Fiber Amplifiers:

Stephanie A. Weiss, Executive Editor

Amplifying telecommunications signals in optical fiber systems is a relatively straightforward process: Signal photons + pump photons + erbium atoms = more signal photons.

Wavelength division multiplexing (WDM) has changed the power equation by multiplying the signal photons tremendously. The trick, these days, is to supply enough pump photons to amplify all of those new signal photons.

Fundamental physics limits the power available from a single-mode semiconductor pump diode laser, so users are combining several pumps or chaining several amplifiers to produce the photons they need. Ultimately, though, they are clamoring for pump sources that will provide more power, reliably - and at a price that can compete with multipump options.

Recent high-power options include multimode lasers, fiber lasers, diode-pumped microlasers and some promised semiconductor devices that have yet to emerge from the lab.