This is specifically in reference to Starlink satellites. I have no idea how they could possibly work. How can thousands of videos, pictures, text, and music, be sent optically through space? I feel like it’s an impossible amount of data to transmit, other than the use of magic.
In: Physics
They communicate with ground via regular radio waves. I am assuming you already know how this works.
To communicate with other satellites, they use lasers.
There are many ways to transmit data via laser, I’m not sure the specific one they will use.
But for simplicity, think of how a CD would work. Based on the burnt markings of a CD, a laser hits the CD, and reflects back into the sensor. Based on the differences of the reflected laser light, you can assign each case to be 1 or 0.
You can do the same with satellites. Only you directly send pulses of laser at another satellite, and the other satellite interprets that as 1s and 0s based on the gaps between pulses.
I have no specific knowledge about starlink sattelites, but I’m an electrical engineer and fiberoptic cables are not really complicated.
You basically just put a Diode on both ends, one that can be used to create light (LED) and turn light back into electric current (Photodiode). Diodes are semiconductor technology, so they are really really fast, you can change it’s state in nanoseconds, so billions of state changes are possible in one second. The limitation on data capacity comes from the cable itself, if bits are too fast they will “smear” into each other because glass has a property that different wavelength of light have a different speed of light. So length of the cable has a maximum for a specific dataspeed and you need to plan for repeater stations.
As a general note light is just another form of electromagnetic radiation, so transmitting works just like a radio signal (but with other materials blocking it)
From my physics textbook:
> […], consider modulating (modifying) the wave by chopping off some of the wave crests. Suppose each crest represents a binary digit, with a chopped-off crest representing a zero and an unmodified crest representing a one.
So light is a wave and they can modify the way so that there is a binary signal.
Optic fibers have this really cool property of being able to keep light inside them very well. They use it by exploiting the way light is reflected and refracted when moving between mediums.
So take any data you want, and write it down in bits of 0 and 1.
Now imagine we’re each at one end of a fiber, and every second I send a strong or weak flash of light. If it’s strong its a 1, weak is a 0.
That’s the basic principle. In effect we use all kind of neat technology to to this very very fast, transmitting up to several GBs of data every second. We can even use different “colors” of light to transmit multiple data stream at the same time.
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