Ubiquitously used for monitoring pipelines and infrastructures, distributed fibre-optic acoustic sensing is becoming an emerging technology for earthquake monitoring thanks to the possibility to interrogate a large vast of distances with a dense number of sensing points in which an optical fiber cable can be retrofitted. Moreover, it can also be used as a tool by geophysicists for the characterization of subsurface elements, such as rocks, faults, and geological structures before excavation work. In this work, we present two applications where DAS technology can contribute to assess rock properties during passive (in a mining site) and active (in a lake) seismic surveys. In both cases, seismograms generated from DAS measurements were comparable to those measured by traditional receivers, paving the way towards their use for assessing rock quality during surveys.

Functional coatings on optical fibers enable selective detection of environmental and chemical parameters, but their use is typically limited to point or quasi-distributed sensing due to localized deposition techniques. In this work, we demonstrate a possible transition towards full-length functional coatings on optical fibers using a draw tower process, enabling their potential use in distributed sensor technology. An optical fiber with Pt:WO<inf>3</inf> nanocomposite polymer functional coating is employed as a proof of concept. The results demonstrate the successful application of this functional coating along hundreds of meters of fibers using a draw tower. When integrated into a distributed sensing configuration, the Pt:WO<inf>3</inf> fiber exhibited a clear change in response with varying hydrogen concentrations from 1% to 4% H<inf>2</inf>, with a temperature increase of 2.5 °C at 4 vol.% indicating a promising performance for distributed hydrogen leak detection. This approach opens new opportunities for applying other functional coatings over extended fiber lengths using draw towers, which could be exploited for novel distributed sensing applications

The paper describes the fabrication of two nanocomposite (NC) coated optical fibers, and their use to enhance the capabilities of distributed fiber sensing. The fibers are produced in a conventional optical fiber draw tower. NC coated fibers with reduced graphene oxide were shown to have enhanced mechanical durability at elevated temperatures and have a low humidity sensitivity compared to standard polyimide coated fibers. NC coated fibers with hydrogen-sensitive materials were shown to enable distributed hydrogen leak detection, in a configuration that is scalable to long lengths.

The HybriDFEM method, short for Hybrid Discrete-Finite Element Method, combines both discrete and finite element approaches in a single numerical model: the method adopts a discrete representation of the structure, but the formulation is designed to integrate continuous parts that can be simulated by the Finite Element Method, allowing hybrid numerical mock-ups to be built. The scope of application of the method is expanded from its original development for uniaxially-discretized (1D) structures to modeling biaxially-discretized (2D) structures and systems of beams connected through rigid-node connections. The possibility to integrate finite elements within HybriDFEM in 2D is initially formalized. A two-step contact detection algorithm, in which the interface detection is preceded by a preliminary rough detection, is then presented. Finally, different approaches to modeling contact are introduced, depending on whether it is meant to reflect the behavior of a continuous material, flexible interfaces, or point-wise contact. These new capabilities of the 2D HybriDFEM method are validated on a series of selected examples including solutions from analytical models, classical finite elements, and limit analysis; among others, the HybriDFEM method is used to evaluate the axial and shear stress distribution in a linear elastic beam with negligible error relative to analytical solutions, and to predict the collapse load of in-plane loaded masonry frames with an error below 0.05% compared to solutions from limit analysis. The adequacy of the method to enhance discrete simulations by integrating finite elements is illustrated in a conclusive example via the pushover analysis of a flexible masonry frame.

A new, modular approach to fibre-optic sensing is presented, where different types of optical fibres and other wires are combined to compact, hybrid cable assemblies, customized for each application. These fibre-optic assemblies can be embedded or integrated in various settings, enabling multi-parameter sensing and the measurement of new parameters. In this work, we describe the fabrication process of these miniature, multi-functional cables and how it can be directly used for sensing purposes in 3 end-user inspired applications.

Fiber Bragg Gratings (FBGs) were used to monitor the manufacturing process and the operation of high voltage bushings. During operation, temperatures at several points inside the bushing were monitored. In another test, during bushing manufacturing, FBGs monitored the filling and curing process of the epoxy in Resin Impregnated Paper (RIP) bushings. Traditionally, temperature measurements inside the bushing core have been performed using thermocouple probes and only in bushings for research, not final products. The use of appropriate FBGs was successfully tested in the harsh environments of operation (under high voltage) as well as in manufacturing (high curing temperature and stress). The results demonstrate the potential of fiber optics to study and improve production methods. The study also shows that fiber optics are suitable for long-term monitoring during bushing operation.

In this study, upcoated and buffered optical fibres with Fibre Bragg Gratings (FBGs) have been used as quasi-distributed pressure sensors that can be embedded into surface materials for composite structures. The main goal has been to develop compact and robust sensors/sensor materials that measure pressures from 10 to 200 kPa. The sensor used for this experiment was FBGs inscribed in 125μm optical fiber having either Polyimide (PI) or Acrylate (Ac) as original coating. The wavelength shift of an FBG can be related to strain, and its sensitivity is approximately 1.2 pm/µstrain. To make the FBG sensitive to pressure, the optical fibers with FBGs were coated with a soft up-coating layer of silicone and a stiffer buffer material. The total outer diameter was 1 mm. Four buffered fibre cables were manufactured with combinations of the two original coating materials and two different buffer materials that were either Polyamide (PA) or Polyetheretherketone (PEEK). The buffered optical fibres were embedded into a couple of different types of surface materials on top of pre-cured 4 mm carbon fibre/epoxy (CFRP) laminates. The surface material was either a syntactic foam material with a 0.1 mm glass fibre/epoxy cover layer or 10 epoxy film layers (36 gsm Hexel 6376 resin) with a 0.1 mm glass fibre/epoxy cover layer. The pressure response of the inbuilt optical fibres was tested in an Instron Machine in the load range of 10 to 200 kPa. The best combination for pressure sensitivity was either to use an optical fibre with PI coating and PEEK buffer or an optical fibre with Ac coating and PA buffer combined with the syntactic foam surface cover material

In this study, upcoated and buffered optical fibres with Fibre Bragg Gratings (FBGs) have been used as quasi-distributed pressure sensors that can be embedded into surface materials for composite structures. The main goal has been to develop compact and robust sensors/sensor materials that measure pressures from 10 to 200 kPa. The sensor used for this experiment was FBGs inscribed in 125μm optical fiber having either Polyimide (PI) or Acrylate (Ac) as original coating. The wavelength shift of an FBG can be related to strain, and its sensitivity is approximately 1.2 pm/µstrain. To make the FBG sensitive to pressure, the optical fibers with FBGs were coated with a soft up-coating layer of silicone and a stiffer buffer material. The total outer diameter was 1 mm. Four buffered fibre cables were manufactured with combinations of the two original coating materials and two different buffer materials that were either Polyamide (PA) or Polyetheretherketone (PEEK). The buffered optical fibres were embedded into a couple of different types of surface materials on top of pre-cured 4 mm carbon fibre/epoxy (CFRP) laminates. The surface material was either a syntactic foam material with a 0.1 mm glass fibre/epoxy cover layer or 10 epoxy film layers (36 gsm Hexel 6376 resin) with a 0.1 mm glass fibre/epoxy cover layer. The pressure response of the inbuilt optical fibres was tested in an Instron Machine in the load range of 10 to 200 kPa. The best combination for pressure sensitivity was either to use an optical fibre with PI coating and PEEK buffer or an optical fibre with Ac coating and PA buffer combined with the syntactic foam surface cover material

Dynamic storage of qubits is crucial for quantum communication networks. Here we present an adjustable buffer capable of storing photonic polarization quantum states in a fiber loop controllable by a poled fiber modulator

Dynamic storage of qubits is crucial for quantum communication networks. Here we present an adjustable buffer capable of storing photonic polarization quantum states in a fiber loop controllable by a poled fiber modulator.