Path: utzoo!utgpu!water!watmath!clyde!att!mtunx!rutgers!gatech!ncsuvx!ece-csc!ncrcae!ncr-sd!rb-dc1!severino
From: severino@rb-dc1.UUCP (Cunnu the Sardinian)
Newsgroups: sci.electronics
Subject: Re: CD Player Questions
Summary: 3-beam or 1-beam lasers
Message-ID: <206@rb-dc1.UUCP>
Date: 7 Jun 88 16:46:55 GMT
References: <3385@ncrcae.Columbia.NCR.COM> <3608@briar.Philips.Com>
Reply-To: severino@rb-dc1.SanDiego.NCR.COM (Cunnu the Sardinian)
Distribution: na
Organization: Gould CSD, San Diego
Lines: 25

In article <3608@briar.Philips.Com> drg@philabs.Philips.Com (Don Gentner) writes:
>As far as I know, all CD players have only one laser.  In 3-beam players,
>the laser beam is split into 3 beam before reflecting off the disc.  In single-
>beam players, the beam is split after reflecting off the disc.  In either
>case one signal is used for data and the other two beams are used for 
>tracking and focus correction.  Both systems work, but the single beam system
>has the advantage of simpler design and fewer parts to get out of alignment.
>I don't know of any advantage of a 3-beam system, except "ad hype" 
>--

How do you manage to correct the tracking and focusing with 1 laser
beam??  It would seem that if you split the laser AFTER it reflects
off the disc you are carrying much less critical info for 
correcting purposes...

Andrea Severino, GOULD-CSD (San Diego Division) (619)485-0910 xt. 272 
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