Optical Gain Depending on Both Size Fluctuations of Quantum Dots and Temperature in InGaAs/GaAs QD-SOA

On the basis of the coupled rate equations of the carriers in different energy states, the optical gain of an InGaAs/GaAs quantum dot (QD) semiconductor optical amplifier (QD-SOA) related to both the standard deviation of QD relative size fluctuation and the temperature is numerically investigated with a fourth-order Runge-Kutta method. Our results show that the quasi-flat gain spectra with the full-width at half-maximum more than 150 nm overlapped by the optical gains of both the ground state (GS) and the excited state (ES) can be achieved by either injection current density or temperature. When a pump light is resonant to the GS transition, the peak gain of the GS is not only varied with pump power, but the peak gain of the ES is also changed with this one. The ES may exhibit abnormal gain saturation at room temperature (300 K), which is considerably different from those of bulk and quantum-well SOAs. We predict that the QD-SOA both acting as an optical amplifier is applied to dense wavelength division multiplexing systems and acting as an all-optical wavelength converter implements the wavelength conversion without inverse codes based on the cross gain modulation.