All-fiber Mach-Zehnder interferometer with dual-waist PCF structure for highly sensitive refractive index sensing

摘要

A simple, highly sensitive, and all-fiber Mach-Zehnder interferometer (MZI) refractive index (RI) sensor was proposed and experimentally demonstrated, which was fabricated by welding a dual-waist photonic crystal fiber (DWPCF) with two single-mode fibers. The two waists in the PCF, which acted as splitter and combiner of the MZI, could be simply formed by fusion-tapering technique. The high-order cladding modes could be largely excited in the first waist region and propagated along the cladding until the second waist region, where it would be returned into the fiber core and interfered with the core mode. When the RI around the DWPCF changed, an effective RI variation of the cladding modes might generate, which resulted in the shift of interference spectrum. Therefore, the external RI variation could be obtained by monitoring the wavelength position of the interference pattern. Experimental results showed that the interference wavelength shifted with the increase of the external RI, and high measurement sensitivity of 263.5nm/RIU was achieved with good linearity.