An optical circulator is a three- or four-port designed such that entering any port exits from the next. This means that if light enters port 1 it is emitted from port 2, but if some of the emitted light is reflected back to the circulator, it does not come out of port 1 but instead exits from port 3. This is analogous to the operation of an electronic. Fiber-optic circulators are used to separate optical signals.
Fibre-optic Link Around the Globe (FLAG) is a 28,000-kilometre-long (17,398 ; 15,119 ) mostly- that connects the,,, and many places in between. The cable is operated by, a subsidiary of. The system runs from the eastern coast of to Japan. Its Europe–Asia segment was the fourth longest cable in the world in 2008.