Comparison of Near Field Simulations of Gratings with the Fourier Modal Method and Thin Grating Approximation

The use of the Fourier Modal Method (FMM) for the calculation of diffraction efficiencies of gratings is well established. However, the simulation of near fields with FMM is not as much discussed, though it gives interesting insight in the near field effects of gratings. In our presentation we discuss the use of FMM for the calculation of various linear gratings like sinusoidal, rectangular and sawtooth. In particular we consider the adjustment of the convergence of the FMM algorithm by investigating the influence of the number of layers and the number of evanescent fields on the convergence. We compare the resulting near fields with the results for the thin grating approximation. Various series of simulation experiments give an insight in the effects dependent on the grating period and the incident angle. The simulations are done with LightTrans VirtualLab(TM) Grating Toolbox.