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 the requested data below and click CALCULATE.

Enter transmitting laser/LED output power:

Enter area of the receiving lens:

Enter loss adjustment factor (0-1):

This accounts for dirty lenses, atmospheric scattering and the like. It's a bit of a guess. 0 = total loss, 1 = no loss. 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 (d) divided by the range (R), would likely also be determined experimentally. In our experiments the beam from a cheap laser pointer diverges about 1 foot at a range of 300 feet, yielding a beam divergence of 0.0033 radians [1/300]. The divergence figure may also be available on a laser module's datasheet expressed in milliradians (.001 radian). Beam divergence for LEDs is usually specified in degrees. In that case enter the degree figure and select degrees from the drop-down menu.