Abstract-Dual resonance phonon–photon–phonon terahertz quantum-cascade laser: physics of the electron transport and temperature performance optimization

 

Aleksandar Demić, Zoran Ikonić, Paul Dean, Dragan Indjin

Schematic diagram of effectively two (a), three (b,c) and four (d,e,f) level schemes of common THz QCL designs. The rectangles illustrate the typical wavefunction localisation (probability density) of each state within the QCL period. The dotted arrow line denotes the tunnelling process between two adjacent periods, while the solid arrow lines denote the transitions. Each level (apart from ULL) may be envisaged as a cluster of narrowly spaced quasi–bound levels, transitions between the effective "levels" also exist, however dominant mechanisms are shown.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-26-38788&id=444650

The state of the art terahertz-frequency quantum cascade lasers have opened a plethora of applications over the past two decades by testing several designs up to the very limit of operating temperature, optical power and lasing frequency performance. The temperature degradation mechanisms have long been under the debate for limiting the operation up to 210 K in pulsed operation in the GaAs/AlGaAs material system. In this work, we review the existing designs and exploit two main temperature degradation mechanisms by presenting a design in which they both prove beneficial to the lasing operation by dual pumping and dual extracting lasing levels. We have applied the density matrix transport model to select potential candidate structures by simulating over two million active region designs. We present several designs which offer better performance than the current record structure.

Published by The Optical Society under the terms of the Creative Commons Attribution 4.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Abstract-High-speed modulation of a terahertz quantum cascade laser by coherent acoustic phonon pulses

• Aniela Dunn, 
• Caroline Poyser, 
• Paul Dean, 
• Aleksandar Demić, 
• Alexander Valavanis, 
• Dragan Indjin, 
• Mohammed Salih, 
• Iman Kundu, 
• Lianhe Li, 
• Andrey Akimov, 
• Alexander Giles Davies, 
• Edmund Linfield, 
• John Cunningham & 
• Anthony Kent 
• 
  

https://www.nature.com/articles/s41467-020-14662-w#Abs1

The fast modulation of lasers is a fundamental requirement for applications in optical communications, high-resolution spectroscopy and metrology. In the terahertz-frequency range, the quantum-cascade laser (QCL) is a high-power source with the potential for high-frequency modulation. However, conventional electronic modulation is limited fundamentally by parasitic device impedance, and so alternative physical processes must be exploited to modulate the QCL gain on ultrafast timescales. Here, we demonstrate an alternative mechanism to modulate the emission from a QCL device, whereby optically-generated acoustic phonon pulses are used to perturb the QCL bandstructure, enabling fast amplitude modulation that can be controlled using the QCL drive current or strain pulse amplitude, to a maximum modulation depth of 6% in our experiment. We show that this modulation can be explained using perturbation theory analysis. While the modulation rise-time was limited to ~800 ps by our measurement system, theoretical considerations suggest considerably faster modulation could be possible.

Abstract-Infinite-Period Density-Matrix Model for Terahertz-Frequency Quantum Cascade Lasers

Aleksandar Demić,  Andrew Grier. Zoran Ikonić, Alexander Valavanis,  Craig A. Evans,  Reshma Mohandas,  Lianhe Li, 

http://ieeexplore.ieee.org/document/7956268/

In this work, we present a density-matrix model, which considers an infinite quantum cascade laser (QCL) and models transport via a nearest neighbor approximation. We will discuss derivation of output parameters of the model in detail and show the direct mathematical link to the semiclassical rate equation approach. This model can be extended to an arbitrary number of states in the QCL period, without a priori specification of upper and lower lasing level. Application of the model to various QCL structures is possible, including bound-to-continuum structures, which typically employ a large number of states per period. The model has been applied to a 2-THz bound-to-continuum QCL, and a very good agreement with measured V–Icharacteristics is obtained along with qualitative agreement with measured L–I characteristics in terms of dynamic range.