We numerically demonstrate two types of metal-clad waveguide polarizers, in which the transmission wave can be selected to be either the TE or TM wave, using the three-dimensional beam-propagation method. The results obtained from a three-dimensional polarizer are compared with those from a two-dimensional structure based on the effective index method. It is found that the thickness and the refractive index of a buffer layer are key parameters to obtain a high extinction ratio. By proper choice of the buffer layer, an extinction ratio of more than 30 dB can be obtained at a wavelength of λ = 0.633μm.
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