Cutoff frequencies in optical fibers of arbitrary refractive index profile using the resonance technique

We present a very simple and accurate numerical method for calculating the cutoff frequencies of arbitrary refractive index profile optical fibers, including discrete numerical data from profile measurements. From Maxwell's equations we derive a transmission line equivalent circuit for any mode of an optical fiber which is cutoff frequency dependent. The problem of finding the cutoff frequency of a mode is transformed into finding the resonance frequency of the equivalent circuit. The algorithm uses no Bessel or other complicated functions and could be implemented on small microcomputers.