Repeater for a long-distance optical communication network and long-distance optical communication network comprising such a repeater

Abstract

The invention relates to a repeater (R) for a long-distance optical communication network. The repeater (R) comprises a container (C) containing an optical amplification unit (AU), a power and control unit (PU) associated with the optical amplification 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) at a target temperature. The invention also relates to a long-distance optical communication network (1) extending from a first end station (A) to a second end station (B), the optical network (1) comprising a repeater (R) electrically coupled to an electrical cable (EC) and being optically coupled to a first optical cable (OC1) and a second optical cable (OC2) respectively. Figure to be published: Fig. 1

Description

Title of the invention: Repeater for a long-distance optical communication network and long-distance optical communication network comprising such a repeater FIELD OF THE INVENTION

[0001] The present invention generally relates to the field of long-distance optical communication networks (backbone networks). TECHNOLOGICAL CONTEXT OF THE INVENTION

[0002] Long-haul optical communication networks refer to optical communication networks that extend between two end stations that may be hundreds or thousands of kilometers apart. In these networks, optical signals propagate along the optical fibers of an optical cable that extends between the two end stations. Losses in the optical fibers, non-linearity effects, and optical amplification noise degrade signal quality and cause the network's range limit. To compensate for these effects, in-line optical amplification (ILA) sites are inserted periodically along the network to maintain transmission quality with minimal degradation.ILA sites are equipped with optical amplifiers that amplify optical signals propagating along optical fibers, usually by direct optical amplification (i.e., without conversion to electrical signals). These amplifier units must be electrically powered and their characteristics, performance, and reliability are highly temperature-dependent.

[0003] Long-distance submarine networks generally have a simple topology, comprising a main section connecting two terminal stations (located at landing sites) and a few branches extending from the main section, called a trunk, to reach other landing sites. The submarine cables composing the main section and the branches of a submarine network combine, in a polymer sheath, optical fibers in an inner tube forming the core of the cable and a copper foil forming an outer tube, constituting the electrical energy conductor of the cable. A steel film is placed between the inner tube and the outer tube to reinforce the strength of the cable, to allow laying and possibly recovery in water (up to 8000 meters deep), and to protect the inner tube from hydrostatic pressure due to the depth of the water.

[0004] For obvious reasons of accessibility and reliability, underwater ILAs (generally called underwater repeaters) are designed to be as simple as possible, with very few characteristics beyond the bare minimum of optical amplification. In particular, it is not possible to change the amplification gain of the optical amplification units, and the optical transmission system always operates with equal ranges in terms of optical loss, regardless of the effective distances between repeaters. The stability of the temperature at the bottom of the sea (typically 5°C) ensures the stability of the optical characteristics of the optical amplifiers, the stability of operation, the performance of the optical transmission system and the reliability of the optical amplification units.

[0005] The typical power consumption of a submarine ILA as part of a 16-pair fiber system is relatively low, in the order of 100W. Power supply equipment (PFE) located in each terminal station supplies electrical energy, via the submarine cable, to the submarine ILAs. This electrical energy (typically a line current of 0.5 to 1.5 A with voltages up to 15-18 kV at the EFP) is consumed by the submarine ILAs and dissipated in the submarine cable itself, due to its electrical resistance (typically 1 ohm / km).

[0006] In contrast, terrestrial networks typically have a mesh topology to serve the largest possible population, often in the heart of cities, and to allow path redundancy to ensure 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. Intermediate sites (ILAs, bypass nodes) are installed in buildings primarily powered by the electrical grid, typically with redundant power (battery, solar, or diesel generator) to protect the network. The buildings are equipped with air conditioning systems to provide the controlled environment necessary for the equipment to operate properly. Therefore, the typical power consumption of a terrestrial ILA for a 16-pair fiber network is relatively large, approximately 10 kW.

[0007] The underwater environment is an ideal location for long-distance optical communication networks due to its safe and temperature-stable nature. There is no need for temperature regulation or complex control of optical amplification units, which reduces the power consumption of the link. This complicates maintenance operations, but the advantages of the underwater environment outweigh the difficulties. SUBJECT OF THE INVENTION

[0008] The demand for transmission capacity continues to increase. However, laying cables on the seabed has limitations, both technically and geopolitically. Moreover, with such a high capacity carried by these cables, it is It is necessary to geographically diversify cable routes. The congestion of some submarine passages, such as the Red Sea, due to the presence of numerous cables, pipelines, and other devices, constitutes a technical limitation. From a geopolitical point of view, it is important to consider alternative communication routes that offer similar advantages to those of submarine communications. The present invention aims to provide a repeater and a long-distance optical communication network using this repeater that solve this problem and allow the creation of new terrestrial routes with the advantages of submarine cable routes. BRIEF DESCRIPTION OF THE INVENTION

[0009] In order to achieve this aim, the object of the invention provides a repeater for a long-distance optical communication network, the repeater comprising: - a container presenting: i. a first optical port and a second optical port for respectively coupling the repeater to optical fibers of a first optical cable and to optical fibers of a second optical cable, the optical fibers propagating optical signals; ii. an electrical port for connecting the repeater to an electrical cable carrying electrical power; - an optical amplification unit arranged in the container between the first optical port and the second optical port for amplifying the optical signals; - a power supply and control unit associated with the optical amplification unit and arranged in the container, the power supply and control unit being electrically powered by the electrical energy supplied by the electric cable; - a thermoelectric module, thermally associated with the container and electrically powered by the electrical energy supplied by the electric cable, the thermoelectric module being actuated to maintain an operating temperature inside the container substantially equal to a target temperature.

[0010] According to other advantageous and non-limiting characteristics of the invention, taken alone or in any technically possible combination: - The thermoelectric module is arranged outside the container, in thermal contact with a wall of the container; - the first optical cable and the second optical cable each comprise a plurality of pairs of optical fibers, the optical fibers of a pair of optical fibers propagating optical signals of opposite directions; - the optical fibers of a pair of optical fibers of the first optical cable are respectively optically connected to the optical fibers of a pair optical fibers of the second optical cable via unidirectional optical amplifiers of the optical amplification unit; - the unidirectional optical amplifiers each comprise an input and an output and the optical amplification unit comprises an optical return path between the outputs of the unidirectional optical amplifiers respectively connecting the fibers of the optical fiber pairs of the first optical cable and the second optical cable; - unidirectional optical amplifiers have a fixed amplification gain.

[0011] According to another aspect, the invention provides a long-distance 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 consisting of at least a first optical cable and a second optical span consisting of at least a second optical cable; - an electrical connection comprising at least one electrical cable connecting the first terminal station and the second terminal station, the electrical cable being separate from the first optical cable and the second optical cable;

[0012] the long-distance optical communication network further comprises a repeater as defined above, the repeater being electrically coupled to the electrical cable via the electrical port and being respectively optically coupled to the first optical cable and the second optical cable via the first optical port and the second optical port.

[0013] According to other advantageous and non-limiting characteristics of this aspect of the invention, taken alone or in any technically possible combination: - the long-distance optical communication network comprises other optical spans and other repeaters electrically coupled to the electrical cable and optically coupled to two optical spans to extend in series the long-distance optical communication network from the first terminal station to the second terminal station; - each optical range has an optical attenuation loss, the optical attenuation losses differing by a maximum of 1 dB from one optical range to another optical range, and preferably by a maximum of 0.5 dB; - the at least first optical cable, the at least second optical cable and the electrical cable are laid in trenches and the repeater is placed in a manhole; - the first optical span consists of a plurality of first optical cables optically connected in series by splice boxes and / or the second optical span is made up of a plurality of second optical cables optically and serially connected by splice boxes. - the first terminal station and the second terminal station comprise respective power supply equipment which supplies electrical energy to the electrical cable; - the first terminal station and the second terminal station are separated by at least 500 km. - the optical link and the electrical link extend parallel to a secure infrastructure such as a pipeline, a railway or a high-voltage power line. BRIEF DESCRIPTION OF THE FIGURES

[0014] Other characteristics and advantages of the invention will emerge from the detailed description of the invention which follows, with reference to the appended figures in which:

[0015] [Fig.l]

[0016] [Fig.l] illustrates a long-distance optical communication network according to the invention;

[0017] [Fig.2]

[0018] [Fig.2] illustrates a manhole equipped with a repeater according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] [Fig.l] represents a long-distance optical communication network 1 extending over 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 example more than 3000 km or even more than 5000 km. Advantageously, to take full advantage 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.

[0020] 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 extending respectively between the two terminal stations A, B. The optical link and the electrical link are separate, that is to say they are made up of separate optical and electrical cables.

[0021] An OC optical cable of the optical link 1a consists of at least one pair of optical fibers, and typically a plurality of pairs of optical fibers, for example between 16 and 96 pairs of optical fibers, arranged in a protective sheath. Each pair of the OC optical cable forms an optical channel ensuring duplex communication, i.e. the optical fibers of a pair of optical fibers propagate optical signals in opposite directions. An OC optical cable may have a length (the distance between two optical connection locations) of a few kilometers, for example about 5 km. The optical link 1a is therefore made up of a plurality of optical cables, interconnected in a daisy chain at successive optical connection locations (splice boxes SB and repeaters R, as will be described in a later passage of this description) to extend the optical link 1a between the first and second terminal stations A,B.

[0022] An EC electrical cable used to form the electrical connection 1b consists of a conductor arranged in its own protective sheath. The EC electrical cables forming the electrical connection are also interconnected in a daisy chain, at electrical connection locations, to constitute the electrical connection 1b of the network 1.

[0023] The electrical cables forming the electrical connection 1 can be associated with optical cables of the same length, so that the optical and electrical connections are made at the same locations SB,R along the network 1. It is also possible to have an electrical connection once every two optical connections for example, but it is generally preferable not to create a location dedicated to the electrical connection alone, in order to maintain the simplicity of the proposed solution. The electrical connection locations are therefore preferably located at the same location as an optical connection location.

[0024] The first terminal station A and the second terminal station B comprise optical interface cards A1, B1, connected to respective telecommunications networks, for sending and receiving optical signals carried by the pairs of optical fibers forming the optical link 1a.

[0025] The first terminal station A and the second terminal station B comprise respective electrical power supply equipment A2, B2 connected to the conductor of the electrical cables EC to supply electrical energy to the elements making up the optical network 1, as will be described in the remainder of this description. The electrical power supply equipment A2, B2 can be connected to the electrical network and can deliver a current of between 0.5 A and 1.5 A to the electrical connection 1b under a voltage difference between each terminal station A, B of at least 6 kV. More generally, the electrical power supply equipment A2, B2 must be sized to supply the expected power to each element of the optical network 1, taking into account the power dissipated in the conductor of the electrical cable, due to its electrical resistance.

[0026] Referring again to [Fig. 1], the optical link 1a is made up of a plurality of optical bays OS having a substantially equal optical attenuation loss. The optical attenuation losses may differ by a maximum of 1 dB from one optical bay OS to any other optical bay OS of the optical link 1a, and preferably by a maximum of 0.5 dB.

[0027] As known to the person skilled in the art, this loss refers to the loss of optical signals that propagate between the input and output of an optical span. Losses in an optical span OS may be due to intrinsic absorption of the material in the optical fibers, intrinsic loss, scattering, bending, etc. Two contiguous optical spans OS are separated by a repeater R to regenerate the optical signals. Since the optical attenuation loss is substantially constant from one optical span OS to another, the repeaters R may have identical and fixed amplification gains.

[0028] 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 may 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 too attenuated and can 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.

[0029] Each optical span OS comprises at least one optical cable OC and is generally made up of a plurality of optical cables OC optically and serially connected by splice boxes SB.

[0030] To obtain a 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 chosen to be similar. They may, for example, differ by a maximum length difference of 20% for reasons such as geographical issues for placing the repeaters R at a given location or the introduction into 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.

[0031] Furthermore, the attenuation may be introduced in an optical span of shorter length (and therefore lower optical attenuation loss) or, more generally, in an optical span having a reduced optical attenuation loss so that, overall, the optical spans OS composing the optical link 1a have a substantially equal optical attenuation loss. This attenuation may be introduced at the repeater R, for example by introducing a dedicated optical attenuator or by controlling the attenuation produced at the splicing of two optical cables, and for example at the splicing of an optical cable and an optical port of the repeater. These techniques are well known to the person skilled in the art and described for example in document US4557557 or in the article by 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. .

[0032] Advantageously, to ensure its protection and security, the long-distance optical communication network 1 is buried. The optical cables OC and the electrical cables EC forming the optical link 1a and the electrical link 1b are arranged in trenches dug in the ground, for example using the conventional "eut and cover" technique. In difficult areas of the network 1, horizontal directional drilling techniques may be preferred. Furthermore, to protect the optical and electrical cables and give flexibility to the network 1, the cables may be placed in conduits such as ducts and / or micro-ducts. The splice boxes SB may be placed in respective splice manholes and the repeaters R in respective repeater manholes into which the trenches open.Burying cables, and in particular OC optical cable, makes it possible to maintain the constant optical attenuation loss of each OS optical span.

[0033] Splice manholes and repeater manholes may include other features than the SB and repeater splice boxes, such as conduits to accommodate a buffer length of cables that will be useful in the event of repair. They must be large enough to allow human intervention during installation and maintenance.

[0034] Preferably, to avoid locations where human activity is intense, the optical link 1a and the electrical link 1b are placed in a trench extending parallel to a secure infrastructure with wide rights of way, such as a pipeline, a railway or a high voltage power line.

[0035] [Fig. 2] shows, by way of illustration, a repeater manhole 2, located below the ground level GL. A repeater R is placed inside the repeater manhole 2. The repeater R comprises a container C having a first optical port and a second optical port for respectively coupling the repeater R to the optical fibers of a first optical cable OC1 and to the optical fibers of a second optical cable OC2. The first optical cable OC1 is the end cable of a first optical span and the second optical cable OC2 is the end cable of a second optical span, distinct from the first, the two optical spans joining at the level of the manhole of the repeater 2.

[0036] The container also comprises at least two electrical ports for respectively connecting the repeater R to the conductors of two separate electrical cables extending in trenches along the first and second optical cables OC1, OC2. In some cases, the container may comprise a single electrical port for coupling the repeater R to the electrical cable EC carrying the electrical power. An electrical port may comprise a grounding connection for electrically contacting a grounding electrode ER, such as a conductive rod. pressed into the bottom of the repeater manhole. The conductive rod may have a terminal block, as shown in [Fig.2]. The ground connection provides a reference voltage and a return path for the circuits comprising the repeater R.

[0037] The container C is hermetically sealed and defines a controlled environment that houses an optical amplification unit AU. The optical amplification unit AU is optically arranged 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 supply and control unit PU, with the corresponding electronics, associated with the optical amplification unit AU, the power supply and control unit PU being electrically connected and powered by the electrical energy supplied by the electrical cable EC through at least one electrical port.

[0038] The optical amplification unit AU may be provided, at its input and at its output, with two sets of pigtail fibers (from the Anglo-Saxon term "pig tail" often used in this technical field). The two sets of pigtail fibers are arranged in hermetic passages of the container C to form the first and second optical ports of the container in order to couple the repeater R to the optical fibers of the first optical cable OC1 and to the optical fibers of the second optical cable OC2 respectively.

[0039] The optical amplification unit AU uses any technique capable of amplifying the optical signals propagating in the optical fibers of the first and second optical cables OC1, OC2, without it being necessary to first convert them into electrical signals. Preferably, the optical amplification unit comprises doped fiber amplifiers, such as erbium-doped fiber amplifiers. These amplifiers A are unidirectional. To ensure the bidirectionality of the optical link 1a, the optical fibers of a pair of optical fibers PI of the first optical cable OC1 are respectively optically connected to the optical fibers of a pair of optical fibers P2 of the second optical cable OC2, via the respective unidirectional optical amplifiers A of the optical amplification unit AU.

[0040] The power control unit PU comprises a power circuit for converting the power supplied by the electrical cable EC to the power required to operate the optical amplification unit AU. It also comprises electronic circuits providing the electrical signals for controlling the optical amplification unit AU.

[0041] The repeater R is designed to be as simple as possible. It is configured to operate with a fixed and predetermined amplification gain and, apart from its initial calibration, it has no means of adjusting during operation this gain and the optical amplifier settings. This is possible because the optical attenuation losses of the optical spans OS comprising optical link 1a of network 1 are all identical. It is therefore not necessary to individually adjust the amplification gain of a repeater R to the specific optical attenuation losses of an optical span OS.

[0042] The power control unit PU is also preferably devoid of any active supervision function, which is preferably located in the first and / or second terminal station A,B.

[0043] To enable this supervision by Coherent Optical Time Reflectometry (CODTR), the optical amplification unit comprises an optical return path between the outputs of the optical amplifiers respectively connecting the fibers of the pairs of optical fibers of the first and second cable OC1, OC2.

[0044] The amplification characteristics, and in particular the gain, of the optical amplification unit AU may be sensitive to temperature due to the variation in the amplification properties of the doped fiber, but also due to the variation in the pumping power affected by the efficiency of the pump laser of the amplifier. To maintain constant amplification characteristics and the proper operation of the network, it is therefore important to maintain an operating temperature in the container C at a target temperature, despite the temperature variations of the environment (for example, the daytime and nighttime temperature variations) and despite the temperature variations caused by the power dissipated by the optical amplification unit AU and the power control unit PU.For example, the target temperature can be between 10°C and 30°C and the operating temperature in container C can be controlled to be constantly within + / - 2°C of the target temperature.

[0045] To this end, a repeater according to the invention also comprises a thermoelectric module TM, thermally associated with the container C and electrically powered by the electric current supplied by the electric cable, for example via the power control unit PU to which it is connected. The thermoelectric module is used to maintain the operating temperature of the container substantially at the target temperature. The thermoelectric module can exploit any effect, such as the Peltier effect.

[0046] The thermoelectric module TM consists of two opposing plates, thermally conductive but electrically insulating, separated by p-type and n-type semiconductor pads, the semiconductor pads extending from one plate to the other. The semiconductor pads are connected together to form a multitude of pn junctions electrically arranged in series. When a current flows Through pn junctions, heat is moved electronically in the direction of current, from one plate to the other.

[0047] Preferably, the thermoelectric module TM is arranged outside the container C, a plate being arranged in contact with the container C, for example in contact with a wall of the container C. But the thermoelectric module can also be arranged inside the container C, in contact with one of the walls of the container. At least the wall of the container in contact with the thermoelectric module TM is preferably made of a thermally conductive material, in order to facilitate the transport of heat. As indicated above, the thermoelectric module is used to maintain an operating temperature inside the container C at the target temperature.

[0048] The thermoelectric module TM can be powered and operated by the control unit PU. The thermoelectric module TM can also operate autonomously. In this case, the thermoelectric module TM is connected to the electrical cable and is equipped with a control circuit and a temperature sensor. The container is equipped with a temperature sensor connected to the power supply and control unit PU and / or to the thermoelectric module TM.

[0049] Of course, the invention is not limited to the methods described and other embodiments may be used without departing from the scope of the invention as defined by the claims.

Claims

Claims

1. Repeater (R) for a long-distance optical communication network, the repeater (R) comprising: - a container (C) having: i. a first optical port and a second optical port for respectively coupling the repeater to the optical fibers of a first optical cable (OC1) and to the optical fibers of a second optical cable (OC2), the optical fibers propagating optical signals; ii.an electrical port for connecting the repeater (R) to an electrical cable (EC) carrying electrical energy; - an optical amplification unit (AU) arranged in the container (C) between the first optical port and the second optical port for amplifying the optical signals; - a power supply and control unit (PU) associated with the optical amplification unit (AU) and arranged in the container (C), the power supply and control unit (PU) being electrically powered by the electrical energy supplied by the electrical cable (EC); - a thermoelectric module (TM), thermally associated with the container (C) and electrically powered by the electrical energy supplied by the electrical cable (EC), the thermoelectric module (TM) being actuated to maintain an operating temperature inside the container (C) substantially equal to a target temperature.

2. Repeater (R) according to claim 1, wherein the thermoelectric module is arranged outside the container (C), in thermal contact with a wall of the container (C).

3. A repeater (R) according to any preceding claim, wherein the first optical cable (OC1) and the second optical cable (OC2) each comprise a plurality of optical fiber pairs (P1,P2), the optical fibers of one optical fiber pair (P1,P2) propagating optical signals of opposite directions.

4. Repeater (R) according to the preceding claim in which the optical fibers of a pair of optical fibers (PI) of the first optical cable (OC1) are respectively optically connected to the optical fibers of a pair of optical fibers (P2) of the second optical cable (OC2) via unidirectional optical amplifiers (A) of the optical amplification unit (AU).

5. Repeater (R) according to the preceding claim in which the unidirectional optical amplifiers (A) each comprise an input and an output and the optical amplification unit (AU) comprises an optical return path between the outputs of the unidirectional optical amplifiers (A) respectively connecting the fibers of the pairs of optical fibers (P1, P2) of the first optical cable (OC1) and of the second optical cable (OC2).

6. Repeater (R) according to claim 4 or 5, wherein the unidirectional optical amplifiers (A) have a fixed amplification gain.

7. A long-distance 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 consisting of, at least, a first optical cable (OC1) and a second optical span consisting of, at least, a second optical cable (OC2); - an electrical link (1b) comprising at least one electrical cable (EC) connecting the first terminal station (A) and the second terminal station (B), the electrical cable (EC) being separate from the first optical cable (OC1) and the second optical cable (OC2);the long-distance optical communication network (1) further comprises a repeater (R) according to any one of the preceding claims, the repeater (R) being electrically coupled via the electrical port to the electrical cable (EC) and being respectively optically coupled, via the first optical port and the second optical port, to the first optical cable (OC1) and to the second optical cable (OC2).;

8. A long distance optical communication network (1) according to claim 7, comprising further optical spans and further repeaters (R) electrically coupled to the electrical cable and coupled optically with two optical spans (OS) for extending in series the long-distance optical communication network (1) from the first terminal station (A) to the second terminal station (B).

9. A long distance optical communication network (1) according to claim 8, wherein each optical span (OS) has 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.

10. A long-distance optical communication network according to one of claims 7 to 9, wherein at least one first optical cable (OC1), at least one second optical cable (OC2) and the electrical cable (EC) are laid in trenches and wherein the repeater is placed in a repeater manhole.

11. A long-distance optical communication network (1) according to one of claims 7 to 10, wherein the first optical span consists of a plurality of first optical cables optically and serially connected by splice boxes and / or the second optical span consists of a plurality of second optical cables optically and serially connected by splice boxes.

12. A long-distance optical communication network (1) according to one of claims 7 to 11, wherein the first terminal station (A) and the second terminal station (B) comprise respective power supply equipments supplying electrical energy to the electrical cable (EC).

13. A long-distance optical communication network according to one of claims 7 to 12, wherein the first terminal station (A) and the second terminal station (B) are separated by at least 500 km.

14. A long-distance optical communication network according to one of claims 7 to 13, wherein the optical link (1a) and the electrical link (1b) extend parallel to a secure infrastructure such as a pipeline, a railway or a high-voltage power line.

Images