The Jargon File (version 4.4.7, 29 Dec 2003):

light pipe
 n.

    Fiber optic cable. Oppose copper.


The Free On-line Dictionary of Computing (30 December 2018):

optical fibre
fibre optics
light pipe
optical fiber

    (fibre optics, FO, US "fiber", light pipe) A
   plastic or glass (silicon dioxide) fibre no thicker than a
   human hair used to transmit information using infra-red or
   even visible light as the carrier (usually a laser).  The
   light beam is an electromagnetic signal with a frequency in
   the range of 10^14 to 10^15 Hertz.

   Optical fibre is less susceptible to external noise than other
   transmission media, and is cheaper to make than copper wire,
   but it is much more difficult to connect.  Optical fibres are
   difficult to tamper with (to monitor or inject data in the
   middle of a connection), making them appropriate for secure
   communications.  The light beams do not escape from the medium
   because the material used provides total internal reflection.

   AT&T Bell Laboratories in the United States managed to
   send information at a rate of 420 megabits per second, over
   161.5 km through an optical fibre cable.  In Japan, 445.8
   megabits per second was achieved over a shorter distance.  At
   this rate, the entire text of the Encyclopedia Britannica
   could be transmitted in one second.  Currently, AT&T is
   working on a world network to support high volume data
   transmission, international computer networking, electronic
   mail and voice communications (a single fibre can transmit
   200 million telephone conversations simultaneously).

   See also FDDI, Optical Carrier n, SONET.

   (1997-05-26)