An optical communications repeater is used in a fiber-optic communications system to regenerate an optical signal by converting it to an electrical signal, processing that electrical signal and then retransmitting an optical signal. Such repeaters are used to extend the reach of optical communications links by overcoming loss due to attenuation of the optical fibre and distortion of the optical signal. Such repeaters are known as 'optical-electrical-optical' (OEO) due to the conversion of the signal.
Repeaters have largely been replaced in long-haul systems by Optical amplifiers since one amplifier can be used for many wavelengths in a Wavelength Division Multiplexing (WDM) system, thereby saving money. Note that this class of device is sometimes called "Optical Amplifier Repeater".
Due to the high data rates that can be achieved with optical systems, OEO repeaters are expensive to implement as electronics to handle those high data rates are expensive and difficult to construct. Also, since one repeater is required for each wavelength, and many tens of wavelengths may be transmitted down a single fibre, a lot of equipment is required for each fibre. In contrast, an optical amplifier can amplify all of the wavelengths in a single device. An amplifier does not provide the regeneration ability of a repeater, but loss, rather than distortion is generally the limiting factor in the design of communications system.
Figure: Sample MPLS Backbone
