Simultaneous measurement of refractive index and temperature based on asymmetric structures modal interference

• We presented a novel MZI fiber-optical sensor combining the SMS structure and the peanut-shape structure for the simultaneous measurement of the ambient RI and temperature.
• We focus on the modal interference.
• The novel sensor processes easy fabrication, low cost, and high sensitivity.A MZI fiber sensor for the simultaneous measurement of the RI and temperature has been proposed, which processes easy fabrication, low cost, and high sensitivity.

An in-line fiber sensor for simultaneous measurement of refractive index (RI) and temperature is proposed and demonstrated. The sensor head is composed of an asymmetric Mach–Zehnder interferometer (MZI), which is combining the single mode-multimode-single mode (SMS) fiber structure and a peanut-shape structure. The transmission dips of the sensor will shift as the ambient RI or temperature variation due to the phase changing. The different wavelength transmission dips formed by the cladding modes interfering with the core mode have different sensitivity responses, so the simultaneous measurement of the RI and temperature can be achieved by monitoring the wavelength shifts of the two transmission dips. The experimental results show that the sensing sensitivities of RI and temperature are −86.7434 nm/RIU and 0.0590 nm/°C in the RI range from 1.3105 to 1.3517 and temperature range from 25 °C to 85 °C, respectively. The novel sensor processes easy fabrication, low cost, and high sensitivity, making it offers high potential applications in physical, biological and chemical sensing.