Leaky waveguide mode

Evanescent Waves of Guided and Leaky Waveguide Modes... 

Fig. 15.2 Illustration of (a) guided waveguide modes and (b) leaky waveguide modes in a three layered waveguide structure...

The sensor systems outlined in the present chapter use evanescent electromagnetic radiation to monitor various analytes in aqueous solutions. Therefore, as a beginning, the basic properties of evanescent electromagnetic waves and the so-called TIR phenomena are summarized. Afterwards, two types of waveguide modes will be briefly discussed guided and leaky modes, which both generate evanescent waves at a solid/liquid boundary. 

This chapter focuses on the characterization of polymer films hy the spectroscopy of (leaky) surface plasmon (SP) and dielectric waveguide modes. The fundamentals of optics that are essential for the understanding and implementation of these techniques are presented (Section 2.26.2). Models that can he employed for the evaluation of optical response in order to assess the information on phenomena including adhesion of polymers on a surface, swelling of polymer films in solvents, and diffusion and interaction of biomolecules in polymers are discussed (Section 2.26.3). The performance characteristics of presented methods are illustrated with a focus on highly swollen polymer networks (cross-linked hydrogels and bmshes) tethered on gold surfaces (Section 2.26.4). 

As mentioned in Sect. 15.2, sometimes a 4th thin layer (M) of metal or die is incorporated between the substrate and waveguide film to decrease the radiation loss into the substrate of the substrate radiation modes. These modes are referred to as leaky modes and the obtained structure is the MCLW. This configuration is also broadly used in evanescent wave sensor systems. 

Luterova K, Skopalova E, Pelant I, Rejman M, Ostatnicky T, Valenta J (2006) Active planar optical waveguides with silicon nanocrystals leaky modes under different ambient conditions. J Appl Phys 100 074307... 

The fundamental modes of all waveguides considered in this text are cut off when F = 0. At cutoff the phase velocity of the mode is equal to that of a z-directed plane wave in an unbounded medium of refractive index n, but the modal fields are not TEM waves except in special cases. In general, a significant fraction of a mode s power can propagate within the core at cutoff, i.e. r]j of Eq. (11-24) is nonzero, and the group velocity differs from the phase velocity. Below cutoff, these modes propagate with loss and are the leaky modes of Chapter 24. 

Characteristics of leaky modes 24-4 Modal parameters 24-5 Modal fields 24-6 Radiation caustic 24-7 Classification of leaky modes 24-8 Plane-wave decomposition 24-9 Weakly guiding waveguides 24-10 Number of leaky modes... 

The description of leaky modes comes from several logical approaches. We begin with a heuristic argument and follow with the detailed mathematical formulation which applies to waveguides of arbitrary cross-section and profile. For clarity, we omit modal subscripts when discussing an individual leaky mode. 

The radiation fields of an optical waveguide can be determined either by modal methods or by Green s function methods, as discussed in Chapters 25 and 34. In Chapter 26, we show how, starting from either representation, the total radiation fields and expressed exactly as a sum of leaky modes... 

We now examine the properties of leaky modes on nonabsorbing, clad fibers of arbitrary profile and cross-section. Later, in Section 24-20, we briefly discuss the leaky modes of planar waveguides. 

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