In a wavelength-division multiplexer/demultiplexer of the free-space kind, which uses a diffraction grating or other angularly-dispersive element, spatially-shaping the light beam(s) to modify the passband response in the dispersion plane results in a substantially flat spectral response. Spatial shaping may be obtained using lenses disposed adjacent ports through which pass a corresponding plurality of angularly-dispersed light beams having different centre frequencies/wavelengths. Each lens may be a cylindrical lens with its cylindrical axis normal to the dispersion plane so as to shape the light beam in only one direction, i.e. that of the dispersion plane. The lenses may each be a single lens, conveniently a microlens, each adjacent a port through which WDM light beams pass. Alternatively, a plurality of microlenses may be provided adjacent the plurality of ports and a single microlens adjacent the single WDM port. The plurality of microlenses and the single microlens cooperate to provide a very small loss multiplexer/demultiplexer with a broad gaussian-type spectral response. The diffraction grating may be reflective or transmissive, and concave so as to combine the functions of a grating and a lens. The microlenses could be spherical lenses, diffractive-type elements, and so on. Other dispersive elements, such as prisms, etc., may be used instead of the diffraction grating. Reversing the light ray direction allow the demultiplexer to act as a multiplexer. One-dimensional spatial-shaping may be implemented in waveguide WDM devices.