Photonic noise with nonlinear gain (semiconductor lasers)

For frequency-independent gain and loss, the circuit theory of photonic noise based on the Nyquist noise sources reduces to a corpuscular theory that postulates independent shot-noise fluctuations of the particle rates. For linear gain, the corpuscular theory coincides with standard rate equations (SREs). When the relative gain compression is comparable with unity, however, SREs are in error by a large factor. The exact theory shows that in the presence of nonlinear gain, photonic noise may be less than shot noise, even when the injected current exhibits shot-noise fluctuations. This new effect cannot be predicted by SREs.