Computing leaky modes of optical fibers using a FEAST algorithm for polynomial eigenproblems

An efficient technique to solve polynomial eigenproblems is shown to result in an accurate method for computing leaky modes of optical fibers. The nonlinear eigenproblem arises from a frequency-dependent perfectly matched layer and is solved using a contour integral eigensolver. Extensive computations on an antiresonant fiber with a complex transverse microstructure are reported. Even when employing up to one million degrees of freedom, the fiber model appears to remain in a preasymptotic regime where computed confinement loss values are likely to be off by orders of magnitude. This and other difficulties in computing mode losses, together with some techniques to overcome them, are detailed.