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What is an Active (Doped) Fiber?
An active, or doped, fiber is an optical fiber whose core contains rare-earth ions that can amplify light when energized by a pump source. Common dopants include erbium, ytterbium, thulium, holmium, and neodymium.
Unlike a passive fiber, an active fiber provides optical gain through stimulated emission. It is therefore a key component of fiber lasers and optical amplifiers, where it can generate or increase the power of an optical signal.
HOW an Active (Doped) Fiber Works
The operation can be understood through three main steps:
Pump absorption
Pump light is injected into the doped fiber and absorbed by the rare-earth ions in its core.
Energy transfer
The absorbed energy excites the dopant ions to higher energy states. When stimulated by the optical signal, these ions release energy as additional photons.
Optical gain
The newly generated photons reinforce the signal as it propagates through the fiber, increasing its optical power and enabling amplification or laser emission.
