Study of Fog Mitigation in Low-cost Visible Band FSO Communication System

Free Space Optical (FSO) Communications data link offers high data rates with low system complexity but atmospheric attenuation, such as fog, alters signal integrity. In the paper, we present a novel low-cost visible band FSO system design and its performance evaluations in foggy conditions. Using LTSPICE design tools, we proposed a low-cost transmitter and receiver circuits. We built a fog-testing chamber and FSO systems to measure different transmitter sources by analyzing DC carrier powers and digital AC signals at 1MHz. A He-Ne laser at 630nm was used to calibrate chamber fog density and measure the steady state performance. Concurrently, we developed a CAD model of our FSO systems using Synopsys Optsim and obtained FSO system performance at different foggy levels to compare with our experimental results. The red laser diode (LD) at 658nm has the best performance in foggy environments with experimental attenuation of -0.20dB and simulated attenuation of -0.63dB. The green LD at 520nm and violet LD at 405nm experience experimental attenuation of -0.35dB and -0.53dB respectively. Despite beam divergence, the red LED at 615nm has good performance in foggy environments with experimental attenuation of -0.33dB and simulated attenuation of -5.2dB. The yellow LED at 590nm, green LED at 522nm, and blue LED at 470nm experience an experimental attenuation of -0.51dB, -2.2dB, and - 0.72dB respectively.