# OpticalTrust: A Sensor-to-Blockchain Framework Using Free-Space Optical Communication
## 2 Related Work
### Free-Space Optics (FSOs)  
Free-Space Optics (FSOs) and fiber optics represent two fundamental approaches in optical communication systems [19]. FSOs technology enables wireless communication through the atmosphere using modulated light beams, capable of achieving multi-gigabit-per-second (Gbps) data rates across urban distances [20; 21; 22]. In contrast, optical fiber transmission operates by guiding light through a specialized glass structure consisting of a core surrounded by a cladding layer with a lower refractive index, enabling signal propagation through total internal reflection [23; 24]. Signal quality in both systems is evaluated through metrics including the Bit Error Rate (BER) and Q Factor, where BER is analyzed using statistical methods like Gaussian and Chi-squared distributions [23], and the Q Factor serves as a critical parameter for assessing transmission pathway performance. These technologies support data transmission rates, with applications ranging from urban communications to island-to-island connectivity [25; 26].  
Several researchers have made significant contributions to the field of FSOs communication systems and optical amplification strategies. In [27], the authors evaluated the performance of FSOs systems incorporating Erbium-Doped Fiber Amplifiers (EDFAs)under various conditions. The study examined different attenuation levels (0.468 dB/km, 10 dB/km, and 22 dB/km) and assessed system performance through Q-factor and Signal-to-Noise Ratio (SNR) measurements. At a link distance of 1000 m under high atmospheric attenuation, systems with an EDFA achieved a Q-factor of 30.9, compared to 13.3 without an EDFA. Similarly, in [28], the authors conducted a comparative analysis of FSOs systems across three optical transmission windows (850 nm, 1310 nm, and 1550 nm) under different atmospheric conditions, including rain and haze, and examined their effects on FSOs link performance. To improve the performance of FSOs systems in the Middle East region under severe storm conditions, this study [29] proposed a dual-channel FSOs system with EDFA amplification to overcome the limitations of traditional FSOs links. Additionally, the implementation of a 1550 nm wavelength with multiple channels and EDFAs not only achieved superior Bit Error Rate (BER) and Q-factor performance metrics but also extended the effective communication range, presenting a robust solution for FSOs deployment in dust-prone environments. A hybrid FSO/RF system [30] was proposed to demonstrate superior performance, achieving a gain exceeding 1 dB under minimum power conditions, thereby addressing the limitations of traditional FSOs systems during adverse meteorological conditions. The main purpose of this study was to validate that the adaptive joint system, utilizing optimal channel mapping and power distribution algorithms, presents a robust and efficient solution for maintaining reliable broadband connectivity across diverse weather conditions. In [31], the authors provided a comprehensive review of hybrid FSO/RF networks, focusing primarily on practical use cases while highlighting their challenges and implementation issues. The hybrid FSO/RF system demonstrated superior performance over traditional systems by effectively combining the complementary strengths of both transmission methods, resulting in enhanced availability and weather-resistant connectivity. Several studies have focused on applications of hybrid FSO/RF communication systems. For instance, ref. [32] discussed UAV-assisted multi-hop parallel hybrid FSO/RF systems. While most FSOs system research has concentrated on improving signal quality, there is a notable gap in the literature regarding data security, both in experimental settings and real-time applications.