High fringe visibility Mach-Zehnder interferometric sensor based on a Four-Core fiber

An in-line optical fiber Mach-Zehnder interferometer (MZI) sensor with high fringe visibility is reported. The sensor is formed by splicing a short section of four-core fiber (FCF) between two coupling sections. The coupling section is fabricated by cascading very short segment of few mode fiber, multimode fiber (MMF), and large core diameter MMF together. A maximum fringe visibility of approximately 30 dB is obtained in the transmission spectrum. The temperature and curvature sensing response were also experimentally investigated. The temperature sensitivities are 61 pm/degrees C and 49 pm/degrees C for dip A and dip B ranging from 30 degrees C to 80 degrees C, respectively. The curvature sensitivities for dip A and dip B are 20.77 nm/m(-1) and 12.89 nm/m(-1) in the range of 0.2983 m(-1) to 0.7916 m(-1), as well as 9.99 nm/m(-1) and 5.38 nm/m(-1) from the range of 0.7916 m(-1) to 1.039 m(-1), respectively. The proposed MZI sensor has the advantage of easy fabrication, compactness, higher fringe visibility, and low cost.