Refractive index and temperature dual-parameter sensors based on loss mode resonance and directional coupler in side-polished hole-assisted dual-core fiber

A refractive index (RI) and temperature dual-parameter sensor, based on a side-polished hole-assisted dual-core fiber (HADCF), has been proposed. In this sensor, SnO₂ film has been deposited on the suspended core of HADCF by RF sputtering to produce loss mode resonance (LMR). The energy of the center core has been shown to be able to be coupled into the suspended core, taking advantage of the small distance involved and phase matching between two cores. The 10 mm long HADCF can be used to form a directional coupler. LMR and the directional coupler are integrated in parallel on the same section of HADCF, which realizes the high integration of sensing measurement. The sensor achieves simultaneous measurement of both RI and temperature through measuring both the LMR dip and coupling dip. The RI and temperature sensitivities achieved were 3812.5 nm/RIU and 521.4 pm/°C, respectively. The sensor discussed shows important advantages of high sensitivity, simple fabrication, high integration, and the ability to make measurements of two key parameters.