In this paper, a comparison study of a quantum cascade laser used for signal transmission by free-space optics is presented. The main goal is to define the capabilities of medium-wavelength infrared lasers operated in pulsed or continuous wave (cw) mode through testing and analyzing a laboratory setup of a data link operated at wavelengths of 4.5 µm (pulsed, peak power 3 W) and 4.8 µm (cw, average power ~20 mW). In this spectral range, the link budget is also defined by radiation attenuation in the atmosphere (absorption, scattering, and turbulence interaction). The performed measurements define unique operational aspects of the quantum cascade lasers considering on–off keying modulation. The registered light pulse changes for different parameters of driving current signals determine some limitations in both rate and data range. Finally, we present eye diagrams of the signals obtained using two data links.
High average power first-order distributed feedback quantum cascade lasers