| DIFFERENT STRUCTURES OF SURFACE PLASMON WAVEGUIDES: | ||
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Contents Surface wave guideSurface plasmon resonamce SPR configuration Surface plasmon wave SPWs Application Differenr structures of plasmon waveguides Metal core dielectric cladding waveguide Metal clad waveguide
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The main feature of the surface waveguide is the interface between two or more different medium having different dielectric constant. In between this interface the wave propagate by total internal reflection method. This is called confined propagation. Three types of structures are described here.
i) SINGLE INTERFACE: Confined propagation of electromagnetic waves can also exist at a single interface between two semi-infinite dielectric homogeneous media provided that they have dielectric constants of opposite signs. This type of waves is called SPWs and as it was discussed in one of their main applications is found in sensing through SPR. Consider a planar interface of two semi-infinite media with relative dielectric constants 2 ξ 1= n1^2 (x > 0) and ξ 2 =n2^2 (x < 0), supporting confined propagation. The coordinate axes have been chosen so that the x axis is normal to the interface with x = 0 corresponding to the interface. The z axis is in the direction of propagation, and y axis lies in the interface plane.
When the two medium have two different dielectric constants which have opposite signs then boundary condition is satisfied. Metal can show negative dielectric constant that means one medium can be metal. When this metal is ideal then it becomes FANO WAVES, otherwise it becomes SURFACE PLASMON WAVES. For non ideal metals the dielectric constant is a complex number i.e. it has a real part and an imaginary part. ξ = ξR- jξI. Because ξ is complex so β (propagation characteristics) is also complex i.e. β= βR - j βi. This βR is called PROPAGATION CONSTANT and βI is called ATTENUATION COEFICIENT.
ii) DOUBLE INTERFACE: Previously we have shown how single interface between two medium is used to provide the wave guide and how the total internal reflection is occurred in between this. Now here we discuss about two interfaces between three medium. These are two types
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