ACCURACY OF COUPLED-WAVE ANALYSIS OF RELIEF DIFFRACTION GRATINGS IN OPTICAL RANGE

摘要

The study explores the convergence of the coupled-wave analysis as applied to some kinds of relief diffraction gratings in the optical and the near infrared range for certain wavelengths. It is shown that the dependence between the transmission and the number of coupled waves in case of TE-wave diffraction by metal narrow-slotted gratings (rectangular relief) in a resonant medium monotonously tends to a certain value with the error of O(1/N~3), and in case of TM-waves - with the error fluctuating around some asymptotic value within the range +-O(1/N~2). The error in the transmission factor with the number of coupled waves N=101 is under 0.001 for TE-polarization and 0.005 - for TM-polarization. In case of a rectangular dielectric relief grating the error for the both polarizations will decrease monotonously according to expression O(1/N~3), still with some minor deviations from this curve. The computation errors for N =101 in case of TE- and TM-polarization are under 10~(-15) and 10~(-3), respectively. If the permittivity of the grating medium changes as cosine, the diffraction efficiency tends rapidly to the asymptotic value as the number of couples waves grows.