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Fault Detection and Isolation in Optical Transmission Systems using Optical Amplifiers

IP.com Disclosure Number: IPCOM000115438D
Original Publication Date: 1995-May-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 4 page(s) / 124K

Publishing Venue

IBM

Related People

Li, CS: AUTHOR [+2]

Abstract

The next generation of optical fiber transmission links will use optical amplifiers instead of repeaters. Links using amplifiers have the potential to provide higher transmission capacity by the use of wavelength division multiplexing. A fault detection and isolation system must be provided as part of any such transmission system. Performing this task in normal electronically regenerated systems is fairly standard because such links operate using well-known protocol, such as Synchronous Optical Network (SONET). In such links the repeater looks at the bits in the signal and can interpose supervisory bits indicating different fault conditions that enable the ends of the link to determine and isolate faults.

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This is the abbreviated version, containing approximately 48% of the total text.

Fault Detection and Isolation in Optical Transmission Systems using
Optical Amplifiers

      The next generation of optical fiber transmission links will
use optical amplifiers instead of repeaters.  Links using amplifiers
have the potential to provide higher transmission capacity by the use
of wavelength division multiplexing.  A fault detection and isolation
system must be provided as part of any such transmission system.
Performing this task in normal electronically regenerated systems is
fairly standard because such links operate using well-known protocol,
such as Synchronous Optical Network (SONET).  In such links the
repeater looks at the bits in the signal and can interpose
supervisory bits indicating different fault conditions that enable
the ends of the link to determine and isolate faults.  However, such
schemes cannot be used in amplified systems because the electronic
signal cannot be monitored and changed at the amplifier, and secondly
the actual protocol being used on the link may not be known and hence
the monitoring system will not know the specific formats being used
in the signal.  One proposed approach in the literature (*) is to
have local monitoring at each amplifier site and connect the
monitoring system to the controllers by a separate out-of-band
electronic network.  This invention allows the fault management
function to be performed inband within the same transmission system.

      The invention assumes the presence of a supervisory signal in
addition to the data signals being transmitted on the link.  It is
possible for the supervisory signal to be part of a data signal
provided the specific protocol used on that signal is known;
otherwise,
a separate signal is required.  The supervisory signal can be carried
on
a separate wavelength, say lambda sub 0, as will be assumed in the
embodiment of the invention, or it can be carried on a subcarrier
channel
on one of the wavelengths.  Assume the presence of a controller, at
either end of the link, which is responsible for fault management.

      Under normal operation, the controllers at the ends of a link
communicate on wavelength lambda sub 0 and monitor this signal
continuously to determine the presence or absence of light.  If loss
of light is detected, the link is assumed to be down and the
transmitters at either end go into a pulsed mode of operation
periodically to determine when the link is back up again.

      Now, treat the situations where a cut occurs along a segment of
this link or one of the amplifiers on the link fails.

      Assume that the fiber amplifiers are always installed in
pairs.  The proposed fault-monitoring mechanism for each pair of
optical
amplifiers is shown in the Figure.  At the input to the amplifier,
the supervisory signal at wavelength lambda sub 0 is completely
tapped off and received and converted to an electrical signal.  This
can be done by a wavelength-selective coupler, and is particularly
easy i...