Laser Communications System Range Calculator

Predicts approximate range of an open-air laser or LED communications system.

Equation lifted from A Practical Introduction to Lightwave Communications, Forrest M. Mims III, H.W.Sams,1982

Enter transmitting laser/LED output power:

Enter area of the receiving lens:

Enter loss adjustment factor (0-1):

This accounts for dirty lenses, air polution and the like. It's a bit of a guess. 0.8 might be a typical value.

Enter receiver threshold power in nanowatts (nW):

The minimun acceptable receiver power level. It's mainly a function of the sensitivity of the receiving
photodiode and associated receiver electronics, though background optical noise is also a factor.
The figure would most likely be determined by experimentation. Mims uses 700 nW in his example.
We have not determined this number for our laser communications system, but DX tests suggest it's
in the neighborhood of 100 nW.

Enter beam divergence:

This number, numerically equal to the beam width divided by the range, would likely also be determined
experimentally. In our experiments, the beam from a cheap laser pointer diverges about 1 foot in 100 yards
(1/300), yielding a beam divergence of .0033 radians. The divergence figure may also be available on a
laser module's datasheet. You can optionally enter beam divergence in degrees (from LED datasheet).

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