EDFAs

Erbium-doped fiber amplifiers (EDFAs) are fiber-optic amplifiers that use lengths of silica fiber doped with erbium ions as the gain medium. When pumped by diode lasers at around 980 nm or 1480 nm, erbium ions are excited to a metastable state. Light in the 1550 nm region experiences stimulated emission, providing gain as it travels through the fiber.

EDFAs are primarily used to amplify signals in the C-band (approximately 1530–1565 nm) and, with specialized designs, in the L-band (1565–1625 nm). They are typically deployed as in-line, preamplifier, or booster stages in WDM networks. Gains are achieved with multi-stage configurations and proper pump power; gain flattening and ASE management help produce a uniform output spectrum.

Typical small-signal gain ranges from about 20 to 40 dB, with a noise figure near 3 dB. Saturation output power depends on fiber design and pump power. The amplifier also generates amplified spontaneous emission, which increases the noise floor and must be managed through design choices and spectral shaping.

EDFA systems are a cornerstone of modern long-haul and metro optical networks, enabling high-gain, low-noise amplification without electrical regeneration. They require pump diodes, isolators, and dispersion management to operate reliably within WDM systems. Temperature and pump stability influence performance but the technology remains scalable and widely deployed.