Fraction of modal power in the core

Fraction of modal power in the core 11-9 Total guided power 11-10 Fraction of total power in the core... 

If we substitute the Gaussian approximation of Eq. (15-2) into Table 13-2, page 292, we obtain the expressions in Table 15-2 for fundamental-mode quantities on an arbitrary profile. We have generalized the function i/-the fraction of modal power within the core-and define tf(R) to be the fraction of modal power within normalized radius R = r/p. This is a more useful quantity for profiles with no well-defined core-cladding interface. The expressions for Vg and D follow from Eqs. (13-17) and (13-18). If for a particular profile the... 

Fig. 12-5 The fraction of modal power residing in the core for each of the first twelve modes as a function of V. The dashed curve is for the fundamental modes when and V fixed.

Fig. 14-3 Fundamental mode quantities for the step-profile fiber, showing (a) the modal parameter U, the fraction of power in the core fj, and the depth of penetration r, (b) the normalized polarization correction SU/AU, (c) the normalized intensity distribution and (d) the normalized variation in group velocity relative to the left ordinate, and the distortion parameter D relative to the right ordinate. Numerical values are given in Table 14-4.

In Section 11-8 we defined r) as the fraction of modal power propagating within the waveguide core. Although there is no formal definition of r) for leaky modes, we can provide an intuitive expression by adopting the description of the previous section and setting... 

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. 

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