• Booster Amplifier: The booster amplifier is placed just after the transmitter to increase the optical power launched to the transmission line. It’s not always required in single-channel links but is an essential part of the DWDM link where the multiplexer attenuates the signal channels. It has high input power, high output power, and medium optical gain.

• Inline Amplifier: The inline amplifiers are placed in the transmission line, compensating for the attenuation induced by the optical fiber. The in-line EDFA is designed for optical amplification between two network nodes on the main optical link. In-line EDFAs are placed every 80-100 km to ensure that the optical signal level remains above the noise floor. It features medium to low input power, high output power, high optical gain, and a low noise figure.

• Pre-Amplifier: The pre-amplifier is placed just before the receiver, such that sufficient optical power is launched to the receiver. It has relatively low input power, medium output power, and medium gain.