Unidirectional WDM is the transmission of all optical channels on a fiber propagating simultaneously in the same direction. Simple design and low requirements. Bidirectional communication has emerged as an effective solution for reducing fiber usage while. In fiber-optic networks, a unidirectional link carries signals in only one direction per fiber. Key characteristics This is the dominant architecture for: Fiber is usually cheaper than complex optics. BiDi optical modules can do this by utilizing full-duplex communication over a single fiber strand via two wavelengths.