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Connecting Theory and Practice in Optoelectronics
Quantum cascade lasers (QCLs) utilize quantized electron states as laser levels, which can be custom-tailored to the specific application by adequately designing the multi-quantum-well active region. With dephasing times between the upper and the lower laser level of about a picosecond, coherent light-matter interaction, along with other effects such as dispersion and spatial hole burning, governs the laser dynamics . Besides leading to multimode instabilities , the ultrafast dynamics in QCLs is increasingly exploited to implement innovative functionalities, such as the generation of frequency combs [2,3] and picosecond optical pulses  in the mid-infrared and terahertz regime.
For a targeted design of such structures and a deeper understanding of the complex QCL dynamics, a detailed theoretical model is required. We have developed a multi-domain simulation approach, which couples a Maxwell-Bloch type description of the light-matter interaction with advanced ensemble Monte Carlo (EMC) carrier transport simulations to eliminate empirical electron lifetimes . In the figure, simulation results for a QCL-based terahertz frequency comb source  are presented. The laser dynamics gives rise to a two-lobed power spectrum consisting of equidistant discrete comb lines [Fig. (a)]. Furthermore, a periodic temporal shifting of the power between the two spectral lobes is observed [Fig. (b)]. The two-lobed comb spectrum and the associated temporal switching dynamics have also been observed in experiment [3,5], validating our simulation model.
At the NUSOD 2017 conference in Copenhagen, we will present a further developed approach based on density matrix EMC simulations of the carrier transport, yielding both the electron lifetimes and dephasing times and thus rendering our simulation model completely self-consistent (talk FA1).
 C. Y. Wang et al., Phys. Rev. A 75, 031802(R) (2007).
 A. Hugi et al., Nature 492, 229 (2012).
 D. Burghoff et al., Nature Photon. 8, 462 (2014).
 C. Y. Wang et al., Opt. Express 17, 19929 (2009).
 P. Tzenov et al., Opt. Express 24, 23232 (2016).