Dipole bound modes

In the previous chapter we examined the excitation of modes of a fiber by illumination of the endface with beams and diffuse sources, i.e. by sources external to the fiber. Here we investigate the power of bound modes and the power radiated due to current sources distributed within the fiber, as shown in Fig. 21-1. Our interest in such problems is mainly motivated by the following chapter, where we show that fiber nonuniformities can be modelled by current sources radiating within the uniform fiber. Thus, isolated nonuniformities radiate like current dipoles and surface roughness, which occurs at the core-cladding interface, can be modelled by a tubular current source. 

Eq. (21-11) that the on-axis dipole excites zero power, while the dipole at = r excites maximum power. Furthermore, the power of the bound mode due to the z-directed... 

The tubular current source was described in Section 21-6, where we showed that it is ineffective in exciting bound modes unless either of the resonance conditions of Eq. (21-15) is satisfied. A similar conclusion holds for the radiation fields. If the tube length 2L is large compared to the spatial period 2n/Sl, where 2 is the frequency in Eq. (21-13), it is intuitive that power will be radiated essentially at a fixed angle to the fiber axis. This is also a consequence of Floquets theorem [7]. However, unlike the current dipole, radiation now depends on the orientation of the currents on the tube. 

Fig. 9.16. Simplified schematics illustrating two different molecular recognition mechanisms exemplified for native (i-CD and propranolol. Case A is the polar-organic phase mode where the solvent molecules occupy the cavity and the SA is bound to the outer surface of the CD via polar interactions (hydrogen bonding and/or dipole-dipole interactions) which contribute to chiral recognition in combination with steric interactions. In the reversed-phase mode, the primary binding mechanism is similar to case B SO-SA association may be driven by inclusion type complexation into the hydrophobic cavity of the CD macrocycle (reprinted with permission from Ref. [27. ]).

The mode is sure to be inactive in free O2, because it would not change the molecule s dipole moment. In a complex in which O2 is bound, the 0—0 stretch may change the dipole moment, but it is not certain to do so at all. let alone strongly enough to provide a good signal.)... 

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