An optical assembly for a wavelength-division-multiplexing (WDM) transmitter or receiver that lends itself to cost-effective production-line manufacturing. In one embodiment, the fiber optic assembly has a vernier-type arrayed waveguide grating (AWG) with five optical ports at one side and fourteen optical ports at another side. Ten of the fourteen ports are optically coupled to ten photo-detectors or lasers. A selected one of the five ports is optically coupled to an external optical fiber. The coupling optics and the mounting hardware for the AWG are designed to accommodate, with few relatively straightforward adjustments performed on the production line, any configuration of the AWG in which any consecutive ten of the fourteen ports are optically coupled to the ten photo-detectors or lasers.