On the convergence of the finite element approximation of eigenfrequencies and eigenvectors to Maxwell's boundary value problem

Mathematical analysis of a finite element method without spurious solutions for computation of dielectric waveguides

“…In the last years a great number of papers (see [10,12,13,16]) were devoted to solving this problem by using classical lagrangian finite element approximations for either electric or magnetic field components. However these finite element solutions have been known to include nonphysical spurious modes.…”