Electroabsorption Modulator-Based Relay for the Transmission of DPSK-Modulated Signals over the Free Space Optical Link

In this paper, an electroabsorption modulator-based relay is employed for the transmission of on-off keying (OOK) and differential phase shift keying (DPSK) signals over a free space optical (FSO) communication link. The FSO link is based upon the Gamma-Gamma (Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varGamma $$\end{document}-Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varGamma $$\end{document}) channel model considering both medium and strong atmospheric turbulence conditions. 10 Gbps modulated OOK and DPSK signals are transmitted over the FSO link by employing all-optical amplify and forward (AOAF) and all-optical regenerate and forward (AORF) relay-assisted techniques. The bit-error-rate results are analyzed with respect to received optical power for the proposed model. It is observed that AORF relay-assisted OOK is performing better than AOAF at high data rates under medium atmospheric turbulence, whereas for DPSK-modulated signals, the performance is almost the same for both AORF and AOAF relay-based FSO links. The AORF-based relay for the transmission of OOK- and DPSK-modulated signals show significant improvement under strong atmospheric turbulence compared to the AOAF-based relay link. Furthermore, under multiple relay scenario for DPSK signal, AOAF results degraded while AORF remains almost the same under strong atmospheric turbulence.