Cosmic communication laser adapted for operation under water

<pre>Cosmic communication laser adapted for operation under water

In 2013, the “Lunar Laser Demonstration Communication System” (LLDKS) successfully established communication with the satellite in the lunar orbit. In the course of the tests, scientists transmitted data for a distance of 380 thousand km at a speed of 622 megabits per second. Today, scientists from Lincoln Laboratories at the Massachusetts Institute of Technology successfully tested the underwater version of this communication system.

Water is a hostile environment, including all communication methods known to mankind. It shields radio waves, dissipates light, creates acoustic interference and can achieve reliable contact only 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 showed that LLDKS has a fundamental drawback, which is not yet possible to correct.

 Laser space communication under water

Even the purest water of the sports pool dissipates the laser beam, and plankton and any debris float in the sea, plus the layers of the liquid have different chemical and physical properties. The laser should hit the target accurately to establish communication, but GPS systems underwater work poorly, and inertial navigation modules tend to accumulate an error, which gives a deviation of tens of meters and more for real objects, the longer they are in free navigation. Without knowing the precise coordinates of the receiver, it is useless to turn on the laser transmitter.

Today, the prototype of underwater LLDX works like this: a low-power laser scans the space around the transmitter in search of a receiver. Then, the target is captured, a control signal is sent and both units assume a fixed position relative to each other. Next, a narrow laser beam begins to transmit data – in the Olympic-type basin, the communication installation took about a second, and during the experiment several hundred gigabytes of data were transferred. Now the engineers want to check whether it will be possible to repeat the same in the real ocean, first in shallow water. And at great distances – from 100 m and further.

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