[Laser] Re: Non-imaging optics - again

n9jim-6 [email protected]
Mon, 13 Jan 2003 20:13:30 -0800


1) TV transmission
Most of the commercial systems laser data comm systems use small lens 
systems of about 3 or 4 inches.
These systems are running in excess of 100MbpS over about a mile.

The lens requirement is related to bandwidth, power transmitted, and 
distance.

For an analog video signal, about 6MHz is required (current commercial TV).
Taking a Sony laser link for TV, it is straight forward to extend the 
range by replacing the LED light source in the camera with a laser diode 
(or building a "repeater" from a Si detector and a laser diode). As was 
pointed out the alignment is critical. But that is the "cost" of 
concentrating the power into a narrow optical beam.  

Improved distance perfromance can be had by adding a lens system in 
front of the receiver input.

2) other light collectors
Cosmetic mirrors (poor for imaging, but often have a focal point "good 
enough" for a larger (and slower) detector
Book magnifiers - 8x10 fresnel lens, similar issues  (also some 
chromatic distortion, this can be used to your advantage as the focal 
points for R, G, B will be different allowing some filtering)
Large lenses from various projection systems (green glass) not as 
efficient but they work
Multi-element mirrors - small flat mirrors arranged to hit a given 
point, not efficient, but if the detector is large enough much of the 
desired light will still hit it.  This construction also allows sampling 
of a signal over a larger area, and can be used to "smooth" cell 
distortions due to air turbulence.
Polished microwave dishes - not efficient but large capture area
Searchlight reflectors - surplus
Multi-element detectors - add up the power collected

Jim




J. Forster wrote:

>If you want to look at a small, distant source as in a data link, either a lens
>or concave mirror is a much better choice. After all, the only light you really
>want to collect comes directly from the source. Small, cheap lenses and mounts
>are available as low priced astronomical telescopes. The only exception would be
>a scattering path (over the horizon) links.
>
>See, for example:  UNIVERSE 6 IN. REFLECTION TELESCOPE 900 mm  Item # 1950387811
>on eBay. All you'd have to do is make a detector mounting adapter.
>
>OTOH, the above has a pretty long focal length. Depending on your path length, a
>cheap telephoto lens, such as :Tamron 400 F = 1: 7.5 Telephoto Lens  Item #
>3000358774 might be a better choice. Cheap filters, tele extenders, and other
>accessories are easily available. You can make a detector mount out of an
>extension ring set and rear dust cover. Consider T mount lenses also.
>
>You will need to match the focal length, detector size and path properties.
>
>-John
>
>
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