MODAL CHARACTERISTICS OF A DOUBLY CLAD STEP-INDEX OPTICAL FIBER - A GENERAL ANALYTICAL APPROACH

Using a fairly rigorous approach, a general characteristic equation for a doubly clad step-index fiber has been derived under the assumption that the refractive-index difference between the inner and outer cladding is small. Two different profiles, i.e., the W profile and the staircase profile, have been treated together and a discussion of their common characteristics has been made. Cutoff conditions for low-order modes have been obtained. For a certain range of values of the transverse-phase parameter ratio, the singly-clad fiber has greater mode cutoff V numbers than those of a doubly clad fiber. The analysis anticipates the possibility of obtaining greater cutoff V numbers for W-profile fibers.