Lasing In Quantum-dot Lasers Research Articles

The influence of carrier dynamics on double-state lasing in quantum dot lasers at variable temperature

It is shown in analytical form that the carrier capture from the matrix as well as carrier dynamics in quantum dots plays an important role in double-state lasing phenomenon. In particular, the de-synchronization of hole and electron captures allows one to describe recently observed quenching of ground-state lasing, which takes place in quantum dot lasers operating in double-state lasing regime at high injection. From the other side, the detailed analysis of charge carrier dynamics in the single quantum dot enables one to describe the observed light-current characteristics and key temperature dependences.

Effect of active-region modulation doping on simultaneous ground-state and excited-state lasing in quantum-dot lasers

The lasing spectra and light-power characteristics of lasers based on InAs/InGaAs quantum dots with p-type modulation doping are studied over a broad range of pump currents. It is shown that p-type doping leads to a significant increase in the threshold current for the onset of lasing at the excited-state transition and makes it possible to attain higher output powers for lasing at the ground-state transition as compared to lasers with an undoped active region. An explanation for the observed features of two-level oscillation in quantum-dot lasers is suggested.

Features of simultaneous ground- and excited-state lasing in quantum dot lasers

The lasing spectra and light-current (L-I) characteristics of an InAs/InGaAs quantum dot laser emitting in the simultaneous lasing mode at the ground- and excited-state optical transitions are studied. Lasing and spontaneous emission spectra are compared. It is shown that ground-state quenching of lasing is observed even in the absence of active region self-heating or an increase in homogeneous broadening with growth in the current density. It is found that the intensities of both lasing and spontaneous emission at the ground-state transition begin to decrease at a pump intensity that significantly exceeds the two-level lasing threshold. It is also found that different groups of quantum dots are involved in ground- and excited-state lasing.

Spectral width of laser generation in quantum dot lasers: An analytical approach

An analytical approach to description of broad spectra of lasing in quantum-dot lasers has been developed. It is shown that the spectral width of the laser generation is determined by three parameters: the spectral width of the gain spectrum, homogeneous broadening of the line, and the effective parameter of the gain saturation. As a result, the dependence of the spectral width of lasing on the laser output power is shown to be universal and can be described as a function of a single dimensionless parameter.

The role of optical gain broadening in the ultrabroadband InGaAs/GaAs interband quantum-dot laser

The details of dynamic phenomena of broadband lasing in quantum-dot lasers in association with the role of both inhomogeneous and homogeneous optical gain broadening is theoretically investigated. The theoretical results of room temperature broadband laser signature are in well agreement with the experimental observation confirming the broadband stimulated emission from the laser is a result of the occurrence of multiple-state lasing in highly inhomogeneity quantum-dot systems.

Electron-hole asymmetry and two-state lasing in quantum dot lasers

We study the decrease of the ground-state output with increasing current in two-state quantum dot lasing. We show that the asymmetry in the thermal population redistribution breaks the symmetric dynamical evolution of the electron-hole pairs. This fully explains the transition from two-state to single-state lasing observed experimentally. The model also reproduces the temperature dependence of the two-state lasing.

Impact of spin blocking on the energy relaxation of electrons in quantum-dot lasers

The impact of the electron spin relaxation time on the electron distribution in quantum-dot lasers is analyzed. The results show that a relatively long spin relaxation time (∼300 ps) can create a nonequilibrium carrier distribution in quantum-dot lasers. It is shown that a mechanism we call “spin blocking” increases emission from the quantum-dot excited states and can lead to excited state lasing in quantum-dot lasers.

Simultaneous two-state lasing in quantum-dot lasers

We demonstrate simultaneous lasing at two well-separated wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, we attribute it to incomplete clamping of the ES population at the GS threshold.