Research On Mach-zehnder Intefrerometer Sensor Based On Tapered Hollow Optical Ifber

Optical fiber sensing and optical fiber communication technology have been rapidlydeveloped since the advent of the optical fiber, and the optical fiber sensors have beenwidely used due to they have the merits of small size, light weight, fast response,corrosion resistance, insulation and electromagnetic immunity when compared to thetraditional electronic ones. In recent years, various fiber optical Mach-Zehnderinterferometer sensors, which are important components of the fiber sensors, with novelstructures or innovative mechanisms have been developed to fulfill the demands of thepeople, such as the sensors with the characteristics of compact structure or highsensitivity.In this paper, we demonstrated the fabrication of a compact fiber Mach-Zehnder (M-Z) interferometer fiber sensor based on a hollow optical fiber taper (HOFT) fabricatedby the tapering technique, i.e., we first spliced a hollow optical fiber (HOF) betweentwo segments of single mode fibers (SMFs) and then tapered the HOF in the middle.During the splicing and tapering processes, the air channel of the HOF around thedischarging regions was collapsed because of the heat effect. The collapsed regionsbetween the HOF and SMF played the roles of modal coupling and re-coupling. Whilein the taper region, the mode interference would be enhanced. The M-Z interferometerwith the SMF-HOFT-SMF structure had a HOF length of about2mm and a taper waistdiameter of about66.5μm. The sensor had a compact structure and a relatively highmechanical strength.We conducted a detailed experiment on the surrounding refractive index (RI) sensingcharacteristics of the fabricated sensor and found that the RI sensitivity of the sensor increased exponentially versus the RI. For the interference peak located around1440nm, the sensor demonstrated a highest RI sensitivity of about7041.21nm/RI unit (RIU)in the range of1.4406~1.4458, thus the sensor had a high RI sensitivity. Meanwhile,we also investigated the stress and temperature response characteristics of the fabricatedsensor, the sensor demonstrated a stress sensitivity of-6.26nm/N in the range of0~1N and a low temperature sensitivity of9.8pm/℃in the range of30℃~100℃.Therefore, the sensor had a low temperature cross-sensitivity. The sensor had theadvantages of compact structure, easy fabrication, low cost, high RI sensitivity and lowtemperature cross-sensitivity, which had potential applications in the biochemical andphysical sensing fields.