Admittance loci design method for multilayer surface plasmon resonance devices

Dielectric mirror types of multilayer structures have been applied to enhance the performance of surface plasmon resonance (SPR) devices. It demands a more robust design method than traditional Fresnel's equations. An admittance locus is a kind of optical thin film design method which has been extensively used for high performance optical coatings. We have applied this method for the design of multilayer SPR devices, including symmetric (glass|Au(40 nm)–[TiO2(20 nm)–SiO2(20 nm)]4–Au(30 nm)) and asymmetric (glass|Ag(50 nm)–[TiO2(20 nm)–SiO2(20 nm)]4–Au(20 nm)) structure. It provides a much necessary guidance for the choices of suitable optical materials, thickness, and number of layers for the intended SPR performance. With a 633 nm light source and a BK7 coupling prism under water, one can shift the resonant angle toward the critical angle and have smaller half maximum band widths (HMBW) at (64°, 2°) and (61.52°, 0.25°) for symmetric and asymmetric designs, respectively.