Path: utzoo!utgpu!attcan!uunet!lll-winken!lll-lcc!pyramid!amdcad!rpw3
From: rpw3@amdcad.AMD.COM (Rob Warnock)
Newsgroups: sci.electronics
Subject: Re: Optical power distribution
Summary: Optically powered telephone is old news.
Keywords: power supplies, batteries
Message-ID: <22497@amdcad.AMD.COM>
Date: 31 Jul 88 09:18:49 GMT
References: <1075@gethen.UUCP> <6315@bloom-beacon.MIT.EDU> <118@luna.UUCP> <5741@pogo.GPID.TEK.COM> <2627@kitty.UUCP> <1355@kodak.UUCP> <17588@glacier.STANFORD.EDU>
Reply-To: rpw3@amdcad.UUCP (Rob Warnock)
Organization: [Consultant] San Mateo, CA
Lines: 28

Quite a few years ago, Bell Labs put together a "fiber optic telephone", in
which a single fiber was used for *both* bi-directional signal *and* power
supply, over (as I recall) a several kilometer fiebr-optic cable. The phone
looked like an ordinary "desk set" (you know, type 2500), except it had this
piece of fiber coming out going to a spool of the stuff.

The article said that they were using a form of TDM on the fiber -- somewhat
like the "ping-pong" versions of ISDN -- wherein more than 90% of the time
was outgoing "power", and the rest of the time was input signal pulse
(with guard "dead time" around it).  The outgoing "signal" was carried
by position-modulation of one edge of the "power" signal. They spent a
lot of time talking about the trouble they went to building a ringer with
enough efficiency to make an acceptably loud sound with the small amount
of power that was available. (The power for the signal electronics was much
less of a problem!)

Cute...

(Of course, there's no way to plug in an "extension" phone without a
locally-powered repeater.)


Rob Warnock
Systems Architecture Consultant

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