A numerical model for investigating the thermal, electrical, and optical characteristics of vertical-cavity surfaceemitting lasers (VCSEL's) with a diffused quantum-well (QW) structure is presented. In the model, the quasi-three-dimensional (quasi-3-D) distribution of temperature, voltage and optical fields as well as the quasi-two-dimensional (quasi-2-D) diffusion and recombination of carrier concentration inside the QW active layer are calculated in a self-consistent manner. In addition, the quasi-3-D distribution of implanted ions before and after thermal annealing are computed. The variation of electrical conductivity and absorption loss as well as the influence of impurity induced compositional disordering on the optical gain and refractive index of the QW active layer are also taken into consideration. Using this model, the steady-state characteristics of diffused QW VCSEL's are studied theoretically. It is shown that significant improvement of stable single-mode operation can be obtained using diffused QW structure.
The enhancement of single transverse mode operation in vertical cavity surface emitting lasers by using interdiffused quantum wells is proposed and analyzed. It is observed that the influence of self-focusing (arising from carrier spatial hole burning and thermal lensing) on the profile of transverse modes can be minimized by introducing a step diffused quantum wells structure inside the core region of quantum-well active layer. Stable single-mode operation in vertical cavity surface emitting lasers can also be maintained.
The influence of non-uniform distribution of electric field on the steady state and dynamic behavior of diffused quantum well lasers is studied by a selfconsistent model. The energy band structure of the quantum well can be distorted significantly by the non-uniform distribution of electric field, especially for devices with diffused quantum well structure. Hence, the evaluation on the optical gain as well as the modulation responses of diffused quantum well lasers using flat band approximation can be deviated significantly with nonuniform distribution of electric field taken into consideration.
This paper presents the bifurcation behaviour of the transient response of vertical cavity surface emitting Iasers (VCSEL's) with different aperture sizes. It is shown that lasers with small aperture size suppress higher order bifurcations and chaos even under large signal modulation and external optical feedback. Therefore, VCSEL's with small aperture size have better immunity to irregular response under direct current modulation and external optical feedback.
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