In the early 20th century armies used search lights to find airplanes in the sky. They sometimes fitted shutters on these lights and used them for Morse-code. The light was pointed at the sky, sometimes at clouds. That enable transmitting "blinky-messages" beyond line of sight over significant distances. Armies eventually abandoned this method of communication for radios.
But there might be cause to bring this idea back. Science has advanced quite a lot in the last 100 years and we can use light to make tiny low power plasma bubbles in the air that emit brief light pulses. Enabling over the horizon optical communication with minimal to no infrastructure costs.
Imagine projecting a tiny holographic blinking dot of light in the sky to transmit information and a photodetector+optic to receive information.
A communication link is configured in 3D space.
-The upside is that the available volume of sky is functionally unlimited, and you never again have to deal with network-collisions and interference from communication signals of others.
-The Downside, it requires a good deal of precision in mechanical systems, so it'll be fiddly for a while. Picture using Binoculars to look at a firefly floating high up in the sky, you need to get up-down, left-right and focal distance just right to see it. There is a technology upgrade path to a solid-state chip version, that works similarly to matrix array antennas, It needs Terra-hertz switching logic, which requires photon-based micro-controller (it exists but it's very bleeding edge)
The range can be tremendous, there is enough gas molecules in the stratosphere to make this work. It will enable hops over the ocean with a small number of relay buoys.
The military might want this technology because
- it's harder to triangulate the origin of a transmission (you need to intersect the light-beam, to find the source), relay-transmitter-stations, soldiers, planes and ships will suffer fewer attacks from signal homing weapons, making it very robust.
- it's very hard to jam, (you need to flood the sky with very thick smoke, usually associated with forest-fires and volcano eruptions)
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