Mode-locked pulses from mid-infrared Quantum Cascade Lasers

TLDR

The authors achieved mid‑infrared mode‑locked pulses by actively modulating the current in a small section of an edge‑emitting quantum cascade laser, producing ~3 ps, 0.5 pJ pulses measured with a nonlinear quantum‑well infrared photodetector and modeled via Maxwell‑Bloch equations in an open two‑level system. This work demonstrates the first unequivocal generation of mid‑infrared mode‑locked pulses from a semiconductor laser, marking a significant advance toward compact, electrically pumped ultrashort‑pulse sources in the mid‑infrared and terahertz ranges.

Abstract

We report the unequivocal demonstration of mid-infrared mode-locked pulses from a semiconductor laser. The train of short pulses was generated by actively modulating the current and hence the optical gain in a small section of an edge-emitting quantum cascade laser (QCL). Pulses with pulse duration at full-width-at-half-maximum of about 3 ps and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The mode-locking dynamics in the QCLs was modelled and simulated based on Maxwell-Bloch equations in an open two-level system. We anticipate our results to be a significant step toward a compact, electrically-pumped source generating ultrashort light pulses in the mid-infrared and terahertz spectral ranges.