Etched addressed fiber Bragg structures for environment pH sensing

Abstract 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.