Test and Analysis of Lateral-Offset Optical Fiber Mach-Zehnder Interferometer Using Near-Infrared Light Employed as Chloride Ion Concentration Sensor

This paper presents a test and analysis of a lateral-offset optical fiber Mach-Zehnder interferometer (MZI) employed as a chloride ion concentration sensor using a near-infrared light source (amplified spontaneous emission, wavelength = 1520–1620 nm). An 8 cm optical fiber MZI sensor was fabricated and fusion-spliced using a lateral-offset process. We used this 8 cm lateral-offset optical fiber MZI to measure chloride ions in samples of sodium chloride solutions with different weight concentrations ranging from 0.015% to 25% and then analyzed the interference spectra regarding their normalized intensity and wavelength shift and three integral area ranges (1520–1580 nm, 1540–1600 nm, and 1520–1620 nm). The comparative spectral analysis results show that the lateral-offset optical fiber MZI sensor exhibited a linear decrease in its normalized intensity as well as a wavelength shift when the concentration increased. The lateral-offset optical fiber MZI sensor displayed a sine wave plot in the three integral area ranges when the concentration increased. Other than sensing parameters such as the normalized intensity (adjusted R-squared = 0.98223) or wavelength shift (adjusted R-squared = 0.94209), the three integral area ranges (adjusted R-squared = 0.96425, 0.91621, and 0.9577, respectively), which possessed adjusted R-squared values greater than 0.9, are also recommended for use as sensing parameters for the testing and analysis of a lateral-offset optical fiber MZI employed as a chloride ion concentration sensor using a near-infrared light source.