We report on the possibility to detect laser emission of microdisk laser having diameter of 24 μm with an active region based on InGaAs/GaAs quantum well-dots using a waveguide photodiode (100x4000 μm) with a similar active region. A photocurrent of ~ 10 μA was obtained under a continuous-wave laser operation, injection current of 20 mA and a distance between the facets of the microlaser and photodiode of about 100 μm. The photodiode’s sensitivity was estimated to be ~ 9 μA / 10 μW.
Gain saturation in a semiconductor optical amplifier with an array of quantum dots was studied analytically and by numerical simulation on the basis of an analysis of the rate equations. It is shown that, at a moderate injection level, the saturation power increases in proportion to the current density, and then reaches its maximum value, limited by the rate of capture of charge carriers to the ground state and by the number of quantum dots interacting with photons. Expressions are proposed that allow an explicit description of the dependence of the saturation power on the current and its relationship with the internal parameters of the active region.
The rate equations are used to analyze the characteristics of a tandem consisting of a laser diode and a semiconductor optical amplifier made of a single heterostructure with quantum dots. The optimal value of the current distribution coefficient the amplifier and the laser, as well as the optimal resonator length that provides the highest output power of the tandem were determined. It is shown that the use of the tandem allows, at the same total consumed current, to significantly (more than 4 times for 1 A) increase the power emitted through the ground-state optical transition in comparison with that achievable with a laser diode solely being limited by the onset of lasing through an excited-state optical transition.
The performance of quantum dot microdisk lasers operating at room temperature without thermal stabilization was experimentally investigated, and the highest modulation bandwidth of microdisks of various diameters was calculated. It is shown that taking into account the self-heating effect of the microlaser at high bias currents, which manifests itself in a decrease in the maximum modulation frequency and in an increase in the current at which the maximum speed is reached, allows us to describe the experimental data well. Self-heating effect has the greatest impact on microlasers of small diameter (less than 20 µm).
A model is developed that allows one to analytically determine the threshold current of a microdisk laser taking into account its self-heating as a function of the ambient temperature and the microlaser diameter. It is shown that there exists a minimal diameter of a microdisk caused by self-heating, up to which it is possible to achieve continuous-wave lasing at a given temperature. Another manifestation of self-heating effect is the existence of a maximum operating temperature, which is the lower the smaller the diameter of the microlaser. Reasonable agreement between the predictions of the model and the available experimental data is shown.
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