Propagation Characteristics of Plasmonic Gap Waveguiding Structures
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Electrical and Computer Engineering Honors Theses; 2007
As devices in current microprocessors continue to scale to ever decreasing dimensions, the concurrent increase in the RC time constants drive the need for next generation interconnects that can propagate signals at higher speeds. Plasmonic waveguides, using materials with a negative permittivity such as the noble metals, have the ability to propagate light signals over the length scale required for microprocessors while keeping the spot size of the light below the diffraction limit. Light propagating in a plasmonic waveguide has the advantage over electrons in a metal wire because it can propagate signals about three orders of magnitude faster. The price that is paid for confining light to dimensions on the order of tens of nanometers is a finite propagation length, due to the finite conductivity of the negative index material. A class of plasmonic waveguides is examined in this research. These waveguides consist of a dielectric core bounded on either side by metallic walls, and are known as “plasmonic gap waveguides.” Physically realizable structures consist of metal films with rectangular channels or gaps etched through them. It is found that making the gap smaller, increasing the refractive index of the dielectric material in the gap above about 1.5, and increasing the frequency of the excitation field has the effect of decreasing the propagation length. Propagation lengths on the order of 100 micrometers or less can be obtained with this type of waveguiding structure. This makes it useful for medium and short distance interconnects. Making the height to width aspect ratio of the gap large enough will allow for more vertical modes to propagate. The fundamental mode is of primary interest because it displays the lowest loss, is the easiest to excite, and is the highest confined mode for subwavelength geometries. As expected, there is transverse power flow into the metal, where it is dissipated. The power flow in the direction of propagation is strongest at the four metal corners of the waveguide. The high power focusing ability of this waveguide could be harnessed to exploit optical nonlinearities of materials used in the core, which could lead to the development of an all-optical plasmonic switch. Advisor: Ronald Reano
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