Surface Plasmon Wave

Abstract

The pervious chapters introduce the dielectric slab waveguide, which is composed by ideal lossless materials; meanwhile, the widely used RF transmission lines and microwave waveguide is made of metallic lines, strip, and tubes. Metal is treated as a perfect conductor in the low-frequency range. Due to its collective electrons excitation, which is called as the plasmon, in the UV and visible region, metal can no longer be treated as a perfect conductor; it can still be applied to build low loss metal waveguide or metal–dielectric waveguide. In these two structures, the electromagnetic field takes the form of evanescent field. On the other hand, for noble metal such as gold, silver, and aluminum, their complex permittivity usually has a relatively larger real part than its imaginary part. In the near infrared and visible region, its real part is usually a large negative number

$$ \varepsilon = \varepsilon_{r} + i\varepsilon_{i} ,\,\varepsilon_{r} < 0,\,\left| {\varepsilon_{r} } \right| \gg \varepsilon_{i} . $$

(5.1)

Due to this optical property of metal, the surface plasmon wave (SPW) can propagate along its interface with dielectric, and the long-range SPW can be excited within a thin metal slab. These two surface waves illustrate different features from the conventional waveguide. Some unique characteristics can be valid, for example, the large range of the effective refractive index and the field enhancement effect. The propagation of SPW not only riches the traditional research field of the waveguide optics, but also finds a wide application in fields such as integrated optics, nonlinear optics, and molecular biology. This chapter first discusses the SPW bounded at a metallic interface and then analyzes the long-range SPW. The excitation method via attenuated total reflection method of these surface waves is introduced, and their applications are also discussed.