Static Gain Saturation Model of Quantum-Dot Semiconductor Optical Amplifiers

We theoretically investigate the gain saturation behavior of a quantum-dot (QD) semiconductor optical amplifier (SOA), focusing on spectral hole burning (SHB) and total carrier density depletion (TCDD). In the static gain model for a QD-SOA, SHB is modeled by the quantum-mechanical density matrix theory and TCDD is described by the shift of the global quasi-Fermi level. We calculate the gain saturation spectra of a QD-SOA at various injection current densities and qualitatively explain how high-speed cross-gain saturation responses can be affected by injection current density. From the quantum-mechanical description for SHB, we show that the optical power for 3-dB gain saturation due to SHB is proportional to the square of the homogeneous linewidth and the functionality of a QD-SOA can be changed by controlling device parameters such as doping density and barrier potential to adjust the homogeneous linewidth.