Nonlinear gain effect and modulation dynamics in quantum well lasers

Investigation of the nonlinear gain in semiconductor lasers is important since those properties play important roles in certain laser characteristics such as modulation dynamics, laser amplification, and phase conjugate wave generation. However, such nonlinear gain properties have not been discussed for quantum well (QW) lasers so far. The authors investigate theoretically the nonlinear gain effect in QW lasers. As a result, it is found that the nonlinear gain is enhanced by the quantum confinement of carriers. In addition, it is pointed out that the different gain is also reduced by the nonlinear gain effect, which significantly affects the modulation dynamics of semiconductor lasers under high photon density conditions. It is emphasized that not only the damping rate but also the resonant frequency is affected by nonlinear gain effects. The significance of the nonlinear gain in quantum well lasers is demonstrated. Those nonlinear properties are more enhanced in the quantum wire laser and quantum box lasers