[Laser] How to Collimate LED? Need info please

[Paul A. Cianciolo]

Hello Folks,

I have decided to start experimenting some more with optical Cloudbounce
communications.

There is a company called LUXEON that make these very high power LEDS

See   http://luxeon.com  and follow the LUXEON products link at the bottom
of the page.


Also to see and her a hacked up version of some of my previous experiments
use
http://www.qsl.net/w1vlf/techinfo/techinfo.html

Then follow the arrow to the pictures of the components used.

This time I have decided to use a tighter beamwidth and also use the color
green instead of IR, for a number of reasons.

1)Green is visible.... easier to work with.
2)Green happens to fall in the peak sensitivity area of many photomultiplier
tubes.
3)The advent of the high power LUXEON 5 Watt emitters
4)I happen to have a 1/2 diameter PMT to use for these experiments
5)Scattering is more predominate at these wavelength

The primary objective will to use the clouds as a reflector which at (say
10,000 feet) will be LOS to more than 1 person.
This would allow a sort of a beacon type operation.  Of course point to
point comm will be part of the fun as well.


So I plan to use as the transmitters a array of 4 of the 5 watt green
emitters and 4 of the same type of projection television lens

Here in lies the problem.

I possible I would like to strike up a conversation (email) about the topic
of collimating these LEDS to a HPBW of only a few degrees.
This to get the power density up and also to minimize the loss on the way to
the scattering surface, the clouds.

Depending on the surface of the clouds and how they are changing I would
imagine that a very tight HPBW of say 1 degree would provide very strong
returns.
But it seems as though the signal may have significant fading due to the
irregular nature of the scattering medium.

On the other hand if the HPBW is wider say 5 degrees the power density would
be less and the returned signals would be weaker but the fading would be
minimized.

These are just guesses on my part.

The LEDS for this experiment are of a Lambertian nature, however there are
several companies that make after market lens to fit on top of these LEDS
with varying degrees of HPBW  form 6 degrees to 10 to 45.

I am able to focus with the projection lens one of the LEDS to a spot 4'
dia. at a distance of 65 feet.  This works out to a and angle from the lens
of about 3.5 degrees.

So does anyone have any comments or resources for this question?

I would surely welcome them


Thank you

Paul A. Cianciolo

1-860-485-0355

W1VLF