Low-frequency fluctuations of a mid-infrared quantum cascade laser operating at cryogenic temperatures

Abstract

This work demonstrates that mid-infrared quantum cascade lasers operating under external optical feedback can output a chaotic dynamics through low-frequency fluctuations close to 77 K. Results also show that the birth of chaotic dynamics is not limited to near-threshold pumping levels. In addition, when the semiconductor material is cooled down from room temperature to 77 K, it is found that the laser destabilization takes place at a lower feedback ratio which proves that quantum cascade lasers are sensitive to temperatures, likely due to changes in the upper state lifetime. These examinations are meaningful for chaotic operation of quantum cascade lasers in secure atmospheric transmission lines and optical countermeasure systems.

Extensive study of the linewidth enhancement factor of a distributed feedback quantum cascade laser at ultra-low temperature

“…The thin chaotic bubbles can for instance be found around F = 20%, F = 28% and F = 33%. A comparison between the simulations and the results shown in experimental works 10,11 tends to confirm a LEF value high above zero since experimentally, the destabilization occurs for feedback ratios in the order of 1%. This is counterintuitive in a sense that the reciprocal space curvature of the subbands in a QCL should give a LEF very close to zero.…”

“…The QCL under study is identical to the one presented in Ref. 10. It emits single mode at 5.45 µm under continuous bias at 77 K and it emits single mode at 5.63 µm under a 3% duty cycle at 290 K. The threshold of this laser is 331 mA at 77 K and 590 mA at 290 K. Below threshold this QCL behaves like a Fabry-Perot laser, as can be seen in Fig.…”

“…19,28 However, the lack of bifurcation is not compatible with experimental studies where the QCL is under conventional optical feedback. 10,11 Figure 2 (b) shows the bifurcation diagram when the LEF is 1.5 and the other parameters remain constant. The output of the laser is constant until the feedback strength reaches 29%.…”

“…7 Depending on the amount of external optical feedback and the length of the external cavity, the QCLs can enter five different non-linear regimes such as coherence collapse followed by restabilization for strong enough feedback ratios, 8 similarly to what has been unveiled more than 30 years ago in the case of distributed feedback laser diodes. 9 In interband lasers, the dynamical properties of the device are governed by several parameters of the lasers such as the carrier-to-photon lifetime, 10 the differential gain of the materials 11 and the linewidth enhancement factor (LEF). 12 In this paper, we focus on the influence of the latter and study its evolution when varying the pump current.…”

Investigation of Chaotic and Spiking Dynamics in Mid-Infrared Quantum Cascade Lasers Operating Continuous-Waves and Under Current Modulation

“…QCLs exhibit much shorter carrier lifetimes in the order of the picoseconds [22] and therefore, the feedback ratio leading to a chaotic behavior is more important (a few percent). Additionally, very low temperatures seem to facilitate this non-linear process [23]. A particular feature of QCLs is the absence of relaxation oscillations [24], which is a direct consequence of the relatively short carrier lifetime compared to the photon lifetime.…”