High FOM PCF-SPR refractive index sensor based on MgF₂-Au double-layer films

A simple twin-core D-shape photonic crystal fiber sensor based on surface plasmon resonance (SPR) is designed for the measurement of refractive indices (RI). The twin-core D-shape structure enhances the SPR effect, and the <i>M</i> <i>g</i> <i>F</i> ₂-Au dual-layer film narrows the linewidth in the loss spectrum, consequently improving both the sensitivity and figure of merit (FOM). The properties of the sensor are analyzed by the finite element method. In the RI range of 1.32-1.42, the maximum wavelength sensitivity, FOM, and resolution are 62,000 nm/RIU, 1281<i>R</i> <i>I</i> <i>U</i> ^-1, and 1.61×10^-6, respectively.