Method and device for two-way communication over a single optical fibre with a single light source

Abstract

The invention relates to a device for two-way communication between a first terminal (4) and at least one second terminal (6), the device including: - a single optical fibre (2) between the first terminal (4) and the at least one second terminal (6); - the first terminal (4) including a radiation source (8) of radiation having at least a first wavelength (λ1), a photodetector (10) and means (12) for directing a signal originating from the second terminal (6) via the optical fibre (2) towards the photodetector (10) and for directing a signal originating from the radiation source (8) towards the optical fibre (2); - the second terminal (6) including at least one modulator (24), a photodetector (22), and power supply means (9).

Description

[0001] DESCRIPTION

[0002] Title: METHOD AND DEVICE FOR BIDIRECTIONAL COMMUNICATION ON A SINGLE OPTICAL FIBER WITH A SINGLE LIGHT SOURCE

[0003] TECHNICAL FIELD AND PRIOR ART

[0004] The invention relates to the field of two-way communication between a first terminal and at least one second terminal.

[0005] In harsh environments, with high environmental constraints such as high temperatures (>200°C), or low temperatures (<-40°C), and / or under high electromagnetic disturbances, 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), electrical wired communication becomes very complex to implement because it requires (i) specific materials resistant to the environment in which they are called upon to operate (conductive materials, insulation, shielding) (ii) specific connection processes (interconnection, soldering, etc.) (iii) as well as relatively high power levels and adapted 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.

[0006] For all these non-exhaustive reasons, an optical fiber is an alternative solution with numerous advantages covering all the limitations of wired solutions mentioned in the previous paragraph, in particular, guaranteeing the integrity of the signals. We know of bidirectional communication systems based on optical fiber(s) which use:

[0007] - either at least two optical fibers, one for the signals from the first terminal to the second terminal and one for the signals from the second terminal to the first terminal and, for each terminal, a photo-detector and a laser source, - or one optical fiber and for each terminal, a photo-detector, a dichroic mirror and a laser source. The two sources have two distinct wavelengths XI and λ2 and the two dichroic mirrors reflect these two wavelengths respectively.

[0008] On this subject, one can for example refer to the articles of M. Yonemura et al., entitled "250 Mbit / s Bi-directional Single Plastic Optical Fiber Communication System", published in R&D Review of Toyota CRDL, Vol.40 No.2 and of Xin Li et al., entitled "pLED-Based Single-Wavelength Bi-directional POF Link With 10Gb / s Aggregate Data Rate", published in Journal of Lightwave Technology, Vol. 33, No. 17, September 1, 2015.

[0009] Bidirectional optical communication with a remote terminal poses other problems when the latter operates in a harsh environment or with high environmental constraints, for example at high temperatures (>200°C), or at low temperatures (<-40°C). In particular, this type of environment, and especially high temperatures, does not tolerate the use of laser-type light sources because the performance of the latter depends greatly on its operating temperature.

[0010] 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 security reasons. In particular, in order to increase the robustness of such a terminal to environmental conditions, it is appropriate to reduce the nomenclature constituting it, 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 for severe operating conditions (temperature, vibrations, acceleration, pressure, etc.) to ensure the reliability and robustness of such a communication solution. In another aspect, we seek to make reliable and reduce the cost of bidirectional optical communication that can operate in a harsh environment (for example in the case of operation in extreme conditions).

[0012] STATEMENT 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 firstly relates 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 the at least one second terminal;

[0016] - the first terminal comprising a light source at at least a first wavelength (Xi), a photo-detector and means for directing a signal which comes from the second terminal via the optical fiber towards the photo-detector and for directing a signal which comes from the radiation source towards the optical fiber;

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

[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 a single optical fiber and a single wavelength for bidirectional communication, in particular in half duplex or full duplex. The invention allows a reduction in the size and nomenclature of the device. The modulator of the second terminal makes it possible to reflect modulated light (which can therefore contain a message) towards the first terminal. The latter comprises, for example, a circulator making it possible to direct the light coming from the second terminal towards a photo-detector. The invention also relates to a method for bidirectional communication between a first terminal and at least one second terminal, for example implementing a device as described above and in the remainder of this application.

[0020] A method according to the invention, or a method as defined above, may comprise the following steps:

[0021] - generating optical signals at at least a first wavelength in the first terminal and transmitting them, via the optical fiber, at least to the second terminal;

[0022] - the second terminal receives the signals sent by the first terminal, possibly modulates these signals (all or nothing or analog), and returns all or part of the signal or signals received to the first terminal, via optical fiber;

[0023] - the photodetector of the first terminal receives the signals returned by the second terminal via the optical fiber.

[0024] In particular embodiments of a device or method according to the invention:

[0025] - the optical fiber can be single-mode or multi-mode fiber.

[0026] - and / or:

[0027] - the first terminal is capable of transmitting, to the second terminal, a continuous light signal and a data signal, at the first wavelength;

[0028] - the second terminal is capable of transmitting to the first terminal a data signal at the first wavelength.

[0029] The light source can be monochromatic; this achievement allows:

[0030] - to use a single wavelength for two-way communication, possibly in Full Duplex;

[0031] - an exchange of digital and / or analog data between terminals.

[0032] In particular embodiments of a device or method according to the invention:

[0033] - the second terminal comprises at least one coupler / separator (in particular full duplex mode), the modulator and the photodetector being mounted in parallel;

[0034] - and / or the first terminal is capable of transmitting, to the second terminal, an offset signal, the second terminal being capable of transmitting to the first terminal, a data signal, by modulating the offset signal;

[0035] - and / or the device further comprises means for carrying out: *modulation, for example amplitude modulation at a first carrier frequency (f p i), signals transmitted from the first terminal to the second terminal, *-a modulation, at a second carrier frequency (fpz), of the signals transmitted from the second terminal to the first terminal.

[0036] The modulator can be of the all-or-nothing type. For example, the modulator includes an optical switch or commutator coupled to a reflection device, for example a mirror. This switch / commutator can therefore either reflect the signal received from the first terminal (to possibly send it back to this 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.

[0037] The modulator can be of analog type.

[0038] 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 can be connected in parallel with the photodetector via a coupler / splitter.

[0039] 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.

[0040] An example of a spectral modulator might include:

[0041] - a part of said optical fiber, which extends at least partly along an axis (XX') and comprising optical functionalization means, presenting a spectrum in reflection of a part of a light radiation circulating in the fiber;

[0042] - an element deformable in a direction parallel to the same axis (XX') and having a length L;

[0043] -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 fixing point 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. The invention therefore also relates to a bidirectional communication device between a first terminal and at least one second terminal, comprising:

[0044] - a single optical fiber between the first terminal and the second terminal;

[0045] - the first terminal comprising a radiation source at at least a first wavelength (Xi), a photodetector and means for directing a signal which comes from the second terminal via the optical fiber towards the photodetector and for directing a signal which comes from the radiation source towards the optical fiber;

[0046] - the second terminal comprising at least one modulator, a photodetector, possibly a mirror which reflects any signal modulated by the modulator, and supply means, the modulator being a spectral modulator, comprising a Bragg grating and / or a Fabry Pérot cavity associated with at least one mechanical stress generator, to generate modifications of the spectral properties in transmission and / or in reflection of the spectral modulator;

[0047] - a portion of said optical fiber extending at least partly along an axis (XX') and comprising said Bragg grating and / or said Fabry Pérot cavity; - an element deformable 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 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, the ratio L / d being 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 the optical fiber with a single wavelength; each modulator may be one of those which have already been described above.

[0051] Each sensor is then associated with a modulator in a second terminal. The different second terminals are for example associated with a coupler / splitter placed 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; - to operate in harsh environments (in particular, in temperature) due to the absence of fragile components, in particular radiation sources, in the second terminal;

[0057] - reduced size and nomenclature.

[0058] BRIEF DESCRIPTION OF THE FIGURES

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

[0060] [Fig.2] represents an “all or nothing” modulator for two-way, half-duplex communication, which can be implemented in a device or method 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 “all or nothing” modulator, for bidirectional communication, in Full Duplex, which can be implemented in a device or a method 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 figure 4A and (figure 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 figure 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 one 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. [Fig.8A] and [Fig.8B] represent an example of a spectral modulator according to one embodiment;

[0069] [Fig.9A] and [Fig.9B] represent another example of a spectral modulator according to another embodiment;

[0070] [Fig.10A], [Fig.10B], [Fig.10C], [Fig.10D], [Fig.10E] and [Fig.10F] represent assembly steps of an example of a spectral modulator;

[0071] [Fig.llA] and [Fig.llB] represent a reflection spectrum of a modulator, in 2 different states;

[0072] [Fig.l2A] and [Fig.l2B] represent the displacement of the reflection spectrum of a modulator, relative to the spectra, centered at 2 different wavelengths, of 2 different laser sources;

[0073] [Fig.13] represents in an enlarged view the means of functionalizing an optical fiber in the context of an implementation.

[0074] DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

[0075] Figure 1 represents a first example of embodiment of a device according to the invention. It comprises a single optical fiber 2, capable of transmitting at least one wavelength Ai. This fiber is arranged between:

[0076] - a first terminal 4, also called interrogator or master terminal;

[0077] - 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 makes it possible to collect data from one or more sensors and send them to the terminal 4 through the single optical fiber 2; the sensor(s) can communicate with the slave terminal 6 via a wired connection, for example by implementing a known communication protocol of the SPI or I2C type.

[0078] The optical link comprises only fiber 2 for data transmission at wavelength Ai.

[0079] According to one embodiment, the terminal 4 comprises: - a light source 8, which can be monochromatic (at the wavelength Xi), adapted to emit light radiation which can be detected by the 2 detectors 10, 22 of the two terminals 4, 6;

[0080] - a photo-detector 10, which converts light into electric current;

[0081] - means, for example a circulator 12, which make it possible to direct the light from the source 8 towards the remote terminal 6 and the light coming from the latter, re-emitted by the modulator, towards the photo-detector 10.

[0082] Remote terminal 6 includes:

[0083] - a photo-detector 22 for converting light into electric current;

[0084] - a modulator 24 making it possible on the one hand to modulate the light emitted by the source 8 of the interrogator terminal 4 and on the other hand to return light to the photo-detector 10 via the optical fiber 2 and the circulator 12;

[0085] - a power source 9, for example a battery (or any other type of external power supply, which does not need to use the fiber) of the detector(s) and / or the sensor(s) of the second terminal; this source is independent of the terminal 4. Another power source can be constituted by 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.

[0086] In general, for the different embodiments presented in the present application: a) - the modulator 24 operates on the basis of the Transmission (T) and the Reflection (R) of the light; b) - when the terminal 4 sends data or a light signal to the terminal 6, the modulator 24 transmits these signals in full to the photodetector 22; c) - when the terminal 6 sends a signal to the terminal 4, the latter continues to emit at least the SPOWER signal to the terminal 6; d) - the modulator makes it possible to modulate the reflection, that is to say, the light returned to the terminal 4 with a rate ranging from 0% to 100%. The invention makes it possible to implement two modulator architectures:

[0087] - all or nothing, with total transmission or total reflection;

[0088] - analog, with partial transmissions and reflections.

[0089] The architecture of the modulator 24 in all-or-nothing mode, with “half-duplex” communication, will be explained in connection with Figure 2 and Figures 3A-3C.

[0090] Half-duplex communication is when the optical fiber allows two-way communication and the two terminals cannot communicate simultaneously.

[0091] The modulator 24 comprises (figure 2) a “switch” 23 (or optical switch) with two possible positions, allowing either to transmit all of the light to the photo-detector 22 or to reflect it completely (all or nothing). In other words, the switch, controlled by control electronics 25, allows a switch between the two states: transmission (T) and reflection (R).

[0092] When switch 23 is in the "Transmission" state, it routes the light to the photodetector 22. When 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 terminal 4.

[0093] Figure 3A represents an example of a signal Ts of analog and / or digital data transmitted from terminal 4 to terminal 6.

[0094] When terminal 6 wishes to communicate with terminal 4, the latter transmits a continuous light (signal) (a “request”) which is then either fully transmitted or fully reflected to form a digital signal representing the message that terminal 6 wishes to transmit to terminal 4.

[0095] More precisely, when terminal 4 ("master") wishes to request a particular piece of data from terminal 6 ("slave"), terminal 4 sends a compound request, for example: a request code, an address, etc. which is then terminated by a continuous signal (offset) so that terminal 6 can respond.

[0096] 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.

[0097] This solution allows:

[0098] - to transmit digital or analog signals from terminal 4 to terminal 6;

[0099] - to transmit digital data from terminal 6 to terminal 4;

[0100] - to establish two-way communication in “Half-duplex”;

[0101] - to facilitate, thanks to the complementarity of the signals of figures 3B and 3C, the verification of the integrity of the signals transmitted from terminal 6 to terminal 4.

[0102] An architecture with an all-or-nothing modulator and full-duplex communication will be explained in relation to figures 4A-4F.

[0103] This modulator comprises, in terminal 6, a device providing the functions of coupler and splitter 26 (also called optical divider or beam distributor). This distributor makes it possible to mount the photo-detector 22 and the modulator 24 in parallel, and to share the power of the signal coming from terminal 4 between the modulator 24 and the photo-detector 22, the energy distribution between these 2 elements depending on the needs.

[0104] The modulator 24 also includes a “switch” 23 (or optical switch), arranged downstream of the distributor 26 and allowing either the transmission of all the light, for example to an absorber 241, or its total reflection (all or nothing). It is controlled by control electronics 25 to switch between the two states: transmission (T), reflection (R).

[0105] When the switch 23 is in the "Transmission" state, it routes 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 the switch 23 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.

[0106] Figure 4B represents an example of signal Ts transmitted from terminal 4 to terminal 6: - initially, a continuous signal, called reference or “offset”, constant and non-zero 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;

[0107] -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.

[0108] Figure 4C shows an example of an RM signal transmitted from terminal 6 to terminal 4:

[0109] - firstly, a data signal is transmitted to terminal 4, this signal being obtained using the offset signal by modulating it (using the switch);

[0110] -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 photo-detector 22 (not to the absorber) and the latter is partially reflective.

[0111] Switch 23 can switch between two states according to two possible configurations:

[0112] (i) Reflection towards terminal 4 and absorption: the offset is either reflected to return an X state (X = low, respectively high) to terminal 4, or absorbed to return a Y state (Y = high, respectively low) to terminal 4;

[0113] (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 verify the integrity of the returned data (Data) which are exactly inverse (logically complementary) (Data) of the data detected by photo-detector 22 (see figures 4D and 4E).

[0114] The transfer of signals / data in “Full-duplex” mode, i.e. the case where the two terminals can communicate simultaneously, is possible thanks to a modulation of the signals, illustrated for example in figure 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 bandwidths BPI and BP2 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).

[0115] This solution offers the same advantages as the previous one but also allows the two terminals to communicate in full-duplex.

[0116] An architecture with analog modulator and full duplex communication will be explained in relation to figures 5A-5D.

[0117] The modulator 34 here comprises an analog attenuator 33 for modulating the 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. In series with this attenuator is mounted the mirror 36 to reflect the light towards the terminal 4. The modulator 33 and the photo-detector 22 are mounted in parallel via the coupler / splitter 26 (also called an optical splitter or beam splitter for sharing the power of the signal coming from the terminal 4 between the modulator 34 and the photo-detector 22.

[0118] When the terminal 4 sends data (analog and / or digital), these are extracted using the electronics associated with the photo-detector 22.

[0119] When terminal 6 communicates with terminal 4, attenuator 34 coupled to its mirror 36, modulates the signal in amplitude to generate the data (analog or digital) reflected towards terminal 4.

[0120] In order for terminal 6 to communicate with terminal 4, the latter sends to terminal 6 a continuous signal, called a reference or "offset", which is constant and non-zero. This continuous offset allows terminal 6 to send data to terminal 4 at any time by modulating it (high state, low state) by modulator 33.

[0121] Figure 5B represents an example of signal Ts transmitted from terminal 4 to terminal 6: -firstly, a continuous signal, called reference or “offset”, constant and non-zero is transmitted to terminal 6, with analog and / or digital data to be communicated to it; 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; -secondly, only the continuous, constant and non-zero signal continues to be transmitted to terminal 6, if terminal 4 wishes to receive data.

[0122] Figure 5C shows an example of an RM signal transmitted from terminal 6 to terminal 4:

[0123] - firstly, an analog and / or digital data signal is transmitted to the terminal 4, this signal being obtained using the offset signal by modulating it (using the modulator 34);

[0124] - in a second step, only the offset signal, for example, continues to be transmitted to terminal 4 to indicate the end of data transmission.

[0125] For a “Full-duplex” communication to take place, the waveforms (signals / data) sent by the terminal 4 are modulated, for example, carried by two carrier frequencies fpl and fp2 (figure 4F), which are preferably sufficiently distant from each other 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 2 terminals can communicate simultaneously and at any time. This solution makes it possible to:

[0126] - transmit digital and / or analog signals from terminal 4 to terminal 6 and vice versa;

[0127] - to establish two-way communication in full duplex or half duplex.

[0128] Another architecture with analog modulator and full duplex communication will be explained in connection with figures 6A-6F.

[0129] The modulator 44 (figure 6A) here comprises means 43, for example a Bragg grating and / or a Fabry Pérot cavity coupled to means 46 forming a mechanical stress generator.

[0130] This type of modulator can be integrated into the optical fiber 2 which also serves as a communication channel or can be independent of it. It is controlled by control electronics 25. This type of modulator makes it possible to produce a spectral modulator, which makes it possible to transmit / reflect partially or completely the light emitted by the terminal 4 for a well-defined range of wavelengths.

[0131] When actuated, the mechanical stress generator 46 modifies the physical properties of the means 43, which causes modifications to the spectral properties in transmission / reflection of the modulator, as explained further below in connection with figures 6B-6F and 11A-11B. In these figures, as well as in figures 12A-12B, the wavelength is on the abscissa and the intensity Ispectrum of the spectrum(s) concerned is on the ordinate.

[0132] A more particular example of a mechanical stress generator 46 and a modulator 44 is given later in connection with figures 8A-10F and 13.

[0133] When terminal 4 sends a signal to terminal 6 in the form of light, the wavelength(s) of the latter is (are) fully or partially transmitted by spectral modulator 44 to photo-detector 22.

[0134] When terminal 6 sends a signal to terminal 4, modulator 44 transmits or reflects this signal according to the following cases:

[0135] * if there is total transmission and reflection (case of figures 6B and 6C): the data is either fully transmitted or fully reflected. When terminal 4 communicates with terminal 6, modulator 44 transmits the signals in full. In the case of reverse communication, thanks to the offset signal emitted by terminal 4, it 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 an exchange in Half-Duplex mode is possible.

[0136] * 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 of the signals. In the opposite case (terminal 6 to terminal 4), the modulator can switch between the two states: partial reflection (with a rate X <100%) and total transmission to represent digital data. Under these conditions, full-duplex communication is possible by means of signal modulations (in amplitude, frequency or phase). * if there is linear modulation in transmission / reflection (case of figure 6F): modulator 44 has a linear characteristic on its reflection slope. This also offers the possibility of carrying out analog amplitude modulations and therefore of exchanging analog signals in both communication 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 full. When terminal 6 sends data, the modulator linearly reflects part of the signals passing through it. In this case, full-duplex communication is possible by means of signal modulations (in frequency, or amplitude, or phase). With regard to half-duplex or full-duplex communication:

[0137] - 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 partially reflecting this signal in the case of analog modulation or by alternating between fully reflecting and fully transmitting in the case of digital modulation.

[0138] - in Full-duplex communication: The data (analog or digital) from terminal 4 are carried, for example, by a frequency fpl (f pl>=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 a partial reflection and a total or partial transmission of the signals. When full-duplex communication is possible, the bandwidths of the signals involved in both directions (BPi and BP2, see figure 4F) are preferably taken into account in the choice of the carrier frequencies / pi and f P 2

[0139] This optical spectrum modulator solution offers all the advantages of the modulator architectures presented above; in addition, it offers:

[0140] - the possibility of full-duplex communication without additional optical components (for example coupler / splitter, and / or mirror); - reduced size and nomenclature because this spectral modulator can be directly integrated into the optical fiber serving as a communication channel, thus contributing to improving the reliability and robustness of the invention.

[0141] Another embodiment is presented in Figure 7A: it is a device comprising several second terminals 6i, each comprising a photo-detector 20i (i = 1, N) for converting light into electric current, combined with a modulator 24j. The first terminal 4 and the second terminals 6i communicate using a single optical fiber 2. The reference The different slave terminals 6i are associated with a coupler / splitter Tl (sensor node) arranged at output 2 S of fiber 2, or downstream of this output, and upstream of each of the slave terminals 6i. The other elements of this variant may be those described above in connection with the previous figures. In particular, each modulator 24i may be one of those which have already been described above.

[0142] Terminal 4 uses an optical multiplexer 15 to address each terminal 6i. The transmitted data frame may include a time slot dedicated to each terminal 6i.

[0143] Alternatively, shown in Figure 7B (same references for the same elements as in Figure 7A), the terminal 4 is connected to the terminals 6i with a single optical fiber 2 and several wavelengths Xi, each wavelength Xi being associated with one and only one terminal 6i. A spectral demultiplexer is used to address each of the terminals 6i.

[0144] The invention allows a reduction in the wiring between the interrogator (or master) terminal 4 and the sensor node(s) and / or actuator(s), located on the side of the remote (or slave) terminal(s) 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). The invention also offers numerous advantages:

[0145] - the “slave” node, or remote terminal 6, does not contain a light source, for example a laser;

[0146] - communication is bidirectional, half duplex or full duplex;

[0147] - a single optical fiber is sufficient;

[0148] - we obtain a reduction in space requirements and nomenclature.

[0149] Figures 8A and 8B represent a particular example of embodiment of a modulator that can be implemented within the framework of the present invention.

[0150] This modulator comprises at least one fiber 2 extending at least partly along an axis XX', this fiber 2 being fixed to the outside of an element 46 deformable or movable in a direction parallel to the same axis XX'.

[0151] 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 the wavelength, properties which will evolve as a function of the deformation of the element 46.

[0152] 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 mobile, but 2 supports or mechanical elements mobile relative to each other are also usable. Each of these 2 supports or mechanical elements is connected on the one hand to the deformable or mobile element 46 and on the other hand to a part 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.

[0153] The deformable or mobile element 46 is preferably of the piezoelectric type; alternatively, it may be a MEMS, or a motor, or a translation element (for example a plate), or a worm screw, 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 longitudinally, along the axis XX', parallel to the optical fiber 2. An example of such a piezoelectric element 46 is illustrated in FIG. 8B. It may be controlled or commanded by means (or an electrical circuit) 55, which will make it possible to control the voltage and its frequency applied to the terminals of the piezoelectric element.

[0154] The fixed mechanical support 80 preferably has a parallelepiped shape, with:

[0155] - a flat lateral face 80b parallel to the direction XX' of extension of at least part of the fiber 2 and against which the latter can be fixed;

[0156] - a main face 80a, facing the piezoelectric element 46, which may have in its middle a hollow 80c forming a receiving volume into which one end of this element 46 can penetrate in order to ensure solid fixing of the latter with the support 80.

[0157] The mobile mechanical support 14 preferably has an overall “U” shape, the lateral branches 14bi, 14b? of the “U” being parallel to each other and to the direction XX' of extension of at least a part of the fiber 2 and of displacement of the element 46. As a variant (not shown in the figures), the mobile mechanical support 14 has a single lateral branch 14bl (therefore no branch 14b2). But the presence of a 360° elbow 14b2 makes it possible to position several optical fibers and to parallelize the phenomena.

[0158] Thus, the distance D between the movable mechanical support 14 and the fixed mechanical support 8 is less than the distance d which separates the fixing 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, relative 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 which penetrates into the piezoelectric element 46 in order to ensure a solid fixing of the latter with the support 14.

[0159] 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.

[0160] The fiber 2 is made integral: - on the one hand with the fixed mechanical support 80 by means of a first means of fixing or anchoring at the first point 16;

[0161] - on the other hand of the mobile mechanical support 14 by means of a second means of fixing or anchoring to the second point 18.

[0162] Each anchoring means is for example a glue, or a cement, or an adhesive tape, or thermal projections, or any means allowing the fiber to be fixed.

[0163] The assembly steps of such a device can be as follows:

[0164] - first, one end of the piezoelectric element 460 is positioned in the receiving volume 80c, if the latter is present; this end can be glued into the fixed mechanical support 80;

[0165] - the movable mechanical support 14, comprising its lateral branches 14bi, 14b? and its central stud 14a is then fixed to the other end of the piezoelectric element; more precisely, the central stud 14a, if it is present, can be introduced into a hollow 10a made in this other end, and can be fixed there by gluing, so that the surfaces 14b and 14b are aligned;

[0166] - finally, the functionalized fiber 2 (therefore comprising a Bragg grating or a Fabry Perrot cavity 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.

[0167] Figures 9A and 9B represent another example of 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 in part along an axis XX', passes inside the deformable or mobile element 46 along the same axis XX'.

[0168] As previously, the fiber 2 is functionalized by means 44, for example a Bragg grating or a Fabry-Pérot cavity.

[0169] 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, it is possible to have two mobile supports or mechanical elements. Each of these two supports or mechanical elements is linked on the one hand to the deformable or mobile element 46 and on the other hand to a part of the optical fiber 2, so that the means 44 are arranged between a first point 260 for fixing or anchoring the fiber to the support 38 and a second point 280 for fixing or anchoring the fiber to the support 34.

[0170] For the reasons already explained above, the deformable or mobile element 46 is preferably of the piezoelectric type; alternatively, it may be a MEMS, or a motor, or a translation element (for example a plate), or a worm screw, or a spring. It deforms longitudinally, along the axis XX'. An example of such a piezoelectric element has already been given above in figure 8B; it is also shown in figure 10D.

[0171] The fiber 2 is positioned in an inner channel 34c of the movable mechanical support and in an inner 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 FIGS. 10B and 10C, so that a flat surface 34e, in the conduit extension 34c into which the fiber is introduced, forms a receiving surface for the latter, on which it can be fixed.

[0172] Thus, the distance D' between the mobile 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).

[0173] Figures 10A-10E show various parts of the device of Figure 8A.

[0174] The piezoelectric element (Figure 10D) is elongated in shape, and has an internal channel 46a inside which the body 34a of the movable mechanical support can be introduced.

[0175] The fixed mechanical support 38 (figures 10E and 10F) preferably has a cylindrical shape, with:

[0176] - an internal channel 38c parallel to the direction of extension of the fiber 2 and into which the latter can be inserted; - a main face 38a, facing the piezoelectric element 46, which can have in its middle a hollow 38d forming a receiving volume into which one end of the element 46 can penetrate in order to ensure solid fixing of the latter with the support 38.

[0177] The inner end of this support 38 is hollowed out to form a half-cylinder, as illustrated in FIGS. 10E and 10F, so that a flat surface 38e forms a receiving surface 38e for the fiber, on which it can be fixed.

[0178] When assembling the device, the surfaces 34e and 38e are arranged to be located in the same plane, so that the fiber 2 can be positioned and fixed on these 2 surfaces.

[0179] More precisely, fiber 2 is made integral:

[0180] - on the one hand of the surface 34e of the mobile mechanical support 34 by means of an anchoring means 280;

[0181] - on the other hand of the surface 38e of the fixed mechanical support by means of an anchoring means 260.

[0182] Each anchoring means 260, 280 is for example a glue, or a cement, or an adhesive tape, or thermal projections, or any means allowing the fiber to be fixed. During assembly, the movable mechanical support 34 is introduced into the channel 46a of the element 46. Then the fiber 2, provided with its functionalization element 44, is introduced into the channel 34c, along the surface 34e. The structure of Figure 9B is thus obtained.

[0183] 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.

[0184] Then the 34th and 38th surfaces are aligned with each other.

[0185] An anchoring point 280 makes it possible to fix the fiber on the surface 34e and an anchoring point 260 makes it possible to fix the fiber on the surface 38e. The means 44 are arranged between these 2 points of fixing or anchoring of the fiber. In the embodiments presented above, in connection with figures 8A-10F, the distance d between the points 16, 18 or 260, 280 of fixing the fiber, on the one hand on the fixed mechanical support on the other hand on the mobile mechanical support is small, less than the extension L of the piezoelectric element itself; in particular, it is possible to have a ratio L / d at least equal to 5 or 10. Figure 13 shows 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.

[0186] Consequently, when activating the element 46, the relative variation Ad / d of the portion of the fiber located between these fixing points is much greater (typically 10 to 20 times) than in the case where these points are separated by a distance substantially equal to the length of the element 46; for example Ad / d can be between 0 and 3%, and go up to 3% (i.e. the deformation limit of a fiber in general), therefore in particular be greater than the usual values ​​which are of 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 presented.

[0187] Generally speaking, a Bragg grating allows the generation of 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 elsewhere (outside of said region).

[0188] Such a Bragg grating makes it possible to generate very different spectral profiles, for example:

[0189] - a profile with several peaks in reflection over a range of wavelengths between Xi and A2; for example 2 peaks, one at A'i and the other at A'2 (Ai < A'i< À'2< À.2), or a multitude of peaks at A'i (i=l, ..., n, Xi < A'i< A2),); such a filter completely reflects the light at A'i and A'2 or at each A'i (i=l, ..., n), the light being in fact reflected over a narrow spectral band around each of the wavelengths A'i, A' 2, A'i since each peak has a certain spectral width;

[0190] - or a broadband filter profile, between A'i and A'2,; such a filter completely reflects the light between A'i and A'2 and transmits the light outside this spectral band; - or a profile comprising a single reflection peak at X'i; such a filter completely reflects the light at X'i (or on a small spectral band around A'i). The shape of the reflection or transmission spectrum of a Bragg grating and / or the various wavelengths Xi, A2, A'i, A' 2, A'i 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 implemented (filament grating(s) or bubble grating(s) or planar grating(s)). For example, the spectral width A' 2 - À'i of a broadband filter is configurable and is, for example, between ten or a few tens of nanometers and a hundred nm, for example between 10 nm and 100 nm.

[0191] A Bragg grating can therefore have a single reflection peak, or several reflection peaks, or form a broadband filter.

[0192] Thus, it is possible to obtain a bandpass filter with configurable width (for example up to several tens of nanometers of spectral width).

[0193] A Fabry-Pérot cavity also allows for the generation of very 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, etc.). It is possible to modulate the length of the cavity and / or to introduce an effect depending on the reflectivity of the faces of the Fabry-Pérot cavity.

[0194] A functionalizing element 44 forms an optical element or component in reflection or transmission or of the bandpass filter type, which can completely or partially reflect (up to X%, X = 100 or X < 100) the light in a certain region of the spectrum and completely or partially let (up to (100- X)%) the light pass elsewhere (outside said region).

[0195] In the case of a modulation device according to the invention, each modulation of length Ad between 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. It is thus possible:

[0196] - in the case of an element 44 having at rest (or in a first state) a reflection spectrum between two wavelengths Xi and A2 (as for example in figure 6B), to modulate the spectrum so that in an “excited” state (or second state) of the element 44 the reflection spectrum is shifted between two other wavelengths A3 and A4 (as for example in figure 6C); thus the radiation from a laser source having a spectrum located outside the reflection window of the modulator, but between the wavelengths A3 and A4, is first transmitted (figure 6B, first state of the modulator) then, when the modulator is excited (figure 6C, second state of the modulator), is reflected, the modulator then acting as an open switch (blocking for the wavelength of the laser);

[0197] - in the case of a partially reflective element 44, having at rest (or in a first state) a spectrum in partial reflection at X% (0 < X ​​< 100) between 2 wavelengths Xi and A2 (as for example in figure 6D), to modulate the spectrum so that in an “excited” state (or second state) of the element 44 the spectrum in partial reflection is shifted between 2 other wavelengths A3 and A4 (as for example in figure 6E); thus the radiation of a laser source having a spectrum located outside the reflection window of the modulator, but between the wavelengths A3 and A4, 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);

[0198] - in the case of an element 44 having at rest (or in a first state) a reflection spectrum having a rising edge between 2 wavelengths Ai and A2 (as for example in figure 6F), then a constant value for A > A2, to modulate the spectrum so that, in an “excited” state (or second state) of the element 44, this edge is displaced between two other wavelengths A3 and A4 (as for example in figure 6F); thus the radiation of a laser source having a spectrum initially located in the reflection window of the modulator, but between wavelengths A3 and A4, is first reflected (figure 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).

[0199] - in the case of an element 44 having at rest (or in a first state) a reflection spectrum around a single wavelength Xi (figure 11A), to modulate this spectrum so that in an “excited” state (or second state) of the element 44 the reflection spectrum is shifted around another wavelength A? (figure 11B), the element 44 becoming at least partially transparent for the wavelength Xi;

[0200] Generally speaking, various combinations of the operating modes set out above can be implemented; for example, a modulator can be combined with a wavelength selector.

[0201] In a general way, the optical frequencies f and their wavelengths A are linked by the relation f = c / A, where c is the speed of light in a vacuum.

Claims

CLAIMS 1. Device for two-way communication 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 source (8) of radiation at at least a first wavelength (Xi), a photodetector (10) and means (12) for directing a signal which comes from the second terminal (6) via the optical fiber (2) towards the photodetector (10) and for directing a signal which comes from the source (8) of radiation towards the optical fiber (2); - the second terminal (6) comprising at least one modulator (24, 34, 44), a photodetector (22), a mirror (36) which reflects any signal modulated by the modulator (34) and supply means (9); the modulator being of the type: * analog attenuator; * or of the all-or-nothing type and comprising an optical switch (24) which reflects the signal received from the first terminal, to return it to this 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 one of claims 1 or 2, the radiation source (8) being monochromatic or polychromatic.

4. Device according to 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 transmitting to the first terminal (4), a data signal, at at least one wavelength.

5. Device according to 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. Device according to one of claims 1 to 5, the first terminal (4) being capable of transmitting, to the second terminal (6), a continuous signal, called an offset signal, the second terminal (6) being capable of transmitting to the first terminal (4), a data signal, by modulating the offset signal.

7. Device according to one of claims 1 to 6, further comprising means for carrying out: - a modulation of signals, at a first frequency (f P i), signals transmitted from the first terminal (4) to the second terminal (6), - a modulation of signals, at a second frequency (f P z), signals transmitted from the second terminal (6) to the first terminal (6).

8. Device according to 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 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 source (8) of radiation at at least a first wavelength (Xi), a photodetector (10) and means (12) for directing a signal which comes from the second terminal (6) via the optical fiber (2) towards the photodetector (10) and for directing a signal which comes from the source (8) of radiation towards the optical fiber (2); - the second terminal (6) comprising at least one modulator (24, 34, 44), a photodetector (22), 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 in reflection of the spectral modulator; - a part of said optical fiber (2) extending at least partly along an axis (XX') and comprising said Bragg grating and / or said Fabry Pérot cavity; - an element (46) deformable in 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 fixing point (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.

Images