Abstract

This study investigates the feasibility of using an etched addressed fiber Bragg structure (EAFBS) as the sensing element in a microwave-photonic system for local pH monitoring. A theoretical model is developed that incorporates transmission-spectrum analysis of the addressed Bragg structure and evaluation of the effective refractive index of the guided mode as a function of the surrounding medium parameters. The model establishes a relationship between the refractive index of the surrounding medium and the spectral response of the EAFBS. Using the proposed mathematical model, numerical simulations are performed for three pH ranges corresponding to various liquid media. The results of numerical studies show that in all in the pH ranges, the address frequency varies nearly linearly, with a sensitivity of approximately 1.66 GHz/pH (pH range of 4–7), 2.64 GHz/pH (pH range of 7–10), and 1.92 GHz/pH (pH range of 10–13), whereas its temperature dependence in the range of 35–45 °C is approximately 1.06 GHz/°C. These results indicate that the proposed EAFBS-based approach can provide a foundation for high-speed pH sensing systems with a simplified interrogation scheme and potential capability for frequency-division multiplexing.

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