As signal intensity rises toward the saturation intensity of the medium, stimulated emission pulls atoms down faster than the pump replenishes them, so gain falls. In a laser this clamps the gain at the loss level and sets steady-state power. In amplifiers it is a feature as much as a problem: running near saturation extracts energy efficiently and stabilizes output, while small signals see full small-signal gain.
The second stage is well into gain saturation, so a 20 percent swing in seed power only moves the output a couple of percent.
Also heard as
- saturation
Related terms
Gain medium
The material inside a laser or amplifier that amplifies light once it is pumped: a crystal, glass, gas, semiconductor or doped fiber.
MOPA
Master Oscillator Power Amplifier: a low-power seed laser followed by amplifier stages that bring it to full power.
EDFA
Erbium-Doped Fiber Amplifier: the optical amplifier that boosts signals near 1550 nm without converting them to electronics.
ASE
Amplified Spontaneous Emission: random spontaneous photons amplified in a gain medium, a broadband noise background.