SUSTAINED MODES IN A WAVE-GUIDE HAVING AN ANNULAR CORE CROSS-SECTION WITH NON-CONCENTRIC CIRCULAR BOUNDARIES

In an earlier communication we reported an analytical study of the mod al cutoff behaviour of a waveguide having an annular core cross-sectio n bounded by two non-concentric circles. Here a detailed study of the characteristic equation has been made. We discuss a number of cases wi th different parameters (dimensions and the refractive indices of the core and the cladding) for this waveguide. In this study we find that nu = 3 is the least possible value of the modal index for real values of the propagation constant beta i.e. for unattenuated modes. Further, as one increases the modal index nu, the beta value increases. Also i n order to decrease the modal index nu for a possible mode, it is nece ssary to reduce the refractive index difference (n(1)-n(2)) for a fixe d dimension of the waveguide. Results show that the present structure supports fewer modes than the concentric annular cross-section wavegui de.