EP0486583A1 - Systeme de communications optiques - Google Patents

Systeme de communications optiques

Info

Publication number
EP0486583A1
EP0486583A1 EP19900912495 EP90912495A EP0486583A1 EP 0486583 A1 EP0486583 A1 EP 0486583A1 EP 19900912495 EP19900912495 EP 19900912495 EP 90912495 A EP90912495 A EP 90912495A EP 0486583 A1 EP0486583 A1 EP 0486583A1
Authority
EP
European Patent Office
Prior art keywords
test
sequence
test pulse
transmission line
pulses
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19900912495
Other languages
German (de)
English (en)
Inventor
Simon Mark James
Dominik Drouet
Stephen Eric Gold
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
British Telecommunications PLC
Original Assignee
British Telecommunications PLC
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by British Telecommunications PLC filed Critical British Telecommunications PLC
Publication of EP0486583A1 publication Critical patent/EP0486583A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
    • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
    • G01M11/3118—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using coded light-pulse sequences
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
    • G01M11/39—Testing of optical devices, constituted by fibre optics or optical waveguides in which light is projected from both sides of the fiber or waveguide end-face

Definitions

  • This invention relates to an optical communications system, and in particular to a line monitoring arrangement for early detection of faults in such a system.
  • An OTDR comprises a pulse source, usually a high power laser, from which a single pulse is launched into the fibre to be tested, and backscattered light returning to the launch end of the fibre is monitored. Peaks in the backscattered light are indicative of faults in the fibre, and the distance of a given fault from the launch end of the fibre is known from the time interval between launch and return of the respective backscattered peak. Once a period of time sufficient to receive all detectable backscattered light has passed, a further pulse may be launched into the fibre. The pulse width may be varied for difference dynamic range or resolution requirements.
  • an increase in the pulse width enables a greater length of fibre to be monitored, that is to say it increases the dynamic range.
  • increasing the pulse width decreases the spatial resolution (that is to say the minimum distance between which events can be distinguished).
  • a particular limitation of using an OTDR of this type is that the optical communications system on the fibre has to be disconnected, or at least discontinued, both to permit the connection of the OTDR, and also to prevent system light from affecting the OTDR trace.
  • the result of this limitation is that an OTDR tends to be utilised only after a failure occurs, and cannot be used for constant line surveillance simultaneously with data transmission.
  • the aim of the present invention is to provide a line monitoring arrangement that may be used simultaneously with data transmission.
  • the present invention provides a line monitoring arrangement of an optical fibre communications system carrying system data, the monitoring arrangement comprising a test sequence generator for generating a sequence of test pulses, means for repeatedly launching the sequence of test pulses into a first end of a transmission line forming part of the communications system, a correlator for correlating signals received at the first end of the transmission line with the sequence of test pulses to identify backscattered test pulse sequences, and an integrator for integrating backscattered test pulse sequences over a predetermined time interval.
  • this line monitoring arrangement can be operated while data is being transmitted, which is not possible with present Optical Time Domain Reflecto eters.
  • This is achieved by superimposing, or slotting in, test pulses along with the system data.
  • the energy of the test pulses launched into the transmission line has to be compatible with the associated equipment, so as to minimise the possibility of damage, and also to minimise interference with the transmitted data.
  • the energy of the test signal can be increased to compensate for this requirement to use low energy OTDR pulses.
  • the test pulse sequence is launched into the transmission line at the system data rate.
  • the test pulses each have a pulse width and height of the same order as the system data pulse width and height.
  • Backscattered light is monitored continuously, from the launch end of the fibre, for changes in the backscattered test sequence intensity that would be indicative of changes in the fibre.
  • test pulse sequence is included in a respective time multiplexed transmission frame, and the test pulse sequence is in a Barker or Golay code.
  • the test sequence in the backscattered light has to be detected against a background not only of noise, as with normal OTDR, but also against backscattered light from the system data, and, in the case of a duplex system, incoming system data transmitted from the distant end of the fibre link.
  • a correlation technique is utilised in which the correlator compares the incoming (returning) signal with a duplicate of the test sequence to establish the position of the test sequence in the backscattered light. From establishment of the position of the returning test sequence, and the repeat pattern or interval, a summation of successive returning sequences is made.
  • the returning test sequences may be integrated over an extended period, possibly of several hours or even several days, and compared with an earlier integrated pattern for the same time period. In this way, modification to the pattern due to stress, degradation or splice loss, which in general exhibits a progressive rather than instantaneous failure, can be detected at an early stage before the fault is sufficient to interupt normal system data.
  • the invention also provides an optical fibre communications system comprising a transmission line, means for launching data signals into a first end of the transmission line, and a line monitoring arrangement as defined above.
  • a frame compiler control comprises the means for launching data signals into the first end of the transmission line, system data being fed to an input of the frame compiler control, and test pulse sequences being fed to another input of the frame compiler control.
  • the frame compiler control is such as to multiplex each test pulse sequence into respective frame in such a manner that the test pulse sequence is inserted into a slot provided in that frame for supervisory and maintenance signals.
  • This invention further provides a method of monitoring an optical fibre transmission line without disrupting data transmission, the method comprising the steps of generating a sequence of test pulses, repeatedly launching the sequence of test p ⁇ lses into a first end of the transmission line, receiving optical signals at the first end of the line, and extracting backscattered test pulse sequences from the received signals.
  • a duplex optical communications system incorporating a line monitoring arrangement constructed in accordance with the invention will now be described in detail, by way of example, with reference to the accompanying drawing, the single figure of which is a schematic representation of the system.
  • the line monitoring arrangement includes a test sequence generator 1 which provides test sequence pulses along a line 2 to an input of a frame compiler control 3.
  • the pulse width of the test pulses is limited to be the same as that of the system data - typically 50 nanoseconds for a 20 megabit data signal.
  • System data is also input to the frame compiler control 3 along with any other elements to be transmitted,
  • the frame compiler control 3 time multiplexes the components of each frame (typically of 10 milliseconds duration) in a predetermined order.
  • the bulk of each frame contains data, but also includes a slot for supervisory and maintenance signals. In the event that all the time slots are not filled, random data is inserted.
  • the test sequence of pulses can be inserted into that part of the frame allocated for maintenance signals.
  • the combined system data and test sequence is then input to an optical transmitter 4, and launched along a fibre link 5, via couplers 6 and 6 ! , to an optical receiver 7 at the far end.
  • System data in the return direction (which could include a different test sequence) is transmitted from an optical transmitter 8 at the far end of the fibre link 5.
  • This return data is launched onto the fibre link 5 via the coupler 6 1 .
  • signals from the optical transmitter 8 and the backscattered light from the signals outbound from the optical transmitter 4 travel towards the first end of the fibre link 5. This light passes through the coupler 6 to an optical receiver 9.
  • the light entering the optical receiver 9 includes relatively high power system data signals transmitted from the far end. Superimposed on these high intensity signals, with no particular synchronism, is the relatively low intensity backscattered light originating from the transmitter 4. The backscattered light produces a voltage ripple superimposed on the data signal voltage at the receiver 9. This ripple voltage is of small magnitude compared with the incoming data voltage levels. Thus, the comparator (which forms part of the receiver 9) effectively ignores the ripple voltage, and provides a digital output of the data signal. An analogue output of the receiver signal voltage (including the ripple voltage) is fed along a line 10 to a correlator 11.
  • the test sequence is also input to the correlator 11, where the start point of the test sequence in the received signal is determined by a rolling comparison.
  • a code for the test sequence such as a Barker or Golay code is used, such a code exhibiting a high correlation when exactly synchronised with itself, but exhibiting a low correlation when out of synchronism with itself or with random or system data.
  • the output ofthe correlator 11 is fed to one input of an integrator 12, a frame synchronism signal from the frame compiler control 3 being fed to another input of the integrator.
  • the integrator 12 uses the frame synchronism signal to superimpose the test sequences output from the correlator 11, the integrator 12 provides a summation of the backscattered test signals. Noise and system data from the transmitter 8 will tend to average out, leaving backscattered test sequence peaks that can be monitored for change.

Landscapes

  • Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optical Communication System (AREA)
  • Testing Of Optical Devices Or Fibers (AREA)

Abstract

Un dispositif de traitement de ligne pour un système de communications optique envoie une séquence d'impulsions d'essai d'une énergie comparable aux impulsions de données du système en une ligne de transmission de fibre optique sous tension (5) et de la lumière rétrodiffusée est contrôlée. La séquence d'essai est séparée des autres signaux par un processus de corrélation, la séquence d'essai étant codée avec un code Barker ou un code Golay. Des séquences d'impulsions rétrodiffusées séquentielles sont intégrées sur une période étendue, et contrôlées pour détecter tout changement.
EP19900912495 1989-08-18 1990-08-09 Systeme de communications optiques Withdrawn EP0486583A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8918862 1989-08-18
GB898918862A GB8918862D0 (en) 1989-08-18 1989-08-18 Line monitoring system

Publications (1)

Publication Number Publication Date
EP0486583A1 true EP0486583A1 (fr) 1992-05-27

Family

ID=10661821

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19900912495 Withdrawn EP0486583A1 (fr) 1989-08-18 1990-08-09 Systeme de communications optiques

Country Status (7)

Country Link
EP (1) EP0486583A1 (fr)
JP (1) JPH05500107A (fr)
AU (1) AU637629B2 (fr)
CA (1) CA2064789A1 (fr)
GB (1) GB8918862D0 (fr)
NZ (1) NZ234860A (fr)
WO (1) WO1991002959A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
ATE123568T1 (de) * 1990-02-15 1995-06-15 British Telecomm Optische testapparatur mit einem otdr.
DE69333369T2 (de) * 1992-05-01 2004-10-07 Sumitomo Electric Industries Verfahren zur Identifikation einer optischen Leitung
GB9524485D0 (en) * 1995-11-30 1996-01-31 Bicc Plc Device for interrogating an optical fibre network
GB2401738A (en) * 2003-05-16 2004-11-17 Radiodetection Ltd Optical fibre sensor
US9118412B2 (en) 2011-09-27 2015-08-25 Broadcom Corporation System and method for performing in-band reflection analysis in a passive optical network

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3340428A1 (de) * 1983-11-09 1985-05-23 Wandel & Goltermann Gmbh & Co, 7412 Eningen Verfahren und einrichtung zur ueberwachung eines optischen nachrichtenuebertragungssystems
GB8906937D0 (en) * 1989-03-28 1989-05-10 Plessey Telecomm Testing optical fibre links
GB9027716D0 (en) * 1990-12-20 1991-02-13 British Telecomm Optical communications system

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9102959A1 *

Also Published As

Publication number Publication date
NZ234860A (en) 1992-10-28
CA2064789A1 (fr) 1991-02-19
AU637629B2 (en) 1993-06-03
AU6182690A (en) 1991-04-03
JPH05500107A (ja) 1993-01-14
GB8918862D0 (en) 1989-09-27
WO1991002959A1 (fr) 1991-03-07

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