Noise analysis of conventional and gain-clamped semiconductor optical amplifiers

We present a numerical study of the noise of conventional and gain-clamped semiconductor optical amplifiers (SOAs), using a detailed device model, The model makes use of a density-matrix gain calculation, and takes into accou nt the forward and backward amplified spontaneous emission (ASE) spectra an d the spatial carrier hole-burning. The device is longitudinally divided in to M sections and a rate equation for averaged photon and carrier densities is used for each section. We demonstrate that the accuracy on the calculat ed noise figure strictly depends on the number of sections M. We obtain a g ood tradeoff between the results accuracy and the computational complexity with M = 8, The model is then applied to study the noise in a distributed B ragg reflector (DBR)-type gain-clamped SOA for varying signal power, pump c urrent, and lasing wavelength. We show that changes in the spatial carrier profile caused by the input signal significantly affect the noise figure, e ven when the gain is constant. A slight dependence of the noise figure on l asing wavelength is also foreseen, while the dependence on the pump current is negligible, A new method for gain-clamped SOA noise figure reduction is proposed, based on unbalanced Bragg reflectors, An improvement of noise fi gure (NF) as large as 2 dB is devised.