Compact multi-period offset-spliced SMO-LPFG for ultralow-crosstalk dual-parameter sensing

Temperature-induced spectral drift limits the accuracy of surrounding refractive index (SRI) sensors. We propose and experimentally demonstrate a compact single-mode-multimode offset-spliced long-period fiber grating (SMO-LPFG) fabricated by three periods of SMF-MMF offset splicing (20µm lateral offset, device length 2.4 mm), and analyzed by beam-propagation simulations and experiments. The sensor shows SRI sensitivities of 14.5 nm/RIU and 217.88 nm/RIU, a temperature sensitivity of 105 pm/°C, and an ultralow temperature crosstalk of 2.04 × 10^-5 RIU/°C. A sensitivity matrix approach enables simultaneous SRI and temperature decoupling. The simple fabrication and compact size make the SMO-LPFG attractive for high-precision multiparameter sensing.