Role of optical and surface plasmon modes in enhanced transmission and applications

An analysis of several types of one-dimensional transmission gratings structures with different metal contact geometries is used to study the role of horizontally oriented surface plasmons, cavity modes and other optical modes in enhanced transmission. Several competing theories of enhanced transmission are presented and the analysis of the structures in this work clearly establishes that horizontal surface plasmons can enhance or inhibit transmission depending on whether the HSPs establish vortices of energy that circulate in a direction that enhances or inhibits the flow of energy through the center of the grooves. Also, we show that enhanced transmission can be achieved using a different mechanism than previously reported in the literature. This new mechanism is a Fabry-Perot resonance produced by small notches in the top metal surface, which concentrates the energy from the incident beam and steers it through the slit openings and into the substrate. Finally, applications of the different structures and their optical modes are discussed including chemical and biological sensors and high bandwidth, high responsivity InGaAs metal-semiconductor-metal photodetectors.