Optical amplifiers can be used at many points in a communication link for several system applications. Three common applications of optical amplifiers are power boosters (of transmitters), in-line amplifiers, and optical pre-amplifiers.
The booster (power) amplifiers are placed at the optical transmitter side to enhance the transmitted power level or to compensate for the losses of optical elements between the laser and optical fibers, such as optical coupler, splitters, WDM multiplexers, and external optical modulators. In another word, the booster amplifiers are used to boost the power of the transmitter befor launching into the fiber link. The increased transmitter power can be used to go farther in the link. In general, the output power of a laser diode or a tunable laser source is moderate, especially if an external modulator is used. The key feature of the booster is a hig saturation output power. Further, the booster should provide bit-pattern effect free amplification of the data signal. In WDM systems it should amplify all signals alike across the spectrum. Booster amplifiers normally are polarization sensitive. This is not an issue for boosters as the input signal polarization is known. Related products in Fiberstore: Booster Amplifiers
The in-line amplifiers are placed along the transmission link to compensate for the losses incurred during propagation of optical signal. They are used at intermediate points in the link to overcome fiber transmission and other distribution losses. An in-line amplifier mainly compensates for fiber losses or splitter losses in an optical transmission system. It takes a small input signal and boosts it for retransmission down the fiber. The most important performance parameters are saturation output power and noise figure because the incoming signals are weak. Controlling the small signal performance and nosie will provide better system results. Noise added by amplifiers in series will limit the system length. The polarization dependance of the gain should be as small as possible due to the random state of polarization within a network. Also, the in-line amplifier need to cope with several wavelength channels simultaneously. Futher, in-line amplifier should process the data signal “transparently” which means that all kinds of modulation formats at ant data rate should be amplified without significant degradation. In addition, there is an increasing interest in low wall-plug power consumption since in-line amplifiers might be placed outside of network central offices. Related products in Fiberstore: In-line Amplifiers
The optical pre-amplifiers are placed just before the receiver to increase the signal level before the photodetection takes place in an ultra-long haul system and thus provide improvement in the receiver sensitivity. In this case, the receiver sensitivity depends on the amplifier gain, noise figure and optical bandwidth which arethe most important parameters of a pre-amplifier. Hence, a pre-amplifier should have a low noise figure and a high gain (not high power) for optimum receiver performance. Typical commercial pre-amplified receivers (i.e. the pre-amplifier) operate with an input signal level of the order of -30 dBm at 10 Gbps. Related products in Fiberstore: Pre-amplifiers