What is the main function of an optical amplifier?

Comprehensive and Detailed Explanation From Nokia Optical Networking Fundamentals:

The primary function of anoptical amplifierin a WDM system is to provide gain to the optical signal tocompensate for optical power attenuation(loss) that occurs as light travels through the optical fiber. As photons travel through kilometers of silica fiber, their energy is absorbed or scattered, leading to a reduction in signal strength. To ensure the signal reaches its destination with sufficient power for the receiver to detect it, amplifiers like theEDFA (Erbium-Doped Fiber Amplifier)orRamanamplifiers are placed at strategic intervals along the fiber span.

It is crucial to distinguish this from Option D; modern optical amplifiers performpurely optical amplification, meaning the signal stays in the photonic domain without being converted to electricity (O-E-O). While some specialized amplifiers (like the RA2P) might interact with other parameters, their fundamental job is power restoration. Furthermore, while amplifiers are essential for a network's reach, they do not compensate forchromatic dispersion—that is the job of Dispersion Compensation Modules (DCM) or electronic dispersion compensation (EDC) in coherent transponders—nor do they demodulate signals, which is the role of the receiver in a transponder.