###### Abstract  
This article is a short study of the application of high-power quantum cascade lasers and photodetectors in medium-infrared optical wireless communications (OWC). The link range is mainly determined by the transmitted beam parameters and the performance of the light sensor. The light power and the photodetector noise directly determine the signal-to-noise power ratio. This ratio could be maximized in the case of minimizing the radiation losses caused by atmospheric attenuation. It can be obtained by applying both radiation sources and sensors operated in the medium infrared range decreasing the effects of absorption, scattering or scintillation, beam spreading, and beam wandering. The development of a new class of laser sources based on quantum cascade structures becomes a prospective alternative. Regarding the literature, there are descriptions of some preliminary research applying these lasers in data transmission. To provide a high data transfer rate, continuous wave (cw) lasers are commonly used. However, they are characterized by low power (a few tens of mWatts) limiting their link range. Also, only a few high-power pulsed lasers (a few hundreds of mWatts) were tested. Due to their limited pulse duty cycle, the obtained modulation bandwidth was lower than 1 MHz. The main goal of this study is to experimentally determine the capabilities of the currently developed state-of-the-art high-power pulsed quantum cascade (QC) lasers and photodetectors in OWC systems. Finally, the data link range using optical pulses of a QC laser of \(\sim\)2 W, operated at the wavelength of \(\sim\)4.5 \(\upmu\)m, is discussed. Keywords:free space optics; quantum cascade lasers; optical wireless communications; infrared detectors : 30 March 2021  
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of light signals. Due to a low carrier lifetime of a QC laser upper-state (in the range of a few ps), the bandwidth above 100 GHz is theoretically possible. However, it requires radio frequency (RF) modulation of the QC laser radiation. Nowadays, RF optical signals are obtained by driving a QC laser with a bias-T circuit. Several works presented a few-GHz direct modulation [1]. Faster modulation speeds also have been reported, but this requires a specially constructed lasing structure to inject the RF signal, or the use of cryogenic cooling [2]. This speed can be improved by designing the device housing and optimizing the laser cavity [3]. Therefore, the main goal of the performed research is to design QC lasers with direct GHz modulation. Regarding the description of the obtained results, there are no comments about power modulation parameters such as power efficiency and depth, critical for communications applications. The conducted literature reviews also show that there is no information about the application of a high-power pulsed QC laser in an OWC system [4]. It results mainly from a low duty cycle (dc) of its generated light pulses limiting the format of signal coding. This low dc is due to the lasing structure heating with high driving currents. Regarding the case of the OWC receiver, there are many radiation sensors that can be used to register data signals. The selection of these sensors is based on their detectivity, dynamic response, time constant, operation temperature, reliability, cost, etc. The technology evaluation of infrared detectors was described in many publications [5; 6; 7; 8]. Nowadays, some technologies based on mercury cadmium-telluride (MCT), quantum well infrared photoconductors (QWIP), and strained layer superlattices (SLS)-have been tested for data transmission in free space. Some properties of these technologies are listed in Table 1.  
Mercury cadmium-telluride (MCT or HgCdTe) is the most often used detector technology tested in an OWC system operated in the MWIR range. MCT detectors are highly advanced and ensure more than an order of magnitude higher detectivity in comparison to the value predicted by Rule 07 [16].