This work theoretically studies the impacts of the inhomogeneous broadening on the modulation dynamics of quantum dot lasers using a multi-population rate equation model. The modulation dynamics shows two distinct regimes depending on the energy separation between the GS and the ES. For broadenings smaller than the GS-ES separation, the K-factor increases while the damping factor offset, the differential gain and the gain compression factor decrease with the inhomogeneous broadening. For broadenings larger than the GS-ES separation, the damping factor offset keeps almost constant while the K-factor, the differential gain and the gain compression factor increases with the inhomogeneous broadening.
The near-threshold dynamics of a QD and a commercial QW laser are investigated both experimentally and theoretically. Below threshold, the resonance frequency and damping factor of the QD laser exhibit a different behaviour as compared to the QW counterpart. In the near-threshold regime, the intra-dot carrier relaxation is predicted from an empirical pairstates model to have a strong impact on the QD laser’s modulation dynamics. The widespread of experimental values for the damping factor reported in the literature for QD lasers is a further indication that this empirical approach is pushed to the limits in this situation. More accurate microscopic modelling should rely on a separation of electron and hole dynamics.
The frequency chirp characteristics of an optically injection-locked quantum cascade laser are theoretically investigated. The key parameter chirp-to-power ratio (CPR) is analytically derived from a full rate equation model. The CPR value can be efficiently reduced by increasing optical injection strength, especially at modulation frequencies less than 10 GHz. In contrast to interband lasers, both positive and negative frequency detuning increase the CPR. Since the frequency detuning is also predicted to enhance the intensity modulation response, a trade-off is required in the optical injection to simultaneously obtain a large modulation bandwidth and low frequency chirp.
Optical injection locking of semiconductor lasers has attracted significant attention due to its applications in laser analysis, modulation characteristic enhancement, and nonlinear dynamics. In many cases, the analysis of the optically injected laser is done by simulation, requiring an accurate laser model and, therefore, an adequate modeling of the gain compression at high photon densities. We use the Kobayashi-Lang rate equations to numerically compare the stable locking range considering four different gain models. Results reveal that at low bias currents, gain compression is significant only under weak injection regime. In contrast, for higher bias current, gain compression must be considered both in weak and strong injection regimes.
Nondegenerate four-wave mixing (NDFWM) in semiconductor gain media is a promising source for wavelength conversion in the wavelength division multiplexed (WDM) systems and for fiber dispersion compensation in long distance fiber links. In contrast to bulk and quantum well (QW) semiconductors, the quantum dot (QD) gain medium is favorable for enhancing the performance of the FWM because of the wide gain spectrum, large nonlinear effect as well as ultrafast carrier dynamics. Especially, the destructive interference can be eliminated due to the reduced linewidth enhancement factor (LEF) for obtaining high efficiency in the wavelength up-conversion. This work reports the NDFWM generation in a dual-mode injection-locked QD Fabry-Perot (FP) laser. The device has a wide gain spectrum with a full width at half maximum of 81 nm, and a peak net modal gain of 14.4 cm-1. The laser exhibits two lasing peaks induced by Rabi oscillation, which provides the possibility for efficient FWM generation. Employing the dual-mode injection-locking scheme, an efficient NDFWM is achieved up to a detuning range of 1.7 THz with a weak injection ratio of 0.44. The highest measured values for both the normalized conversion efficiency (NCE) and the side-mode suppression ratio (SMSR) with respect to the converted signal respectively are -17 dB and 20.3 dB at the detuning 110 GHz.
Taking into account the carrier dynamics in the wetting layer, excited state and the ground state, the intensity modulation properties of an injection-locked quantum dot laser are studied theoretically through a semi-analytical approach. It is demonstrated that both high carrier capture and relaxation rates enhance the modulation bandwidth as well as the resonance-peak amplitude. Moreover, the pre-resonance dip arising under positive detuning can be eliminated as well, which is beneficial for further bandwidth enhancement. It is also found that a large capture time reduces both the resonance frequency and the damping factor while both are increased by a large relaxation time.
The intensity modulation (IM) property of an optical injection-locked quantum cascade (QC) laser is theoretically investigated via a three-level rate equation model. The locking regime is obtained based on the local bifurcation theory. It is shown that the injection-locked QC laser exhibits a rather flat modulation response at zero detuning, whose bandwidth increases with the injection level. In contrast to interband lasers, both positive and negative detunings enhance the modulation bandwidth. Besides, a large linewidth enhancement factor (LEF) can increase the peak amplitude in the response. Moreover, it is found that no frequency dip occurs in the IM response of injection-locked QC lasers.
The three-dimensional confinement of electrons and holes in the semiconductor quantum dot (QD) structure profoundly
changes its density of states compared to the bulk semiconductor or the thin-film quantum well (QW) structure. The aim
of this paper is to theoretically investigate the microwave properties of InAs/InP(311B) QD lasers. A new expression of
the modulation transfer function is derived for the analysis of QD laser modulation properties based on a set of four rate
equations. Analytical calculations point out that carrier escape from ground state (GS) to excited state (ES) induces a
non-zero resonance frequency at low bias powers. Calculations also show that the carrier escape leads to a larger
damping factor offset as compared to conventional QW lasers. These results are of prime importance for a better
understanding of the carrier dynamics in QD lasers as well as for further optimization of low cost sources for optical