Abstract
The field of diffractive optical elements has a long history, and various fabrication methods have been developed over time. Recent progress in nanotechnology further facilitated fabrication of diffractive optical elements with a periodic structure that has less than one wavelength. In the case of this type of element (e. g. device structure of which the size is less than one wavelength or a deep trench that is several times longer than its wavelength), a rigorous method is required for analyzing polarization, evanescent waves and beam propagation inside grating structures. This paper provides a brief overview of numerical methods for electromagnetic wave analysis, with particular focus on the difference between the Finite-Difference Time-Domain (FDTD) Method and Rigorous Couple-Wave Analysis (RCWA). The latter method is suitable for analyzing diffractive optical elements with binary sub-wavelength structures and Volume Phase Holographic (VPH) gratings. Furthermore, the paper introduces the authors' numerical analysis based on RCWA, underlining its merit and applications to design and evaluation of diffractive optical elements.
