Analysis Of The Transmission Characteristics Of Blue-Green Light In Seawater

Underwater blue-green optical communication with high bandwidth and high information transmission rate has attracted the attention of researchers.The strong scattering effect of seawater on light makes the blue-green light in seawater can achieve communication by non-line-of-sight(NLOS)transmission in addition to line-of-sight(LOS)transmission.Since the scattering coefficients of seawater at different depths are different,this paper studies the characteristics of LOS and NLOS transmission of blue-green light in seawater at different depths under the effect of absorption and scattering of seawater.In addition to absorption and scattering by seawater,ocean turbulence also attenuates the light transmission.In this paper,we take Gaussian beam as an example to analyze its transmission in ocean turbulence and the effect of ocean turbulence characteristic parameters on the scintillation index,beam wander and bit error rate(BER)of Gaussian beam.The specific work in this paper is as follows.1.The absorption and scattering coefficients of seawater and the albedo of blue-green light in seawater were calculated based on the absorption and scattering coefficients of various suspended particles in pure seawater an d seawater,and the scattering angle of scattered photons from seawater was calculated using the HG phase function.2.Using Monte Carlo method to track the transmission trajectory of photons in seawater,we study the normalized received optical power and BER of photodetectors for horizontal,vertical and oblique range LOS transmission of blue-green light under the effect of absorption and scattering of seawater.3.Compared with LOS transmission,NLOS transmission does not require alignment and can be adapted to various underwater environments.A Monte Carlo method is used to study the received optical power and BER of blue-green light in class a form for NLOS transmission under the effect of absorption and scattering by seawater.A single scattering link model is developed to study the received optical power and BER at the receiver when the blue-green light is transmitted in class b form and in class c form NLOS transmission.4.The effects of Gaussian beam transmission in ocean turbulence and the characteristic parameters of ocean turbulence on the scintillation index,beam wander and BER of Gaussian beam are investigated.The results show that the transmission attenuation of blue-green light in seawater depends mainly on the absorption of seawater when the transmission distance is less than about 10 m.The transmission attenuation depends mainly on the scattering effect of seawater when the transmission distance is greater than about 10 m.The strength of the scattering effect is shown by the size of the albedo,and the greater the albedo,the stronger the scattering effect of seawater.Transmission distance greater than about 10m,the same transmission mode of blue-green light in seawater LOS communication at the same distance when the attenuation of blue light is greater than green light,the same information transmission rate of blue light BER is greater than green light;the same transmission mode of blue-green light in seawater NLOS communication at the same distance when the attenuation of blue light is also greater than green light,the same information transmission rate of blue light BER is greater than green light.The scintillation index,beam wander and BER of Gaussian beam transmission in ocean turbulence increase with increasing temperature-induced to salinity-induced ratio,decrease with increasing kinetic energy dissipation rate,and increase with increasing temperature dissipation rate.