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'[EE] Request for Source for Laser diode or module'
2006\02\09@220042 by Ling SM

picon face
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

2006\02\09@222826 by Marcel Duchamp

picon face
Ling SM 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.

Just out of curiosity, are you:
a) using lenses to focus your LEDs?
b) using lenses to focus your receiver?
c) using long tubular light shields on your receiver?
d) using modulation of some sort on your LEDs?
e) using AC coupled, high gain, demodulation stages on your receiver?

Most of the above will also be needed with lasers as well.
What baud rates are you hoping for?

2006\02\09@224805 by Ling SM

picon face
> Just out of curiosity, are you:
> a) using lenses to focus your LEDs?
Yes, I did.  I was trying on a 6 degree collimator.
> b) using lenses to focus your receiver?
> c) using long tubular light shields on your receiver?
Yes, to both.  I think it is quite a decent set.
> d) using modulation of some sort on your LEDs?
> e) using AC coupled, high gain, demodulation stages on your receiver?
Not yet, when I tune the receiver to be insensitive to daytime light, it
can pick up my beam 10m away.  If it is tuned to be sensitive to my
beam, the daytime light saturated the Rx.

> Most of the above will also be needed with lasers as well.
> What baud rates are you hoping for?
Have not reached this state yet.

Ling SM

2006\02\09@225248 by Ling SM

picon face
typo, my bad.

 Not yet, when I tune the receiver to be insensitive to daytime light,
it *cannot* pick up my beam 10m away.  If it is tuned to be sensitive to
my beam, the daytime light saturated the Rx.

2006\02\09@232413 by David VanHorn

picon face
>
> Not yet, when I tune the receiver to be insensitive to daytime light, it
> can pick up my beam 10m away.  If it is tuned to be sensitive to my
> beam, the daytime light saturated the Rx.


What are you using as a detector?
The problem here is that light varies tremendously during the day, if I
remember right it's something like 10,000-1 ratio.

Going with a laser gets you more output per watt in, but it is also
spectrally narrow, allowing you to use narrow bandpass optical filters to
cut out most of the ambient light.

Edmund scientific is a pretty good source on optics and filters.

2006\02\09@232911 by Chen Xiao Fan

face
flavicon
face

> From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu
> [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf Of Ling SM
>
> typo, my bad.
>
>   Not yet, when I tune the receiver to be insensitive to
> daytime light, it *cannot* pick up my beam 10m away.  If it
> is tuned to be sensitive to my beam, the daytime light
> saturated the Rx.

I do not know much about laser communication. I can
only suppose that our methods of suppressing ambient
light in the optic proximity switch might be of some help
to you.

1) add ambient light filter for the receiver or use
receiver with built-in ambient light cut filter.

2) modulate the emitter (high current low duty ratio
pulse) and use AC coupling in the receiver side.

3) reduce the DC biasing resistor of the receiver and reduce
the aperture size so DC light will not saturate the receiver.

4) reduce the gain of the receiver amplification stage
(band pass filter/amplifier) so that noise cause by the
ambient light will not cause problem.

Regards,
Xiaofan

2006\02\10@004705 by KY1K

picon face
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:

{Quote hidden}

>

2006\02\10@005016 by Ling SM

picon face
I was testing on Hamamatsu module C5460, reluctant (or lazy) to fix up a
receiver myself.  It looks like this unit is a DC supersensitive type.
Guess, it is a reset to start from scratch again.

In meantime, keep your data and suggestions coming.

Ling

{Quote hidden}

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