Newsgroups: comp.robotics
Path: cantaloupe.srv.cs.cmu.edu!nntp.club.cc.cmu.edu!godot.cc.duq.edu!news.duke.edu!convex!cs.utexas.edu!usc!elroy.jpl.nasa.gov!decwrl!netcomsv!ix.netcom.com!netcom.com!nagle
From: nagle@netcom.com (John Nagle)
Subject: Re: laser diode modulation
Message-ID: <nagleCx0EwF.7rv@netcom.com>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <36gtso$dh1@sun4.bham.ac.uk>
Date: Sat, 1 Oct 1994 19:45:51 GMT
Lines: 20

HargSJ@ugsun1a.bham.ac.uk (Simon Hargreaves (PH)) writes:
>Does anyone have any figures on to what frequency a laser diode (like the
>one in a CD player) can be modulated.
>    I am using it for a laser range finder using a psd to estimate range.
>and I need a modulation frequency of about 50Mhz.

      Tell us more.  I tried to build one of those, but I had problems
with crosstalk into the receiver.  

      Modulation is not fundamentally hard, but because of the annoying
way laser diodes fail, power control for modulated laser diodes is 
essential and messy.  What matters is the peak current, not the the
average (the failure mode is mirror overload, not thermal heating),
the feedback photodiode doesn't have as much bandwidth as the laser diode,
the current needed varies with temperature, and different laser diodes
have widely different operating currents for the same output.

      I finally bought a commercial modulator.

					John Nagle
