Hybrid Wavelength and Time Division Multiplexed High Capacity Inter-Satellite Optical Wireless System

Abstract

Introduction: Optical Code Division Multiplexing (OCDM) combined with Free Space Optics (FSO) communication presents a superior solution for achieving greater data speeds and extended reach. FSO communication, which operates in the near-infrared (IR) spectrum, enables high-speed data transmission over long distances between fixed locations. However, atmospheric conditions significantly influence the strength of absorbed radiation, affecting system performance. This study investigates the impact of these conditions on FSO systems both empirically and conceptually, emphasizing outdoor terrestrial optical wireless communication (OWC) networks.

Objectives: The primary objective of this study is to analyze the effect of atmospheric conditions on the transmission performance of FSO communication. To achieve this, a laboratory test stand was established for an FSO system operating in the third-atmosphere propagation window (8–12 µm). The study further aims to conduct experimental analysis in both laboratory and real-world environments under varying atmospheric conditions and compare the transmission characteristics of optical light at 10 µm with near-infrared wavelengths under limited visibility scenarios.

Methods: The research involved the development of a laboratory test setup for FSO communication operating in the third-atmosphere propagation window (8–12 µm). Experimental evaluations were performed using two optical lines of 1.5 m and 10 m in length. The system was tested under different atmospheric conditions, including light rain and fog, to assess transmission efficiency. Analytical investigations were also conducted to validate the experimental findings. Key components utilized in the study included Quantum Cascade Lasers (QCLs) and HgCdTe photodiodes.

Reuslts: The experimental results indicated that optical light with a wavelength of approximately 10 µm demonstrated superior transmission characteristics compared to near-infrared wavelengths under limited visibility conditions, such as light rain and fog. This finding was supported by analytical investigations, reinforcing the potential of longer wavelengths for reliable FSO communication in adverse weather conditions.

Conclusion: In conclusion, FSO communication, particularly at 10 µm wavelengths, provides enhanced transmission capabilities in challenging atmospheric conditions. The study confirms that operating in the third-atmosphere propagation window improves the reliability and efficiency of terrestrial OWC networks. These findings highlight the importance of wavelength selection in optimizing FSO system performance for real-world applications.