Leaky guide

The first HWGs confined light to their core either by total internal reflection (attenuated total reflection guides) or by reflection off a metallic surface (leaky guides) as discussed in Sect. 2.3.1. The latest generation of HWGs is based on PBG materials as discussed in Sect. 2.3.2. 

Fig. 2.3. Experimental layout for the fully leaky guided mode technique. (Reproduced from Taphouse et with the permission of the Institute of Physics.)...

The fully leaky guided mode technique makes use of a thin 3 pm) HAN sample between glass plates with a refractive index lower than both the principal indices of the nematic. A p or 5 polarized He-Ne laser beam, with the electric vector in the plane of incidence or orthogonal to it, respectively, incident in an appropriate range of incident angles / (see... 

S.A. Jewell and J.R. Sambles, Fully leaky guided mode study of the flexoelectric effect and surface polarization in hybrid aligned nematic cells, J. Appl. Phys. 92(1), 19-24, (2002). doi 10.1063/1.1483392... 

Evanescent Waves of Guided and Leaky Waveguide Modes... 

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. 

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

The products of hybridization are detected through the use of fluorescent labeling. These molecular complexes can either be homogeneously distributed in the liquid core or be bound to the interior surface of the capillary through covalent bonding. In both cases, labeled molecules can be excited either by direct illumination with the leaky modes of the liquid filled core, or by the evanescent waves arising from the guided modes of the capillary wall. Direct excitation is less wasteful of incident photon flux and is the method of choice in conventional fluorometers. Evanescent wave excitation becomes a necessity when direct excitation is either not feasible or results in undesirable sensor performance. Both methods of illumination are possible for the CWBP. 

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