Abstract
An underwater wireless red-light laser transmission system using 10-Gbps 16-quadrature amplitude modulation–orthogonal frequency-division multiplexing (OFDM) modulation based on a high-speed multimode 680-nm vertical-cavity surface-emitting laser (VCSEL) was proposed and demonstrated. This study is the first attempt to adopt red light for transmitting a 10-Gbps wireless signal 6-m underwater. With the adoption of the appropriate OFDM base bandwidth and modulation parameters after studying the frequency characteristics of the high speed multimode 680-nm VCSEL and contrast experiment of modulation parameters, a good bit error rate performance and clear constellation maps are achieved.
Highlights
In the past, underwater wireless laser transmission systems adopted a 405-nm blue-laser light for underwater transmission, which has minimum attenuation in clear water.[1,2,3,4,5] Compared with blue-laser light, the absorption rate of redlaser light in clear water is higher, resulting in a shorter transmission distance
The OFDM signals generated by an inverse fast Fourier transform (IFFT) was added with a cyclic prefix (CP) before the 16-QAMOFDM data are converted into parallel binary data by the S/P module
With the use of the OFDM base 2.5-GHz bandwidth, a 10-Gbps 16-quadrature amplitude modulation (QAM)-OFDM signal can be transmitted in good condition
Summary
Underwater wireless laser transmission systems adopted a 405-nm blue-laser light for underwater transmission, which has minimum attenuation in clear water.[1,2,3,4,5] Compared with blue-laser light, the absorption rate of redlaser light in clear water is higher, resulting in a shorter transmission distance. A study on underwater transmission characteristics, attenuation coefficient, and channel bandwidth regarding blue, green, and red lights had been proposed,[7,8] from which an interesting finding was obtained—red light has a better transmission performance compared with blue and green lights in high turbidity water.[9,10,11,12,13,14] an underwater wireless red-light laser transmission (UWRLLT) system is expected to provide a short-distance underwater highspeed link, similar to Wi-Fi-on-air in terms of function. In the situation of increasing popularity of oceanic exploration and oceanic leisure activities, the sense of distance experienced underwater or in the ocean is more obvious than that on the land Whether it is for activity, construction, exploration and tracking, or research and development, underwater communication facility is in urgent need for managing site condition, making UWRLLT extremely attractive to the application of underwater communication
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