Free Space Optics (FSO) has the potential to offer fast broad-bandwidth communication, but experiences signal loss due to atmospheric attenuation. Our study assesses the performance of different lens configurations to mitigate the fog scattering loss in a low-cost visible-band FSO communication system. We built a fog-testing chamber and novel transmitter board to evaluate our FSO link at four different visible-band wavelengths and three different lens configurations. We also analyze the receiver signal strength to determine the fog-induced attenuation and compare each lens performance in the system. To design and evaluate the optimum lens system, several novel transmitterreceiver lens configurations are analyzed and compared: plano-convex to plano-convex (P-P), bi-convex to planoconvex (B-P), and bi-convex to bi-convex (B-B). We observe that the visible-band wavelength can minimizes the amount of fog-induced signal loss. The lens configuration in conjunction with the most optimal visible-band wavelength is then analyzed with various fog levels. We determine the most efficient double-lens configuration in the FSO system with fog-induced noise. On average, the biconvex-planoconvex system performed 63.85% better than the planoconvex-planoconvex system and 50.42% better than the biconvex-biconvex system. These results can be attributed to the spherical aberration from the transmitter lens and will be discussed in the paper.
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.