Multiple surface-plasmon-polariton waves guided by a chiral sculptured thin film grown on a metallic grating
With fields confined to the metal/dielectric interface, surface plasmon polaritons (SPPs) can be very sensitive to small changes in dielectric properties, making them ideal for sensing applications. Multichannel SPP sensors are desirable for achieving simultaneous detection of multiple analytes and high-throughput screening. Conventional metal/dielectric configurations involving a homogeneous dielectric support only one p-polarized SPP mode for a given wavelength. Therefore, a wavelength division multiplexing scheme is usually adopted in order to virtually achieve a multichannel sensor, which is referred to as a multispectral sensor. Recently, it has been shown that, by replacing the homogeneous dielectric material with a periodically nonhomogeneous material, for example a sculptured thin film (STF), multiple p- and s-polarized SPP modes can be supported at the same wavelength. These provide novel approaches to increase the number of sensing channels. In this work, Erten el al. from The Pennsylvania State University systematically investigate the grating excitation of multiple isofrequency SPP modes guided by a metal/chiral-STF interface. They provide not only theoretical procedures to find the propagation properties and to model grating-coupled plane wave excitations of these SPP modes, but also experimental procedures to fabricate and characterize the metal/chiral-STF samples. Under illumination of p- or s-polarized light at a specific wavelength and with a varying angle of incidence, both theoretical calculations and experimental data indicate that three p- and s-polarized SPP modes can be excited by the grating.