Few-Mode Fiber Temperature Sensor Based on Interference Between LP01 and LP11 Modes

A few-mode fiber (FMF) temperature sensor based on the interference between LEH and LP,, modes is proposed. The sensor is fabricated with an FMF, of which one end is spliced to a lead-in single-mode fiber (SMF) with small lateral core-offsets and the other is spliced to a lead-out SMF with alignment. Firstly, the theoretical model of FMF is established with the scalar method and the characteristic equation of FMF is derived by the light field of continuous electromagnetic boundary condition. Through the numerical solution of the characteristic equation, the transmission mode of FMF is analyzed in detail. Then, the theoretical results arc verified through the finite element analysis. Finally, the sensor is used for temperature sensing experiments. Through the Fourier transform of the transmission spectra at different temperatures, the two modes of interference arc analyzed. According to the thermo optic effect, the temperature sensing model is established. The temperature sensitivity of the sensor is analyzed and calculated, which is consistent with the experimental results. The temperature measurement experiment is carried out with the proposed sensor, and the results show that when the temperature changes, the interference peak drifts, and the temperature sensitivity of a 16-mm-long sensor is 158.06 pm/degrees C at 25.3-77.3. The temperature sensor can be widely used in industrial production, biomedical and other fields.