Coupled mode equations weak power transfer

Coupled mode equations 27-2 Weakly guiding fibers 27-3 Example Weak power transfer... 

Under certain resonance conditions, a small perturbation of the fiber leads to the transfer of a large proportion of total power between only two modes of the complete set of modes of the unperturbed fiber, e.g. resonant coupling on a sinusoidally deformed fiber as discussed below. The coupled mode equations describe arbitrary power transfer exactly, whereas the induced-current method of Chapter 22 is inaccurate, since it assumes only a slight transfer of total mode power. If we ignore the weak power transfer to all other modes, the set of coupled mode equations reduces to just two equations for the resonant modes. 

In Section 27-1 we showed that in applying the coupled mode equations there is an intrinsic restriction to weakly guiding waveguides. This restriction does not occur in the application of the coupled local-mode equations. A general solution of the coupled local-mode equations is derived for weak power transfer in the following section, and the radiation modes are discussed later in the chapter. 

An important application of the solution of the coupled local-mode equations for weak power transfer determines how slowly a waveguide must vary along its length in order that an individual local mode can propagate with negligible variation in its power. If we assume the /th local mode alone is initially excited with unit power, i.e. h((0) = 1, then the fraction of power excited in the jth... 

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See also in sourсe #XX -- [ , ]

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