AU637629B2 - Creation of Inventions and Patents with Artificial Intelligence

AU637629B2 – Optical communications system
– Google Patents

AU637629B2 – Optical communications system
– Google Patents
Optical communications system

Info

Publication number
AU637629B2

AU637629B2
AU61826/90A
AU6182690A
AU637629B2
AU 637629 B2
AU637629 B2
AU 637629B2
AU 61826/90 A
AU61826/90 A
AU 61826/90A
AU 6182690 A
AU6182690 A
AU 6182690A
AU 637629 B2
AU637629 B2
AU 637629B2
Authority
AU
Australia
Prior art keywords
test
sequence
test pulse
pulses
transmission line
Prior art date
1989-08-18
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.)

Ceased

Application number
AU61826/90A
Other versions

AU6182690A
(en

Inventor
Dominik Drouet
Stephen Eric Gold
Simon Mark James
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.)
1989-08-18
Filing date
1990-08-09
Publication date
1993-06-03

1990-08-09
Application filed by British Telecommunications PLC
filed
Critical
British Telecommunications PLC

1991-04-03
Publication of AU6182690A
publication
Critical
patent/AU6182690A/en

1993-06-03
Application granted
granted
Critical

1993-06-03
Publication of AU637629B2
publication
Critical
patent/AU637629B2/en

2010-08-09
Anticipated expiration
legal-status
Critical

Status
Ceased
legal-status
Critical
Current

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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

Description

OPTICAL COMMUNICATIONS SYSTEM
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.
If an installed optical fibre is to be tested for an apparent or suspected fault, the way in which this is presently performed is by utilising an Optical Time Domain Reflectometer (OTDR). 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. Thus, for a given amplitude, “an increase in the pulse width enables a greater length of fibre to be monitored, that is to say it increases the dynamic range. Unfortunately, however, 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.
Thus, 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. However, because there is data transmission, 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. This results in having to use comparatively low energy pulses compared-to usual OTDR pulse energy, for example by limiting the pulse width of the test pulses to that compatible with the system data,

which may typically be at 20 megabits with a pulse width of 50ns. However, by using a sequence of test pulses rather than a single pulse, the energy of the test signal can be increased to compensate for this requirement to use low energy OTDR pulses.
In a preferred embodiment, the test pulse sequence is launched into the transmission line at the system data rate. Preferably, 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.
Advantageously, the 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. To extract the returning backscattered test sequence from the background, 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.
Since the intensity of the returning test sequence will be low, and it is not envisaged that a single test sequence will be utilised to locate a fault, 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.
Advantageously, 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. Preferably, 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 pμlses 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.
Referring to the drawing, 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 61. Thus, 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. Thus, the position of the test sequence in the returning backscattered signal can be located, and the test sequence separated from the backscattered 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. Using 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.

Claims (13)

1. 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.

2. An arrangement as claimed in claim 1, wherein the test pulse sequences are launched into the transmission line at the system data rate.

3. An arrangement as claimed in claim 1 or claim 2, wherein the test pulses each have a pulse width and height of the same order as the system data pulse width and height.

4. An arrangement as claimed in any one of claims 1 to 3, wherein each test pulse sequence is included in a respective time multiplexed transmission frame.

5. An arrangement as claimed in any one of claims 1 to 4, wherein the test pulse sequence is in a Barker or Golay code.

6. 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 claimed in any one of claims 1 to 5.

7. A system as claimed in claim 6, wherein a frame compiler control comprises the means for launching data signal 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.

8. A system as claimed in claim 7 when appendant to claim 4, wherein 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.

9. 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 pulses 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.

10. A method as claimed in claim 9, wherein backscattered test pulse sequences are extracted by a correlation and integration procedure.

11. A method as claimed in claim 9 or claim 10, wherein the width and height of each of the pulses in the test pulse sequence is comparable with the width and height of the data pulses being transmitted.

12. A method as claimed in any one of claims 9 to 11, wherein each test pulse sequence is- incorporated into a respective time multiplexed transmission frame.

13. A method’ as claimed in any one of claims 9 to 12, wherein the test pulse sequence is encoded in a Barker or Golay code.

AU61826/90A
1989-08-18
1990-08-09
Optical communications system

Ceased

AU637629B2
(en)

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 (2)

Publication Number
Publication Date

AU6182690A

AU6182690A
(en)

1991-04-03

AU637629B2
true

AU637629B2
(en)

1993-06-03

Family
ID=10661821
Family Applications (1)

Application Number
Title
Priority Date
Filing Date

AU61826/90A
Ceased

AU637629B2
(en)

1989-08-18
1990-08-09
Optical communications system

Country Status (7)

Country
Link

EP
(1)

EP0486583A1
(en)

JP
(1)

JPH05500107A
(en)

AU
(1)

AU637629B2
(en)

CA
(1)

CA2064789A1
(en)

GB
(1)

GB8918862D0
(en)

NZ
(1)

NZ234860A
(en)

WO
(1)

WO1991002959A1
(en)

Families Citing this family (5)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

AU636719B2
(en)

1990-02-15
1993-05-06
British Telecommunications Public Limited Company
Optical test apparatus

US5506674A
(en)

1992-05-01
1996-04-09
Sumitomo Electric Industries, Ltd.
Method for identifying an optical fiber using a pattern of reflected light

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

Citations (2)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

AU9096591A
(en)

1990-12-20
1992-07-22

British Telecommunications Public Limited Company

Optical communications system

AU627853B2
(en)

1989-03-28
1992-09-03

Gec Plessey Telecommunications Limited

Testing optical fibre links

Family Cites Families (1)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

DE3340428A1
(en)

1983-11-09
1985-05-23
Wandel & Goltermann Gmbh & Co, 7412 Eningen
Method and device for monitoring an optical data transmission system

1989

1989-08-18
GB
GB898918862A
patent/GB8918862D0/en
active
Pending

1990

1990-08-09
CA
CA 2064789
patent/CA2064789A1/en
not_active
Abandoned

1990-08-09
AU
AU61826/90A
patent/AU637629B2/en
not_active
Ceased

1990-08-09
EP
EP19900912495
patent/EP0486583A1/en
not_active
Withdrawn

1990-08-09
JP
JP51180590A
patent/JPH05500107A/en
active
Pending

1990-08-09
WO
PCT/GB1990/001250
patent/WO1991002959A1/en
not_active
Application Discontinuation

1990-08-10
NZ
NZ23486090A
patent/NZ234860A/en
unknown

Patent Citations (2)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

AU627853B2
(en)

1989-03-28
1992-09-03
Gec Plessey Telecommunications Limited
Testing optical fibre links

AU9096591A
(en)

1990-12-20
1992-07-22
British Telecommunications Public Limited Company
Optical communications system

Also Published As

Publication number
Publication date

WO1991002959A1
(en)

1991-03-07

CA2064789A1
(en)

1991-02-19

NZ234860A
(en)

1992-10-28

JPH05500107A
(en)

1993-01-14

AU6182690A
(en)

1991-04-03

GB8918862D0
(en)

1989-09-27

EP0486583A1
(en)

1992-05-27

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