This book serves as an introduction to the now largely completed theory of light propagation in dielectric waveguides. For physical understanding, the classical method of analyzing given non-optimal refractive index profiles is briefly presented, along with an introduction to the extensive literature on the subject. The field distributions can be represented in the case of the so-called step-index fiber using cylindrical functions. In optimal fibers, pulse distortions are to be flattened over frequency. This results in optimal profiles for the refractive index as solutions. The field distributions are also found and presented as a result of numerical calculations, without the approximate use of standard functions that have become irrelevant. This point should be particularly emphasized. The numerical treatment of the optimization problem is discussed with the help of...