[Laser] CW or AM/FM

[Charles Pooley]

JR Linden <deleted this because messages bounce> wrote:
   
  Most of the posts I seen are primarily the physics and challenge of 
transmitting and receiving a light signal over a distance. Is anyone 
familar with a website/s dealing with the transmitting of information on 
that light? 
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  You can start with the fact that 3 mw of 635 or 650 nm is almost 
exactly 10e16 photons/sec, and the optics design (beamwidth, receiver 
diameter etc) can give the number of photons/sec received.
   
  Then if the quantum efficiency of the receiver diode and losses in 
the optics is 50%, then about 6x10e12 photons/sec into the receiver 
optics will give about 3 x 10e12 electrons/sec or about 500 nanoamps of 
photocurrent.
   
  There are "geiger mode" photodiodes which can count to the 100's per 
sec if chilled.
   
  Or the system can now use 405 nm lasers (used in the new generations 
of DVD) and 5 mw of that is 10e16 photons/sec.  Standard 
photomultipliers can count those photons and have a QE of over 20%.
   
  In my www.microlauncher.com website I will soon have a section 
devoted to optical data links, mostly laser.  It will probably be 
microlaunchers.com/optics or something like that.
   
  Charles Pooley   KD6HKU