Abstract
Interferometric systems are frequently utilized in metrology due to their enhanced sensitivity, and combining these systems with resonance effects enables advantageous interrogation capabilities. The Fano resonance is a phenomenon that exploits the interplay between interference and resonance. In this research, a cleaved fiber Bragg grating is simulated to demonstrate the possibility of inducing Fano resonance through the interference of Bragg and Fresnel reflections. The device can adjust the asymmetrical spectrum, which can be leveraged as a dynamic sensor for a variety of applications, including polarization-based measurements and remote sensing.

Abstract
Detection of leaks in hydrogen (H2) infrastructure is required on a large scale to enable a safe widespread use of this clean energy source. Sensing solutions must be low-cost, use scalable fabrication methods and allow multiplexed detection while providing reliable safety alarms as fast as possible. Optical methods can make this possible while avoiding the risk of ignition due to electronics at the point of detection. Metal hydride-based micro-mirror configurations benefit from a simple interrogation scheme, as long as the sensitive element can produce a large optical response. Magnesium thin films undergo a drastic variation of properties when hydrogenated, making them suitable for this application. In this work, a micro-mirror device using single-mode fibers capable of detecting the presence of H2 with a loading t10 and t90 of 1.2 and 3.0 s, respectively, is demonstrated. A complete interrogation unit was developed, presenting a solution suited for widespread deployment using industry-standard optical components and equipment.

Abstract
Over the past 18 months, we have performed hundreds of temperature characterizations of fiber Bragg gratings inscribed in different germanium-doped silica glass fibers. Under experimental conditions, the main conclusions are as follows: the temperature dependence of the temperature gauge factor or the normalized temperature sensitivity, K-T, was found to be quadratic in the -50-200 degrees C range, while it may be considered linear for the -20-100 degrees C range; K-T values at 20 degrees C vary from 5.176 x 10(-6) K-1, for a B/Ge co-doped fiber up to 6.724 x 10(-6) K-1, for a highly Ge-doped fiber; K-T does not depend on the hydrogen-loading process or the gratings coupling strength; K-T is essentially independent of wavelength in the 1500-1600 nm range, its value being accurately determined with a relative error similar to 0.2%; based on the accurate value of K-T = 6.165 x 10(-6) K-1, at 20 degrees C, obtained for gratings inscribed in the SMF-28 fiber, we calculated a value of 19.4 x 10(-6) K-1 for the thermo-optic coefficient of bulk germanium glass; and gratings produced by femtosecond-laser radiation and UV-laser radiation exhibit comparable values of K-T. The previous achievements allow, by having knowledge of K-T for a single grating, the accurate determination of the temperature dependence of the Bragg wavelength for any other grating inscribed in the same fiber; the presented methodology enables one to determine the unknown gratings' temperature sensitivity, typically with an error of 0.01 pm/degrees C, being, therefore, very useful in research labs and computer simulations. Thus, expressions for the temperature dependence of K-T for gratings inscribed in several fibers are given, as well as an expression for K-T as a function of the effective refractive index. We have also fully analyzed the potential sources of error in K-T determination.

Abstract
Technological advances in global communications depend significantly on robust and efficient long-distance infrastructures. One notable example is the submarine cable network. Installed on the ocean floor, these cables use fiber optic technology to transmit large volumes of data at high speed and low latency between continents. Beyond their primary communication function, recent innovations allow these cables to serve as Distributed Acoustic Sensing (DAS) systems, effectively converting tens of kilometers of passive fiber into massive, coherent arrays of vibration sensors. The primary objective of this project is to enhance maritime surveillance capabilities by integrating DAS technology with advanced kinematic modeling. This paper establishes a rigorous physical and mathematical framework for interpreting the acoustic signatures of surface vessels detected by bottom-mounted fibers. We derive the complete opto-acoustic transfer function, formulate the hyperbolic moveout equations based on a moving point-source solution to the wave equation, and implement a stochastic inversion scheme using Differential Evolution. By optimizing a correlation-based loss function, we demonstrate the ability to recover vessel trajectory, speed, and depth from complex interferometric patterns with speed estimation errors consistently below 1%. This approach allows for the extraction of quantitative physical parameters from raw optical data, bridging the gap between photonics and hydroacoustics.

Abstract
Blending green hydrogen into gas networks is subject to strict quality regulation. As Europe diversifies its Liquefied Natural Gas supply, existing literature often ignores the extreme chemical variability of these sources by assuming a static composition. This study proposes a nonlinear steady-state optimization model, strictly adhering to European standards, to maximize hydrogen injection across eight real-world LNG profiles. Results reveal severe sensitivity to the carrier gas: lean gas (Trinidad and Tobago, USA) restricts maximum hydrogen integration to 8.89% and 11.40% by volume due to insufficient heavy hydrocarbons. Conversely, carbon-rich gas (Nigeria) allows up to 20.10%, although inert gases degrade this capacity. Ultimately, this 20.10% maximum blend yields only a 6.77% emission reduction. The imported chemical profile dictates absolute limits, proving that static universal hydrogen quotas are thermodynamically unachievable year-round without continuous dynamic quality tracking.

Abstract