An apparatus includes a support section which supports a further section, an optically transmissive substrate, and a dispersive section, the further section transporting plural signal components at respective frequencies along a path of travel. A plurality of optical fibers have ends fixedly coupled to a surface on the substrate. The dispersive section has a dispersive characteristic which deviates a direction of travel of each signal component by a respective different amount to optically map each signal component between the end portion of a respective fiber and the path of travel in the further section. During assembly, the fiber ends are moved relative to the surface while radiation passing through them is monitored, and then they are fixedly coupled to the surface in a selected position.