ACCURACY IMPROVEMENT OF THE FOURIER SERIES EXPANSION METHOD FOR FLOQUET-MODE ANALYSIS OF PHOTONIC CRYSTAL WAVEGUIDES

The Fourier series expansion method is a useful tool to approach the problems of discontinuities in optical waveguides, and it applies to analyze the Floquet-modes of photonic crystal waveguides. This paper shows that the Floquet-mode calculation with large truncation order is limited and explains the reason. Furthermore, two techniques of the formulation are presented to relieve this limitation. One of them is a use of the symmetric properties of the Floquet-modes, and another is a use of the Rayleigh quotients to improve accuracy of eigenvalue calculation. They are validated by numerical experiments.