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From: grege@gold.GVG.TEK.COM (Gregory Ebert)
Newsgroups: sci.electronics
Subject: Re: tapping into a fiber optic cable
Message-ID: <1048@gold.GVG.TEK.COM>
Date: 31 May 90 16:28:01 GMT
References: <46249@iuvax.cs.indiana.edu>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 17

In article <46249@iuvax.cs.indiana.edu> beckman@iuvax.cs.indiana.edu (Peter Beckman) writes:
>Can a fiber optic cable be "tapped" into without disturbing the data
>being transmitted?  

 Yes, and no. Any 'tapping' will reduce the amount of energy sent to the
 receiver, unless you install a 'repeater'. The loss in energy may or may
 not be an important issue. Regarding security, there will be a period of time
 which the cable is 'broken', thus a break-in will be detected. Even if
 you tap-in without initial detection, there is equipment available (OTDR-
 Optical Time Domain Reflectometry) which will detect even _minute_ variances
 in line impedance, and their exact location. This technique is commonly used
 in the electrical realm to find flaws in coax cable; it's so sensitive that
 you can squeeze or bend the cable and get a detectable reflection. Ask any
 cable TV technician about how they detect and bust bootleggers. All this
 aside, I've heard that someone manufactures fiberoptic cable which can be
 pressurized with some gas; cut/poke/tap/etc the cable, and the pressure
 drop signals an alarm. Bizarre.