Fiber Bragg grating (FBG) sensors have emerged as advanced tools for monitoring a wide range of physical parameters in various fields, including structural health, aerospace, biochemical, and environmental applications. This review provides a comprehensive overview of FBG sensor technology, focusing on their operating principles, key advantages such as high sensitivity and immunity to electromagnetic interference, and common challenges like temperature-strain cross-sensitivity and the high cost of interrogation systems. Additionally, this review compares FBG sensors with other sensing technologies and highlights recent innovations in design, packaging, and implementation techniques. Finally, future research directions are discussed to enhance the performance, scalability, and long-term reliability of FBG-based sensing systems.

Measuring pH is a critical parameter in environmental monitoring, biomedical diagnostics, food safety, and industrial processes. Optical fiber sensors have proven highly effective for pH detection due to their exceptional sensitivity, rapid response, and resistance to electromagnetic interference, making them well suited for real-time monitoring. This review offers a comprehensive analysis of recent advances in optical fiber-based pH sensors, covering key techniques such as fluorescence-based, absorbance-based, evanescent wave, and interferometric methods. Innovations in Fiber Bragg Grating and Surface Plasmon Resonance technologies are also examined. The discussion extends to the impact of pH-sensitive coatings—ranging from nanomaterials and polymeric films to graphene-based compounds—on enhancing sensor performance. Recent advancements have also enabled automation in data analysis and improvements in remote sensing capabilities. The review further compares the economic viability of optical fiber sensors with traditional electrochemical methods, while acknowledging persistent issues such as temperature cross-sensitivity, long-term stability, and fabrication costs. Overall, recent developments have broadened the functionality and application scope of these sensors by improving efficiency, accuracy, and scalability. Future research directions are outlined, including advanced optical interrogation techniques, such as Addressed Fiber Bragg Structures (AFBSs), microwave photonic integration, and optimized material selection. These approaches aim to enhance performance, reduce costs, and enable the broader adoption of optical fiber pH sensors.

In this paper, an application of an artificial neural network algorithm is proposed to enhance the accuracy of temperature measurement using a fiber-optic sensor based on a Fabry–Perot interferometer (FPI). It is assumed that the interrogation of the FPI is carried out using an optical comb generator realizing a microwave photonic approach. Firstly, modelling of the reflection spectrum of a Fabry–Perot interferometer is implemented. Secondly, probing of the obtained spectrum using a comb-generator model is performed. The resulting electrical signal of the photodetector is processed and is used to create a sample for artificial neural network training aimed at temperature detection. It is demonstrated that the artificial neural network implementation can predict temperature variations with an accuracy equal to 0.018 °C in the range from −10 to +10 °C and 0.147 in the range from −15 to +15 °C.

The paper presents a novel pH-sensor architecture based on an addressed fiber Bragg structure (AFBS) with fully-etched segment, designed for reliable operation in thermally unstable industrial environments. The sensor employs a fiber Bragg grating with dual π phase shifts, where one of the segments is fully etched to the core to enhance evanescent field interaction with the environment. This geometric modification significantly increases sensitivity to refractive index variations, which correlate with local pH changes. Numerical simulations confirm a near-linear dependence of the address frequency on pH levels ranging from 11.0 to 13.7, with thermal invariance maintained from −100 °C to +100 °C. The sensor’s dual-resonance spectral profile enables high-resolution microwave photonic interrogation and supports wavelength-division multiplexing for distributed measurements. A simulated multisensor configuration demonstrates clear spectral separation and addressability. Beyond refractive index sensitivity, the design provides electromagnetic immunity, real-time response, and compatibility with remote optical interrogation. These features make the etched AFBS (EAFBS) sensor highly suitable for deployment in industrial environments. Future work will focus on integrating EAFBS into multi-parameter fiber-optic platforms capable of simultaneous monitoring of pH, temperature, and flow rate.

Accurate and continuous monitoring of blood pH is crucial in clinical diagnostics, especially in critical care scenarios where metabolic disturbances like acidosis or alkalosis can pose serious health risks. Conventional electrochemical pH sensors often face challenges such as limited operational stability, susceptibility to biofouling, and incompatibility with long-term monitoring in complex biological fluids like whole blood. In this work, we present a novel pH sensing platform based on an Etched Addressed Fiber Bragg Structure (EAFBS), interrogated through a microwave-photonic system. This sensor detects pH variations by monitoring shifts in its address frequency, which correlate with changes in the effective refractive index induced by hydrogen ion concentration. While similar technologies have been explored in aqueous or environmental samples, our study is among the first to adapt and validate this approach for use in whole blood-a medium characterized by high optical scattering, protein content, and dynamic behavior. Through a combination of numerical simulations and experimental calibration, we demonstrate that the EAFBS sensor achieves sub-unit $\mathbf{p H}$ resolution under physiological conditions $\left(37^{\circ} \mathrm{C}\right)$ while remaining largely unaffected by thermal fluctuations. These findings highlight the potential of this fiber-optic platform for real-time, reagent-free, and non-invasive monitoring of blood pH, paving the way for advanced diagnostic tools in critical and continuous care settings.

The method of indirect pH measurement using etched addressed Bragg structures (EAFBS) is presented. The sensor detects changes in the effective refractive index associated with pH levels. Modeling confirmed the thermal stability of the address frequency, ensuring reliable measurements under external influences.