Abstract: A single-mode optical waveguide polarizer for use in conjunction with electrooptical devices that operate best when presented with only a single polarization mode. The polarizer is fabricated on a conventional substrate, such as lithium niobate, using a waveguide strip of indiffused material, such as titanium. To achieve polarization discrimination, a polarizer section of the waveguide strip is made small enough in width to support only a single polarization mode, specifically the TM mode, but not the orthogonal TE mode. Losses are minimized by the use of tapered waveguide sections adjacent to the polarizer section.