NUSOD Blog

Connecting Theory and Practice in Optoelectronics

NUSOD 2017 Preview: Dynamic simulation of quantum cascade laser structures with optical nonlinearities

QuantuQCL_combm 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 [1]. Besides leading to multimode instabilities [1], 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 [4] 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 [5]. In the figure, simulation results for a QCL-based terahertz frequency comb source [3] 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).

[1] C. Y. Wang et al., Phys. Rev. A 75, 031802(R) (2007).
[2] A. Hugi et al., Nature 492, 229 (2012).
[3] D. Burghoff et al., Nature Photon. 8, 462 (2014).
[4] C. Y. Wang et al., Opt. Express 17, 19929 (2009).
[5] P. Tzenov et al., Opt. Express 24, 23232 (2016).

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