All-Optical Multihop Free-Space Optical Communication Systems

All-optical relaying techniques are proposed to improve the error performance and overall distance coverage of free-space optical (FSO) communication systems. An all-optical amplify-and-forward (OAF) relaying technique is presented where the received optical field is amplified at each relay. A novel channel model is developed including field distributions and weak turbulence. Simulation results indicate that OAF significantly enhances the BER performance, but is severely degraded by background light. In order to remove the impact of background noise, an optical regenerate-and-forward (ORF) relaying technique is also presented. At a bit rate of 10 Gbps, using two equally-spaced OAF relays under a turbulence-free atmospheric condition increases the total communicating distance by 0.9 km over direct transmission at a BER of $10^{-5}$, while using two ORF relays provides an additional gain in range of 1.9 km. In general, replacing OAF relays by ORF relays extends the total communicating distance at a cost of implementation complexity.