Title : Impacts of environmental parameters to underwater optical wireless communication system
Abstract:
An underwater optical wireless communication (UOWC) system using 450 nm green light laser source is constructed and studied. The 450 nm blue-light laser is selected as the light source because the characteristics of low absorption in the water. The open sea water is simulated in the 1.5 m length of water tank filled with water conduct in the laboratory. The blue laser light that is collimated with collimated lens is injected into the water tank using 1.25 data rate and PRBS 31. The mirror placed inside the water tank to prevent the higher optical loss also used to reflect the light back and forth to obtain higher transmission distance. The Bit Error Rate (BER), eye diagram, and optical power were measured to analyze the UOWC system quality. According to the result the bigger angle of reflection inside the water tank, the higher BER of 2.967 x 10-8 at -13.06 dBm of received optical power will be obtained. The coupling efficiency of the laser was measured by adjust the laser spot size diameter. The experiment also measured in the OptiSystem 15.0 software using the same experimental setup.
Then, the UOWC transmission system was carried out under several parameters such as temperature, turbulence, and turbidity were conduct to make the scenario of open sea water in the water tank. Artificial seawater by adding salt to simulate practical application in river or sea is also conducted. When a submerged motor with an output of 1200 L/h is used as water flow turbulence source, the impact to BER and transmission quality is little. For temperature change issue, the experiment shows that at original temperature of 25°C has the best BER as compared to low temperature of 10-20°C or high temperature of 30-50°C. We found that water flow disturbance has little impact to BER and eye diagram quality. Finally, artificial seawater is used to simulate the real seawater environment. Under such situation, the UOWC transmission system can only transmit 3 m instead of 6 m due to impure particles and water disturbance. Both may degrade the BER quality in seawater. In the end, the external parameter such as seawater experiment was conducted using the sea salt inside the water tank. A 520 nm green-light laser and 450 nm blue-light laser was compared the signal quality in the seawater experiment. The result is the blue laser has better signal quality than the green laser.
