Research and development for practical use of underwater optical wireless communication

JAMSTEC has developed underwater optical wireless communication with a view to its use in underwater robots. Using a photomultiplier tube as a light receiving element and a wide light distribution LD as a light emitting element, a communication speed of 20 Mbps was achieved between underwater vehicles 120 m away. Furthermore, optical Wi-Fi is established between the autonomous underwater vehicle and the underwater station. Camera images in the station were transmitted when the autonomous underwater vehicle passes above the ocean lander through the optical Wi-Fi link. We now study underwater optical wireless communication device that transmits and receives optical signals at the end face of an optical fiber. It realizes arbitrary light distribution characteristics at arbitrary positions. In the tank test, the device was installed in the imitation underwater station. The underwater robot was operated in the tank wirelessly without a cable while we were watching the video image from the camera on the robot. In research on underwater image sensor communication using an underwater camera and an LED array type of underwater light, we control the blinking of each of the independent RGB LEDs arranged two-dimensionally on a plane, photograph them with a camera, and the data is decoded from the taken images. The optical axis alignment affects the communication performance greatly. We started to study on optical axis alignment (or optical tracking) using light itself. By combining rough tracking using a ring laser and fine tracking using a photon receiver, we try to align the laser optical axis with the opponent 300m away.