Couplers and splitters are the passive devices that are used in every photonic system. They are used to split, combine, and route signals within systems.

Some of the most common applications for couplers and splitters include:

• Local monitoring of a light source output • Distributing a common signal to several locations simultaneously

An optical splitter is a passive device that splits the optical power carried by a single fiber into two or more outputs. These devices have at least three ports but may have more than 32 in more complex configurations. Figure 6.1 illustrates a simple three-port device, also called a tree splitter.