Salinity Effect on Red-light laser transmission based on Underwater Wireless Optical Communication system.

Abstract

In this work, the behavior of 650 nm red laser signals based on underwater wireless optical communication system was experimentally and theoretically investigated in different salinity levels (0–60)g/L. The values of absorption and scattering coefficients for marine environment have been theoretically estimated based on visible wavelength region.  The theoretical results showed that the (400-550) nm intervals consider high windows for the laser light leading to lower absorption coefficients. However, at high salinity marine environment (Coastal-ocean), the light windows of water showed almost non-existent or negligible effects for the entire visible region. This finding indicated that the scattering process at specific water type slightly decreases with increasing the wavelength. This investigation is important to select 650 nm red lasers as best visible widow of efficient UWOC system especially for high impurity (dense) and/or saline water. It was found that the amount of losses in power at maximum link decrease with increasing salt concentration due to the negative effect of salinity on underwater signal transmission. When the salt concentration increased the practical signal-to-noise ratio value decreases due to large increasing in the transmission losses due to negative effect of the attenuation onto transmitted signal. Furthermore, the experimental of refraction index based on different water channels and temperatures was measured and compared with and theoretical estimation. This finding show that increases the salt concentrations led to increasing the index, while it decreases with increasing the temperatures.