High-resolution polymer optical fibre humidity sensor utilizing single-passband microwave photonic filter

Water affinity property of the polymer optical fibre (POF) makes it possible for humidity sensing. In this paper, we propose and experimentally demonstrate a high-resolution POF-based humidity sensor that utilizes microwave photonic interrogation technique. A Mach-Zehnder interferometer (MZI) of one arm inserted with the POF is used as the interrogator, and a single-passband microwave photonic filter is developed for interrogation. The change of the humidity is then converted to the frequency shift of the radio-frequency (RF) filter's passband. A humidity sensor with sensitivity of 84 MHz/RH% and resolution of 0.0119 RH% is achieved in the experiment. Thanks to the introduction of microwave photonic interrogation technique, the proposed humidity sensor owns the abilities of high resolution and anti-vibration. These advantages make it suitable for the potential applications with high precision requirement or in an unstable environment.