Simultaneous measurement of temperature and refractive index based on a hybrid surface plasmon resonance multimode interference fiber sensor

We propose and demonstrate a hybrid fiber-based sensor combining a multimode interference (MMI) structure and a surface plasmon resonance (SPR) structure for simultaneous measurement of temperature and refractive index (RI) of a liquid sample. We configure the MMI structure by connecting a single-mode fiber, a no-core fiber, and a single-mode fiber sequentially. We set up the SPR structure by coating a gold film with a thickness of 50 nm on the surface of the no-core fiber. We measure the sensitivity of RI and the temperature of the MMI and SPR structure, respectively. Then we obtain the coefficient matrix to simultaneously measure the temperature and RI of a liquid sample and obtain the highest RI sensitivity of 2061.6 nm/RIU and temperature sensitivity of 37.9 pm/°C. We verify the feasibility of the sensor in liquid alcohol. The testing results indicate that the proposed sensor and testing method are feasible, accurate, and convenient.