Abstract: The polarizer is formed on a silicon rib waveguide (4) having an upper face and two side faces, and comprises a section of the silicon rib waveguide (4) with a buffer layer (6) and a light absorbing layer (7) on either the upper face of the rib or at least one side face of the rib. The buffer layer (6) has a refractive index similar to that of the waveguide (4) such that light traveling along the waveguide (4) and incident upon the respective face thereof passes into the buffer layer (6) and then into the light absorbing layer (7) so either the TM (transverse magnetic) or TE (transverse electric) mode of the light traveling along the waveguide is attenuated.