WO2025158195A1

WO2025158195A1 - Terrestrial optical communication network

Info

Publication number: WO2025158195A1
Application number: PCT/IB2024/061321
Authority: WO
Inventors: Herve Fevrier
Original assignee: Landelles Consulting LLC
Current assignee: Landelles Consulting LLC
Priority date: 2024-01-26
Filing date: 2024-11-14
Publication date: 2025-07-31
Anticipated expiration: 2026-07-26
Also published as: FR3158807A1

Abstract

The invention relates to a repeater (R) for a long-haul optical communication network. The repeater (R) comprises a container (C) containing an optical amplifier unit (AU), a power and control unit (PU) associated to the optical amplifier unit (AU). The repeater (R) also comprises a thermoelectric module (TM) thermally associated with the container (C) and operated to maintain an operating temperature inside the container (C) to a target temperature. The invention also relates to a long-haul optical communication network (1) extending from a first terminal station (A) to a second terminal station (B), the optical network (1) comprising a repeater (R) electrically coupled to an electrical cable (EC) and being respectively optically coupled to a first optical cable (OC1) and to a second optical cable (OC2).

Description

Terrestrial optical communication network

FIELD OF INVENTION

This invention relates generally to the field of long-haul optical communication networks (backbone networks).

TECHNOLOGICAL BACKGROUND TO THE INVENTION

Long-haul optical communication networks refer to optical communication networks that extend between two terminal stations which may be hundreds or thousands of kilometers apart. In such networks, optical signals are propagating along the optical fibers of an optical cable extending between the two terminal stations. Optical fiber losses, nonlinearity effects, optical amplification noise are degrading the signal quality and are the cause of the network reach limit. To compensate for these effects, in-line optical amplification sites (ILA sites) are inserted periodically along the network to keep the transmission quality with minimum degradation. ILA sites are generally small buildings, either existing or purpose-built, with electric power coming from different possible sources. Inside the ILA, one will find the telecom equipments which provide optical amplifier units that amplify the optical signals propagating along the optical fibers, usually by direct optical amplification (i.e. without conversion into electrical signals). Such amplifier units require to be electrically powered and their characteristics, performance and reliability are strongly dependent on temperature.

Submarine long-haul networks, such as the one described in US2020403699A1, usually have a straightforward topology, comprising of a primary section connecting two terminal stations (located at landing sites) and a few branches extending from the main section, called the trunk, to reach additional landing sites. The submarine cables composing the main section and branches of a submarine network are combining, in a polymer cladding ensuring electrical insulation, optical fibers in an inner tube forming the core of the cable and a copper sheet forming an outer tube, constituting the electrical power conductor of the cable. A steel wire strand is disposed in between the inner and outer tube to get the cable strong, to enable the laying and possibly recovering operation in waters (as deep as 8000 meters), and to protect the inner tube from the hydrostatic pressure due to the water depth.

For obvious reasons of accessibility and reliability, submarine ILAs (usually named submarine repeaters) are designed to be as simple as possible, including very few features beyond the bare minimum of optical amplification. In particular, there is no possibility to change the amplification gain of the optical amplifier units, and the optical transmission system is always operating with equal spans in terms of optical loss, whatever the effective distances are between the repeaters. The stability of the temperature at the bottom of the sea (temperature is typically 5°C) ensures the stability of the optical characteristics of the optical amplifiers, the stability of the operation, performance of the optical transmission system and reliability of the optical amplifier units.

Typical power consumption of a submarine ILA part of a 16 fiber-pair system is relatively low, about 100W. Power Feed Equipements (PFE) disposed at each terminal station deliver the electric power, through the submarine cable, to the submarine ILAs. Such electric power (typically with a line current of 0.5-1.5A with voltages up to 15-18kV at the PFE level) is consumed by the submarine ILAs and dissipated into the submarine cable itself, due to its electrical resistance (typically 1 ohm/km).

In contrast, terrestrial networks usually have a mesh topology to serve the maximum possible population, often in the heart of cities, and to allow for path redundancy for network availability. These networks are meshed, resulting in nodes with a high degree of connectivity, which can make the equipment operating the nodes quite complex. The intermediate sites (ILAs, branching nodes) are sheltered in buildings primarily powered by the electrical grid, usually with a redundant power supply (battery, solar power or diesel generator) in order to protect the network. The buildings are equipped with air conditioning systems to provide the required controlled environment necessary to the equipment proper operations. Consequently, typical power consumption of a terrestrial ILA for 16 fiber-pair network is relatively important, about 10 kW. A disclosure of a terrestrial network is for instance described in US20120237215A1.

The underwater environment is an ideal location for long-haul optical communication networks due to its secure and temperature-stable nature. There is no need for temperature regulation or complex control of the optical amplifier units, leading to reduced energy consumption of the link. This makes maintenance operations more complicated, but the benefits of the underwater environment outweigh the challenges.

OBJECT OF THE INVENTION

The demand for transmission capacity is continuously increasing. However, there are limitations to laying cables on the seabed, both technically and geopolitically. Moreover, with such capacity carried by these cables there is a need for geographic diversity of the cable routes. Congestion of certain submarine passages and straits, such as in the Red Sea, due to the presence of numerous cables, pipelines, and other devices, is a technical limitation. Geopolitically, it is important to consider alternative communication routes that offer similar benefits to undersea communications. The present invention aims at providing a repeater and a long-haul optical communication network employing this repeater that address this problem and allows to create new terrestrial routes with the benefits of submarine cable routes.

BRIEF DESCRIPTION OF THE INVENTION

In order to achieve this aim, the object of the invention proposes a terrestrial optical communication network extending from a first terminal station to a second terminal station, the optical network comprising:

an optical link extending from the first terminal station to a second terminal station and comprising at least a first optical span made of, at least, a first optical cable and a second optical span made of, at least, a second optical cable ;
a first electrical link, comprising a plurality of electrical cables, connecting the first terminal station and the second terminal station, the electrical cables being distinct from the first optical cable and the second optical cable;

the terrestrial optical communication network further comprising at least a repeater formed of:

a container presenting:
1. a first optical port and a second optical port for respectively coupling the repeater to optical fibers of the first optical cable and to optical fibers of the second optical cable, the optical fibers propagating optical signals;
2. two electrical ports for coupling the repeater to the conductors of two distinct electrical cables transporting electrical power;
an optical amplifier unit disposed in the container between the first optical port and the second optical port to amplify the optical signals, the optical amplifier unit comprising at least one doped fiber amplifier;
a power and control unit associated to the optical amplifier unit and disposed in the container, the power and control unit being electrically powered by the electrical power supplied by the electrical cables ;
a thermoelectric module, thermally associated with the container and electrically powered by the electrical power supplied by the electrical cables, the thermoelectric module being operated to maintain an operating temperature inside the container to a target temperature.

According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination:

the thermoelectric module is disposed outside of the container, in thermal contact with a wall of the container;
the first optical cable and the second optical cable each comprises a plurality of optical fibers pairs, the optical fibers of an optical fiber pair propagating optical signals of opposite directions;
the optical fibers of one optical fiber pair of the first optical cable are respectively optically connected to the optical fibers of one optical fiber pair of the second optical cable via unidirectional optical amplifiers of the optical amplifier unit;
the unidirectional optical amplifiers each comprise an input and an output and the optical amplification unit comprises an optical feedback path between the outputs of the unidirectional optical amplifiers respectively connecting the fibers of the optical fiber pairs of the first optical cable and of the second optical cable;
the unidirectional optical amplifiers present a fixed amplification gain;
the terrestrial optical communication network comprises further optical spans and further repeaters electrically coupled to the electrical cable and optically coupled to two optical spans to serially extend the terrestrial optical communication network from the first terminal station to the second terminal station;
each optical span presents an optical attenuation loss, the optical attenuation losses differing by a maximum of 1dB from one optical span to any other optical span, and preferably by a maximum of 0,5 dB ;
the at least a first optical cable, the at least a second optical cable and the electrical cable are laid in trenches and wherein the repeater is disposed in a repeater manhole;
the first optical span is made of a plurality of first optical cables optically and serially connected by splicing boxes and/or the second optical span is made of a plurality of second optical cables optically serially connected by splicing boxes;
the first terminal station and the second terminal station comprises respective power feed equipment providing the electrical power to the electrical cable;
the terrestrial optical communications network comprises at least one second electrical link connecting the first terminal station and the second terminal station;
the first electrical link provides electrical power to some of the repeaters of the terrestrial optical communications network and the second electrical link provides electrical power to the other repeaters of the terrestrial optical communications network;
each repeater is associated with two electrical switches enabling it to be selectively connected, upstream and downstream, to the first electrical link or to the second electrical link, which then forms a backup electrical link;
each repeater is associated with two electrical switches and with a distribution board coupled to the first electrical link and to the second electrical link, the distribution board enabling the repeater to be selectively connected, upstream and downstream, to the first electrical link or to the second electrical link;
the first terminal station and the second terminal station are separated by at least 500 km;
the optical link and the electrical link are extending in parallel of a secured infrastructure such as a pipeline route, railway or a high-voltage electric line;
the power and control unit comprises a telecommunications unit.

BRIEF DESCRIPTION OF FIGURES

Further features and advantages of the invention will be apparent from the detailed description of the invention which follows with reference to the appended figures on which :

illustrates a terrestrial optical communication network according to the invention;

illustrates a repeater manhole comprising a repeater according to the invention;

illustrates a terrestrial optical communication network according to an embodiment in which the network is provided with a second electrical link ;

illustrates a repeater connected to a backup electrical link;

illustrates a repeater according to an embodiment with two electrical links of a terrestrial optical communication network.

DETAILED DESCRIPTION OF THE INVENTION

represents a terrestrial optical communication network 1 extending on land from a first terminal station A to a second terminal station B. The two terminal stations A,B may be hundreds or thousands of kilometers apart, for instance more than 3000 km or even more than 5000 km apart. Advantageously, to take the full benefits of a network according to the invention, the first terminal station A and the second terminal station B are separated by at least 500 km.

In order to transmit information between the two terminal stations A,B, the optical network 1 comprises an optical link 1a and an electrical link 1b, the optical and electrical links 1a,1b respectively extending between the two terminal stations A, B. The optical link and the electrical link are separate, i.e. they consist of separate optical and electrical cables.

An optical cable OC of the optical link 1a consists of at least one pair of optical fibers, and typically of a plurality of pairs of optical fibers, for example between 16 and 48 pairs of optical fibers, arranged in a protective sheath. Each pair of the optical cable OC forms an optical channel ensuring duplex communication, i.e. the optical fibers of an optical fiber pair are propagating optical signals along opposite directions. An optical cable OC may present a length (the distance between two optical connection locations) of a few kilometers, for instance about 5 km. The optical link 1a is therefore made of a plurality of optical cables, interconnected in a daisy chain fashion at successive optical connection locations (splice boxes SB and repeaters R as this will be described in a further passage of this description) to extend the optical link 1a between the first and second terminal stations A,B.

An electrical cable EC used to form the electrical link 1b is made of a conductor arranged in its own protective sheath. Electrical cables EC forming the electrical link are also interconnected in a daisy chain fashion, at electrical connection locations, to constitute the electrical link 1b of the network 1.

The electrical cables forming the electrical link 1 may be paired with optical cables of the same length, such that optical and electrical connection are performed at the same locations SB,R along the network 1. It is also possible to have electrical connection once every two optical connections for example, but it is usually preferable not to create location dedicated to electrical connection alone, to keep the simplicity of the proposed solution. Electrical connection locations are therefore preferably co-located with one optical connection location.

The first terminal station A and the second terminal station B comprises optical interface cards A1,B1, connected to respective telecommunication networks, to send and receive optical signals carried by the pairs of optical fibers forming the optical link 1a.

The first terminal station A and the second terminal station B comprise respective power feed equipment A2,B2 connected to the conductor of the electrical cables EC for providing the electrical power to the elements composing the optical network 1, as this will be described in further passage of this description. The power feed equipment A2,B2 may be connected to the electrical grid and may be delivering a current comprised between 0.5 A to 1.5 A to the electrical link 1b under a voltage difference between each terminal station A,B of at least 6 kV. More generally, the power feed equipment A2,B2 should be dimensioned to supply the expected power to each element of the optical network 1, taking into account the power dissipated into the electrical cable conductor, due to its electrical resistance.

Referring back to , the optical link 1a is made up of a plurality of optical spans OS of substantially equal optical attenuation loss. The optical attenuation losses may differ by a maximum of 1dB from one optical span OS to any other optical span OS of the optical link 1a, and preferably by a maximum of 0,5 dB. For avoidance of doubt, the span loss is the difference between the output of one optical amplifier and the input of a following optical amplifier.

As this is well known to the skilled person, such loss refers to the loss of optical signals that propagates between an optical span input and an optical span output. Losses in an optical span OS may be originating by intrinsic material absorption in the optical fibers, intrinsic loss, scattering, bending, splice losses, connection losses, … Two contiguous optical spans OS are separated by a repeater R to amplify the optical signals. Since the optical attenuation loss is substantially constant from one optical span OS to the other, the repeaters R may present identical and fixed amplification gains.

In order to limit the number of repeaters R along the network 1, it is generally sought to maximize the length of the optical spans OS. They can have a length of between 50 km and 100 km so that the optical signal propagating in the optical fibers of the optical link 1a is not excessively attenuated and may be amplified by the repeater R. For example, the optical attenuation loss over an optical span OS may be of the order of 10 dB or 12 dB.

Each optical span OS comprises at least one optical cable OC and is generally made up of a plurality of optical cables OC connected optically and serially by splice boxes SB.

To achieve substantially equal optical attenuation loss for each optical span OS of the optical link 1a and between the different optical channels of the optical link 1a, the lengths of the optical spans OS are selected to be similar. They may for instance differs by a maximum length difference of 20% for reasons such as geographic issues to lay the repeaters R at a given place or introduction in the network 1 of other network elements such as branching units. They generally comprise an identical number of optical cables OC and an identical number of splice boxes SB.

In addition, attenuation may be introduced in an optical span of shorter length (and hence of smaller optical attenuation loss) or more generally to optical span exhibiting reduced optical attenuation loss such that, overall, the optical spans OS composing the optical link 1a exhibits substantially equal optical attenuation loss. Such attenuation may be introduced at the repeater R, for instance by introducing a dedicated optical attenuator or by controlling the attenuation produced at the splicing of two optical cables, and for instance at the splicing of an optical cable and a repeater optical port. Such techniques are well known to the skilled person and described for instance in US4557557 or in the article from Yaguang Yang, "Attenuation splice control in the manufacture of fiber optical communication system," in IEEE Transactions on Control Systems Technology, vol. 14, no. 1, pp. 170-175, Jan. 2006, doi: 10.1109/TCST.2005.860512.

Advantageously, to ensure its protection and security, the terrestrial optical communication network 1 is buried. The optical cables OC and electrical cable EC forming the optical link 1a and electrical link 1b are disposed in trenches formed in the ground, for instance using conventional “cut and cover” technique. In difficult areas of the network 1, horizontal directional drilling techniques may be preferred. Also, to protect the optical and electrical cables and to give some flexibility to the network 1, the cables may be located in conduits like ducts and/or micro-ducts. Splicing boxes SB may be disposed in respective splicing manholes and repeater R disposed in respective repeater manholes into which the trenches open. Entrenching the cables, and notably the optical cable OC, help in maintaining the constant optical attenuation loss of each optical span OS.

The splicing manholes and repeater manholes may comprise other elements than the splicing boxes SB and repeater, such as slacks for receiving a buffer length of cables which will prove useful in case of repairs. They should be large enough to allow human intervention for installation and maintenance.

Preferably, to avoid locations with intense human activity, the optical link 1a and the electrical link 1b are disposed in a trench extending in parallel of a secured infrastructure with large rights of way such as a pipeline, a railway, or a high-voltage electric line.

represents, for illustration purpose a repeater manhole 2, disposed below ground level GL. A repeater R is disposed inside the repeater manhole 2. The repeater R comprises a container C presenting a first optical port and a second optical port for respectively coupling the repeater R to optical fibers of a first optical cable OC1 and to optical fibers of a second optical cable OC2. The first optical cable OC1 is the extremity cable of a first optical span and the second optical cable OC2 is the extremity cable of a second optical span, distinct from the first one, the two optical spans meeting at the repeater manhole 2.

The container also comprises at least two electrical ports for respectively connecting the repeater R to the conductors of two distinct electrical cables extending in trenches along the first and second optical cables OC1,OC2. An electrical port may comprise a ground connection for electrically contacting an earthing electrode ER, such as a conductive rod driven into the repeater manhole bottom. The conductive rod may present a terminal plate, as represented on . The ground connection provides a reference voltage and return path for the circuits composing the repeater R.

The container C is hermetically sealed and defines a controlled environment that houses an optical amplifier unit AU. The optical amplifier unit AU is optically disposed between the first optical port and the second optical port, connected to the optical fibers of the first optical cable OC1 and to the optical fibers of the second optical cable OC2. The container also houses a power and control unit PU, with corresponding electronics, associated to the optical amplifier unit AU, the power and control unit PU being electrically connected and powered by the electrical power supplied by the electric cable EC through the at least one electrical port.

The optical amplifier unit AU may be provided, at its input and output, with two sets of pigtail fibers. The two sets of pigtail fibers are disposed within hermetic passages of the container C to form the first and second optical port of the container for respectively coupling the repeater R to the optical fibers of the first optical cable OC1 and to the optical fibers of the second optical cable OC2.

The optical amplifier unit AU employs any technique able to amplify the optical signals propagating in the optical fibers of the first and second optical cables OC1,OC2, without the need to first convert them into electrical signals. Preferably, the optical amplifier unit comprises doped fiber amplifiers, such as erbium-doped fiber combined with a pump laser or more generally with means to provide optical pump energy to the amplifier. These amplifiers A are unidirectional. To provide bidirectionality of the optical link 1a, the optical fibers of one optical fiber pair P1 of the first optical cable OC1 are respectively optically connected to the optical fibers of one optical fiber pair P2 of the second optical cable OC2, via respective unidirectional optical amplifiers A of the optical amplifier unit AU.

The power and control unit PU comprises power circuit allowing converting the power provided by the electrical cable EC to the power required to operate the optical amplifier unit AU. It also comprises electronic circuits providing the electric signals that enable to control the optical amplifier unit AU. As this will be detailed later, the power and control unit PU may in some cases comprise, or be associated with, a supervision unit and/or a telecommunication unit.

The repeater R is designed to be as simple as possible. It is configured to operate at a fixed and predetermined amplification gain and, apart from its initial calibration, is deprived of any means for adjusting during its operation this gain and the settings of the optical amplifier. This is possible because the optical attenuation losses of the optical spans OS composing the optical link 1a of the network 1 are all the same. Hence, there is no need to adjust individually the amplification gain of a repeater R to the specific optical attenuation losses of an optical span OS.

The power and control unit PU is also preferably deprived of any active supervision function, which are preferably located at the first and/or at the second terminal station A,B, although it may include such active supervision function in some embodiments.

To allow this remote supervision, for instance by coherent and/or correlation Optical Time Reflectometry (ODTR), the optical amplification unit comprises an optical feedback path between the outputs of the optical amplifiers respectively connecting the fibers of the optical fiber pairs of the first and second cable OC1,OC2.

In some cases, active supervision and/or telecommunication functions may be integrated into the power and control unit PU. To this end, the power and control unit PU may comprise, or be associated with, a supervision unit and/or a telecommunications unit.

Communication between a repeater R and one and/or the other of the terminal stations A, B implemented by the telecommunications equipment can be carried out using part of the transmission spectrum of at least one of the pairs of optical fibers of the optical cables forming the optical link 1a. This may involve the use of a dedicated monitoring wavelength, for example on one side of the useful optical spectrum dedicated to signal transmission, or low frequency overmodulation of part of this useful optical spectrum.

Alternatively, a separate telecommunications network may be used, such as a GSM network or a low power wide area network of the LPWAN type.

Irrespective of the telecommunications means used to enable the repeaters R of the network 1 to communicate with at least one of the terminal stations A, B, it is possible to return data collected by sensors present on the repeater R, for example the temperature prevailing in the container C and/or in the manhole containing this container C, the voltage present at the electrical cable supplying the power and control unit PU. Similarly, at least one of the terminal stations A, B can communicate with the telecommunication unit of a repeater R, for example in order to configure its connection to one of the end electrical cables of a plurality of electrical links, as will be explained in a subsequent section of this description.

The amplification characteristics, and notably the gain, of the optical amplification unit AU may be sensible to the temperature because of the amplification properties variation of the doped fiber but also because of the pump power variation affected by the efficiency of the amplifier pump laser. To maintain constant amplification characteristics and proper functioning of the network, it is therefore important to maintain an operating temperature in the container C to a target temperature, despite temperature variation of the environment (for instance day and night temperature variation) and despite temperature variation provoked by the power dissipated by the optical amplification unit AU and power and control unit PU. For instance, the target temperature may be comprised between 10°C and 30°C and the operating temperature in the container C may be controlled to be lying at all times in a range of +/- 2°C from the target temperature. By controlling the temperature in the container, the temperature of both the amplifier pump laser(s) and of the doped fiber(s) are kept under controlled and the amplification characteristics (in particular the amplification gain) may be maintained in acceptable ranges.

For this purpose, a repeater according to the invention also comprises a thermoelectric module TM, thermally associated with the container C and electrically powered by the electrical power supplied by the electrical link, for instance through the power and control unit PU to which it is connected. The thermoelectric module is operated to maintain an operating temperature of the container to the target temperature. The thermoelectric module may exploit any effect, such as the Peltier effect.

The thermoelectric module TM is made of two thermally conductive, but electrically insulating, opposing plates separated by p-type and n-type semiconductor studs, the semiconductor studs extending from one plate to the other. The semiconductor studs are connected together to form a multitude of pn junctions electrically arranged in series. When a current is circulated through the pn junctions heat is moved electronically in the direction of the current from one plate to the other.

Preferably the thermoelectric module TM is disposed outside of the container C, one plate being disposed in contact with the container C, for instance in contact with a wall of the container C. But the thermoelectric module may also be disposed inside the container C, in contact with one of the container walls. At least the wall of the container in contact with the thermoelectric module TM is preferably made of a thermally conductive material, to facilitate heat transport. As mentioned above, the thermoelectric module is operated to maintain an operating temperature inside the container C to the target temperature.

The thermoelectric module TM can be powered and operated by the power and control unit PU. Alternatively, the thermoelectric module TM can operate autonomously. In this case, the thermoelectric module TM is connected to the electrical link and is equipped with a control circuit and a temperature sensor. The container is equipped with a temperature sensor connected to the power and control unit PU and/or to the thermoelectric module TM.

represents a particular embodiment of the invention that differs from the one presented in the preceding sections in that the terrestrial optical communication network 1 comprises a second electrical link 1b' arranged between the two terminal stations A, B.

This second electrical link 1b' is independent of the electrical link 1b (referred to in the remainder of this description as the “first electrical link” 1b). To this end, the two terminal stations are provided with respective second electrical supply equipment A2’, B2’ connected to the conductor of the electrical cables constituting the second electrical link 1b'.

The second electrical link 1b' consists of electrical cables similar to, but distinct from, the electrical cables of the first link 1b. In the embodiment shown in , the electrical cables of the first electrical link 1b supply certain repeaters R1 of the terrestrial optical communication network 1, while the electrical cables forming the second electrical link 1b’ supply the other repeaters R2 of the optical communication network 1.

As shown in , the two electrical links 1b, 1b’ can be used to supply power to the repeaters R1, R2 in an interleaved manner: the first electrical link supplying power to one of two successive repeaters R1, R2 of the communication network, the second electrical link 1b’ supplying power to the other of the two repeaters R1, R2. Of course, any other configuration enabling the repeaters R1, R2 of the communication network to be supplied electrically by the two electrical links 1b, 1b' is possible.

This particular embodiment is advantageous in that it enables the terminal stations A,B to be provided with power supply equipment A2,A2’,B2,B2’ having reasonable electrical characteristics (voltage and current delivered), even when the communications network is deployed over a very long distance.

For example, a long-distance terrestrial optical communications network is 4000 km long and comprises an optical link 1a made up of optical cables comprising 48 pairs of fibers. The electrical power required to provide the optical, electrical and thermal stabilization functions of a repeater is 300W. This is based on an optical span of 80 km (resulting in 49 repeaters in the network), a current of 1A and an electrical cable resistivity of 1 ohm/km. The voltage drop of the cable for an optical span is 80V and the voltage drop of the repeater R is 300V.

For a communications network with a single electrical link, the power supply equipment A2,B2 located in the terminal stations A,B must therefore be capable of supplying 18.7 kV, which may exceed a typical voltage available at such stations (typically of the order of 15 kV to 18 kV).

In a communications network equipped with a double electrical link each supplying around 25 repeaters, the A2,B2,A2’,B2’ power supply equipment located in the terminal stations must be capable of supplying 11.5 kV to each electrical link, which is much more acceptable.

To generalize this embodiment, a terrestrial optical communication network 1 in accordance with the invention can thus present a plurality of electrical links, independent of each other’s. These electrical links are made up of separate cables and are respectively connected to some of the repeaters R of the network 1 in order to collectively supply them all electrically.

If an electrical cable EC running along an optical span OS is cut or damaged, the power supply equipment A2, B2 located at each end of the link, at the terminal stations A, B, can adapt their voltage to supply the part of the link extending up to the affected span.

This possible mode of operation is intended to be transitory, as it allows only one power cut to be dealt with. After the second power cut, the system is out of service. To repair a cut or damaged electrical cable, the electrical link must be de-energized, which means that the traffic must first be rerouted to another part of the network or to another network.

To overcome this difficulty, and according to another embodiment, a backup electrical link 1b’’ can be provided, consisting of electrical cables similar to, but separate from, the electrical cables of the first link 1b. Each repeater R is therefore associated, upstream and downstream, with two electrical cables EC, EC'. One of the cables EC is part of the electrical link 1b, and the other cable EC’ is part of the backup electrical link 1b’’. Two high-voltage electrical switches HVS1, HVS2 are respectively arranged, upstream and downstream of each repeater R, between the power and control unit PU and the pair of cables EC, EC'. The electrical switches HVS1,HVS2 are controlled by a control signal which enables the power and control unit PU of the repeater R to be selectively connected to the electrical link 1b or to the backup electrical link 1b’’. The control signal can be sent by the power and control unit PU on command from one of the terminal stations A, B.

Such a configuration is shown in , in which the power and control unit PU is configured to produce two control signals ctrl1, ctrl2 for selectively connecting the electrical link 1b or the backup electrical link 1b’’. As part of this embodiment, a repeater R is provided with a telecommunications unit (for example integrated into the power and control unit PU), enabling at least one of the terminal stations A, B to remotely operate the electrical switches HVS1, HVS2.

The electrical switches HVS1, HVS2 may be integrated into the power and control unit PU or arranged separately in the container C or arranged outside this container, in the manhole in which the repeater R resides, as shown in .

When a problem is detected on the electrical link 1b by the electrical supply equipment A2, B2 arranged at each end of this link, it is possible to locate (by means of voltage ramps applied by this equipment or by means of voltage information transmitted by the repeaters themselves) the optical span where the interruption or degradation occurs. Once detection and location have been carried out, it is possible to switch the upstream electrical switch and the downstream electrical switch respectively of the two R repeaters surrounding the optical span along which the faulty electrical cable is located. The electrical path is then restored from one end to the other and normal operation can resume.

The two previous embodiments can be combined, and, in this case, a second electrical link can be used both to supply some of the repeaters in the optical communication network and to act as a backup electrical link for the other repeaters in the network.

shows a schematic diagram of such a combined configuration. In this figure, a repeater R is associated with a first electrical switch HVS1 and a second electrical switch HVS2, each of which connects the repeater R to an electrical cable EC, EC' at the end of one of the two links, as illustrated in the previous implementation mode. The assembly is also associated with a distribution board D arranged between the end cables EC of the first electrical link 1a and the end cables EC' of the second electrical link. The distribution board comprises 4 additional electrical switches HVSa respectively associated with each of the electrical cables EC, EC'. Each additional electrical switch HVSa makes it possible to selectively connect this electrical cable EC, EC’ to the repeater R, via one of the first and second electrical switches HVS1, HSV2 or to the other electrical cable EC, EC’ of the same electrical link, via the additional electrical switch HVSa which is associated with this other cable.

It is understood that, by operating the electrical switches HVSa, HVS1, HVS2 of this arrangement, it is possible to choose which electrical link to connect upstream and downstream to a repeater R, and to reconfigure at least one of these upstream and downstream links to deal with any electrical incident on one of the electrical cables arranged between two repeaters R. It should be noted that such a system is able to compensate for incidents affecting a plurality of electrical cables insofar as the cables affected are not arranged between the same two repeaters and in two distinct electrical links.

It is of course possible to provide more than two distinct electrical links in an optical communication network in accordance with this embodiment. In such a case, a distribution board D is configured with sufficient additional electrical switches to distribute these links to the two electrical switches HVS1, HSV2 associated with a repeater R.

Of course, the invention is not limited to the methods described, and alternative embodiments may be used without departing from the scope of the invention as defined by the claims.

For example, it may be possible to use at least one of the pairs of optical fibers in the optical cables forming the optical link 1a to monitor the integrity of the network, for example using distributed acoustic sensing. According to this approach, laser pulses are injected into a fiber (for example in one of the terminal stations A,B), part of which is backscattered by the Rayleigh effect. By monitoring variations in the backscattered part associated with each pulse, it is possible to identify and locate vibrations or sounds emitted in the vicinity of an optical cable on optical link 1a.

These vibrations or sounds may correspond to operations carried out in the vicinity of the cables and likely to affect the smooth running of the network. Their detection alerts the operator of the network 1 so that action can be taken.

It is not necessary for all the repeaters R of a terrestrial optical communication network conforming to the invention to be identical to one another. In particular, some repeaters may not have a thermoelectric module if temperature control is not a constraint for these repeaters. This may be the case, for example, when these repeaters are positioned in pre-existing buildings, which are themselves temperature controlled.

Claims

Terrestrial optical communication network (1) extending from a first terminal station (A) to a second terminal station (B), the optical network (1) comprising :
an optical link (1a) extending from the first terminal station (A) to a second terminal station (B) and comprising at least a first optical span made of, at least, a first optical cable (OC1) and a second optical span made of, at least, a second optical cable (OC2);

a first electrical link (1b), comprising a plurality of electrical cables (EC), connecting the first terminal station (A) and the second terminal station (B), the electrical cables (EC) being distinct from the first optical cable (OC1) and the second optical cable (OC2);
the long-haul optical communication network (1) further comprising at least a repeater (R)formed of :
a container (C) presenting:

a first optical port and a second optical port for respectively coupling the repeater to optical fibers of the first optical cable (OC1) and to optical fibers of the second optical cable (OC2), the optical fibers propagating optical signals;

two electrical ports for coupling the repeater (R) to the conductors of two distinct electrical cables (EC) transporting electrical power;

an optical amplifier unit (AU) disposed in the container (C) between the first optical port and the second optical port to amplify the optical signals, the optical amplifier unit (AU) comprising at least one doped fiber amplifier;

a power and control unit (PU) associated to the optical amplifier unit (AU) and disposed in the container (C), the power and control unit (PU) being electrically powered by the electrical power supplied by the electrical cables (EC);

a thermoelectric module (TM), thermally associated with the container (C) and electrically powered by the electrical power supplied by the electrical cables, the thermoelectric module (TM) being operated to maintain an operating temperature inside the container (C) to a target temperature.
Terrestrial optical communication network (1) according to claim 1 wherein the thermoelectric module is disposed outside of the container (C), in thermal contact with a wall of the container (C).
Terrestrial optical communication network (1) according to any preceding claims, wherein the first optical cable (OC1) and the second optical cable (OC2) each comprises a plurality of optical fibers pairs (P1,P2), the optical fibers of an optical fiber pair (P1,P2) propagating optical signals of opposite directions.
Terrestrial optical communication network (1) according to the preceding claim wherein the optical fibers of one optical fiber pair (P1) of the first optical cable (OC1) are respectively optically connected to the optical fibers of one optical fiber pair (P2) of the second optical cable (OC2) via unidirectional optical amplifiers (A) of the optical amplifier unit (AU).
Terrestrial optical communication network (1) according to the preceding claim wherein the unidirectional optical amplifiers (A) each comprise an input and an output and the optical amplification unit (AU) comprises an optical feedback path between the outputs of the unidirectional optical amplifiers (A) respectively connecting the fibers of the optical fiber pairs (P1,P2) of the first optical cable (OC1) and of the second optical cable (OC2).
Terrestrial optical communication network (1) according to claim 4 or 5 wherein the unidirectional optical amplifiers (A) present a fixed amplification gain.
Terrestrial optical communication network (1) according to any preceding claims comprising further optical spans and further repeaters (R) electrically coupled to electrical cables and optically coupled to two optical spans (OS) to serially extend the long-haul optical communication network (1) from the first terminal station (A) to the second terminal station (B).
Terrestrial optical communication network (1) according to the preceding claim wherein each optical span (OS) presents an optical attenuation loss, the optical attenuation losses differing by a maximum of 1dB from one optical span (OS) to any other optical span (OS), and preferably by a maximum of 0,5 dB.
Terrestrial optical communication network according to any preceding claims, wherein the at least a first optical cable (OC1), the at least a second optical cable (OC2) and the two distinct electrical cables electrical cables (EC) are laid in trenches and wherein the repeater is disposed in a repeater manhole.
Terrestrial optical communication network (1) according to any preceding claims wherein the first optical span is made of a plurality of first optical cables optically and serially connected by splicing boxes and/or the second optical span is made of a plurality of second optical cables optically serially connected by splicing boxes.
Terrestrial optical communication network (1) according to any preceding claims wherein the first terminal station (A) and the second terminal station (B) comprises respective power feed equipment providing the electrical power to the electrical cable (EC).
Terrestrial optical communication network (1) according to one of claims 7 to 11 comprising at least one second electrical link (1b’, 1b’’) connecting the first terminal station (A) and the second terminal station (B).
Terrestrial optical communication network (1) according to the preceding claim in which the first electrical link (1b) electrically supplies some of the repeaters (R) of the terrestrial optical communication network (1) and the second electrical link (1b') electrically supplies the other repeaters (R) of the Terrestrial optical communication network (1).
Terrestrial optical communications network (1) according to claim 12, in which each repeater (R) is associated with two electrical switches (HVS1, HVS2) enabling it to be selectively connected, upstream and downstream, to the first electrical link (1b) or to the second electrical link, which then forms a backup electrical link (1b’’).
Terrestrial optical communications network (1) as claimed in claim 12, in which each repeater (R) is associated with two electrical switches (HVS1, HVS2) and with a distribution board (D) coupled to the first electrical link (1b) and to the second electrical link (1b’), the distribution board (D) making it possible selectively to connect the repeater (R), upstream and downstream, to the first electrical link (1b) or to the second electrical link (1b’).
Terrestrial optical communication network according to any preceding claims wherein the first terminal station (A) and the second terminal station (B) are separated by at least 500 km.
Terrestrial optical communication network according to any preceding claims wherein the optical link (1a) and the electrical link (1b) are extending in parallel of a secured infrastructure such as a pipeline, railway or a high-voltage electric line.