Star coupler

Note: An optical signal introduced into any input port is distributed to all output ports. Because of the nature of the construction of a passive star coupler, the number of ports is usually a power of 2; i.e. , two input ports and two output ports (a "two-port" coupler, customarily called a "directional coupler," or "splitter" ); four input ports and four output ports (a "four-port" coupler); eight input ports and eight output ports (an "eight-port" coupler); etc.

Source: from Federal Standard 1037C and from the FAA Glossary of Optical Communications Terms[?]