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• A dual-parameter sensor based on four-core fiber (FCF) with a hybrid sensing mechanism is proposed. • The surface of FCF is covered with gold film to excite the SPR and MZI for measuring refractive index (RI) and temperature. • The proposed sensor exhibits a high RI sensitivity of 2091 nm/RIU and a temperature sensitivity of 0.0398 nm/°C. A dual-parameter sensor based on a hybrid sensing mechanism of surface plasmon resonance (SPR) and Mach–Zehnder interference (MZI) using a four-core fiber (FCF), is proposed and implemented. The designed sensor is fabricated by cascading a sandwich structure of the FCF, multimode fiber and lead-in/out single-mode fiber. The gold-coated FCF as the critical component, enabling the excitation of the SPR and MZI for measuring refractive index (RI) and temperature. The proposed sensor exhibits a high RI sensitivity of 2091 nm/RIU and a temperature sensitivity of 0.0398 nm/°C. The proposed dual-parameter sensor based on FCF provides a new insight for the design of fiber SPR sensor, which can be used to measure multiple physical parameters in various fields such as biochemistry, gene diagnosis, environmental monitoring, and so on. [ABSTRACT FROM AUTHOR]

• Balloon-like and waist-enlarged structures are proposed for RI and temperature measurement. • The sensor is constructed using single-mode optical fiber, which is simple and inexpensive. • The RI and temperature sensitivity of the proposed sensor can be up to 340.9 nm/RIU and −0.162 nm/°C, respectively. A balloon-like composite optical fiber interferometer, integrated with a waist-enlarged structure, is presented for measuring refractive index (RI) and temperature. The waist-enlarged fusion tapers (WEFTs) are spliced to the single-mode fiber (SMF) to form a Mach-Zehnder interferometer (MZI). Meanwhile, the WEFTs structure is curved into a balloon-like structure. When the two structures are integrated, a larger evanescent field is formed, which can interact with the external environment better. The experiment results indicate that the best sensitivity of RI and temperature can achieve 340.9 nm/RIU and −0.162 nm/℃, respectively. In addition, the interferometer is small, easy to manufacture, and can be widely applied in various measurement applications. [ABSTRACT FROM AUTHOR]