Cutoff Frequency of a Homogeneous Optical Fiber with Arbitrary Cross Section

Through an original derivation of the boundary conditions right at cutoff, the method of circular-harmonic expansion proposed by Goell to calculate propagation constants is extended to treat cutoff frequencies of homogeneous optical fibers with arbitrary cross sections in the rigorous vector form. This circular-harmonic method is also extended to the scalar form, from which the cutoff frequency can be obtained in a simpler way. Numerical results of cutoff frequencies of both the vector and the scalar forms are presented.