## 2 Materials and Methods  
### Calculations  
OWC system transmits the data using optical radiation; therefore, its main elements are a transmitter (laser source) and a receiver (photodetector). Data link range is determined by the required ratio of the received signal power to the noise power. Power of the detected signal \(P_{d}\) is determined by [17]:  
\[P_{d}=P_{0}Ge^{-\gamma(\lambda)L}, \tag{1}\]  
where \(P_{0}\) is the laser light power, \(\gamma(\lambda)\) is an extinction coefficient [1/km], \(L\) is a link distance, and \(G\) is a gain. In such a case, the gain is defined by geometrical relation:  
\[G=\frac{D_{d}^{2}}{(D_{0}+\theta_{div}L)^{2}}, \tag{2}\]  
where \(\theta_{div}\) is the beam divergence, \(D_{0}\) and \(D_{d}\) are the aperture diameters of the transmitter and optical receiver components. The coefficient \(\gamma(\lambda)\) accounts for the beam attenuation caused by the absorption and scattering because of the light interaction with air molecules and aerosol particles [18; 19]. The absorption attenuation is minimized by working in the spectral range of atmospheric windows, so in practice, scattering becomes one of the \"bottlenecks\" of the entire OWC system operation. Its character depends on the size distribution of the scattering particles \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Wavelength** & **Laser** & **Data Rate** & **Modulation * ** & **Distance** & **Temperature** & **Year** \\ \hline
3.0 \(\upmu\)m & ICL & 70 Mb/s & \(NRZ\)-OOK & 1 m & 77 K & 2009 [4] \\ \hline
4.7 \(\upmu\)m & QCL & 40 MHz & Analog & 2.5 m & 293 K & 2015 [5] \\ \hline
4.65 \(\upmu\)m & QCL & 3 Gb/s &
\begin{tabular}{c} \(NRZ\)-OOK, \\ \(PAM\)-4, \\ \(PAM\)-8 \\ \end{tabular} & 5 cm & 293 K & 2017 [6] \\ \hline
4.65 \(\upmu\)m & QCL & 4 Gb/s &
\begin{tabular}{c} \(PAM\)-4, \\ \(DMT\) \\ \end{tabular} & cm & 293 K & 2017 [9] \\ \hline
4.8 \(\upmu\)m & QCL & 10 MHz & Analog & m & 293 K & 2020 [7] \\ \hline
3.0 \(\upmu\)m & ICL & 70 Mb/s &
\begin{tabular}{c} \(OOK\) \\ \end{tabular} & cm & 77 K & 2010 [8] \\ \hline
4.0 \(\upmu\)m & ICL & \
\begin{tabular}{c} \(70\) Mb/s \\ \(155\) Mb/s \\ \end{tabular} &
\begin{tabular}{c} \(NRZ\)-OOK \\ \(RZ\)-OOK \\ \end{tabular} & 2 m & 298 K & This work \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Examples of the OWC system operated in the MWIR spectrum. in comparison to the radiation wavelength. For MWIR radiation, the scattering effects are described using the Mie theory. The light losses are estimated using \"visibility--Vis\" combined with weather conditions [20; 21]. This attenuation can be transferred into MWIR range using a function described empirically by [PERSON] [22]:  
\[\beta(\lambda)=\frac{3.91}{Vis}\bigg{(}\frac{\lambda}{\lambda_{0}}\bigg{)}^{-q}, \tag{3}\]  
where \(\lambda_{0}\) = 550 nm is the reference wavelength, and q is the particle size distribution coefficient. [PERSON] model describes this coefficient as 1.6 for visibility better than 50 km, 1.3 for visibility in the range of 6 km \(\div\) 50 km and equals to 0.585 \(Vis^{1/3}\) for visibility below 6 km. However, the [PERSON] model is assumed to be good enough for visibility better than 1 km. To analyze other propagation conditions, one would need to utilize other models of scattering losses, which can be found in the literature [23]. In the case of fog attenuation, two attenuation functions are described [24]. Because the advection fog is characterized by a linear attenuation wavelength dependence and the radiation fog by a quadratic one, higher light losses are observed for the radiation fog. There is also a third scattering effect caused by rain, snow, and dust. Some models are also available to determine their respective attenuation [25]. Generally, these particles are larger than the operating wavelength, and scattering becomes wavelength independent [26; 27; 28].