Bidirectional WDM is the transmission of optical channels on a fiber propagating simultaneously in both directions. They consist of thin strands of glass or plastic that carry light signals along their core. However, these cables are not immune to external influences that can affect their performance and. Most optical fibers have a single fiber core, which is usually located on the fiber axis. (For example, a seven-core fiber may have six cores on the. Fiber optic cables are the invisible highways of our digital world, carrying massive amounts of data at the speed of light. But what happens when you need to join two cables to extend a network or repair a break? You can't just twist them together.