Single vs. multiple beams?
The more receive intensity available at each end of an FSO link, the longer the distance it can accommodate, and the greater its weather penetration.
Let's start with the advantages of multiple beams:
First, assuming that a given FSO link needs to be eye safe, there is a limit
to the amount of allowable optical intensity exiting the aperture.
So, how do you increase the receive intensity, without increasing the "point intensity" of the beam(s) exiting the aperture?
Solution: deploy multiple beams with adequate separation to prevent intensity aggregation in close proximity to the aperture. This is a means of increasing their intensity only as the beams converge down stream where dispersion has reduced the aggregated intensity to a safe level.
The benefits include not only increased received beam intensity, but this increase also means that the beam divergence rate can be "upped" increasing the link's "wiggle" or mis-targeting tolerance, a benefit for both mount rigidity issues as well as atmospheric beam steering (scintillation) issues.
There are some strikes against multiple beams though:
Cost, size, and optical complexity are all disadvantages of multiple beam systems. In spite of these, multiple beams has been the choice for most first generation products.
But the biggest issue is that active alignment
solves some of the same problems as multiple beams, and can do it at less cost, smaller
size, and with a simpler single beam optical design.
Best of both worlds: active alignment with multiple beams.
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What's HOT, what's not...
Auto tracking? >>
Single vs. multiple beams? >>
Hybrid FSO + RF? >>
850nm vs. 1550nm? >>
Passive vs. Active? >>
Wikipedia on FSO >>
FSO vs. RF? >>
Security? >>
Eye Safety >>
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Where does Free-space Optics not fit? >>
Competitive comparison of the major Free-Space Optics solutions. >>
Free-Space Optics White Papers. >>
Who are we, and what’s our motivation for supporting this web site? >>
And last but not least…here’s our Free-Space Optics commercial website for specific product and/or service inquiries. >>
...and our refurbished FSO equipment site. >>