Several problems come to mind immediately, although there might be others.

Let's work on the serious problems first, so you can properly 
evaluate the transmitting hardware you already have.

You say the LED average current is lower than expected..... These 
large LEDs are very capacitive, to turn them on and off at high rates 
(above a few Khz), you will need a totem pole driver. Suspect your 
Luxeon is not completely turning on/off, which might account for the 
unexpected average current readings.

And, you say the receiver is being overpowered by ambient 
daylight...... I strongly suspect you are using a baseband receiver, 
which will not work in anything but near total darkness. If this is 
the case, you can use a dynamic light cancelling receiver, which uses 
another op amp to cancel the effect of the ambient light in what is 
called a 'leaky' integrator circuit. This will allow you to use a 
baseband receiver in subdued daylight with very little loss in 
receiver sensitivity.

Don't jump to the laser diode camp yet.....your receiver will still 
have problems dealing with the ambient daylight and aiming a laser 
with a tight beamwidth is easier said than done.

If you need immunity to fog, going to IR (whether laser or LED) will 
cut through fog and rain much better.....to the best of my knowledge, 
the luxeons do not come in IR, only visible.

Have you subscribed to the free space laser communications email list????

What's your budget?

Is this a full time link or sporadic? Will it carry emergency or life 
critical information (if it goes down temporarily due to weather, 
what are the ramifications of the lost link)?

What type of receiver are you using?

What data rate do you require (video or communications quality analog voice)?

Are you using baseband, or a more appropriate daylight tolerant mode??

Write me directly if you need more help than the PIC list can give.

Regards,

Art



At 10:00 PM 2/9/2006, you wrote:

>I have spent some time playing around with the 1W Luxeon LED to do 1km
>optical data transfer.  But base on my experiments so far, the LED has
>problem overpowering the daytime sun.  And the limited 500mA peak
>current for a 350mA rated LED does not hel.  But the low peak current
>still puzzle me.  The latest 1.54A LED will not do unless its peak
>current can take more abuse.  Anyone has data to fault the brief datasheet?
>
>So I am jumping over to the laser diode camp.  I had sent out some
>enquiries?  To cut short this process, do piclist have some references
>and shops (online) of liking.
>
>Thanks.
>
>Cheers, Ling SM
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