Analytical approximations for the propagation characteristics of dual-mode fibers

In this paper we present accurate analytical approximations for the modal fields of dual-mode optical fibers with power law profiles based on a scalar variational analysis. We propose single parameter and two parameter trial functions and use these to study the dispersion characteristics and estimate the value of the normalized frequency corresponding to zero intermodal dispersion, which defines the operating point for such fibers. Our results show that the relatively simple single parameter field for the LP 11 mode gives a good fit to the field inside the core and estimates the propagation constant fairly well, but is inadequate to calculate the dispersion characteristics. On the other hand, the two parameter field estimates all these characteristics with a high degree of accuracy and enables one to accurately compute the normalized frequency for zero intermodal dispersion as well as dispersion tolerance around this value.