High-sensitivity special open-cavity Mach-Zehnder structure for salinity measurement based on etched double-side hole fiber

A special open-cavity Mach-Zehnder salinity sensor is presented and verified in this Letter, which has obvious advantages in salinity sensitivity and loss. The open-cavity structure is composed of a short section of etched double-side hole fiber spliced between a pair of multimode fibers and connected in series between a pair of single-mode fibers, which is the SMF-MMF-etched DSHF-MMF-SMF structure proposed in the paper. According to the experiment results, when the cavity length is about 100 mu m, the salinity sensitivity of the sensing probe can reach 2 nm/%, and its refractive index (RI) sensitivity can be more than 10,000 nm/RIU, while having a low loss of 15 dB and a detection limit of 0.23 parts per thousand. Based on its characteristics, the sensor is a prospective online monitor of ocean salinity. At the same time, it also provides a low-cost way to construct an open cavity instead of femtosecond inscribing. (C) 2021 Optical Society of America

Automated summary

This study presents a special open-cavity Mach-Zehnder salinity sensor with advantages in salinity sensitivity and loss, making it a potential online monitor of ocean salinity and providing a low-cost way to construct an open cavity.