We propose a new, to our knowledge, method for determining the two main critical parameters of periodi one-dimensional lamellar structures, namely, linewidths and etched depths. The method is simple and requires only two measurements for the phase of the zero-transmitted order under two orthogona polarizations. It is inspired by the analogy between subwavelength gratings and anisotropic homoge neous thin films. The method is tested with experimental data obtained with a Mach-Zehnder inter ferometer. Etched depths and linewidths derived from the interferograms and electromagnetic theory are compared with scanning-electron-microscope observations.
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