Numerical analysis of the frequency chirp in quantum dot semiconductor lasers

We present a numerical model for the analysis of the chirp dynamics of quantum-dot (QD) semiconductor laser under large signal current modulation. The model is based on the multi-population rate equation formalism, and it includes all the peculiar characteristics of the active QD material such as the inhomogeneous broadening of the gain spectrum, the presence of an excited state confined in the QDs and the presence of nonconfined states due to the wetting layer and the barrier. In this paper the model is applied to the analysis of the chirp of two,QD single-mode lasers emitting from the ground state and from the excited state, respectively. In order to make comparisons of the chirp in various operating conditions, we define some equivalent parameters for quantifying the adiabatic and transient contributions to the chirp. These parameters,are then used to analyze the chirp as function of the bias current, of the modulation depth and of the modulation frequency. All the various simulation results show that the carrier accumulation in the QD states, poorly involved in the stimulated emission process and the carrier dynamics in these states, can cause a nonzero chirp under current modulation even for the ideal condition of zero linewidth enhancement factor (or alpha-parameter) at the laser threshol

Analysis of self-pulsating three-section DBR lasers

The characteristics of a three-section distributed Bragg reflector laser showing self-pulsation have been analyzed using a large signal time-domain traveling-wave simulator. The device dynamic properties have been investigated in all their complexity and analyzed as functions of the linewidth enhancement factor and of the injected current in the active and in the phase control sections. The simulation results have clearly shown the fundamental role of four wave mixing on the laser characteristics (output power, spectrum, etc.) and have been quantitatively correlated with the few available theoretical and experimental results. The considered self-pulsation operation frequencies around 40 GHz are of interest for practical applications

The Complex Way to Laser Diode Spectra: Example of an External Cavity Laser With Strong Optical Feedback

An external cavity laser with strong grating-filtered feedback to an antireflection-coated facet is studied with a time-domain integral equation for the electric field, which reproduces the modes of the oscillation condition as steady-state solutions. For each mode, the stability and spectral behavior is determined by analysis of the location of side modes in the complex frequency plane. The complex frequency diagrams are shown to be a useful tool to determine the self-stabilization effect of mode coupling and its dependence on laser parameters and external cavity design. The model is used to simulate the large signal time evolution after start from unstable mode

Modeling passive mode-locking in InAs quantum dot lasers with tapered gain sections

We propose a computationally efficient approach for the simulation and design of index-guided quantum-dot (QD) passively mode-locked lasers with tapered gain section; the method is based on the combination of simulations based on a finite differ-ence beam-propagation-method and dynamic simulations of mode-locking via a multi-section delayed differential equation model. The impact of varying the taper full angle on the pulse duration and peak power is investigated; simulations show that a correct choice of this parameter enables the generation of sub-picosecond optical pulses with peak power exceeding 5

A GTD Analysis of discontinuities in rectangular waveguides

The problem of the junction between two rectangular waveguides is examined. by ray methods. Results are presented taking into account only a first order approximation (singly diffracted rays)

Cavity optimization of 1.3um InAs/InGaAs quantum dot passively mode-locked lasers

Performance improving for monolithic two-section passively mode-locked (ML) quantum dot lasers has been systematically investigated using the Finite-Difference Traveling-Wave numerical model. Two approaches have been considered. For the first case, we changed simultaneously the length of the saturable absorber and the output facet reflectivity. We demonstrate that, by properly choosing these two parameters, a reduction of the pulse width from 3.4 ps to 1.1 ps and an increase the peak power 1 W to 1.6 W were obtained. For another case, we exchanged the optical power reflectivities at two end facets. We found that this approach can be used to further improve the ML stability for devices considered in the first approach where trailing edge instability is the main restrictio