| The study of diffraction properties of grating can fall into two theories: the scalardiffraction theory and the vector diffraction theory. When the feature size of grating issmall to the order of wavelength, the polarization dependence of the diffraction fieldbecomes obvious so that the scalar diffraction theory could not be used any more andthe vector diffraction analysis method is necessary. In this paper, we propose amethod for analyzing the grating's Fraunhofer diffraction based on the FDTDalgorithm and the Fourier transform. As an example, the diffraction properties ofone-dimensional transmittance metal grating are studied intensively. The polarizationdependence of the diffraction field is analyzed. Gratings with various parameters are studied for normal incident wave. Thecalculation results show that the Fraunhofer diffraction field is polarization dependentwhen the feature size of grating is small to about 8 times of wavelength. Besides, thediffraction field is affected by many factors including the grating's feature size, slitwidth, and thickness. A group of plots and graphs are given to show the results. The polarization dependent diffraction properties of one-dimensionaltransmittance metal Gratings with slanted incident wave are also computated. We canalso find when the feature size of grating is small to about 8 times of wavelength ,thediffraction field is polarization dependent, besides, the incident angle also affect theFraunhofer diffraction field's distribution . By the analyzing of the process of diffraction, we find that the diffraction field ofTE wave at the rear plane of the grating is different from that of TM wave, and thedifference becomes more and more obvious when the feature size of grating is gettingsmaller. This is the reason why the Fraunhofer diffraction field of TE wave is differentfrom that of TM wave when the feature size of grating is small to about 8 times ofwavelength.. |
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