In this mode, multi-wavelength optical signals are transmitted through only one fiber in both receive and transmit directions. Simple design and low requirements. Here the WDM network elements include. TOKYO, May 26, 2026 -- As part of the Ministry of Internal Affairs and Communications-commissioned research and development project, "Research and Development (JPMI00316) of Advanced Optical Transmission Technology Contributing to a Green Society", Oki Electric Industry Co. In contrast, bidirectional transmission enables simultaneous data exchange in both directions within a single optical fiber, using different wavelengths to separate the two directions of communication.