Abstract:
Free-Space Optical (FSO) communication networks offer ultra-fast data transmission
that exploits license-free spectrum and are also a good replacement of the traditional
communication technologies. While multiple environmental factors including atmospheric
conditions, electromagnetic disturbances, and physical obstacles causing significant
degradation of signal quality and therefore data transmission reliability are
highlighted, the question remains whether the current solutions and problems with
respect to technology can be overcome. This thesis aims to address these challenges
by examining the effectiveness of single and dual-stage amplification approaches for
All-Optical Amplify and Forward (AOAF) relays in FSO links, with Differential
Quadrature Phase Shift Quadrature Phase Keying (DQPSK) signal messages. The
methodology consists of a structural comparison of some single-stage amplification
applications with and without filters against different dual-stage amplification cases
that contain one or two filters. The filter types used in this study are Bessel, Butterworth,
Gaussian type, which are spectrum models. The results indicate similar
performance for Bessel and Butterworth filters. The solution deals with signal degradation
by strengthening the signal using amplification techniques that evenly overcome
fading and multipath interference as well as reduce bit error rate to enhance
reliability of such a link for more than 1km. Results from these experiments demonstrate
that two-stage amplification method is the best option of all the options when
it comes to reducing signal loss and ensuring signal transmission reliability, especially
in high turbulence environments. These findings highlight the key role of a strategic
amplification and filtering approach in optimal functioning of FSO systems aimed at
achieving a better signal-to-noise ratio and stronger signal, which results in a minimal
attenuation loss. In addition, this thesis explores on the fundamental limitations
of FSO communication and gives realistic solutions to deal with the problems affecting
the system performance.
