Propagation properties of a surface plasmonicwaveguide with a bowtie air cores

A kind of surface plasmonic waveguide with a bowtie shaped air core was designed. The dependence of distribution of longitudinal energy flux density, effective index and propagation length of the fundamental mode supported by this waveguide on geometrical parameters and working wavelength were analyzed using the finite-difference frequency-domain (FDFD) method. Results show that the longitudinal energy flux density distributes mainly in the center region which is formed by the top and the bottom ridge. The effective index and propagation length of the fundamental mode can be adjusted by the geometric parameters as well as the working wavelength. At a given working wavelength, the effective index decreases as the radius of ridge increases, meanwhile propagation length and mode area of the fundamental mode increase as radius of ridge increases. The geometric parameter of radius of circles at four corner can affect the propagation properties slightly. The radius of sectors on both sides can effect propagation properties obviously. With given geometric parameters, relative to the case of λ=705.0 nm, in the case of larger λ, the area of field distribution is larger, and the size of the contact area of field and metallic surface is also larger, then the interaction of field and silver is weaker, and the effective index becomes smaller, so the propagation length becomes larger. The possibility of applying this kind of surface plasmonic waveguide to the field of sensors was discussed.