Embedded optical ring communication network for aircraft

1. Technical field of the invention

The invention relates to an on-board optical network of the ring network type. In particular, the invention relates to an optical communication network that can be on board an aircraft in order to allow communication of equipment of the aircraft with one another.

2. Technological background

The state of the art includes in particular the documents <patcit id="pcit0001" dnum="US4366565A"><text>US-A-4,366,565</text></patcit> and <patcit id="pcit0002" dnum="US2013294776A1"><text>US-A1-2013 / 294776</text></patcit>.

In order to connect the items of equipment of an aircraft to one another for communication purposes, the aircraft are equipped with different cabling forming a network, the installation and maintenance of which can be complex. In addition, this wiring has a significant cost, on the one hand in terms of the price of the cables but also in terms of weight, resulting in an increase in fuel consumption during the flight.

In addition, current networks generally use copper cables forming a mixture of star and ring networks, of the AFDX “Switched Ethernet” type. The cables use a copper backing of two redundant twisted pairs.

This type of copper cable network has several drawbacks: metal cables pose problems of electromagnetic interference (electromagnetic compatibility, current induction, etc.), the network is not very adaptable to modifications (addition of new equipment for example), the network has a speed limited to a few tens of Mb / sec (mainly due to the deterministic aspect of the TCP protocol), and the weight of the cables is high (around 32kg / km, an airplane can include for example several hundred kilometers of cables). In addition to all these drawbacks, there is also a high cost of maintenance and modification.

One solution proposed to at least some of these drawbacks has been to replace copper cables with optical fibers. However, the network obtained r does not allow great adaptability.

3. Objectives of the invention

The invention aims to overcome at least some of the drawbacks of known communication networks.

In particular, the invention aims to provide, in at least one embodiment of the invention, a communication network making it possible to improve communications between equipment items of an aircraft.

The invention also aims to provide, in at least one embodiment, a communication network allowing an increase in the throughput of data exchanges.

The invention also aims to provide, in at least one embodiment of the invention, a communication network allowing easy connection or disconnection of equipment.

The invention also aims to provide, in at least one embodiment of the invention, a communication network offering better security of data transmissions.

The invention also aims to provide, in at least one embodiment of the invention, a communication network allowing redundancy in the event of degradation of a part of the network.

4. Disclosure of the invention

To do this, the invention relates to an on-board optical communication network in a ring adapted to allow data transmission between equipment, comprising:<ul id="ul0001" list-style="dash" compact="compact"><li>a set of junction boxes each connected on the one hand directly to two other junction boxes by multimode and bidirectional optical fibers so as to form a ring, and adapted to be connected on the other hand to at least one multiplexer / demultiplexer by multimode and bidirectional optical fibers,</li><li>each optical fiber is adapted to allow the transport of optical signals of at least three different modes,</li><li>each multiplexer / demultiplexer comprises a plurality of passive optical elements and makes it possible to transmit at least three equipment signals coming from the equipment via modal multiplexing in an optical fiber or to separate the modes of an optical signal coming from the optical fiber to at least three equipment signals,</li></ul>characterized in that:<ul id="ul0002" list-style="dash" compact="compact"><li>the junction boxes each include three splitters to which the optical fibers are connected and each directed towards at least one prism, said splitters and said prism being configured to direct an optical signal coming from an optical fiber and entering one splitter to the other two splitters and for each splitter to receive optical signals from the other two splitters and send these signals to the optical fiber to which it is connected.</li></ul>

An optical communication network according to the invention therefore allows communication between different equipment at a high rate (up to several tens of Gb / second over more than a hundred meters): multiplexing by propagation modes makes it possible to s' add to commonly used multiplexing (in particular wavelength multiplexing and time multiplexing) in order to increase the number of devices that can communicate simultaneously on the network. In addition, mode multiplexing makes it possible, by controlling the injection and propagation of the modes of the optical signals, to overcome modal dispersion.

The splitters and the prism of the junction boxes are passive components, which allow optical signals to be transmitted without losing the modes of the optical signal transmitted. The separators make it possible to form, from a received optical signal and by means of passive optical elements, two identical optical signals which are directed towards different parts of the prism. By reflection or refraction, the prism directs a first of these two optical signals towards a first of the other separators and a second of these two signals towards a second separator. Likewise, by reverse operation, each separator receives two optical signals originating from the other two separators, thus allowing bidirectional operation of the transmission between each separator two by two.

The passive operation of the junction boxes also allows them to operate without the presence of a multiplexer / demultiplexer connected to one of the splitters. In this case, the junction box behaves like a socket in the network, transmitting optical signals from a neighboring junction box to the next junction box in the ring, and available to be able to connect new equipment to the network. Thus, the junction boxes can be distributed in the infrastructure in which the network is deployed, for example an aircraft, in anticipation of new equipment to be added in the future. Likewise, when an item of equipment or a set of items of equipment must be removed from the network, the associated multiplexer / demultiplexer can be disconnected from the junction box, without requiring network reconfiguration for its correct operation.

Mode multiplexing also improves the security of data transmission, since the mode separation operation (demultiplexing) can be performed only by modal demultiplexers: data interception at the optical fiber level, for example by stripping and bending this optical fiber, it will not make it possible to obtain a readable optical signal.

In addition, due to the configuration of the ring network and the fact that each optical fiber allows the transmission of optical signals in both directions (bidirectional fiber), the optical network has redundancy allowing, in the event of network failure, to allow all equipment to stay connected.

Finally, a communication network according to the invention makes it possible to transmit, in the same multiplexed optical channel, independent information segregated according to their criticalities or their types in an optical (or modal) manner, without interference from one optical mode to another.

Advantageously and according to the invention, the prism is a right prism having an equilateral triangle as its base.

According to this aspect of the invention, the splitter directs a first optical signal towards a first lateral (rectangular) face of the prism. By reflection on this face, this first optical signal is directed towards a first of the other separators. Likewise, the splitter directs a second optical signal towards a second lateral face of the prism and by reflection on this face, this second optical signal is directed towards a second of the other splitters. The prism thus plays the role of a multifaceted mirror. The angles of incidence and the refractive index of the prism are configured to allow these reflections.

Advantageously and according to the invention, multimode optical fibers have a core diameter greater than 50 μm.

According to this aspect of the invention, the multimode fiber has a sufficiently large core diameter to allow the propagation of signals of different modes in the fiber.

Advantageously and according to the invention, the junction boxes and the optical fibers forming the ring are arranged in the same plane, and the optical network comprises a sensor making it possible to measure the propagation time of two optical signals in the ring, the two optical signals traveling through the ring in an opposite direction of propagation.

According to this aspect of the invention, the optical ring network makes it possible to form a Sagnac effect gyrometer, allowing the measurement of the angular speed of a means of transport in which the optical network is on board, according to the plane in which s' extend the junction boxes and optical fibers forming the ring. This aspect of the invention is particularly useful in an aircraft, and depending on the configuration of the ring, makes it possible to measure the angular speed according to the plane in which the ring extends (for example measurement of the roll, pitch or yaw of the aircraft).

The invention also relates to an aircraft comprising a plurality of items of equipment, characterized in that it comprises an optical network according to the invention for the transmission of data between said items of equipment.

The equipment of the aircraft can thus transmit data via the optical network, even if the latter emit their signals at the same wavelengths.

The invention also relates to an optical communication network and an aircraft characterized in combination by all or some of the characteristics mentioned above or below.

5. List of Figures

Other aims, characteristics and advantages of the invention will become apparent on reading the following description, which is given only without limitation and which refers to the appended figures in which:<ul id="ul0003" list-style="dash" compact="compact"><li>the <figref idref="f0001">figure 1</figref> is a schematic view of an optical communication network according to one embodiment of the invention,</li><li>the <figref idref="f0001">figure 2</figref> is a schematic view of a multiplexer of an optical communication network according to one embodiment of the invention,</li><li>the <figref idref="f0002">figure 3</figref> is a schematic view of different modes that can be transported in the same multimode optical fiber of an optical communication network according to one embodiment of the invention,</li><li>the <figref idref="f0002">figure 4</figref> is a schematic view of a junction box of an optical communication network according to one embodiment of the invention,</li></ul>

6. Detailed description of an embodiment of the invention

The following embodiments are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the characteristics apply only to a single embodiment. Simple features of different embodiments can also be combined to provide other embodiments. In the figures, the scales and proportions are not strictly observed, for purposes of illustration and clarity.

The <figref idref="f0001">figure 1</figref> schematically represents an optical ring communication network 10 according to an embodiment of the invention, for example on board an aircraft. The optical network 10 is intended to allow transmission of computer data between equipment 12a-12h. To do this, the communication network comprises a set of branch boxes 14a-14h, each connected directly to two other branch boxes by multimode and bidirectional optical fibers 16a-16h so as to form a ring. As visible in particular by the loops formed by the 16th and 16h optical fibers making it possible to represent a large length of fiber, the<figref idref="f0001">figure 1</figref> is not to scale and the junction boxes may be further apart and distributed differently on the ring.

Each junction box is further adapted to be connected to a multiplexer / demultiplexer by a multimode and bidirectional optical fiber. In normal network configuration, each junction box may or may not be connected to a multiplexer / demultiplexers: the branch boxes connected to a multiplexer / demultiplexer, here the branch boxes 14b, 14d, 14g, allow the connection to the optical network of the equipment connected to the multiplexer / demultiplexer, and the branch boxes not connected to a multiplexer / demultiplexer allow offer a connection socket if it is necessary to add equipment to the network via a multiplexer / demultiplexer. In practice, the junction boxes can thus be distributed throughout the aircraft in anticipation of new equipment to be added in the future.

In this embodiment, the branch box 14b is connected to a multiplexer / demultiplexer 18a allowing the connection of the devices 12a, 12b, 12c to the network, the branch box 14d is connected to a multiplexer / demultiplexer 18b allowing the connection of the devices 12d, 12e, 12f, 12g to the network, and the branch box 14g is connected to a multiplexer / demultiplexer 18c allowing the connection of the equipment 12h to the network.

By measuring the difference in the propagation time in the ring of an optical signal propagating in the multimode optical fibers 16a-16h during a full turn of the ring in one direction and in the reverse direction, the optical network can allow to measure the angular speed of the aircraft in the plane in which the ring extends.

The <figref idref="f0001">figure 2</figref> schematically represents a multiplexer / demultiplexer 18 of an optical network according to one embodiment of the invention.

The operation of the multiplexer / demultiplexer 18 is explained here in its operation as a multiplexer. The demultiplexer function is analogous in the reverse direction.

The multiplexer / demultiplexer 18 receives optical signals coming from the equipment and intended to be transmitted to the optical network, here three equipment signals 20a, 20b, 20c, which may have an equal or different frequency. If the equipment does not transmit optical signals but signals, for example electrical, the multiplexer / demultiplexer can include means for converting electrical signals into optical signals. By passing the three equipment signals 20a, 20b, 20c through a plurality of passive optical elements, the equipment signals will be combined to form a single optical signal 21 in which each equipment signal has been modulated so to present a particular mode of propagation. The multiplexer / demultiplexer 18 carries out to do this a succession of several optical Fourier transforms via the passive optical elements, for example in this embodiment a mirror 22 and a phase network 24, the equipment signals effecting several reflections between the phase network 24 and mirror 22 until segregation by mode and combination. The passive optical elements also include a collimating lens 26a and focal length lenses 26b, as well as return mirrors 28.

As explained previously, the demultiplexer function works in the opposite direction, that is to say that a single optical signal enters the multiplexer / demultiplexer 18 and is decomposed into several output signals transmitted to each equipment, using the same components.

The segregation of the signals by mode at the end of this multiplexing is described on <figref idref="f0002">figure 3</figref>.

The <figref idref="f0002">figure 3</figref> schematically represents the different modes that can be transported in the same multimode optical fiber of an optical communication network according to one embodiment of the invention.

Reference 21 represents the shape of the optical signal as propagated in a multimode optical fiber according to a cross section of said fiber. The optical signal 21, for example during the combination of the three signals 20a, 20b, 20c as described above, can be considered as the sum of the three modes used for the propagation of these equipment signals in the single optical signal. In this embodiment, the first mode 30 is a TEM type mode₀₀, the second mode 32 is a TEM type mode₀₁ (or a combination of two TEM-type modes 32a and 32b₀₁), the third mode 34 is a TEM mode₀₂ (or a combination of three TEM-type modes 34a, 34b and 34c₀₂). Reference 21 thus represents the sum of the groups of modes 30, 32 and 34, themselves made up of modes 30, 32a and 32b, 34a and 34b and 34c.

The embodiment of the invention described is only indicative as a solution for combining three equipment signals. According to other embodiments, more modes can be used to allow the combination of more than three equipment signals, depending on the needs of the network and the number of connected equipment. In addition, the types of modes used may be different.

The <figref idref="f0002">figure 4</figref> schematically represents a junction box of an optical communication network according to one embodiment of the invention.

The junction box comprises three separators, a first separator 36a, a second separator 36b and a third separator 36c, as well as a right prism 38 having an equilateral triangle as its base. Each splitter 36a, 36b, 36c is connected to a multimode optical fiber, and receives an optical signal coming either from another neighboring junction box in the ring, or from a multiplexer / demultiplexer. In the illustrated embodiment, the splitters 36a, 36b receive, for example, optical signals from other junction boxes and the splitter 36b can receive an optical signal from a multiplexer / demultiplexer.

The splitters make it possible to divide the optical signals to transmit them to the other two splitters, as well as to receive the optical signals coming from the other two splitters. To do this, the first splitter 36a for example divides the signal received into two identical optical signals, forming optical beams, a first optical beam 40a and a second optical beam 42a. The first optical beam 40a is directed towards one face of the prism and is reflected towards the second splitter 36b. The second optical beam 42a is directed towards one face of the prism 38 and is reflected towards the third splitter 36c.

Conversely, the first splitter receives an optical beam 40b coming from the second splitter 36b and reflected by the prism 38 and an optical beam 42c coming from the third splitter 36c and reflected by the prism 38. Finally, the second splitter 36b sends a beam 44b optical to the third splitter 36c and receives an optical beam 44c from the third splitter 36c.

In the event that the second splitter 36b is not connected to a multiplexer / demultiplexer (the junction box is thus available to connect new equipment), the splitters can be configured so that the first splitter 36a and the third splitter 36c send / receive only the optical beams 42a and 42c.

Upon reception of the optical beams from the other splitters, each splitter combines these optical beams and transmits the resulting optical signal to the optical fiber to which it is connected.

The invention is not limited to the only embodiments described. In particular, other types of optical networks are possible. For example, the configurations of the passive optical elements of multiplexers / demultiplexers as well as of the junction boxes can be modified as long as the function performed is identical and that only passive optical elements are used, because they allow the conservation of the modes of the optical signals. .