Abstract
Underwater wireless optical communication (UWOC) has been considered a promising technology for high-speed underwater transmission. Some Gb/s level UWOC systems applying visible light have been demonstrated with a transmission distance of several meters or more. Many of the previous works focus on the advanced technologies to push the systems’ capacity–distance performance. However, practical environmental factors issue such as flow turbulence and temperature variation are seldom studied through specific statistical/theoretical models. In this paper, a UWOC system using a 450 nm blue light laser source was set up using a 1.5-m water tank with mirrors located on both sides for single or multiple reflections corresponding to different transmission distances. The blue laser was modulated by a 1.25 Gbps NRZ-OOK format with PRBS of 7, 24 or 31, respectively, for system performance comparison. The bit error rate (BER) values were measured in 1.5, 3.0 and 6 m, respectively, for system evaluation. At room temperature, the BER value was down to 10 × 10−8 for a 1.25 Gbps data rate in a 6 m transmission. Then, the UWOC transmission system experiment was carried out under several environmental parameters such as temperature, turbulence, artificial seawater by adding salt to simulate practical application in river or sea. When a submerged motor with an output of 1200 L/h was used as a water flow turbulence source, the impact to BER and transmission quality was negligible. For the temperature change issue, the experiment shows that around the original temperature of 25 °C had the best BER as compared to other temperature ranges from 10 to 50 °C. For artificial seawater issues by adding salt to simulate the real seawater environment. The transmission distance was only 3-m instead of 6 m, mainly due to particle scattering and water disturbance. With the motor pump on, the power penalty was 1 dB at 10 × 10−8 BER when compared to the motor pump off.
Highlights
Gilbert proved that the attenuation of blue-green light in water is relatively small, which laid the foundation for the Underwater wireless optical communication (UWOC) system [10]
The UWOC 1.25 Gbps data rate digital transmission was carried out under 6-m transmission with a bit error rate (BER) value better than 10 × 10−8 at room temperature
The BER value decreases with the increase of SNR, as is up to 6 m at a 1.25 shown
Summary
Gilbert proved that the attenuation of blue-green light in water is relatively small, which laid the foundation for the UWOC system [10] These applications in the underwater medium environment are required to communicate with the outside world. Li et al proposed a wavelength division multiplexing (WDM), four-level pulse amplitude modulation (PAM4) methodology with a channel capacity of 100 Gb/s They set up a 500 m free-space and 5 m UWOC system [16]. The UWOC 1.25 Gbps data rate digital transmission was carried out under 6-m transmission with a BER value better than 10 × 10−8 at room temperature Several parameters such as temperature, turbulence, artificial seawater by adding salt to simulate practical application in a river or sea were studied and discussed. It provides useful references and suggestions for further research in UWOC
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