Specialty Optical Fibers Handbook

confined in the hollow core, but one must still evaluate the losses that result from

the small portion of the mode that penetrates the cladding. As is discussed later

in this chapter, such losses decrease rapidly with the core radius and quickly

become several orders of magnitude smaller than the bulk absorption rates of the

cladding materials.

Although a variety of computational methods allow one to evaluate directly

the electromagnetic modes in absorbing materials, modeled by a complex re-

fractive index at a given wavelength, more general insights can be obtained by

perturbative methods. In particular for all dielectric materials considered here,

the imaginary part of the refractive index is much smaller than the real part

(<1% even for the polymer ...