W-band geodetic observations will allow an improvement of the accuracy of the resulting group delays through broad bandwidth synthesis from 20 to 100 GHz. Furthermore, the Frequency Phase Transfer method will also be explored together with the use of PCAL systems installed at the radio telescopes to improve phase stability and thus allow a better estimation of the station clock parameters.

Optical clocks have achieved remarkable estimated fractional frequency uncertainties reaching the 10^-18 level and below, enabling applications in fundamental physics, general relativity, and geodesy. However, the challenge of verifying the international consistency of optical clocks remains critical as efforts intensify toward redefining the SI second based on an optical transition or transitions. We report on a two-month international clock comparison campaign involving seven optical clocks in four national metrology institutes (INRIM, LNE-OP, NPL, and PTB) connected via the optical fiber network established in Europe. The campaign resulted in optical frequency ratios with uncertainties ranging from 7.7×10^-18 to 6.1×10^-17. Among the results, the ^171Yb^+(E3) clocks at NPL and PTB demonstrated agreement within an uncertainty of 7.7×10^-18, marking the first international verification of two independently developed optical clocks below one part in 10^17. The operation of the ^199Hg clock at LNE-OP (formerly LNE-SYRTE) resulted in frequency ratios with improved uncertainties with ^171Yb^+(E3), ^171Yb, and ^87Sr optical clocks. These results provide input for the redefinition of the second and underscore how fiber-linked clock networks can advance metrology and scientific applications.

Transforming optical transport networks into a distributed sensing grid is a promising pathway to enhance infrastructure resilience and environmental awareness. To achieve widespread scalability without disrupting data traffic, operators can exploit the synergy between different sensing techniques naturally coexisting on the same infrastructure. In this paper, we present an in-field demonstration of a multi-technique sensing framework operating on live terrestrial optical networks, combining interferometric phase sensing and state of polarization (SOP) monitoring. We first propose and validate an unsupervised anomaly detection pipeline based on autoencoders, applied to a 38 km regional link connecting Ascoli Piceno and Teramo (Italy), and show some examples of detected events. This framework proves capable of automatically identifying signal anomalies across different physical observables without relying on manual labeling. Subsequently, we move to a metropolitan urban scenario in the city of Turin and assess a multi-tech sensing analysis using coherent transceivers and state-of-polarization metrics obtained from polarimeters and a cost-effective polarization beam splitter-based device. We highlight the correlation between specific sensing metrics and standard network telemetry data, such as the bit error rate (BER) and temperature, and validate the system’s capability to detect mechanical perturbations originating from human activity along the cable or from controlled experiments using a robotic arm. These results confirm the feasibility of aggregating heterogeneous data sources into a unified sensing plane to enable pervasive infrastructure supervision.

Fiber-optic (FO) sensing adopting Laser Interferometry (LI) promises high sensitivity and distributed measurements for structural health monitoring (SHM), on the other hand, practical performance depends critically on how fibers are coupled to the host structure. In this study, a coherent LI technique, recently developed for underground seismicity detection, is applied for SHM and a systematic laboratory investigation is reported on a simply supported timber beam. Natural frequencies and damping ratios identified from coherent LI-based FO strain measurements are compared with conventional accelerometers under hammer-impact excitation. The comparison covers total of nine attachment strategies: the three configurations include the bare beam and a PVC conduit mounted on the beam with either weak (clamped) or strong (screwed) coupling. Each of the three configurations is instrumented with a single coupled, partially coupled, and uncoupled fiber. Across all attachment configurations, LI-based FO and accelerometer modal frequencies agree within ≲1% for the first three modes; however, FO-derived damping ratios are generally lower and more variable, with the largest scatter in weakly coupled (clamped) cases. Under ambient vibration, LI-based FO robustly identified the first mode even when the accelerometers used here were not sufficiently sensitive. The results confirm that the proposed methodology can track frequency shifts induced by attachment-dependent stiffness changes, similar to those induced by structural damage, suggesting feasibility for SHM and offering practical guidance on coupling considerations for field applications. In the longer term, the main purpose is to enable dual use of telecommunication fiber infrastructure in buildings by employing the coherent LI technique for SHM

Fibre-optic telecommunication networks are increasingly emerging as pervasive sensing infrastructures for geophysical and environmental monitoring. Beyond their primary role in data transmission, optical fibres are intrinsically sensitive to external perturbations: mechanical strain induced by seismic waves modifies both the optical phase and the state of polarization of the propagating light. This property enables existing fibre networks to act as large-scale distributed or integrated sensors, offering a promising complement to conventional seismic instrumentation. In highly active volcanic and seismic areas, such as Campi Flegrei, dense and continuous monitoring is particularly relevant for improving event detection, risk assessment and early response. However, established fibre-sensing techniques often rely on dedicated fibres, specialized interrogators or highly stable laser sources, which may limit scalability and increase deployment costs. For this reason, low-complexity sensing approaches that can operate over in-service telecom infrastructure are of strong interest.In this work, we present a multi-technology fibre-sensing testbed deployed over operational and production fibre infrastructure owned by the italian operator Open Fiber in the Campi Flegrei area. The testbed combines three complementary techniques: state-of-polarization (SOP) sensing, distributed acoustic sensing based on ϕ-OTDR, and interferometric phase sensing. As shown in figure, the SOP and phase measurements are implemented over FTTH links departing from the same point of presence and reaching street cabinets in Agnano and Posillipo, while the DAS reference is acquired over another 22 km FTTH dark fibre owned by another italian operator (Fibercop). The SOP system uses a low-tech polarization-beam-splitter-based receiver that measures the normalized difference between two orthogonal polarization components of an intensity-modulated telecom signal. This architecture avoids coherent receivers and ultrastable lasers, and it can operate by tapping only a small portion of the optical power, preserving compatibility with live data transmission.The experimental campaign demonstrates that the low-tech SOP approach can detect local seismic events down to magnitude 1.9. Earthquakes recorded in November 2025 were analysed and compared against independent reference measurements from DAS, interferometric phase sensing when available, and INGV seismic stations. The SOP traces clearly capture seismic signatures associated with P- and S-wave arrivals, with waveform features and spectral content consistent with the established fibre-sensing techniques. In particular, consecutive M1.9 and M3.0 events were detected by the SOP system and validated against DAS and INGV seismic-station data, while an M3.3 event was jointly observed by SOP, interferometric phase sensing, DAS and the INGV seismic network. These results show that simple SOP monitoring over in-service FTTH links can provide reliable seismic information while significantly reducing system complexity and cost, paving the way for scalable and minimally invasive seismic monitoring using existing telecom networks.

Optical telecommunication networks offer a geographically pervasive infrastructure for environmental monitoring alongside data transmission. We investigate earthquake detection through state-of-polarization (SOP) sensing on operational, buried fiber-to-the-home (FTTH) links in Campi Flegrei, a densely populated and highly seismic area. We compare path-integrated SOP measurements obtained with a low-complexity polarization-beam-splitter receiver against reference measurements from coherent interferometry, distributed acoustic sensing, and a conventional seismic station. Four earthquakes recorded in November 2025, with duration magnitudes from 1.9 to 3.3, produced SOP signatures whose timing and spectral evolution were consistent with the available reference measurements and predicted seismic-wave arrivals. During the seismic sequence spanning 31 July and 1 August 2026, which began with a magnitude 4.7 event, manual inspection identified SOP signatures for 10 of the 16 catalogued events with magnitude above 2, including successive events separated by less than one minute. Detection varied between fiber routes because of differences in cable coupling, background noise, and polarization operating point. These results show that low-complexity SOP monitoring can provide complementary seismic observations over live FTTH infrastructure and motivate future networks of synchronized receivers for automated detection and event localization.

We present a sensing testbed on a live telecom fiber combining phase and polarization analysis. An unsupervised autoencoder-based pipeline detects deformations, quantitatively comparing sensitivity and performance of the two approaches for intelligent, large-scale cable-safety monitoring.

Submarine regions remain sparsely instrumented, limiting the spatial coverage of seismic monitoring in offshore environments. Recent studies have shown that optical fibers, including those actively used for telecommunications, can detect ground motion through laser interferometry. We present an ongoing evaluation of the seismic sensitivity of a 260 km optical fiber link between Malta and Catania, predominantly submerged in the Ionian Sea and continuously carrying internet traffic.The optical-fiber recordings were analysed for signals corresponding to the arrival times of ~1500 earthquakes listed in the INGV catalogue between January 2023 and March 2025. The waveforms were manually inspected for seismic arrivals and compared to seismic data recorded on nearby land stations on Malta and Sicily. Earthquakes ranging from magnitude 1.4 to 7.9 originating from distance of 3 to 16,000 km were successfully observed. Each event was assigned a category according to signal clarity and confidence, ranging from clearly visible arrivals (category A) to non-detectable signals (category E). Preliminary results indicate that 30% in category E, providing an initial characterisation of the optical-fiber cable’s sensitivity. While a majority of observations fall within lower quality categories (D-E), at least 35% of the analysed events remain robustly identifiable, highlighting the contribution of the submarine fiber to existing land-based seismic networks and extending observational coverage in submarine regions. The sensitivity of the fiber strongly depends on the earthquake magnitude-distance relationship, as expected. We compare our results with previously reported measurements on terrestrial fibers (Donadello, et al., 2024), and show that the Malta-Catania submarine cable can be a reliable new seismic tool for a submarine environment, although recording fewer high-confidence events than onshore systems.Noise in the fiber exhibits correlations with wind and with daytime anthropogenic activity. This reduces the signal-to-noise ratio and limits the detectability of earthquakes with M

Optical clocks provide ultra-precise frequency references that are vital for international metrology as well as for tests of fundamental physics. To investigate the level of agreement between different clocks, we simultaneously measured the frequency ratios between ten optical clocks in six different countries, using fiber and satellite links. This is the largest coordinated comparison to date, from which we present a subset of 38 optical frequency ratios and an evaluation of the correlations between them. Four ratios were measured directly for the first time, while others had significantly lower uncertainties than previously achieved, supporting the advance towards a redefinition of the second and the use of optical standards for international time scales.

Optical fiber sensing represents a promising technology for seismological monitoring, leveraging the widespread deployment of optical networks, and representing an important opportunity for the development of early warning systems. While so far Distributed Acoustic Sensing (DAS) has been widely employed in geosciences, this technology shows some limitations, like a restricted working range, requirement of dedicated fibers and criticalities in the management of big datasets. We focus on an alternative technique, coherent interferometry relying on ultrastable lasers, which is characterized by high sensitivity, long range, and full compatibility with the existing telecommunication infrastructure. The method allows detecting perturbations induced by seismic events through the measurement of the phase accumulated by an optical signal along the fiber path. The best performances are obtained employing narrow-linewidth lasers inherited from metrological applications due to their high coherence. While the technique was initially demonstrated on subsea cables, its application to on-land fibers poses new challenges. Indeed, the phase measurement integrates all the perturbations occurring along the fiber: this means that anthropic activities, such as vehicle traffic, represent important noise sources that must be taken into account. We present the details of an in-field implementation over a commercial fiber deployed in a highly seismic region in central Italy and connecting two populated towns. The experimental setup employs self-heterodyne interferometry detection, utilizing a continuous wave laser stabilized to an optical cavity through the Pound-Drever-Hall technique. The laser operates within a single channel of the Dense Wavelength Division Multiplexing (DWDM) grid, sharing the fiber with standard internet services. We show the results of continuous observations performed over a period of two years. We demonstrate the detection of about one hundred earthquakes, distinguishing them from typical noise sources such as acoustic interference and infrastructure oscillations. The results include the detection of both local and distant earthquakes, demonstrating the robustness of the technique. This allowed us to characterize for the first time the sensitivity curve of the technique, described by the probability of the event detection as a function of its magnitude and epicenter distance. We also show the correlation between the source magnitude and signal spectral analysis.In conclusion, we present an operational fiber-based earthquake observatory, highlighting the compatibility of coherent interferometry with the existing telecommunication infrastructures and its effectiveness in seismic monitoring. The results are promising for the development of scalable sensing networks utilizing the extensive optical fiber infrastructure already in place, which can conveniently integrate in real-time the data acquired with the existing networks of classical seismological sensors.

Fiber sensing holds potential for global environmental monitoring and cable supervision, provided that compatibility with conventional network architectures and ability to localize and interpret events autonomously are demonstrated. We show our progress on these aspects, based on years-long fiber sensing data analysis in real environments. (c) 2025 The Author(s)

We demonstrate coherent fiber interferometry with localization capabilities using two-way heterodyne detection. Implemented on optical data networks, it enables environmental disturbance monitoring with spatial resolution at the kilometer level.

The international scientific community has established a roadmap for the redefinition of the second based on optical clocks, identifying challenges and criteria to be achieved before a successful redefinition. Those include: continuity with the definition based on caesium atoms, validation of frequency ratios at the 10-18 level, sustainable comparisons between clocks, access for national metrology institutes and users to the realization of the new definition and regular contributions of optical clocks to the International Atomic Time (TAI) and Coordinated Universal Time (UTC). In the poster we will discuss how INRiM is meeting the challenge. INRiM has maintained the ytterbium atom optical frequency standard IT-Yb1 since 2015, now with a relative uncertainty of 2x10-17. We measured the absolute frequency of IT-Yb1 relative to the INRIM caesium fountain IT-CsF2 in 2016 and 2022. The last measurement achieved an uncertainty of 2.7x10-16, limited by the fountain, thanks to a measurement campaign that collected more than 900 h of data. The ability of IT-Yb1 to operate reliably has allowed us to contribute the optical clock data to the steering of TAI and UTC since 2019, with 16 consecutive months in 2022 and 2023. Up to now, 8 optical clocks worldwide have contributed to the steering, with a significant contribution of optical clocks to the realization of TAI and UTC. INRiM enables user access to the local realization of UTC called UTC(IT), which has been consistently within ±5 ns over the last few years using IT-CsF2 as the primary frequency standard and a robust steering algorithm. Including IT-Yb1 optical clock data, we tested the generation of an optical time scale with sub-nanosecond performance, demonstrating our capability to implement the optical time scale with minimal manual intervention despite the nonstationary flywheel oscillator, long down-time of the optical frequency standard and the irregularly spaced data. To achieve more comparisons between optical clocks, INRiM participates in international efforts to push the boundaries of traditional satellite-based comparison techniques (based on Global Navigation Satellite Systems and Two-Way Time and Frequency Transfer). However, it is necessary to go beyond satellites: INRiM established the fibre backbone for time and frequency dissemination in Italy, to the radio telescope of the National Astrophysics Institute (INAF) in central Italy (Medicina), the LENS atomic physics laboratory in Florence, and the telescopes of the Italian Space Agency (ASI) in southern Italy (Matera). Since 2020, the European network of fibre links has connected INRiM with the NPL in the UK, SYRTE in France and PTB in Germany. Fibre link measurements between IT-Yb1 and other optical clocks in Europe were carried out in 2022 and 2023, with more planned. However, not every clock can be connected by fibre: on one hand, INRiM is developing a transportable ytterbium optical clock in an industrial framework funded by ASI, expected for 2027. On the other hand, INRiM is exploring intercontinental clock comparisons with the use of radio-astronomy techniques based on very long baseline interferometry (VLBI) in collaboration with NICT in Japan, KRISS in Korea and INAF in Italy.

We implement a multi-technique seismic observatory on a live optical link in central Italy, using phase and state-of-polarization sensing coexisting with data traffic. Combining diverse fiber sensing and traditional tools enables turning telecom infrastructure into a resilient smart grid for interpreting complex and heterogeneous events. (c) 2025 The Author(s)

Rapid and reliable structural health assessment is crucial after earthquakes to ensure safety and informed disaster response. Structural Health Monitoring (SHM) has emerged as a more quantitative alternative, offering the ability to continuously monitor structures and detect early signs of damage. However, conventional SHM systems, which rely on dense sensor grids or costly fiber optic installations, face significant challenges in terms of scalability and costeffectiveness. This study addresses these challenges by employing laser interferometry (LI) to convert the strain of fiber optic (FO) cables into damage-sensitive signals. Our approach reveals the preliminary feasibility of using LI with FO infrastructure in buildings to develop a scalable and low-cost SHM framework for damage assessment. By converting fiber signals into structural strains using interferometric techniques, the proposed approach bypasses the need for dedicated sensors. We demonstrate the potential of this technique through simulated and experimental results assessing the feasibility of real-world applications. This research aims to bridge the gap between the need for rapid damage assessment and the limitations of current SHM systems, offering a practical solution for large-scale implementations using existing FO networks.

We demonstrated the quantitative use of a coherent laser interferometry technique, originally used for the frequency comparison of remote high accuracy atomic clocks, to fibre sensing, and in partiuclar to seismic detection. After first implementations in submarine and land fibre networks, we further developed this technique on land realizing a permanet observatory and gaining quantitative characterization of the sensor and its potential capabilities.

Optical measurements enable non-contact and high-speed monitoring of physical processes, offering a non-invasive and versatile approach across a wide range of fields, from scientific research to industrial applications. In this work, an optical sensor capable of simultaneously measuring the distance and thermal emission of surfaces is presented, based on a simple laser diode probe. The principle of operation integrates triangulation with pyrometry in a single device, utilizing the monitor photodiode embedded within the probe package. By alternating the laser emission, the readout can rapidly switch between dimensional and thermal measurements, resulting in combined data acquisition. The presented method is compact, easy to integrate, and cost-effective. The hybrid sensor is implemented into a laser processing setup, where a metallic target is heated and melted by a high-power laser beam. Its inline operation is demonstrated in real-time for dynamic measurements of melt pool distance and radiance. This innovative approach can find applications in diverse fields, such as remote environmental sensing and closed-loop control systems for stabilizing high-temperature processes, including laser welding and additive manufacturing.