[Laser] Researchers show-off high-speed laser communications device for space

[Tim Toast]

Hi Bernie,
After seeing a picture of this chip they're talking about, It looks like they are focusing 
the light with a  lens on all 4 of the detectors at once. So all the detectors are within 
the small spot of light normally focused on one detector in other systems. All the 
detectors being within a millimeter or so square. If they make a 64 N detector then 
presumably all of those will also be very close together and all within the small focused 
spot of the lens. 

I can see how this would tend to 'harvest' more information from the beam. Even 
though a single detector, of a given area, can count individual photons and be 
capable of millions of counts  per second, by dividing up this same area into separate 
detector areas, you can divide the job between multiple detectors - each capable of 
millions of counts per second. The individual photons would be hitting here and there 
within the spot, striking different detectors. Each detector would have some 'breathing 
room' in effect due to the other detectors capturing photons slightly to the left or right, 
up/down within the small spot.  I think this increases the bandwidth beyond what an 
individual detector in the array is capable of due to the ability to resolve two photons 
only slightly separated in time that might otherwise be obscured by the 'recovery time' 
of a single detector. 
It seems like i have read before that the transmitting laser is a pulsed type but i forget 
exactly what kind it is - modelocked maybe, that free runs with millions of pulses per 
second and can be PPM modulated.
Interesting stuff for sure.

-toast