Passive mode-locking in quantum-well semiconductor laser based on InGaAs/InGaAlAs/InP heterostructure

We propose a model of passive mod-locking (ML) laser diode based on quantum wells. This model is a comprehensive numerical study of the operation regimes of semiconductor laser and can estimate main characteristics of ML... [ view full abstract ]

We propose a model of passive mod-locking (ML) laser diode based on quantum wells. This model is a comprehensive numerical study of the operation regimes of semiconductor laser and can estimate main characteristics of ML pulses such as the repetition rate, width and shape of the pulse depending on different parameters of laser structure such as the absorber length and relaxation rate, pumping current, number and width of quantum wells. Our model is based on travelling wave equations which shall be completed with boundary conditions, which link amplitudes at the boundaries of different laser sections and initial conditions responsible for the first pulse of laser radiation. Here we accompany the wave equation with a spontaneous noise function that is responsible for the initial generation of laser radiation. The spontaneous noise function is complex, random both in space and time while having no correlation between the real and imaginary parts. The distribution density of such parts is described by a Gaussian distribution. Numerical results for InGaAlAs/InGaAs/InP laser heterostructure emitting at 1.55 um wavelength with 5 quantum wells in active region are presented. It has been shown that two modes are possible in the given structure - fundamental and second harmonic. The appearance of the second harmonic radiation in the laser cavity is due to insufficient absorber relaxation rate. We have demonstrated that it is possible to achieve the most effective transition to the passive ML by varying the length of the absorber. For the structure under study the optimal length was equal to 637 μm. The pulse duration was amounted to 2 ps, repetition rate to 10 GHz and average output power - to 9.4 mW. Figure 1 shows the distribution of radiation intensity along the laser resonator in fundamental mode-locking.