As can be seen from the name Amplified Spontaneous Emission (ASE), this is a process in which a spontaneously emitted radiation is amplified. This is also referred to as superluminescence. The ASE effect occurs wherever light signals are amplified, including in lasers, superluminescent diodes, fiber amplifiers, and other optical amplifiers( OA).
The ASE effect is an undesirable effect that can lead to parasitic reflections and natural oscillations of the laser and can also destroy it. It limits the possible gain from a single-stage optical amplifier to about 40 dB to 50 dB. Higher gains are possible for light pulses and can be achieved by using optical amplifiers connected in series. In addition, the Amplified Spontaneous Emission directly enters into the noise and thus into the Optical Signal to Noise Ratio( OSNR).