METHOD AND DEVICE FOR BIDIRECTIONAL COMMUNICATION OVER A SINGLE OPTICAL FIBER WITH A SINGLE LIGHT SOURCE

Abstract

The invention relates to a bidirectional communication device between a first terminal (4) and at least one second terminal (6), comprising: - a single optical fiber (2) between the first terminal (4) and at least one second terminal (6); - the first terminal (4) comprising a radiation source (8) at at least one first wavelength (λ1), a photodetector (10), and means (12) for directing a signal from the second terminal (6) via the optical fiber (2) to the photodetector (10) and for directing a signal from the radiation source (8) to the optical fiber (2); - the second terminal (6) comprising at least one modulator (24), a photodetector (22), and power supply means (9). Figure 1

Description

Title of the invention: METHOD AND DEVICE FOR BIDIRECTIONAL COMMUNICATION OVER A SINGLE OPTICAL FIBER WITH A SINGLE LIGHT SOURCE. TECHNICAL FIELD AND PRIOR ART

[0001] The invention relates to the field of bidirectional communication between a first terminal and at least one second terminal.

[0002] In harsh environments, with high environmental constraints such as high temperatures (>200°C), or low temperatures (<-40°C), and / or under high electromagnetic interference, and / or in a liquid and / or a corrosive environment, and / or in the case of links over medium or long distances (for example >10m), wired electrical communication becomes very complex to implement because it requires (i) specific materials resistant to the environment in which they are to operate (conductive materials, insulation, shielding) (ii) specific connection processes (interconnection, soldering, etc.) (iii) as well as relatively high power levels and suitable electronics to guarantee a certain level of signal integrity.Beyond technological aspects, applications may also require significant constraints in terms of size, weight, flexibility, ease of integration, robustness, and signal integrity for security reasons.

[0003] For all these non-exhaustive reasons, an optical fiber is an alternative solution with many advantages covering all the limitations of wired solutions mentioned in the previous paragraph, in particular, guaranteeing the integrity of signals.

[0004] Bidirectional communication systems based on optical fiber(s) are known which use:

[0005] - i.e. at least two optical fibers, one for the signals from the first terminal to the second terminal and one for signals from the second terminal to the first terminal and, for each terminal, a photodetector and a laser source,

[0006] - i.e., an optical fiber and, for each terminal, a photodetector, a mirror dichroic and a laser source. The two sources have two distinct wavelengths XI and / .2 and the two dichroic mirrors reflect these two wavelengths respectively.

[0007] In this regard, one can, for example, refer to the articles by M. Yonemura et al., entitled "250 Mbit / s Bi-directional Single Plastic Optical Fibre Communication System", published in R&D Review of Toyota CRDL, Vol. 40 No. 2 and by Xin Li et al., entitled “itLED-Bascd Single-Wavelength Bi-directional POF Link With lOGb / s Aggregate Data Rate”, published in Journal of Lightwave Technology, Vol. 33, No. 17, September 1, 2015.

[0008] Bidirectional optical communication with a remote terminal presents other problems when the latter operates in a harsh environment or under significant environmental constraints, for example at high temperatures (>200°C) or low temperatures (<-40°C). In particular, this type of environment, and especially high temperatures, does not tolerate the use of laser light sources because their performance depends greatly on their operating temperature.

[0009] Beyond the above aspects, the various applications may also require significant constraints in terms of size, weight, flexibility, ease of integration, robustness and signal integrity for safety reasons.

[0010] In particular, in order to increase the robustness of such a terminal to environmental conditions, it is necessary to reduce the nomenclature of its constituent parts, in particular optical components requiring precise positioning and alignment (sensitivity to vibrations, accelerations) and / or containing specific surface treatments (delamination, pollution, oxidation, etc.).

[0011] We therefore seek to reduce the complexity and nomenclature of such a system and to choose robust components, particularly under severe operating conditions (temperature, vibration, acceleration, pressure, etc.) to ensure the reliability and robustness of such a communication solution.

[0012] According to another aspect, the aim is to improve the reliability and reduce the cost of bidirectional optical communication capable of operating in harsh environments (for example, in the case of operation under extreme conditions). Description of the invention

[0013] The invention aims to solve all or part of the problems set out above or in the remainder of this application.

[0014] The invention relates first to a bidirectional communication device between a first terminal (or "master" terminal) and at least one second terminal (or "slave" terminal), comprising:

[0015] -an optical fiber, preferably a single optical fiber, between the first terminal and at least one second terminal;

[0016] - the first terminal comprising a light source at least at a first wavelength (XJ, a photodetector and means for directing a signal from the second terminal via the optical fiber to the photodetector and for directing a signal from the radiation source to the optical fiber;

[0017] - the second terminal comprising at least one modulator and one photodetector, and means of feeding.

[0018] The invention makes it possible to remove the light source (in particular any laser source) in the slave terminal and replace it with a light modulator.

[0019] The invention makes it possible to use only one optical fiber and one wavelength for bidirectional communication, in particular in half duplex or full duplex.

[0020] The invention allows a reduction in the size and nomenclature of the device.

[0021] The modulator of the second terminal allows modulated light (which may therefore contain a message) to be reflected back to the first terminal. The latter includes, for example, a circulator that directs the light from the second terminal towards a photodetector.

[0022] The invention also relates to a bidirectional communication method between a first terminal and at least a second terminal, for example implementing a device as described above and in the remainder of this application.

[0023] A method according to the invention, or a method as defined above, may comprise the following steps:

[0024] - generate optical signals at at least a first wavelength in the first terminal and transmit them, via optical fiber, at least to the second terminal;

[0025] - the second terminal receives the signals sent by the first terminal, possibly modulates these signals (on / off or analog), and sends all or part of the received signal(s) back to the first terminal, via optical fiber;

[0026] - the photodetector of the first terminal receives the signals returned by the second terminal via fiber optic cable.

[0027] In particular embodiments of a device or method according to the invention:

[0028] - the optical fiber can be a single-mode or multi-mode fiber.

[0029] - and / or:

[0030] - the first terminal is capable of transmitting a signal to the second terminal continuous light and a data signal, at the first wavelength;

[0031] - the second terminal is capable of transmitting a data signal to the first terminal, at the first wavelength.

[0032] The light source can be monochromatic; this embodiment allows:

[0033] - to use a single wavelength for bidirectional communication, possibly in Full Duplex;

[0034] - an exchange of digital and / or analog data between terminals.

[0035] In particular embodiments of a device or method according to the invention:

[0036] - the second terminal includes at least one coupler / separator (in particular mode full duplex), the modulator and the photodetector being mounted in parallel;

[0037] - and / or the first terminal is capable of transmitting a signal to the second terminal offset, the second terminal being able to transmit a data signal to the first terminal, by modulating the offset signal;

[0038] - and / or the device further comprises means for achieving:

[0039] *a modulation, for example an amplitude modulation at a first carrier frequency (fpl), of the signals emitted from the first terminal to the second terminal,

[0040] *-a modulation, at a second carrier frequency (fp2), of the signals emitted from the second terminal to the first terminal.

[0041] The modulator can be of the on / off type. For example, the modulator includes a switch or optical switch coupled to a reflecting device, for example, a mirror. This switch can therefore either reflect the signal received from the first terminal (and possibly send it back to that same first terminal) or transmit it to the photodetector, for example. In Full-Duplex mode, this type of modulator is connected in parallel with the photodetector via a coupler / splitter. The latter is not necessary in Half-Duplex mode.

[0042] The modulator may be of the analog type.

[0043] In this case, the second terminal includes an analog modulation device, for example a light attenuator coupled to a mirror that reflects any signal modulated by the analog modulator. This entire modulator assembly can be connected in parallel with the photodetector via a coupler / separator.

[0044] Alternatively, the modulator may be a spectral modulator. For example, it comprises a Bragg grating and / or a Fabry-Pérot cavity associated with at least one mechanical stress generator.

[0045] An example of a spectral modulator may include:

[0046] -a portion of said optical fiber, which extends at least in part along an axis (XX') and comprising optical functionalization means, exhibiting a reflection spectrum of a portion of a light radiation circulating in the fiber;

[0047] -a deformable element along a direction parallel to the same axis (XX') and having a length L;

[0048] - a first mechanical element and a second mechanical element fixed to the deformable element and capable of undergoing relative deformation or relative displacement under the action of this deformable element, said optical fiber being fixed to the first mechanical element at a first fixing point and to the second mechanical element at a second fixing point, these two fixing points being arranged on either side of the optical functionalization means, the distance (d) between the first point of fixing and the second fixing point being preferably less than the length (L) of the deformable element, the ratio L / d being for example at least equal to 5.

[0049] The second terminal of a device according to the invention may comprise several sensors, which therefore communicate with the first terminal via the second terminal using a single optical fiber 2 with a single wavelength. In particular, the modulator may be one of those already described above.

[0050] A device according to the invention may comprise, or a method according to the invention may implement, several second terminals, each comprising a photodetector and a modulator; the first terminal and the second terminals therefore communicate using optical fiber with a single wavelength; each modulator may be one of those that have already been described above.

[0051] Each sensor is then associated with a modulator in a second terminal. The various second terminals are, for example, associated with a coupler / splitter located at the output of the fiber and upstream of each of the second terminals.

[0052] A device or method according to the invention allows:

[0053] - not to use any light source in the second terminal;

[0054] - to use a single optical fiber;

[0055] - bidirectional communication (first terminal to second terminal and second terminal to first terminal) on the same optical fiber, possibly in "Full Duplex" (full duplex or simultaneous bidirectional) or in "half duplex" (alternating bidirectional);

[0056] - the exchange of digital and analog data;

[0057] - to operate in harsh environments (in particular, in temperature) due to the absence of fragile components, particularly radiation sources, in the second terminal;

[0058] - reduced size and nomenclature. BRIEF DESCRIPTION OF THE FIGURES

[0059] [Fig.1] represents an example of an embodiment of a device according to the invention;

[0060] [Fig.2] represents an "on / off" modulator for communication bidirectional, in half duplex, which can be implemented in a device or process according to the invention;

[0061] [Fig.3A], [Fig.3B] and [Fig.3C] represent examples of signals transmitted between 2 terminals of a device according to an embodiment of the invention;

[0062] [Fig.4A] represents an "on or off" modulator, for bidirectional communication, in Full Duplex, which can be implemented in a device or process according to the invention;

[0063] [Fig.4B], [Fig.4C], [Fig.4D], [Fig.4E] and [Fig.4F] represent (Figures 4B -4E) examples of signals transmitted between 2 terminals of a device according to [Fig.4A] and ([Fig.4F]) carrier frequencies for modulation;

[0064] [Fig.5A] represents an analog modulator, for communication in Full-duplex mode, which can be implemented in a device or method according to the invention;

[0065] [Fig.5B] and [Fig.5C] represent examples of signals transmitted between 2 terminals of a device according to [Fig.5A];

[0066] [Fig.6A], [Fig.6B], [Fig.6C], [Fig.6D], [Fig.6E] and [Fig.6F] represent a spectral modulator and examples of operating modes of such a modulator;

[0067] [Fig.7A] represents a device according to an embodiment of the invention, connected to several sensor nodes.

[0068] [Fig.7B] represents another device according to an embodiment of the invention, implementing several sensors.

[0069] [Fig.8A] and [Fig.8B] represent an example of a spectral modulator according to one embodiment;

[0070] [Fig.9A] and [Fig.9B] represent another example of a spectral modulator according to another embodiment;

[0071] [Fig.1OA], [Fig.10B], [Fig.10C], [Fig.10D], [Fig.1OE] and [Fig.10F] represent assembly steps of an example of a spectral modulator;

[0072] [Fig. 1 IA] and [Fig. 1 IB] represent a reflection spectrum of a modulator, in 2 different states;

[0073] [Fig. 12A] and [Fig. 12B] represent the shift of the reflection spectrum of a modulator, relative to the spectra, centered at 2 different wavelengths, of 2 different laser sources;

[0074] [Fig. 13] represents in an enlarged view means of functionalizing an optical fiber within the framework of an embodiment.

[0075] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0076] Fig. 1 represents a first example of an embodiment of a device according to the invention.

[0077] It comprises a single optical fiber 2, capable of transmitting at least one wavelength Xp. This fiber is arranged between:

[0078] - a first terminal 4, also called interrogator terminal or master;

[0079] - a second terminal 6 (sensor node), which may be located in a harsh environment; this terminal is also called a remote or slave terminal; this terminal 6 allows the collection of data from one or more sensor(s) and their transmission to terminal 4 via the single optical fiber 2; the sensor(s) can communicate with the slave terminal 6 via a wired connection, by for example, by implementing a known communication protocol such as SPI or I2C.

[0080] The optical link comprises the single fiber 2 for data transmission at wavelength Xb

[0081] According to one embodiment, terminal 4 comprises:

[0082] - a light source 8, which can be monochromatic (at the wavelength Xi), adapted to emit a light radiation that can be detected by the 2 detectors 10, 22 of the two terminals 4, 6;

[0083] - a photo-detector 10, which allows light to be converted into electric current;

[0084] - means, for example a circulator 12, which allow the light to be directed from the source 8 towards the remote terminal 6 and the light from the latter, re-emitted by the modulator, towards the photo-detector 10.

[0085] Remote terminal 6 includes:

[0086] - a photo-detector 22 allowing the conversion of light into electric current;

[0087] - a modulator 24 allowing, on the one hand, the modulation of the light emitted by the source 8 of the interrogating terminal 4 and on the other hand to send light back to the photodetector 10 via the optical fiber 2 and the circulator 12;

[0088] - a power source 9, for example a battery (or any other type external power supply, which does not need to use the fiber) of the detector(s) and / or sensor(s) of the second terminal; this source is independent of terminal 4. Another power supply source may be any energy source, solar and / or wind and / or thermal and / or vibrational and / or kinetic, and / or chemical, for example of the type which can produce energy in small quantities, energy which is then stored to allow autonomous operation of the sensors.

[0089] In general, for the different embodiments presented in this application:

[0090] a) - the modulator 24 operates on the basis of the Transmission (T) and Reflection (R) of light;

[0091] b) - when terminal 4 sends data or a light signal to terminal 6, the modulator 24 transmits these signals in full to the photo-detector 22;

[0092] c) - when terminal 6 sends a signal to terminal 4, the latter continues to emit at least the SPOWer signal to terminal 6;

[0093] d) - the modulator allows the reflection, i.e. the light returned to terminal 4, to be modulated with a rate ranging from 0% to 100%.

[0094] The invention allows for the implementation of two modulator architectures:

[0095] - all or nothing, with total transmission or total reflection;

[0096] - analog, with partial transmissions and reflections.

[0097] The architecture of the modulator 24 in on / off mode, with "half-duplex" communication, will be explained in relation to [Fig.2] and figures 3A-3C.

[0098] “Half-duplex communication” refers to the case where the optical fiber allows bidirectional communication and the two terminals cannot communicate simultaneously.

[0099] The modulator 24 includes ([Fig.2]) a "switch" 23 (or optical switch) with two possible positions, allowing either all the light to be transmitted to the photodetector 22 or all of it to be reflected (on or off). In other words, the switch, controlled by control electronics 25, allows switching between the two states: transmission (T) and reflection (R).

[0100] When the switch 23 is in the "Transmit" state, it routes the light to the photo-detector 22. When the switch 24 is in the "Reflection" state, it routes the light to a mirror 242 whose role is to reflect the light, which is then returned to the terminal 4.

[0101] Fig. 3A represents an example of an analog and / or digital data signal Ts transmitted from terminal 4 to terminal 6.

[0102] When terminal 6 wishes to communicate with terminal 4, the latter transmits a continuous light (signal) (a "request") which is then either totally transmitted or totally reflected to form a digital signal representing the message that terminal 6 wishes to transmit to terminal 4.

[0103] More precisely, when terminal 4 (“master”) wants to request a particular piece of data from terminal 6 (“slave”), terminal 4 sends a composite request, for example: a request code, an address, etc., which is then terminated by a continuous signal (offset) so that terminal 6 can respond.

[0104] Figures 3B and 3C represent an example of a Ts signal of data transmitted from terminal 4 to terminal 6 (Data) and of RM (Data) data transmitted from terminal 6 to terminal 4, in "half duplex" mode: when data is sent from terminal 4 to terminal 6, no data is sent from terminal 6 to terminal 4, and when data is sent from terminal 6 to terminal 4, no data is sent from terminal 4 to terminal 6.

[0105] This solution allows:

[0106] - to transmit digital or analog signals from terminal 4 to the terminal 6;

[0107] - to transmit digital data from terminal 6 to terminal 4;

[0108] - to establish bidirectional communication in "Half-duplex";

[0109] - to facilitate, thanks to the complementarity of the signals in Figures 3B and 3C, the verification of the integrity of the signals transmitted from terminal 6 to terminal 4.

[0110] An architecture with an on / off modulator and full-duplex communication will be explained in relation to figures 4A-4F.

[0111] This modulator includes, in the terminal 6, a device providing the functions of coupler and splitter 26 (also called optical divider or beam splitter). This splitter allows the photodetector 22 and the modulator 24 to be mounted in parallel, and the power of the signal coming from the terminal 4 to be shared between the modulator 24 and the photodetector 22, the energy distribution between these 2 elements being dependent on the requirements.

[0112] The modulator 24 also includes a "switch" 23 (or optical switch), located downstream of the distributor 26, which allows either all the light to be transmitted, for example to an absorber 241, or all of it to be reflected (on or off). It is controlled by control electronics 25 to switch between the two states: transmission (T), reflection (R).

[0113] When switch 23 is in the "Transmit" state, it directs the light either to an absorber 241 or, for example, to the photodetector 22 to increase the amplitude of the signals that the latter receives. When switch 23 is in the "Reflect" state, it directs the light to a mirror 242, the role of which is to reflect the light, which is then returned to terminal 4.

[0114] Fig. 4B represents an example of a Ts signal transmitted from terminal 4 to terminal 6:

[0115] - initially, a continuous, constant, and non-zero reference or "offset" signal is transmitted to terminal 6; digital and / or analog data to be communicated to the latter are superimposed on this signal; in other words, the continuous offset signal allows terminal 6 to send data to terminal 4 at any time by modulating it (high state, low state) by switch 24;

[0116] -in a second step, only the continuous, constant and non-zero signal continues to be transmitted to terminal 6 when terminal 4 is waiting for data.

[0117] Figure 4C represents an example of an RM signal transmitted from terminal 6 to terminal 4:

[0118] - initially, a data signal is transmitted to terminal 4, this signal being obtained using the offset signal by modulating it (using the switch);

[0119] -in a second step, only a continuous signal is transmitted to terminal 4. In this example, this signal corresponds to the case where the switch is connected to the photo-detector 22 (not to the absorber) and the latter is partially reflective.

[0120] Switch 23 can toggle between two states according to two possible configurations:

[0121] (i) Reflection to terminal 4 and absorption: the offset is either reflected to return a state X (X = low, respectively high) to terminal 4, or absorbed to send back a state Y (Y = high, respectively low) to terminal 4;

[0122] (ii) Reflection to terminal 4 and transmission to photo-detector 22: the offset is either reflected to return a state X (X = low, respectively high) to terminal 4 or transmitted to photo-detector 22 to return a state Y (Y = high, respectively low) to terminal 4; in this case, terminal 6 is able to check the integrity of the returned data (Data) which are exactly inverse (logical complement) (Data) of the data detected by photo-detector 22 (see figures 4D and 4E).

[0123] Full-duplex signal / data transfer, i.e., the case where both terminals can communicate simultaneously, is possible thanks to signal modulation, illustrated for example in [Fig. 4F], where the signals between the two terminals are carried by two distinct carrier frequencies fpl and fp2, which are preferably sufficiently far apart to take into account the BPI and BP2 bandwidths of the signals / data involved. Amplitude modulation is given here as an example, but any other type of modulation can be applied (frequency or phase modulation).

[0124] This solution offers the same advantages as the previous one but also allows the two terminals to communicate in full-duplex.

[0125] An architecture with an analog modulator and full-duplex communication will be explained in relation to figures 5A-5D.

[0126] The modulator 34 here comprises an analog attenuator 33 for modulating transmission / reflection in an analog manner, control electronics 25, and a mirror 36. The attenuator is controlled by the control electronics 25 to control its transmission. The mirror 36 is mounted in series with this attenuator to reflect the light towards the terminal 4. The modulator 33 and the photodetector 22 are connected in parallel via the coupler / splitter 26 (also called an optical divider or beam splitter) which allows the power of the signal from the terminal 4 to be divided between the modulator 34 and the photodetector 22.

[0127] When terminal 4 sends data (analog and / or digital), this data is extracted using the electronics associated with the photo-detector 22.

[0128] When terminal 6 communicates with terminal 4, the attenuator 34 coupled to its mirror 36 modulates the signal in amplitude to generate the data (analog or digital) reflected towards terminal 4.

[0129] For terminal 6 to communicate with terminal 4, the latter sends terminal 6 a continuous, non-zero signal, called a reference or "offset" signal. This continuous offset allows terminal 6 to send data to terminal 4 at any time by modulating it (high state, low state) using modulator 33.

[0130] Figure 5B represents an example of a Ts signal transmitted from terminal 4 to terminal 6:

[0131] - initially, a continuous, constant, non-zero signal, called the reference or "offset" signal, is transmitted to terminal 6, with analog and / or digital data at communicate it to him; this continuous offset allows terminal 6 to send data to terminal 4 at any time by modulating it (high state, low state) by modulator 34;

[0132] -in a second step, only the continuous, constant and non-zero signal continues to be transmitted to terminal 6, if terminal 4 wishes to receive data.

[0133] Figure 5C represents an example of an RM signal transmitted from terminal 6 to terminal 4:

[0134] - initially, an analog and / or digital data signal is transmitted to terminal 4, this signal being obtained using the offset signal by modulating it (using modulator 34);

[0135] -in a second step, only the offset signal, for example, continues to be transmitted to terminal 4 to signify the end of data transmission.

[0136] For full-duplex communication to occur, the waveforms (signals / data) sent by terminal 4 are modulated, for example, carried by two carrier frequencies fpl and fp2 ([Fig. 4F]), which are preferably sufficiently far apart, taking into account the bandwidths (BPI and BP2) of the signals involved. Amplitude modulation is given here as an example, but any other type of modulation (frequency or phase) can be applied. Under these conditions, the two terminals can communicate simultaneously at any time.

[0137] This solution allows you to:

[0138] - transmit digital and / or analog signals from terminal 4 to the terminal 6 and vice versa;

[0139] - to establish bidirectional communication in full duplex or half duplex.

[0140] Another architecture with analog modulator and full-duplex communication will be explained in connection with figures 6A-6F.

[0141] The modulator 44 ([Fig.6A]) here comprises means 43, for example a Bragg grating and / or a Fabry-Pérot cavity coupled(s) to means 46 forming a generator of mechanical stresses.

[0142] This type of modulator can be integrated into the optical fiber 2, which also serves as a communication channel, or it can be independent of it. It is controlled by control electronics 25.

[0143] This type of modulator makes it possible to create a spectral modulator, which makes it possible to transmit / reflect partially or totally the light emitted by terminal 4 for a well-defined range of wavelengths.

[0144] When actuated, the mechanical stress generator 46 modifies the physical properties of the means 43, which in turn causes changes in the transmission / reflection spectral properties of the modulator, as explained later with reference to Figures 6B-6F and 11A-11B. In these figures, as well as in Figures 12A-12B, the Wavelength is on the x-axis and the intensity of the spectrum of the spectrum(s) concerned is on the y-axis.

[0145] A more particular embodiment of a mechanical stress generator 46 and a modulator 44 is given later in connection with figures 8A-10F and 13.

[0146] When terminal 4 sends a signal to terminal 6 in the form of light, the wavelength(s) of the latter is / are transmitted in whole or in part by the spectral modulator 44 to the photo-detector 22.

[0147] When terminal 6 sends a signal to terminal 4, modulator 44 transmits or reflects this signal as follows:

[0148] * if there is total transmission and reflection (case of figures 6B and 6C): the data The signals are either fully transmitted or fully reflected. When terminal 4 communicates with terminal 6, the modulator 44 transmits the signals in full. In the case of reverse communication, thanks to the offset signal emitted by terminal 4, this signal is either fully transmitted or reflected by the modulator to represent the digital data to be communicated to terminal 4 by terminal 6. In this case, only half-duplex communication is possible.

[0149] * if there is total transmission and partial reflection (case of figures 6D and 6E): When terminal 4 sends data to terminal 6, the modulator transmits all the signals. Conversely (from terminal 6 to terminal 4), the modulator can switch between two states: partial reflection (with a reflection rate X < 100%) and full transmission to represent digital data. Under these conditions, full-duplex communication is possible through signal modulation (amplitude, frequency, or phase).

[0150] * if there is linear modulation in transmission / reflection (case of [Fig.6F]): the Modulator 44 exhibits a linear characteristic on its reflection slope. This also allows for analog amplitude modulation and thus the exchange of analog signals in both directions, which is not possible in the two previous cases. When terminal 4 communicates with terminal 6, the modulator transmits the digital and / or analog signals in their entirety. When terminal 6 sends data, the modulator linearly reflects a portion of the signals passing through it. In this case, full-duplex communication is possible through signal modulation (frequency, amplitude, or phase).

[0151] Regarding half-duplex or full-duplex communication:

[0152] - in half-duplex communication: during the period when terminal 6 sends Data, terminal 4 sends a non-zero continuous signal (reference or offset signal) which is then amplitude modulated by modulator 44 by reflecting partially this signal in the case of analog modulation or by alternating between reflecting entirely and transmitting entirely in the case of digital modulation.

[0153] - in Full-duplex communication: Data (analog or digital) in The signals originating from terminal 4 are carried, for example, by a carrier frequency fpl (fpl>=0) and superimposed on a non-zero continuous signal (reference or offset signal). When terminal 6 sends data to terminal 4, the signals from the latter (data + offset signal) are partially amplitude modulated with a carrier frequency fp2 higher or lower than fpl. This amplitude modulation is generated by partial reflection and total or partial transmission of the signals. When full-duplex communication is possible, the bandwidths of the signals involved in both directions (BP1 and BP2, see [Fig. 4F]) are preferably taken into account in the choice of the carrier frequencies fpl and fp2.

[0154] This optical spectrum modulator solution offers all the advantages of the modulator architectures presented above; in addition, it offers:

[0155] - the possibility of full-duplex communication without optical components additional (e.g. coupler / splitter, and / or mirror);

[0156] - reduced size and nomenclature because this spectral modulator can to be directly integrated into the optical fiber serving as a communication channel, thus contributing to the improvement of the reliability and robustness of the invention.

[0157] Another embodiment is shown in [Fig. 7A]: it is a device comprising several second terminals 6i, each comprising a photodetector 20i (i = 1, ..., N) for converting light into electrical current, combined with a modulator 24i. The first terminal 4 and the second terminals 6i communicate using a single optical fiber 2. The various slave terminals 6i are associated with a coupler / splitter 27 (sensor node) located at the output 2s of the fiber 2, or downstream of this output, and upstream of each of the slave terminals 6i. The other elements of this variant can be those described above in connection with the preceding figures. In particular, each modulator 24i can be one of those already described above.

[0158] Terminal 4 uses an optical multiplexer 15 to address each terminal 6;. The transmitted data frame may include a time slot dedicated to each terminal 6;.

[0159]

[0160] Alternatively, as shown in [Fig. 7B] (same references for the same elements as in [Fig. 7A]), terminal 4 is connected to terminals 6i with a single optical fiber 2 and several wavelengths Xi, each wavelength Xi being associated to one and only one 6i terminal. A spectral demultiplexer is used to address each of the 6i terminals.

[0161] The invention allows a reduction of cabling between the interrogator terminal (or master) 4 and the sensor node(s) and / or actuator(s), located on the side of the remote terminal(s) (or slave) 6, which may be in harsh environments (high temperature), by transferring the power and data from the sensors through bidirectional communication on a single optical fiber (with two wavelengths and a modulator on the slave side).

[0162] The invention offers numerous additional advantages:

[0163] - the "slave" node, or remote terminal 6, does not contain a light source, by for example, a laser;

[0164] - communication is bidirectional, in half duplex or in full duplex;

[0165] - a single optical fiber is sufficient;

[0166] - a reduction in size and nomenclature is obtained.

[0167] Figures 8A and 8B represent a particular example of an embodiment of modulator that can be implemented within the framework of the present invention.

[0168] This modulator includes at least one fiber 2 extending at least partly along an axis XX', this fiber 2 being fixed outside of a deformable or movable element 46 along a direction parallel to the same axis XX'.

[0169] The fiber 2 is functionalized by means 44, for example a Bragg grating or a Fabry-Pérot cavity, each having light reflection properties as a function of wavelength, properties which will evolve as a function of the deformation of the element 46.

[0170] The device further comprises a first support or mechanical element 8 and a second support or mechanical element 14. In this example, the first support or mechanical element 80 is fixed and the second support or mechanical element 14 is movable, but two supports or mechanical elements movable relative to each other are also usable. Each of these two supports or mechanical elements is connected on one side to the deformable or movable element 46 and on the other side to a portion of the optical fiber 2, so that the means 44 are arranged between a first point 16 for fixing or anchoring the fiber to the support 80 and a second point 18 for fixing or anchoring the fiber to the support 14.

[0171] The deformable or movable element 46 is preferably of the piezoelectric type; alternatively, it may be a MEMS, a motor, a translational element (for example, a plate), a worm gear, or a spring, which makes it possible to modulate the spectrum at high rates: up to several hundred kHz or even more (for example, at frequencies less than or equal to 500 kHz or 1 MHz), or even > 1 MHz. For example, this piezoelectric element deforms in a way longitudinal, along the axis XX', parallel to the optical fiber 2. An example of such a piezoelectric element 46 is illustrated in [Fig.8B]. It can be controlled or commanded by means (or an electrical circuit) 55, which will allow the voltage and its frequency applied to the terminals of the piezoelectric element to be controlled.

[0172] The fixed mechanical support 80 preferably has a parallelepiped shape, with:

[0173] - a flat lateral face 80b parallel to the extension direction XX' by at least one part of fiber 2 and against which the latter can be fixed;

[0174] - a main face 80a, facing the piezoelectric element 46, which can presenting in its middle a hollow 80c forming a receiving volume into which one end of this element 46 can penetrate in order to ensure a solid fixing of the latter with the support 80.

[0175] The movable mechanical support 14 preferably has an overall U-shape, the lateral arms 14bi, 14b2 of the U being parallel to each other and to the XX' extension direction of at least a portion of the fiber 2 and the displacement of the element 46. Alternatively (not shown in the figures), the movable mechanical support 14 has only one lateral arm 14bl (therefore no arm 14b2). However, the presence of a 360° bend 14b2 allows for the positioning of several optical fibers and the parallelization of the phenomena.

[0176] Thus, the distance D between the movable mechanical support 14 and the fixed mechanical support 8 is less than the distance d separating the fixation points 16, 18 of the optical fiber against the surfaces 80b and 14b. The fiber is fixed against the outer wall 14b of the branch 14bi, located on the same side, with respect to the deformable element 46, as the surface 80b against which the fiber is fixed. This movable mechanical support 14 may have in its middle a stud 14a that penetrates the piezoelectric element 46 in order to ensure a solid fixation of the latter to the support 14.

[0177] The outer surface 14b of the mechanical support 14 and the surface 80b of the fixed mechanical support 80 against which the fiber 2 is fixed are flat and aligned in the same plane.

[0178] Fiber 2 is made solid:

[0179] - on the one hand, the fixed mechanical support 80 by means of a first means of fixing or anchoring at the first point 16;

[0180] - on the other hand, the mobile mechanical support 14 by means of a second means of fixing or anchoring at the second point 18.

[0181] Each anchoring means is, for example, glue, cement, adhesive tape, thermal projections, or any means enabling the fiber to be fixed.

[0182] Assembly steps for such a device may be as follows:

[0183] - first, one end of the piezoelectric element 460 is positioned in the reception volume 80c, if present; this end can be glued into the fixed mechanical support 80;

[0184] - the movable mechanical support 14, comprising its lateral arms 14bb 14b2et the central stud 14a is then fixed to the other end of the piezoelectric element; more precisely, the central stud 14a, if present, can be inserted into a hollow 10a made in this other end, and can be fixed there by gluing, so that the surfaces 14b and 80b are aligned;

[0185] - finally, the functionalized fiber 2 (therefore comprising a Bragg grating or a cavity Fabry Perrot 4) is positioned against the lateral surfaces 80b and 14b on which it is fixed as explained above, the means 4 being arranged between the 2 fixing or anchoring points 16, 18.

[0186] Figures 9A and 9B represent another embodiment of a modulator 1' that can be implemented within the framework of the present invention. In this variant, the fiber 2, which extends at least partially along an axis XX', passes inside the element 46, which is deformable or movable along the same axis XX'.

[0187] As before, fiber 2 is functionalized by means 44, for example a Bragg grating or a Fabry-Pérot cavity.

[0188] The device further comprises a fixed support or mechanical element 38 and a mobile support or mechanical element 34, in the shape of a "T", comprising a head 34 and an elongated body 34a; here again, two mobile supports or mechanical elements may be present.

[0189] Each of these two supports or mechanical elements is linked on one side to the deformable or mobile element 46 and on the other side to a part of the optical fiber 2, so that the means 44 are arranged between a first point 260 of fixing or anchoring of the fiber to the support 38 and a second point 280 of fixing or anchoring of the fiber to the support 34.

[0190] For the reasons already explained above, the deformable or movable element 46 is preferably of the piezoelectric type; alternatively, it may be a MEMS, or a motor, or a translational element (for example, a plate), or a worm gear, or a spring. It deforms longitudinally, along the axis XX'. An example of such a piezoelectric element has already been given above in [Fig. 8B]; it is also shown in [Fig. 1OD].

[0191] The fiber 2 is positioned in an internal channel 34c of the movable mechanical support and in an internal channel 38a of the fixed mechanical support. The end 34d of the elongated body 34a is not solid and comprises a solid half-cylinder and a hollow half-cylinder, as illustrated in Figures 10B and 10C, so that a flat surface 34e, in the extension conduit 34c into which the fiber is introduced, forms a receiving surface for the latter, on which it can be fixed.

[0192] Thus, the distance D' between the movable mechanical support 34 and the fixed mechanical support 38 is less than the distance d which separates the fixing points 260, 280 of the optical fiber against these supports, more precisely against the surfaces 34e and 38e (see below).

[0193] Figures 10A-10E represent various parts of the device in [Fig.8A].

[0194] The piezoelectric element ([Fig. 10D]) is elongated in shape, and has an internal channel 46a into which the body 34a of the movable mechanical support can be introduced.

[0195] The fixed mechanical support 38 (Figures 10E and 10F) preferably has a cylindrical shape, with:

[0196] - an internal channel 38c parallel to the extension direction of fiber 2 and in which the latter can be inserted;

[0197] - a main face 38a, facing the piezoelectric element 46, which can present in its middle a hollow 38d forming a receiving volume into which one end of the element 46 can penetrate in order to ensure a solid fixing of the latter with the support 38.

[0198] The inner end of this support 38 is hollowed out to form a half-cylinder, as illustrated in figures 10E and 10F, so that a flat surface 38e forms a receiving surface 38e for the fiber, on which it can be fixed.

[0199] During the assembly of the device, the surfaces 34e and 38e are arranged so as to be located in the same plane, so that the fiber 2 can be positioned and fixed on these 2 surfaces.

[0200] More specifically, fiber 2 is made bonded:

[0201] - on the one hand of the surface 34e of the movable mechanical support 34 by means of a anchoring means 280;

[0202] - on the other hand, of the surface 38e of the fixed mechanical support by means of a means anchoring 260.

[0203] Each anchoring means 260, 280 is for example an adhesive, or a cement, or an adhesive tape, or thermal projections, or any means enabling the fixation of the fiber.

[0204] During assembly, the movable mechanical support 34 is introduced into the channel 46a of the element 46. Then the fiber 2, equipped with its functionalization element 44, is introduced into the channel 34c, runs along the surface 34e. This gives the structure of [Fig.9B].

[0205] The free end of the element 46 is then introduced into the hollow part 38d of the fixed mechanical support, the free end of the fiber enters the channel 38c and runs along the surface 38e.

[0206] Then surfaces 34th and 38th are aligned with each other.

[0207] An anchor point 280 allows the fiber to be fixed to the surface 34e and an anchor point 260 allows the fiber to be fixed to the surface 38e. The means 44 are arranged between these 2 fiber fixing or anchoring points.

[0208] In the embodiments presented above, in connection with figures 8A-10F, the distance d between the fiber fixing points 16, 18 or 260, 280, on the one hand on the fixed mechanical support and on the other hand on the mobile mechanical support, is small, less than the extension L of the piezoelectric element itself; in particular, we can have a ratio L / d of at least 5 or 10. In [Fig.13], schematically, the part of the fiber 2 comprises the element 44 as well as the fixing points 16, 18, on either side of the latter and separated by the distance d.

[0209] Consequently, when element 46 is activated, the relative variation Ad / d of the portion of the fiber located between these fixation points is much greater (typically 10 to 20 times) than when these points are separated by a distance approximately equal to the length of element 46; for example, Ad / d can be between 0 and 3%, and up to 3% (i.e., the deformation limit of a fiber in general), thus notably being greater than the usual values, which are on the order of 0.15% or 0.2%. These variations will affect the optical properties of the functionalization element 4, for example, a Bragg grating or a Fabry-Pérot cavity. These properties will now be described.

[0210] In general, a Bragg grating makes it possible to generate a bandpass filter, which can completely reflect (up to about 100%) the light in a certain region of the spectrum and completely let (up to about 100%) the light pass through elsewhere (outside of said region).

[0211] Such a Bragg grating makes it possible to generate very different spectral profiles, for example:

[0212] - a profile exhibiting several peaks in reflection over a range of wavelengths between Xi and X2; for example 2 peaks, one at X'i and the other at X'2(Xi < X'i< X'2< X2), or a multitude of peaks at X'i (i=l,..., n, Xi < X';< X2),); such a filter completely reflects the light at X'i and at X'2 or at each X'; (i=l, ..., n), the light being in fact reflected on a small spectral band around each of the wavelengths X'i, X'2, X'i since each peak has a certain spectral width;

[0213] - or a broadband filter profile, between X' i and X'2>; such a filter reflects completely transmits light between X' and X'2 and transmits light outside this spectral band;

[0214] - or a profile having a single reflection peak at X\; such a filter reflects completely the light at X'i (or on a small spectral band around X'i).

[0215] The shape of the reflection or transmission spectrum of a Bragg grating and / or the various wavelengths Xb, X2, X'b, X'2, X' can be adapted according to the physical properties of the grating, for example, according to the inscription pitch and / or the inscription energy and / or the type of inscription used (filament grating(s), bubble grating(s), or planar grating(s)). For example, the spectral width X'2 - X' of a broadband filter is parameterizable and is, for example, between tens or tens of nanometers and one hundred nm, for example, between 10 nm and 100 nm.

[0216] A Bragg network can therefore include a single reflection peak, or several reflection peaks, or form a broadband filter.

[0217] Thus, it is possible to obtain a bandpass filter with a configurable width (for example up to several tens of nanometers of spectral width).

[0218] A Fabry-Pérot cavity also allows for the generation of highly varied spectral profiles. Here again, the shape of the reflection or transmission spectrum of a Fabry-Pérot cavity can be adapted according to its properties (for example, size and / or reflectivity). It is possible to modulate the length of the cavity and / or introduce an effect based on the reflectivity of the faces of the Fabry-Pérot cavity.

[0219] A functionalization element 44 forms an optical element or component in reflection or transmission or of the bandpass filter type, which can reflect light completely or partially (up to X%, X = 100 or X < 100) in a certain region of the spectrum and let light pass completely or partially (up to (100-X)%) elsewhere (outside said region).

[0220] In the case of a modulation device according to the invention, each modulation of length Adentre the fixing points, on either side of the element 44, imposed by the element 46 also affects the element 4 whose optical properties are in turn modulated.

[0221] It is therefore possible:

[0222] - in the case of an element 44 having at rest (or in a first state) a spectrum in reflection between two wavelengths X1 and X2 (as for example in [Fig. 6B]), to modulate the spectrum so that in an "excited" (or second state) of element 44 the reflected spectrum is shifted between two other wavelengths X3 and X4 (as for example in [Fig. 6C]); thus the radiation from a laser source having a spectrum lying outside the reflection window of the modulator, but between wavelengths X3 and X4, is first transmitted ([Fig.6B], first state of the modulator) then, when the modulator is excited ([Fig.6C], second state of the modulator), is reflected, the modulator then acting as an open switch (blocking for the wavelength of the laser);

[0223] - in the case of a partially reflective element 44, having at rest (or in a first state) a partial reflection spectrum at X% (0 < X ​​< 100) between 2 wavelengths Xi and X2 (as for example in [Fig.6D]), to modulate the spectrum so that in an "excited" state (or second state) of element 44 the partial reflection spectrum is shifted between 2 other wavelengths X3 and X4 (as for example in [Fig.6E]); thus the radiation from a laser source having a spectrum outside the reflection window of the modulator, but between wavelengths X3 and X4, is first transmitted (first state of the modulator) then, when the modulator is excited (second state of the modulator), is partially reflected and partially (100-X)% transmitted; the modulator then acts as a partially open switch (partially blocking for the wavelength of the laser);

[0224] - in the case of an element 44 having at rest (or in a first state) a spectrum in reflection having a rising front between 2 wavelengths Xi and X2 (as for example in [Fig.6F]), then a constant value for X > X2, to modulate the spectrum so that, in an "excited" state (or second state) of the element 44, this front is moved between two other wavelengths X3 and X4 (as for example in [Fig.6F]); thus the radiation from a laser source having a spectrum which is first in the reflection window of the modulator, but between the wavelengths X3 and X4, is first reflected ([Fig.6F], first state of the modulator) then, when the modulator is excited (second state of the modulator), partially transmitted, the modulator then acting as a variable analog modulator (modulating the proportion of laser radiation transmitted).

[0225] - in the case of an element 44 having at rest (or in a first state) a spectrum in reflection around a single wavelength Xi ([Fig. 11 A]), to modulate this spectrum so that in an "excited" state (or second state) of element 44 the reflected spectrum is shifted around another wavelength X2 ([Fig. 11 B]), element 44 becoming at least partially transparent for wavelength XI;

[0226] In general, various combinations of the operating modes described above can be implemented; for example, a modulator can be combined with a wavelength selector.

[0227] In general, optical frequencies f and their wavelengths X are related by the relation f = c / X, where c is the speed of light in a vacuum.

Claims

Demands

1. A bidirectional communication device between a first terminal (4) and at least one second terminal (6), comprising: - a single optical fiber (2) between the first terminal (4) and the second terminal (6); - the first terminal (4) comprising a radiation source (8) at at least one first wavelength (XJ), a photodetector (10), and means (12) for directing a signal from the second terminal (6) via the optical fiber (2) to the photodetector (10) and for directing a signal from the radiation source (8) to the optical fiber (2); - the second terminal (6) comprising at least one modulator (24, 34, 44), a photodetector (22), a mirror (36) that reflects any signal modulated by the modulator (34), and power supply means (9); the modulator being of the type: * analog attenuator;* or of the on / off type and comprising an optical switch (24) which reflects the signal received from the first terminal, to send it back to the same first terminal, or which transmits it to the photodetector (22) or to an absorber (241).;

2. Device according to claim 1, the optical fiber (2) being single-mode or multi-mode.

3. Device according to any one of claims 1 or 2, the radiation source (8) being monochromatic or polychromatic.

4. Device according to any one of claims 1 to 3: - the first terminal (4) being capable of emitting, towards the second terminal (6), a continuous light radiation signal and a data signal, at at least one wavelength; - the second terminal (6) being capable of emitting towards the first terminal (4), a data signal, at at least one wavelength.

5. Device according to any one of claims 1 to 4, the second terminal (6) comprising at least one coupler / separator (26), the modulator (24) and the photodetector (22) being mounted in parallel.

6. A device according to any one of claims 1 to 5, the first terminal (4) being capable of transmitting, to the second terminal (6), a continuous signal, referred to as an offset signal, the second terminal (6) being capable of transmit to first terminal (4), a data signal, by modulating the offset signal.

7. Device according to any one of claims 1 to 6, further comprising means for carrying out: - modulation of signals, at a first frequency (fpl), of the signals emitted from the first terminal (4) to the second terminal (6), - modulation of signals, at a second frequency (fp2), of the signals emitted from the second terminal (6) to the first terminal (6).

8. Device according to any one of claims 1 to 7, the communication between the first terminal and the second terminal being of the "half duplex" type.

9. Bidirectional communication device between a first terminal (4) and at least a second terminal (6), comprising: - a single optical fiber (2) between the first terminal (4) and the second terminal (6); - the first terminal (4) comprising a radiation source (8) at at least a first wavelength (XJ, a photodetector (10) and means (12) for directing a signal from the second terminal (6) via the optical fiber (2) to the photodetector (10) and for directing a signal from the radiation source (8) to the optical fiber (2);- the second terminal (6) comprising at least one modulator (24, 34, 44), a photodetector (22), and power supply means (9), the modulator (44) being a spectral modulator, comprising a Bragg grating and / or a Fabry-Pérot cavity associated with at least one mechanical stress generator (46), to generate modifications of the spectral properties in transmission and / or reflection of the spectral modulator; - a portion of said optical fiber (2) extending at least in part along an axis (XX') and comprising said Bragg grating and / or said Fabry-Pérot cavity; - an element (46) deformable along a direction parallel to the same axis (XX') and having a length L;-a first mechanical element (80) and a second mechanical element (14) fixed to the deformable element (46) and capable of undergoing relative deformation or relative displacement under the action of this deformable element (46), said optical fiber being fixed to the first mechanical element (80) at a first point of attachment; (16, 260) and to the second mechanical element (14) at a second fixing point (18, 280), these 2 fixing points being arranged on either side of said Bragg grating and / or said Fabry Pérot cavity, the distance (d) between the first fixing point and the second fixing point being less than the length (L) of the deformable element (46), the ratio L / d being at least equal to 5.

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