On 21/09/2007, Steven G. Johnson <[EMAIL PROTECTED]> wrote: > By the way, I should just make one general comment about this formula: it > is only strictly valid in the limit of low index contrast, although many > people blindly plug it in even for high-contrast fibers. > > A typical use for the effective area is as a figure of merit for the > strength of nonlinearities in the fiber. The above formula is derived in > the low-contrast scalar limit, but the correct generalization to > high-contrast fibers is different and was derived in: > Tzolov et al, Optics Letters, vol. 20 (no. 5), p. 456 (1995).
Yes, I was aware of this fact, I was using the formulation given in JOSA B, vol. 20 (10) p. 2037 (2003), which appears to be similar. > You most definitely should be wary of these scalar-based formulas for > micron-scale silica strands surrounded by air! In such a high-contrast > case, the scalar-based formulas give at best only qualitative information. Well only, if you are using a scalar approximation. The silica strand in air can be solved analytically without approximation right? I have been following the solution in Snyder and Love, Optical Waveguide Theory. They do not make a low-index contrast approximation for cylindrically symmetric step-index fibers. Although the formula I gave does not give a useful value of effective index for nonlinearity it ought to agree with the value calculated for the analytic fields. Happily it does to within the numerical tolerances I used. Anyway, thanks for responding, and for the excellent software. Best regards, John Travers _______________________________________________ mpb-discuss mailing list [email protected] http://ab-initio.mit.edu/cgi-bin/mailman/listinfo/mpb-discuss
