Talk:Terminology:Communication (Insystem/Interstellar)

Microwave as primary with laser for alignment? I don't think so!

Lasers themselves are low bandwidth, but keep in mind that the highest bandwidth long-distance links in use by humans in the 21st century are fiber optic. You are correct that it doesn't work very well to modulate the power or frequency of the the laser itself, although it's doable. (I've seen an analog audio signal transmitted by modulating the voltage to a laser diode, the quality at the receiver wasn't much worse than at the headphone jack feeding the transmitter.)

Current transmitters gate the output the laser by passing the beam through a material whose opacity depends on an applied electric field. These can switch _very_ fast (easily 10 GHz, currently) and you can multiplex your signal over multiple nearby light frequencies if needed. (In the 21st century, it's cheaper to add more lasers and fancier receivers than it is to dig up everything and lay a second fiber, if the distance is long enough.)

The modulated laser beam can be amplified with stimulated emission (as is currently done at relay stations along the length of e.g. undersea fiber links). Light can go a long way and be amplified up to ~10 times before you need to convert to electrical and back to clean up the signal into square waves again. With optical transistors/optical computer tech, it could be all optical.

Nyquist/Shannon information limits mean that you can get a lot more information onto an optical frequency beam than onto a microwave beam, because the frequency of even infrared light used currently is ~200 THz. (Silicon emits and receives 1550nm light most efficiently. Optical wavelengths require e.g. gallium arsenide.)

I had a summer job with JDS Uniphase, a maker of optical communication components, once when I was a physics student. I learned lots of neat facts like these. :)

BTW, non-fiber laser comms currently exist: http://www.mdatechnology.net/techsearch.asp?articleid=536 --peter 07:03, 4 March 2007 (PST)

jackS 11:43, 5 March 2007 (PST) Point taken. As you have superior expertise to mine in this area, feel free to edit the description to something more rational. The non-laser nature of the comm system came out of a discussion with a friend of mine who does wireless communications research and who balked a bit when I ran the concept of "comm laser" past him as he proceeded to discuss the bandwidth limitations of lasers.