A method for preparing a fiber-optic polarizer involves a first step in which the cladding layer of a single-mode optical fiber is side-polished to form a planar surface contiguous to the core region of the single-mode optical fiber. The planar surface is formed thereon a buffer dielectric/metal composite thin film, or the planar surface is coated by sputtering with a metal layer which is then coated with a medium having a refractive index matching to that of the optical fiber. The polishing of the single-mode optical fiber is done by using a semiconductor substrate having one or more V-shaped recesses having a large curvature radius.