We develop an optical wireless communication-based 2K real-time video surveillance system prototype with field- programmable gate arrays. Using a 3-W blue light-emitting diode and an avalanche photo-diode, 20-m and 1.5-m real-time picture/video transmission with a high resolution of 1920 × 1080 pixels is implemented in free space and pure water channel, respectively. It indicates the good performance of the prototype, which is the first step to realize underwater visual monitoring in future human-robot interaction applications.
The underwater wireless optical communication (UWOC) technology is vastly developing due to its advantages of high bandwidth, large capacity, and low latency. However, the complex underwater channel characteristics and strict requirements on pointing, acquisition, and tracking (PAT) systems hinder the performance and augmentation of UWOC. A large-area scintillating-fiber-based UWOC system is proposed to solve the PAT issue while offering high-speed, omnidirectional data detection over turbulent underwater channels. In this work, we utilized 120-cm2 coverage area scintillating fibers as a photoreceiver. The large area scintillating fibers realize omnidirectional signal detection by absorbing an incident optical radiation, re-emitting it at a longer wavelength, and then guided to the end of the fibers connected with an avalanche photodetector. The UWOC system offers a 3-dB bandwidth of 66.62 MHz, and a 250 Mbit/s data rate is achieved using non-return-to-zero on-off keying (NRZ-OOK) modulation. The system was tested over a 1.5-m underwater channel under turbulences of air bubbles, temperature, salinity, and turbidity. We generated bubbles by blowing 0.20, 0.63, and 1.98 mL/s speeds of Nitrogen gas flow. A temperature gradient of 1.33 and 2.67 Celsius/m was introduced by circulating warm and cold water at the two tank ends, respectively. Salinity concentrations at 35 and 40 ppt were introduced to emulate the salinity in the Red Sea. Lastly, different volumes of MaaloxTM were added into pure water to emulate pure sea, coastal ocean, and turbid harbor water. The fiber-based UWOC system operates under those turbulence conditions with error-free communication and 0% outage probability.
With the growing number of underwater vehicles and devices used for marine environmental monitoring, there is an urgent need for real-time and high-speed underwater wireless communication technologies to transmit huge amounts of data. This poses great challenges to conventional underwater acoustic communication technology due to its low bandwidth and high latency. Therefore, underwater wireless optical communication with high bandwidth and low latency has become a promising technology. To this end, we develop the first underwater optical wireless sensor network prototype in this work. It consists of two sensor nodes and an optical hub. There is a transceiver circuit, a pH sensor, and an integrated temperature, salinity, and conductivity sensor in the sensor nodes enabling real-time underwater environmental monitoring. There are four transceivers facing four sides in the optical hub to implement bi-directional optical wireless communication with the sensor nodes. In a laboratory testbed and a field trial conducted in an outdoor diving pool, 100% packet success rates are achieved between the optical hub and the sensor nodes at a transmission distance of 60 cm. In the field trial, one of the sensor nodes is placed 60 cm away from the optical hub for real-time underwater environmental monitoring. The other sensor node is mounted on a remotely operated vehicle to collect underwater environmental information. This prototype shows great potential in future underwater mobile sensor networks and the underwater Internet of Things.
There exists a demand for radiation-safe and high-speed communication systems available to public users in the fifthgeneration (5G) communication and beyond. In this regard, visible light communication (VLC) stands out offering multiGigabit-per-second (Gbit/s) data transmission, energy efficiency and illumination, while being free from electromagnetic interference. Here, we report a high-speed VLC link by using a 443-nm GaN-based superluminescent diode (SLD) and bit-loading discrete-multiple-tone (DMT) modulation. Analysis of the device characteristics and modulation parameters shows a feasible bit allocation of up to 256-QAM while obtaining up to 3.8 Gbit/s data rate. These results, together with the electro-optical properties of the SLD such as being droop-free, speckle-free and high-power, make it an attractive solution for the future of public communications and smart lighting, while complementing traditional fiber-based and millimeter-wave technology.
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