Optical Signal Processing based Regeneration for Free Space Optical Links

Abstract

Relay nodes that are proposed for extending the length of free space optical links are generally based upon simple optical amplifiers.In this thesis i have proposed an all-optical relay that performs regeneration of optical signals along with the conventional optical amplification. Our proposed regenerator is based upon a dual-drive Mach-Zehnder modulator. The optical pulsed signal received at the input of the regenerator is divided into two outputs using an optical splitter. One of the splitter outputs is converted into an electrical signal while the signal in the other path is given as input to the optical modulator. The negative slope of the modulator is used to com press intensity fluctuations over the pulsed optical signal by combining the converted electrical signal with the bias voltage of the modulator. We have compared the performance of our proposed regeneration scheme with the conventional optical amplifier based relay nodes in a free space optical link that is modelled by the GammaGamma channel model. To simulate the effect of medium and strong turbulence of the free space optical link, the refractive index structure parameters chosen for the Gamma-Gamma channel model are 0.5×10−14m−2/3 and 0.5×10−9m−2/3, respectively. It was observed that our proposed dual-drive Mach-Zehnder modulator based relay significantly improves the receiver sensitivity by 4 dB under strong turbulence conditions and by 0.7dB under medium turbulence conditions, respectively.