Space laser communication adapted to work underwater

In 2013, the Lunar Laser Demonstration Communication System (LLDCS) successfully established communication with a satellite in lunar orbit. During the tests, scientists transmitted data over a distance of 380 thousand km at a speed of 622 megabits per second. Scientists at Lincoln Laboratories at the Massachusetts Institute of Technology have successfully tested an underwater version of this communications system today.

Water is a hostile environment, including for all communication methods known to mankind. It shields radio waves, scatters light, creates acoustic interference, and reliable contact can only be achieved by connecting two respondents with a rigid cable. A laser that can focus very accurately and transmit energy very far could solve this problem. However, the experiments of MIT engineers have shown that LLDCS has a fundamental flaw, which is not yet possible to fix.

Even the purest water of a sports pool scatters the laser beam, and plankton and any debris also float in the sea, plus layers of liquid have different chemical and physical properties. The laser must hit the target accurately in order to establish a connection, however, GPS systems do not work well under water, and inertial navigation modules tend to accumulate error, which gives a deviation of tens of meters and more for real objects, the longer they are in free swimming. Without knowing the exact coordinates of the receiver, turning on the laser transmitter is useless.

Today, the prototype of an underwater LLDCS works like this: a low-power laser scans the area around the transmitter in search of a receiver. Then the target is captured, a control signal is sent and both vehicles take a stationary position relative to each other. Further, a narrow laser beam begins to transmit data - in an Olympic-type pool, the installation of communication took about a second, and during the experiment, several hundred gigabytes of data were transferred. Now engineers want to test whether they can do the same in the real ocean, starting in shallow water. And at long distances - from 100 m and more.