> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@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

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