Simultaneous measurement of refractive index, strain, and temperature based on a Mach–Zehnder interferometer with hybrid structure optical fiber

An optical fiber sensor based on a Mach-Zehnder interferometer with hybrid structure optical fiber for simultaneous measurement of refractive index (RI), strain, and temperature is proposed and demonstrated. The proposed structure is a hybrid structure based on a non-core fiber combined with few-mode fiber. The possibility of simultaneously measuring RI, strain, and temperature relies on the different sensitivity responses of three resonance peaks in the transmission spectrum. Thus, simultaneous measurement of RI, strain, and temperature is realized by calculating the wavelength shift of the three resonance peaks. The experimental results show that the sensitivities of RI are 22.9 pm/RIU, 24.6 pm/RIU, and 97 pm/RIU when RI changes from 1.3707 to 1.39809, respectively. The sensitivities of strain are $ - {3.5}\,\, \text{pm}/ \unicode{x00B5}\unicode{x03B5}$-3.5pm/µε, $ - {1.9}\,\, \text{pm}/ \unicode{x00B5} \unicode{x03B5}$-1.9pm/µε, and $ - {4.1}\,\, \text{pm}/ \unicode{x00B5} \unicode{x03B5}$-4.1pm/µε in the range from 0 to 1400 pm/µ$\unicode{x03B5}$ε. The sensitivities of temperature ranging from 35°C to 55°C are 162 pm/°C, 194 pm/°C, and 162 pm/°C, respectively. The proposed sensor, with advantages of simple configuration, compact structure, and high sensitivity, exhibits great potential in fields of multi-parameter measurement.