Sandwich structured Ω-shaped fiber optic-based sensor with dual signals for simultaneous temperature and refractive index detection

Measurements of refractive index (RI) and temperature play a vital role in a wide range of applications. Nevertheless, cross-sensitivity remains a major obstacle when RI and temperature need to be measured simultaneously. In this study, a novel sandwich structured Ω-shaped fiber optic-based sensor was designed and fabricated. The sensing structure was prepared by splicing a no core fiber (NCF) segment between two single mode fibers (SMFs), followed by bending the SMF-NCF-SMF structure into an Ω shape. After the sandwich nanolayer was deposited on the fiber surface, the Ω-shaped bending region promoted leakage of the core mode into cladding modes, thereby inducing a localized surface plasmon resonance (LSPR) response. Meanwhile, mode mismatch effect at the SMF-NCF interface excited Mach-Zehnder interference (MZI) signal. The LSPR and MZI components were effectively separated using fast Fourier transform (FFT) combined with filtering, which allowed RI and temperature to be detected independently. The sensitivities of the LSPR and MZI signals to RI were 3.29 (a.u)/RIU and 2.94 (a.u)/RIU, respectively. Meanwhile their sensitivities to temperature were −0.0009 (a.u)/°C and −0.0007 (a.u)/°C, respectively. These results demonstrate that the sandwich nanolayer modified sandwich structured Ω-shaped fiber sensor provides an effective platform for simultaneous dual-parameter detection.