An optical communications repeater is used in a

fiber-optic communication Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of infrared light through an optical fiber. The light is a form of carrier wave that is modulated to carry information. Fiber is pr ...

s system to regenerate an optical signal. Such repeaters are used to extend the reach of optical communications links by overcoming loss due to

attenuation In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at var ...

of the optical fiber. Some repeaters also correct for

distortion In signal processing, distortion is the alteration of the original shape (or other characteristic) of a signal. In communications and electronics it means the alteration of the waveform of an information-bearing signal, such as an audio signa ...

of the optical signal by converting it to an electrical signal, processing that electrical signal and then retransmitting an optical signal. Such repeaters are known as optical-electrical-optical (OEO) due to the conversion of the signal. These repeaters are also called regenerators for the same reason.

Classification of regenerators

Optical regenerations are classified into 3 categories by the 3 R's scheme. # R : reamplification of the data pulse alone is carried out. # 2R : in addition to reamplification, pulse reshaping is carried out. E.g.:

Mamyshev 2R regenerator The Mamyshev 2R regenerator is an all-optical regenerator used in optical communications. In 1998, Pavel V. Mamyshev of Bell Labs proposed and patented the use of the self-phase modulation (SPM) for single channel optical pulse reshaping and re-ampl ...

. # 3R : in addition to reamplification and reshaping, retiming of data pulse is done.

All-optical regenerators

An alternative method of regeneration is through all-optical regenerators without the additional requirement to convert back and forth between optical and electronic signals. Non-linear optical fibers allow the use of frequency shifting and frequency generation effects for regeneration. The key advantage of all-optical regeneration is the power efficiency provided by the device and simpler integration into an optical network.

Optical amplifiers

Cost efficiency has led to OEO repeaters being largely replaced in long-haul systems by

optical amplifier An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback fr ...

s since one (

broadband In telecommunications, broadband is wide bandwidth data transmission which transports multiple signals at a wide range of frequencies and Internet traffic types, that enables messages to be sent simultaneously, used in fast internet connections. ...

) amplifier can be used for many wavelengths in a

Wavelength Division Multiplexing In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths (i.e., colors) of laser light. This techniqu ...

(WDM) system. Note that this class of device is sometimes called "Optical Amplifier Repeater".Cisco part reference for an optical amplifier repeater
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Electronic vs optical regeneration

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 fiber, a lot of equipment is required for each fiber. Electrical repeaters are also limited in bandwidth and modulation format. In contrast, an optical amplifier can amplify all of the wavelengths in a single device and works for all modulation formats. 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 an optical communications system.

References

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Repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Som ...