Peculiarities and predictions of rogue waves in mid-infrared quantum cascade lasers under conventional optical feedback

Quantum cascade lasers (QCLs) are optical sources exploiting radiative intersubband transitions within the conduction band of semiconductor heterostructures.¹ Mid-infrared QCLs have been thoroughly considered for applications such as spectroscopy,² free-space communications³ and countermeasure systems.⁴ Under conventional optical feedback, QCLs have been proven to operate in several non-linear dynamic regimes, including deterministic chaos,⁵ entrainment of low-frequency fluctuations⁶ and square wave all-optical modulation.⁷ We extend the understanding of non-linear phenomena in QCLs with the experimental study of rogue waves. Rogue waves represent random isolated events with amplitudes well above that of neighboring ones, occurring more often than expected from the distribution of lower amplitude events.⁸ In the optical domain, rogue waves were first demonstrated experimentally in 2007 in the context of super-continuum generation in optical fibers⁹ and have since been observed in a wide variety of configurations such as semiconductor lasers.¹⁰ In QCLs, the extra power from these sudden bursts can be used in order to improve the efficiency of mid-infrared remote sensing or countermeasure systems. It can also be a helpful tool for neurophotonics clusters aiming to reproduce synaptic transmissions in an all-optical system. As a step toward a reliable control over these rare spikes, we carry out a statistical analysis of the interval between rogue events and show that precursors always occur before these events. The advantage of these precursors is to have a characteristic time longer than that found in other semiconductor lasers exhibiting the same non-linear phenomena. Birth of giant pulses like dragon-kings events are also discussed and analyzed.