High-Sensitivity Microfluidic Mach-Zehnder Interferometric Salinity Sensor Based on C-Type Dual-Core Eccentric-Hole Fibers

A Mach-Zehnder interferometric (MZI) salinity sensor based on C-type dual-core eccentric-hole fibers (DCEHFs) is proposed and experimentally demonstrated. The proposed salinity sensor is fabricated by splicing C-type DCEHFs with lead-in and lead-out no-core fibers (NCFs) with predesigned lateral offsets. Experimental results indicate that smaller lateral offsets would benefit to improve the transmission spectral fringe visibility and higher sensitivity could be obtained by employing the sensor structure with longer fiber length. The experimentally acquired salinity sensitivity reaches -2.664 nm/‰ (-15100.67 nm/RIU) with a lateral splicing offset of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$9.3~\mu $ </tex-math></inline-formula>m and DCEHFs of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$343~\mu $ </tex-math></inline-formula>m in length. The small lateral offset and large contact area of the C-type DCEHFs significantly enhance the stability of the fabricated sensor structure, while the fiber core proximity to open microcavity yields a strong evanescent field which considerably improves the sensitivity. The proposed sensor possesses several desirable merits such as high sensitivity, compactness, ease of fabrication, and microfluidic operation for real-time measurement, which is anticipated to find applications in high-precision seawater salinity measurement.