High-performance Grating Coupled Surface Plasmon Resonance Sensor Based on Al-Au Bimetallic Layer

A high-performance grating coupled surface plasmon resonance (GCSPR) sensor based on Al-Au bimetallic layer is proposed. High sensitivity is obtained by replacing the positive diffraction order with negative diffraction order of metallic grating to excite the surface plasmon. Compared with the conventional Au-based GCSPR sensor, the sensor with aluminum as the SPR active metal exhibits a sharper (i.e. larger depth-to-width ratio) reflectivity dip, which increases the signal-to-noise ratio (SNR) and enhances its resolution. In addition, an ultrathin gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the angular sensitivity of the sensor reaches 187.2°/RIU (degree per refractive index unit) with good linearity and the FWHM (full width at half maximum) of the resonant dip is only 0.93°.