Design of beam positioning and wavefront distortion compensation system using adaptive controller for free space optical communication

Abstract

Free Space Optical Communication (FSOC) system is a line-of-sight technique in which laser signal is used to establish optical connectivity to provide very high speed and large bandwidth data communication between the end users. These huge bandwidth and ultra high speed feature has been making FSOC technology an attractive and alternative solution for large bandwidth wireless applications including audio, video file transferring and uninterrupted access to information via internet during the natural disasters and COVID-19 pandemic, future mobile telephony networks (5G and 6G), satellite communication offering high quality and in areas to replace RF based services. The operation of FSOC system relies on several factors such as power and wavelength of the optical source used, communication bandwidth, optical signal loss, receiver sensitivity, atmospheric attenuation, atmospheric turbulence strength, scintillation and etc. Therefore suitable mitigation techniques should be adopted to enhance the performance of the FSOC system and the behavior of the communication channel also be analyzed under different seasons using suitable tools. The periodic observation of the received optical power, intensity, optical wavefront, strehl ratio, atmospheric turbulence strength and its characteristics on the established communication link under different weather conditions becomes important to investigate the performance of FSOC system. Real time FSOC transmitter and receiver assembly are built with suitable optoelectronic components on Block-II of our college. The transmitter and receiver assembly are constructed at a height of 15.25m with an optical communication link distance of 70m. The FSOC Transmitter assembly consists of 155Mbps data generator, 850nm/50mW laser source and transmit optics whereas the receiver experimental setup consists of receiving telescope, narrow band interference filter, avalanche photo detector, signal processing and control electronics architecture. Both transmitter and receiver setups are arranged in