A (de)multiplexer for use in optical communications systems includes a diffraction grating optically coupled between a multiplex optical waveguide and a plurality of single channel optical waveguides for diffracting an optical signal between a receiving/transmitting end of the multiplex optical waveguide and a receiving/transmitting end of the single channel optical waveguide. The diffraction grating has al least two surfaces optically coupled to the waveguides. Each of the surfaces is angularly displaced relative to one another a select amount such that a portion of the optical signal diffracted by each surface is offset the direction of dispersion relative to the portions of the optical signal diffracted by the other surfaces to broaden the transmission band. A method for broadening The transmission band of a (de)multiplexer includes dividing the diffraction grating into distinct surfaces and angularly displacing the surfaces relative to one another a select amount such that a portion of the optical signal diffracted by each surface is offset in a direction of dispersion.