OOO - technical definition

A device that is purely optical in nature, rather than having electrical or electronic as well as optical components. The repeaters used in fiber optic transmission systems (FOTS), for example, are Optical-Electrical-Optical (OEO). Optical switches used in wavelength division multiplexed (WDM) transmission systems sometimes are purely optical. See also FOTS, OEO, optical, and WDM.