Investigation of giant Kerr nonlinearity in quantum cascade lasers using mid-infrared femtosecond pulses

Abstract

We study the Kerr nonlinearity of quantum cascade lasers (QCLs) by coupling resonant and off-resonant mid-infrared (mid-IR) femtosecond (fs) pulses into an active QCL waveguide. We observe an increase in the spectral width of the transmitted fs pulses as the coupled mid-infrared (mid-IR) pulse power increases. This is explained by the self-phase modulation effect due to the large Kerr nonlinearity of QCL waveguides. We further confirm this effect by observing the intensity dependent far-field profile of the transmitted mid-IR pulses, showing the pulses undergo self-focusing as they propagate through the active QCL due to the intensity dependent refractive index. We experimentally estimate the nonlinear refractive index n2 of a QCL to be ∼8 × 10−9 cm2/W using the far-field beam profile of the transmitted pulses. The finite-difference time-domain simulations of QCL waveguides with Kerr nonlinearity incorporated show similar behavior to the experimental results.

Femtosecond pulses from a mid-infrared quantum cascade laser

“…Moreover, better feedback suppression could obviate the use of an optical isolator. These peak powers compare well with intensities needed to perform supercontinuum generation 42 , emphasizing the potential of such sources also for broadband mid-infrared comb generation.…”

Femtosecond pulses from a mid-infrared quantum cascade laser

“…Moreover, better feedback suppression could obviate the use of an optical isolator. These peak powers compare well with intensities needed to perform supercontinuum generation 42 , emphasising the potential of such sources also for broadband mid-infrared comb generation.…”