Integrated temperature and humidity sensor based on the harmonic Vernier effect with a dual-MZI-in-one-fiber

A novel, to the best of our knowledge, highly sensitive, and compact optical fiber sensor for measuring temperature and relative humidity (RH) is proposed and demonstrated. The sensor integrates two parallel Mach-Zehnder interferometers (MZIs) within a dual-side hole fiber (DSHF). One of the MZIs detects temperature with the help of polydimethylsiloxane (PDMS), and the other detects RH using polyvinyl alcohol (PVA), labeled as MZI₁ and MZI₂, respectively. The sensing materials are injected into the holes of the DSHF through laterally pre-ground side holes. The formation of both MZIs is caused by light interference between the core and the partially filled holes of the DSHF. By controlling the lengths of the PDMS and PVA within the holes of the DSHF, we obtained a first-order harmonic Vernier effect. The as-fabricated sensor exhibits sensitivities of 5.899 nm/°C and -0.496 nm/%RH, respectively. The excellent sensing performance, compactness, and cost-effectiveness of our sensing structure make it a highly promising candidate for temperature and RH monitoring applications.