A common type of optical amplifier used in optical communication

A common type of optical amplifier used in optical communication

When optical signals are transmitted in optical fibers, as the distance increases, the optical signals will gradually weaken and even cause communication disruptions… Until the appearance of optical amplifiers, they are like a “gas station”, replenishing the energy of the optical signals so that they can smoothly carry data to the destination. This issue will introduce to you a common optical amplifier in optical communication – the erbium-doped fiber amplifier (EDFA optical amplifier).

An erbium-doped fiber amplifier, as the name suggests: Erbium (Er), a rare earth element, is incorporated into the quartz fiber. When an input optical signal passes through the erbium-doped fiber, the trivalent erbium ions (Er³⁺) will absorb the energy of the pump light and transition to a higher energy level. The number of particles in the excited state undergoes inversion. Under the induction of the input signal light, the excited-state rare earth ions undergo stimulated emission and release photons of the same frequency as the signal light, thereby achieving optical amplification.
The components that make up an EDFA optical amplifier generally include optical couplers (often using wavelength division multiplexers WDM), optical isolators, erbium-doped fibers, filters, and pump sources. Among them, the optical coupler ingeniously combines the input light and the pump light to ensure that the signal is accurately injected into the erbium-doped fiber; the role of the optical isolator is to suppress the useless light reflection in the optical path to prevent unnecessary interference signals from forming, ensuring the unidirectional transmission of the signal; the optical filter removes unwanted noise to improve the signal-to-noise ratio and ensure the clarity of information transmission.
Currently, researchers are developing dual-band fiber amplifiers (DBFA) and ultra-wideband amplifiers (UWOA), aiming to extend the gain bandwidth to the entire wavelength division multiplexing (WDM) frequency band. Recently, a joint research team from European research institutes has developed a traveling wave parametric amplifier based on photonic chips. Through a compact structure, it achieves ultra-wideband signal amplification, with a bandwidth of 140 nm (three times that of traditional EDFA), and the volume has been reduced to centimeter level, providing ultra-high-speed support for data centers and AI computing. These “super amplifiers” will support transmission of over a hundred wavelengths per fiber, laying the foundation for holographic communication and intelligent factories and other applications in the 6G era.