HIGH-FREQUENCY ASYMPTOTICS OF GUIDED MODES IN OPTICAL FIBERS

The high-frequency asymptotics of guided modes of dielectric waveguide s is studied, firstly under the weak guidance assumptions which lead t o a scalar problem, and then for Maxwell's system. The authors prove t hat the field tends to vanish everywhere the refractive index is not m aximum. Moreover, for the vector model, it is proved that the field te nds to become transverse. If the core of the guide is homogeneous, the n the limit problem, which is an eigenvalue problem set inside the cor e, is derived. Various asymptotic estimates on the dispersion curves a re established.