Microfiber Knot With Taper Interferometer for Temperature and Refractive Index Discrimination

A compact sensing structure using two distinct optical devices, a microfiber knot resonator and an abrupt taper-based Mach-Zehnder interferometer (MZI), is presented. The device was fabricated using only CO2 laser processing. The transmission spectrum presents two different components with different sensitivities to different physical and chemical parameters. The sensor was characterized in temperature and refractive index. For temperature sensing in water, the MZI component presents a sensitivity of -196 ± 2 pm/°C while the microfiber knot resonator (MKR) component shows a sensitivity of 25.1 ± 0.9 pm/°C, for water temperature variations of 12 °C. Sensitivities of 1354 ± 14 nm/RIU and -43 ± 4 nm/RIU were achieved for refractive index sensing for the MZI and the MKR components, respectively, in a refractive index range from 1.32823 to 1.33001. The matrix method was used for the simultaneous measurement of temperature and refractive index.