Patent ID: 7525672

Claim:
A system for optically determining one or more parameters of a 2-D grating having substantial reflection symmetry in a grating reflection plane, the system comprising: a) an optical source providing optical radiation at a variable wavelength and illuminating said 2-D grating, wherein said radiation has a wave vector in said reflection plane; b) an optical detector receiving radiation from said 2-D grating and providing a measured spectral response; and c) a processor receiving said measured spectral response and providing a modeled spectral response of said 2-D grating having said parameters as variables, wherein said processor determines said one or more parameters by adjusting said variables to fit said modeled spectral response to said measured spectral response; wherein said modeled spectral response is provided by a symmetry-simplified rigorous coupled wave analysis (RCWA); wherein said grating is in an x-y plane, wherein said reflection plane is an x-z plane, wherein said RCWA accounts for N x positive diffraction orders and N x negative diffraction orders in the x direction, and wherein said RCWA accounts for N y positive diffraction orders and N y negative diffraction orders in the y direction; wherein said grating reflection plane is perpendicular to a plane in which said 2-D grating is disposed.