An optical coupler for coupling a multimode waveguide and two or more other waveguides. In one embodiment, the optical coupler has an optical phase mask disposed between the multimode waveguide and two or more other waveguides. The optical phase mask imposes on the light passing therethrough a spatial phase pattern that causes selective mode-to-waveguide coupling between the multimode waveguide and the other waveguides. The optical coupler can be used, e.g., in transmitters and receivers of optical transverse-mode-multiplexed signals.