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From: pahsnsr@nmt.edu (Paul A. Houle)
Newsgroups: sci.electronics,sci.physics
Subject: Re: Lasers for communication
Message-ID: <1990Sep13.020325.10622@nmt.edu>
Date: 13 Sep 90 02:03:25 GMT
References: <1064.26E59478@ofa123.fidonet.org> <1872@oucsace.cs.OHIOU.EDU> <153DAVE@ORION>
Organization: New Mexico Institute of Mining and Technology
Lines: 21


      Making an optical link with a laser is very possible,  and actually
can be very easy if you've got the right kind of laser.  It only takes
two technological tricks to pull it off - one is that you have to be
able to modulate the laser beam,  and the other one is to detect the
modulations.  Number 2 is exactly the same as if you did it with LED's.
The same circuits work,  and HeNe lasers don't produce enough power to
ruin photocells or CdS cells.  Some lasers have a modulation jack that
you can plug your audio/data (or even video with some models!) source
into that will automatically modulate the beam.  Most of these lasers use
a stable cavity but have a modulator in the beam path -- something that
gets dark when you apply electricity through it.  There are many physical
properties that you can use to get this effect - best known is the
"Kerr Cell" which works like a LCD.  Controlling power input to the
laser is also possible,  but tends to add more noise and,  for most models,
you'll have to considerably modify the power supply.  A final trick is to
use a bit of mirror that you can vibrate to move the beam on and off the
detector.
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