Accurate humidity and pH synchronized measurement with temperature compensation based on polarization maintaining fiber

TL;DR

This paper presents a fiber-optic sensor system that enables real-time, simultaneous measurement of humidity, pH, and temperature with high sensitivity and minimal crosstalk, using a polarization maintaining fiber functionalized with specialized nanofilms.

Contribution

The work introduces a novel fiber-optic sensor platform that combines humidity and pH sensing with temperature compensation in a single Sagnac loop, improving accuracy and enabling multi-parameter monitoring.

Findings

Achieved simultaneous real-time measurement of humidity, pH, and temperature.

Enhanced humidity sensitivity and stability through microporous polymer films.

Effectively eliminated temperature crosstalk in multi-parameter sensing.

Abstract

Real-time and accurate monitoring of humidity and pH is of great significance in daily life and industrial production. Existing humidity and pH measurement suffer from limitations such as low sensitivity, signal crosstalk, complex system structures, and inability to achieve real-time monitoring. In this work, the surface of a polarization maintaining fiber (PMF) was functionalized with a composite humidity-sensitive polymer composed of polyvinyl alcohol (PVA) and carbon nanosheets (CNs). A humidity-sensitive film with a microporous structure was prepared on the PMF cladding through high-temperature rapid film formation and laser processing, enhancing humidity sensitivity and stability. To enable pH sensing, poly(allylamine hydrochloride) (PAH) and poly (acrylic acid) (PAA) were successively adsorbed onto the PMF surface via electrostatic self-assembly, forming a pH-sensitive nanofilm structure. By connecting a temperature-compensated PMF within the same Sagnac loop and combining it with a multi-wavelength matrix, simultaneous real-time monitoring of humidity, pH, and temperature was achieved, effectively solving the issue of temperature crosstalk and extending toward a universal optical fiber multi-parameter measurement platform.