SPR sensor based on exposed core micro-structured optical fiber for salinity detection with temperature self-compensation

Abstract

A surface plasmon resonance (SPR) sensor based on exposed core micro-structured optical fiber (EC-MOF) for temperature self-compensated salinity detection is proposed. The sensing channel is fabricated by sequentially coating indium tin oxide (ITO) and Au layers at the exposed region of the fiber core. Benefiting from the large dynamic refractive index (RI) range of ITO induced by dispersion, two separated SPR peaks with equal intensity can be excited at visible spectrum by Kretschmann configuration and near-infrared spectrum by Otto configuration. The RI sensing performance at 1.33–1.39 is investigated and optimized using finite element method, with maximum wavelength sensitivities of 2000 nm/RIU and 3000 nm/RIU, respectively. The distinct RI responses of two SPR peaks make the dual-parameter demodulation realizable, which shows great potential in multiplex or self-compensated sensing applications. The temperature self-compensated salinity sensing ability is demonstrated with high sensitivity of 4.45 nm/% and a temperature compensation coefficient of −0.12%/°C. To the best of our knowledge, this is the first time temperature self-compensation of fiber SPR sensors with a single sensing channel and the single demodulation method has been realized.