Pressure and liquid depth sensing using a Fabry–Perot probe based on a silica capillary fiber and an agar membrane

The continuous evolution of fiber optics technology drives the photonics community to explore novel sensing configurations, aiming at developing optical sensors with enhanced capabilities. Among these efforts, Fabry–Perot interferometers (FPIs) emerge as a promising strategy for building fiber sensors due to their simplicity, miniature size, resolution tunability, and capability of acting as platforms for humidity, temperature, and pressure sensors. In addition to traditional materials for constructing FPIs, agar appears as a promising photonic material, offering biocompatibility, flexibility, and ease of preparation. In this manuscript, we present the development of a FPI sensing probe based on a silica capillary and an agar membrane for pressure and liquid depth sensing. Our report encompasses the description of the probe preparation procedure, the FPI spectral characterization, and the sensing measurements. Our efforts allowed us to demonstrate sensors with sensitivities of (− 4.9 ± 0.1) nm/bar and (− 5.9 ± 0.2) pm/mm. We consider that our work expands the application scenario of agar within photonics and offers a new avenue for realizing biocompatible pressure and liquid depth sensors.