Semi-open cavity grapefruit-microstructured-optical-fiber-based Mach-Zehnder interferometric sensor for high-sensitivity simultaneous measurement of salinity and temperature

A Mach-Zehnder interferometric (MZI) sensor based on semi-open cavity grapefruit microstructured optical fibers (GMOFs) is proposed and experimentally demonstrated for highly sensitive simultaneous measurement of salinity and temperature of aqueous solution. The sensor structure is constructed by sandwiching one segment of pre-processed semi-open cavity GMOF between two sections of no-core fibers (NCFs) spliced with the lead-in and lead-out single-mode fibers (SMFs). The semi-open cavity serves as the microfluidic channel. And moreover, due to the asymmetric geometry of the semi-open cavity GMOF, additional lateral offset is not required and the sensor robustness can be significantly improved. As the fiber core is close to the semi-open microcavity, a strong evanescent field can be produced to enhance the sensor sensitivity. Experimental results show that the salinity and temperature sensitivities reach -2.7401 nm/parts per thousand and 1.6498 nm/degrees C, respectively. Our proposed sensor possesses several desirable merits such as ease of fabrication, compact structure, and high sensitivity, which make it a promising candidate in high-precision seawater environmental monitoring applications.