Novel optical fiber refractive sensor fabricated with an alcohol-filled photonic crystal fiber based on a Mach–Zehnder interferometer

Abstract A novel alcohol-filled optical fiber sensor that consists of a single-mode fiber–photonic crystal fiber–single-mode fiber (SMF–PCF–SMF) structure is proposed and experimentally validated. The proposed sensor is based on a Mach–Zehnder interferometer, which is fabricated by splicing a section of uncoated photonic crystal fiber (PCF) between two short sections of single-mode fibers with a fiber fusion splicer. The air holes of the PCF are filled with alcohol to fabricate a refractive sensing probe that can detect changes in the external refractive index (RI). Experimental results show that changes in the external RI cause shifts in the positions of wavelength peaks. The sensitivity of the proposed structure reaches 386.66 nm/RIU under the external RI of 1.335–1.350. The linearity of the shift of the wavelength valley with RI is 97.9%. Construction methods for a measurement system based on the SMF–PCF–SMF structure are also proposed. Notably, voltage change indirectly reflects the change in the external RI. Given this characteristic, the SMF–PCF–SMF structure has potential applications in fiber-based RI sensing.