Optics of nanogratings

Modeling of optical properties of nanogratings (sub-wavelength gratings) is of scientific and technological interests for (i) application of nanogratings as new artificial effective materials with unusual optical properties and (ii) application in non-destructive optical testing of nanogratings using optical spectroscopic ellipsometry and polarimetry. This paper deals with anisotropic lamellar nanogratings described by Effective Medium Approximation (EMA). Analytical formulae for effective medium optical parameters of nanogratings from arbitrary anisotropic materials are derived using approximation of zero-order diffraction mode. The method is based on Rigorous Coupled Wave Analysis (RCWA) combined with proper Fourier factorization method. Good agreement between EMA and the rigorous model is observed, where slight differences are explained by the influence of higher Fourier harmonics in the nanograting. Analytical spectral formulae for ordinary and extraordinary effective optical functions are derived for nanogratings consisting of material described by Sellmeier, damped harmonic oscillator, and Drude formulae. Spectral origin for birefringence of dielectric nanogratings and linear dichroism for absorbing ones is discussed.