In-line fiber Mach–Zehnder interferometer for simultaneous measurement of refractive index and temperature based on thinned fiber

Abstract In this letter, we propose and demonstrate a novel and simple method for simultaneous measurement of refractive index and temperature using all-fiber in-line single-mode-multimode-thinned-single-mode (SMTS) fiber structures based on a small core and cladding diameters thinned fiber Mach–Zehnder interferometer (MZI). The principle of operation relies on the strong effect of the core and cladding mode interference of the thinned fiber through the employing of a multimode fiber. By measuring the shifts of the attenuation peak wavelengths of the two arbitrarily selected interference orders in the transmission spectrum, we can simultaneously measure the refractive index and temperature surrounding the sensor. Results indicate that the selected two interference orders have sensitivities of −2.85 × 10 −3  RIU with 3.49 × 10 −1  °C, and −1.12 × 10 −3  RIU with 4.07 × 10 −1  °C respectively at RI range from 1.3325 to 1.3715 and temperature range from 24 °C to 84 °C. The fabrication is easy, safe and cost effective, and includes only the fusion splicing, making the device properly attractive for physical, biological and chemical sensing in practical applications.