AU651677B2

AU651677B2 - Remote monitoring of optical transmission line

Info

Publication number: AU651677B2
Application number: AU14019/92A
Authority: AU
Inventors: Jean-Paul Tache
Original assignee: Alcatel NV
Current assignee: Alcatel Lucent NV
Priority date: 1991-04-16
Filing date: 1992-04-03
Publication date: 1994-07-28
Anticipated expiration: 2012-04-03
Also published as: NZ242189A; EP0509434A3; EP0509434B1; ES2103850T3; FR2675650A1; DE69220836D1; DE69220836T2; EP0509434A2; AU1401992A; FR2675650B1

Description

P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990 C>~C CC cC f4~ I cC C CCC 0CC (CO fC C CC

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ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Invention Title: "REMOTE MONITORING OF OPTICAL TRANSMISSION LINE" The following statement is a full description of this invention, including the best mecthod of per-forming it known to us:- 2 This invention relates to installations designed for the transmission of signals over an optical link and for remote monitoring of the link.

In transmission installations using fibre optic links, electro-optical transmit/receive terminals are coupled to the individual optical fibres of the link which carry mutually useful signals. For remote monitoring of the optical link. a remote monitoring terminal is coupled to the transmit end of the optical fibres. It is used to detect, from this end, eventual faults such as breaks or other faults generating abnormal attenuation over the monitored optical fibre(s) to which is coupled a remote monitoring equipment, and to localise the faults detected.

Remote monitoring equipments as such are common knowledge. In particular, they use an optical reflcctometer periodically generating brief pulses which are set at o a defined wavelength and make-up the measuring signal injected in the monitored optical fibre, and detecting in response the feedback signals caused, in particular, by faults in the fibre; this reflectometer is associated with a computer used to localise faults in the fibre from the feedback signals received from the reflcctometer.

For remote monitoring of an optical link, together with the transmission of useful signals over the link, useful signals and measuring signals are emitted at different wavelengths and wavelength multiplexed to be injected at the transmit end of the relevant optical fibre.

o 20 A remote monitoring system for an optical transmission installation is known in o.0.n which the fibre optic link is of the point-to-point type between multiple terminals of two remote stations, or of the point-multipoint type between the terminal(s) of a Sa central station and the terminals of several other stations referred to as secondary.

Optical fibres are multimode or, preferably, single-mode when remote monitoring a relatively long link.

According to this known system, the remote monitoring system, with reflectometer and associated computer, is located in at least one of the two remote stations or in the central station, depending on the type of installation or link. It is coupled to the fibre transmit and in the relevant station via a duplexer also connecting each of these fibres to the transmitter of the terminal corresponding to this station.

One port of the duplexer is connected to the transmitter of the corresponding terminal, a second port is coupled with the remote monitoring system and a third port is connected to the transmit end of the fibre. Coupling of the remote monitoring system may occur sequentially on the second ports of the various duplexers or by a h- -i 3 serial transmission of the sole measuring signal from one of these fibres to another fibre via the duplexers whose second ports are connected in series to one another.

In particular, according to this known system, the optical link using single-mode fibres, useful signal transmission and remote monitoring occur on a Swavelength of 1310 Onm and 1550nm respectively. The first and second ports of each duplexer are tuned to these respective wavelengths. The third common 4 port has a broadband including both wavelengths.

In the resulting installation, useful signal transmission is therefore limited F 10 by remote monitoring which is performed on one of these wavelengths and therefore leaves only the other wavelength available to the useful signals.

The purpose of the present invention is to eliminate this drawback.

Its purpose is an installation for transmission over a remotely monitored optical link, whereby the link uses single-mode optical fibres coupling a central station transmitting/receiving the useful signals to the subscribers' terminating 0 equipment; the said station being fitted firstly with some electro-optical means of transmitting/receiving the said useful signals on a first, defined transmit 4 00 ;o wavelength, a remote monitoring unit with optical reflectometer generating a o, signal, referred to as a measuring signal, on a measuring wavelength different 0 from the first transmit wavelength, and some coupling means having, on the S one hand, some wavelength-selective ports individually coupled to the said first transmit/receive means and to the said reflectometer, and on the other hand, a common broadband port including at least the said first transmit wavelength and the said measuring wavelength, characterised in that the said reflectometer is a reflectometer tuned to the measuring wavelength selected with a nominal value substantially equal to 1480nm, and in that, the said first transmit/receive means have the first said wavelength tuned indifferently to one of the two nominal values substantially equal to 1310Onm and 1550nm.

*o0 Preferably, the said central station includes, in addition to the said first o electro-optical transmit/receive means, some second electro-optical means of transmitting/receiving the said useful signals on a second transmit wavelength, te said ,rt wavelength and the said second transmit wavelength having

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4 nominal values of 1310nm and 1550nm respectively, and in that the said coupling means have three selective ports AV 1 AS) for the said first and second transmit wavelengths and the said measuring wavelength, individually coupled to the said first and second electro/optical means of j 5 transmitting/receiving the useful signals, and to the reflectometer.

the measuring signal transmitting power is in the order of the said first and second electro-optical means of transmitting/receiving the useful signals consist of a telephone exchange and at least a first associated electro-optical component modulated by the information signals of the said exchange to be transmitted over the said link, and by a video network and at least a second associated electro-optical component modulated by the data signals of the said network to be transmitted over the said link.

The characteristics and advantages of the present invention are highlighted in the following description of an example of implementation illustrated in the single figure attached.

o This single figure is a diagrammatical representation of a transmission o installation with remote monitoring of the fibre optic link.

In this installation we have shown only one optical fibre used for the o0,o transmission useful signals from a central transmitting/receiving station to a 0 j 2X'

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Y subscriber's terminating equipment Optical fibre is a single mode fibre. It is useful for unilateral transmission, in which case it is associated with another similar fibre for transmission in the reverse direction in order to form a transmit pair in the optical link; or it is used for bilateral signal transmission with a protocol for transmission of the useful signals between the central station and the j subscriber's terminating equipment.

Other similar fibres or fibre pairs service other subscribers' terminating equipment from this central station. The resulting optical link may be of the *o°o known point-to-point or point-multipoint type and is implemented via a 3i" o sub-distributor.

Central station groups a telephone exchange and a video signal distribution network For a given point-to-point link with n-fibres or fibre

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a pairs between the central station and n-subscriber terminating equipment similar to terminating equipment the telephone exchange has n-ports for these n-fibres or fibre pairs, items T 1 to and the video network has n-ports for these n-fibres or fibre pairs, items V, to V n In central station a first laser is connected to port (T 1 of the telephone exchange in order to be modulated by the information signal from the exchange, at the bit rate of the narrow band used for the information signal from the exchange. A second laser is connected to port (Vj of video network in order to be modulated by the broadband data coming from the network, at the bit rate of this data. Other lasers, identical to the first laser (6) are connected to other ports to T, of exchange and similarly, other lasers identical to the second laser are connected to other ports (V 2 to V n of the network, for transmission of useful signals over the other fibres identical to fibre The first laser is selected to have a nominal wavelength of 1310nm, while the second laser has a nominal wavelength of 1550nm, for S° transmitting the useful signals issued from the exchange and the network at o each of these values respectively.

A remote monitoring unit also in the central station performs remote monitoring of fibre and other fibres transmitting the useful signals from the central station This remote monitoring unit includes a reflectometer a computer (12) coupled via bus (13) to the reflectometer, and an alarm (14) connected to the computer in order to be triggered when a fault occurs in either one of the fibres such as An electronic switch (15) is coupled to the monitoring input/output port, item S, of reflectometer in order to transmit the measuring signal and receive the response signal sequentially over fibre and the other fibres used to transmit the useful signals from the central station. This switch has n-ports for these n-fibres, items A, to A. It is controlled in synchronism with the reflectometer by a signal delivered by the computer onto bus (13).

This reflectometer (11) has an internal laser of nominal wavelength of 1480 nm, which is already common knowledge, and used in particular for

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6 i ptical amplifier pumping, components which are passive at this wavelength, such as multiplexers or optical isolators, and necessary to build the reflectometer and the transmission installation in accordance with the present invention are readily available on the market.

In this central station a multiplexer (20) connects the first laser the second laser and sequentially the reflectometer (10) to fibre for wavelength rnultipl6xing of the useful signals issued from the exchange (4) and/or the video network and of the reflectometer measuring signals and their transmission over fibre This multiplexer (20) has three selective ports (AT, AV, and As individually tuned to wavelengths 1310nm, 1550nm and 1480nm, and connected as follows: the first (AT, to the first laser the second (AV, to the second laser and the third (As) is sequentially connected to the reflectometer (11) via port of the electronic switch It has a fourth common broadband port, item C, substantially centred on the 1480nm intermediate wavelength assigned to the reflectometer and includes the two 1310nm and 1550nm wavelengths assigned to the useful signals. This 44o common port is connected to fibre transmit input, for the central station.

Other multiplexers, identical to multiplexer are connected in the same way to other transmit fibres, for transmission of the useful signals at the 0 o two abovementioned wavelengths assigned to the useful signals, and for remote monitoring of measuring signals at the third intermediate wavelength assigned to the reflectometer, Multiplexer shown with three selective ports individually tuned to the three abovementioned wavelengths, may of course be replaced by two duplexers mounted in cascade. The first of these two duplexers has, for instance, two selective ports for useful signals at 1550nm and measuring signals at 1480nm, and one common broadband port centred on 1480nm and including the 1550nm wavelength, but not the 1310nm wavelength, The second of these two duplexers has one of its selective ports connected to the common port of the first duplexer and the other tuned on the other 1310nm wavelength of the useful signals, its common port has a broadband including these three wavelengths.

o *v ^y 7 Furthermore, some sensors are installed at possible fault locations in the link, in particular at splicing locations; these sensors, such as sensor shown on fibre can detect the environmental conditions prevailing at the splicing locations, ie. humidity or other. The sensor illustrated detects whether humidity or faults of another origin have occurred in the splice. In response to this detection, it generates a small fault in fibre which does not hamper the transmission of useful signals but which can be detected by the remote monitoring system for automatic monitoring of the ageing condition of the link.

Since optical link remote monitoring occurs on the 1480 nm wavelength, the 1550nm and 1310nm wavelengths remain available for useful signal transmission. The advantage of a 1480nm reflectometer laser is that measuring signal transmission can occur at high power, in the order of 70mW, since this signal does not reqire a very wide pass band for a distance between two faulty points to be differentiated, in the order of or greater than 500m. This useful signal transmitting power improves the measuring dynamics for remote monitoring of the link.

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Claims

1. An installation for transmission over a remotely monitored optical link, whereby the link uses single-mode optical fibres coupling a central station transmitting/receiving the useful signals to the subscribers' terminating S 5 equipment; said station being fitted firstly with electro-optical means of transmitting/receiving said useful signals on a first, defined transmit wavelength, a remote monitoring unit with optical reflectometer generating a signal on a measuring wavelength different from the first transmit wavelength, and coupling means having, on the one hand, wavelength-selective ports ti S10 individually coupled to said first transmit/receive means and to the said I reflectometer, and on the other hand, a common broadband port including at least the said first transmit wavelength and said measuring wavelength, wherein said reflectometer is a reflectometer tuned to the measuring wavelength i selected with a nominal value substantially equal to 1480nm, and wherein said first transmit/receive means have the first said wavelength tuned indifferently to one of the two nominal values substantially equal to 1310nm and 1550nm.

2, An installation as claimed in claim 1, wherein said central station includes, in addition to the said first electro-optical transmit/receive means, second electro-optical means of transmitting/receiving the said useful signals on a second transmit wavelength, said first wavelength and said second transmit wavelength having nominal values of 1310nm and 1550nm respectively, and wherein said coupling means have three selective ports for the said first and second transmit wavelengths and the said measuring wavelength, individually coupled to the said first and second electro/optical means of transmitting/receiving the useful signals, and to the said reflectometer.

3. An installation as claimed in claim 1, wherein said first and second electro-optical means of transmitting/receiving the useful signals comprise a S telephone exchange and at least a first associated electro-optical component modulated by the information signals of the said exchange to be transmitted i over the said link, and by a video network and at least a second associated electro-optical component modulated by the data signals of the said network to be transmitted over the said link, 9

4. An installation as claimed in any one of claims 1 to 3, wherein said reflectometer has a laser for transmission of said measuring signal with a transmitting power in the order of An installation as claimed in claim 4, wherein said link is also fitted, at each splicing location within the link, with a sensor detecting the environmental conditions and generating, in response to the condition detected, a small fault in the said link which does not hamper the transmission of useful signals but which can be detected by the said remote monitoring system for automatic monitoring of the link condition, 6, An installation substantially as herein described with reference to the figure of the drawing, DATED THIS TWELVTH DAY OF APRIL 1994 ALCATEL NVY. 4 4a '4o 41(0 44*4OP 4l 5,4p ABSTRACT An installation for transmission over a remotely monitored optical link coupling a central station transmitting/receiving useful signals to subscribers' terminating equipment. The installation includes a remote monitoring system with a reflectometer tuned to a wavelength different from the wavelength used to transmit the useful signals over the single mode optical fibres of the link. According to the invention the reflectometer (20) is tuned to a wavelength se- lected at 1480nm and leaves either or both of the 1310 nm and 1550nm wavelengths available for transmission of the useful signals by first and/or second transmit/receive means (4,6 5,7) of the central station coupled with the reflectometer of the link S g Single figure.