Stable mode-locked pulses from mid-infrared semiconductor lasers

TL;DR

This paper demonstrates stable, ultrashort mid-infrared pulses from a semiconductor quantum cascade laser using active modulation, advancing compact, electrically-pumped sources for mid-infrared and terahertz applications.

Contribution

First demonstration of actively mode-locked mid-infrared quantum cascade lasers producing 3 ps pulses with detailed modeling of the mode-locking dynamics.

Findings

Generated 3 ps pulses with 0.5 pJ energy

Mode-locking achieved via active current modulation

Modeling confirms the mode-locking mechanism

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.