High Frequency Modulation Characteristics of Mid-Infrared Ring Quantum Cascade Lasers

In this work we investigate the high frequency modulation characteristics of mid-infrared surface-emitting ring quantum cascade lasers (QCLs) in comparison to Fabry-Pérot (FP) cavity devices from identical laser material. Both device types are single-mode emitting based on either 2
^nd
-order (ring-QCL) or 1
^st
order (FP-QCL) distributed feedback (DFB) gratings with an emission wavelength around 7.56 mm. Their modulation characteristics are investigated in the frequency-domain using an optical frequency-to-amplitude conversion technique based on the ro-vibrational absorptions of CH
₄
[1].