Abstract
The topic of external optical feedback in quantum-cascade lasers is relevant for stability and beam-properties considerations. Albeit less sensitive to external optical feedback than other lasers, quantum-cascade lasers can exhibit several behaviors under such feedback, and those are relevant for a large panel of applications, from communication to ranging and sensing. This work focused on a packaged Fabry–Perot quantum-cascade laser under strong external optical feedback and shows the influence of the beam-splitter characteristics on the optical power properties of this commercially available laser. The packaged quantum-cascade laser showed extended conditions of operation when subject to strong optical feedback, and the maximum power that can be extracted from the external cavity was also increased. When adding a periodic electrical perturbation, various non-linear dynamics were observed, and this complements previous efforts about the entrainment phenomenon in monomode quantum-cascade lasers, with the view of optimizing private communication based on mid-infrared quantum-cascade lasers. Overall, this work is a step forward in understanding the behavior of the complex quantum-cascade-laser structure when it is subjected to external optical feedback.
Highlights
Quantum-cascade lasers (QCLs) are semiconductor lasers relying on intersubband transitions that are able to exhibit high optical power and superior beam-quality features in the mid-infrared domain [1]
When a QCL is under external optical feedback and periodic forcing, a pattern called the entrainment phenomenon can be found in the laser output [17]
We focused on a Fabry–Perot (FP)-packaged QCL, and we showed in a first part that the maximum output power of a QCL can be increased by applying a strong optical reinjection
Summary
Quantum-cascade lasers (QCLs) are semiconductor lasers relying on intersubband transitions that are able to exhibit high optical power and superior beam-quality features in the mid-infrared domain [1]. Free-running QCLs are touted for applications such as countermeasure systems [2] and selective surgery [3], because of mid-infrared high-atmosphere transmission and strong human-tissue absorption, respectively. Due to their overdamped nature, QCLs are less sensitive to external optical feedback ( called reinjection) than interband semiconductor lasers exhibiting relaxation oscillations [4,5,6]. We focused on a Fabry–Perot (FP)-packaged QCL, and we showed in a first part that the maximum output power of a QCL can be increased by applying a strong optical reinjection This configuration was found to increase the maximum temperature at which the laser can be operated. Low and strong feedback ratios lead to a stable sine pattern, and when changing the feedback ratio, destabilization islands were found with a combination of various dynamics
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