System for identifying at least one beacon

Abstract

A system for identifying at least one beacon (B) comprising night-vision goggles or a scope incorporating an image intensifier tube (13). The image intensifier tube (13) comprises a diffraction grating (20) placed between an entrance window (15) and a photocathode (16) so as to diffract photons onto said photocathode and to allow the photocathode to have quantum efficiency (QE):  greater than 1% in a range of imaging wavelengths and;  lying between 0.001 and 1% in a range of detection wavelengths, distinct from said range of imaging wavelengths, said range of detection wavelengths being at least between 1000 nanometres and 1100 nanometres; the image intensifier tube being configured to capture electromagnetic radiation emitted by said beacon in said second range of detection wavelengths.

Description

[0001] IDENTIFICATION SYSTEM OF AT LEAST ONE BEACON

[0002] FIELD OF THE INVENTION

[0003] The technical field of the invention relates to systems for identifying beacons using night vision binoculars or night vision goggles, particularly in low light conditions. The beacons can be carried by individuals, animals, vehicles or placed in strategic locations.

[0004] The invention finds a particularly advantageous application in the military field. Indeed, for friend or foe identification on a military operation field, also known by the English acronym IFF for "Identification Friend or Foe", the beacons can be carried by soldiers. In this context, the invention allows a soldier equipped with a scope or binoculars to identify friendly forces, reliably and discreetly. Thus, this system makes it possible to prevent incidents of fratricidal fire and to optimize coordination between friendly units, while offering a response capacity adaptable to various operational scenarios.

[0005] STATE OF THE ART

[0006] In the context of military operations, it is known to use night vision devices 110. As schematically illustrated in Figures 1 and 3 of the prior art, a night vision device 110 is conventionally in the form of a goggle intended to be placed in front of a sensor, the eye of a user, or both eyes when two devices are juxtaposed to form night vision binoculars, also known by the English acronym NVG for “Night Vision Goggle”.

[0007] This night vision device 110 integrates several elements placed on the optical axis al of the sensor or the user's eye, in order to transform the image of the observed scene. More precisely, the scope comprises, from the scene external to the sensor or the user's eye, an objective 12, an image intensifier tube 130 and an eyepiece 14. The objective 12 conventionally comprises one or more lenses for capturing the photons of the electromagnetic radiation of the observed scene. The eyepiece 14, similarly to the objective 12, comprises one or more lenses for capturing and incidentally viewing the photons of the light signal emitted by the image intensifier tube 130. The image intensifier tube 130 comprises at least three distinct elements: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0008] The photocathode 16 is in the form of a semi-transparent photosensitive layer receiving the photons of the incident electromagnetic radiation, i.e. the photons transmitted by the objective 12. To do this, an entry window 15 transmits the photons from the objective 12 onto the photocathode 16 while ensuring the hermeticity of the external wall 23 of the image intensifier tube 130.

[0009] The photocathode 16 is generally made in the form of a thin layer of metal or semiconductor applied to a layer of glass or material transparent to light. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of the photons of the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by photoelectric effect, an emission of electrons, called photoelectrons.

[0010] These photoelectrons are then subjected to a first electric field within a first acceleration zone 17, making it possible to direct the photoelectrons towards the electron multiplier 18. This first electric field is produced by applying a voltage between the photocathode 16 and the electron multiplier 18, typically a voltage of the order of 50 to 500 volts to best guarantee a straight path for the electrons.

[0011] The electron multiplier 18, also called an electron amplifier, typically comprises a microchannel plate 25 covered by electrodes. This microchannel plate is also known by the acronym GMC or MCP for "microchannel plate" in the English literature. It is made from a plate of resistive or dielectric material with a thickness typically between 0.2 and 1 millimeter.

[0012] The microchannels 25 of this wafer have an axis of revolution «2 inclined at an angle «3 of a few degrees, typically between 4 and 12 degrees, relative to the normal of the surface of the electron multiplier 18, so as to induce multiple collisions of the photoelectrons 28 in the microchannels 25. In addition to the first electric field created between the photocathode 16 and the electron multiplier 18, a second electric field is created between the inlet and the outlet of the electron multiplier 18 by means of the electrodes placed on either side between the inlet and the outlet of the microchannel wafer 25.

[0013] This electric field makes it possible to charge the internal semiconductor layer of the microchannels 25, so that the multiple collisions of the photoelectrons 28 in the microchannels 25 generate a large number of secondary electrons 29. This electric field also makes it possible, on the one hand, to accelerate the first secondary electrons 29 inside the microchannels 25, so that these first secondary electrons 29 collide again with the surface of the microchannels 25 producing in turn other secondary electrons 29, and so on generating by this physical process a large number of secondary electrons 29; and on the other hand to accelerate the secondary electrons 29 by supplying energy, in order to orient them from the entrance of the microchannels 25 to the exit of the microchannels 25. Typically, the photoelectrons 28 are multiplied by a factor of between 10 2 and 10 4 in the electron multiplier 18.

[0014] At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly towards the phosphorescent screen 20, within a second acceleration zone 19, under the effect of a third electric field generated between the exit of the electron multiplier 18 and the phosphorescent screen 20, typically an electric field generated by a voltage of between 4 and 10 kV.

[0015] The phosphorescent screen 20 makes it possible to transform the secondary electrons 29 into photons producing a luminous intensity. It is in the form of a phosphorescent layer or a layer of a luminophore material deposited on a substrate, conventionally made of glass. At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, conventionally a network of optical fibers 21, possibly making it possible to return the image formed on the phosphorescent screen 20 to obtain a correct visualization of the observed scene.

[0016] To generate the three electric fields, electronic components 22 are conventionally arranged around an internal vacuum enclosure 24. The night vision system 110 thus formed therefore has optical elements, electronic components 22, and possibly a system for viewing the scene observed on the eyepiece 14. A night vision system 110 currently available on the market conventionally makes it possible to capture and amplify photons over a wavelength range 1 between 450 nanometers and 900 nanometers. More precisely, the operational wavelength range 1 of a night vision system 110 is mainly conditioned by the sensitivity spectrum of the photocathode 16.

[0017] As illustrated in Figure 2, the sensitivity spectrum of the photocathode 16 is defined as a function of the wavelength of the photons received by the photocathode 16 and the quantum efficiency, also known by the English acronym QE for “Quantum Efficiency”, that is to say the ratio between the number of photoelectrons 28 generated and the number of photons received by the photocathode 16. For a sensitivity spectrum of a night vision system 110 of the state of the art, the quantum efficiency QE is typically greater than 1% between 450 nanometers and 900 nanometers and less than 0.001% outside this operational wavelength range 1.

[0018] In addition to the photons of the observed scene, this operational wavelength range 1 also allows signals to be captured.

[0019] For example, as described in EP 0 560 470, an identification friend or foe (IFF) system can be implemented using NVG night vision goggles to detect a beacon B carried by an ally. Figure 4 of the prior art illustrates a possible implementation of the teaching of EP 0 560 470. In this example, the NVG night vision goggles are associated with an activation device 310 of the beacon B. This activation device 310 generates a signal Sa which activates the beacon B so that the beacon B in return produces a manifestation signal Sm detectable via the NVG night vision goggles. To achieve this, the beacon B can use an infrared diode which flashes in the operational wavelength range 1 of the NVG night vision goggles when it is activated.

[0020] Other similar solutions are described in documents US5299227, US5375008, US20070236384 and WO2022 / 103941.

[0021] In all these solutions, the detection of B beacons is carried out in the operational wavelength range 1 of the night vision system 110. However, the detection of a B beacon in the operational wavelength range 1 necessarily degrades the quality of the image obtained because the signal received from a B beacon replaces the information of the observed scene.

[0022] In addition, the development of night vision systems 110 in the operating fields results in a reduction in the stealth of B beacon carriers because opponents / enemies can be equipped with NVG night vision binoculars which also make it possible to detect the Sm manifestation signal emitted by the B beacons because NVG night vision binoculars are practically all sensitive in the wavelength range 1 between 450 nanometers and 900 nanometers.

[0023] There is therefore a need to improve state-of-the-art beacon identification systems in order to guarantee image quality and preserve the stealth of beacon carriers.

[0024] STATEMENT OF THE INVENTION

[0025] The invention proposes to address this technical problem by using night vision binoculars or a scope incorporating a tube with an extended operational wavelength range so as to detect beacons outside the wavelength range used to form images of the scene.

[0026] More specifically, the invention stems from an observation that the use of a diffraction grating interposed between the input window and the photocathode makes it possible to modify the shape of the operational wavelength range and to obtain a quantum efficiency of between 0.001 and 1% in a specific wavelength range, between 1000 and 1100 nanometers, preferably between 1050 and 1075 nanometers.

[0027] The invention therefore proposes to use beacons emitting a manifestation signal between 1000 and 1100 nanometers, preferably between 1050 and 1075 nanometers, associated with night vision binoculars or a scope incorporating an image amplifier tube operating in a first wavelength range, called the image formation wavelength range, to observe the scene and in a second wavelength range, called the detection wavelength range, to detect the beacons. Indeed, although the quantum efficiency is not sufficient in the detection wavelength range between 1000 nanometers and 1100 nanometers to form an image of the scene, this quantum efficiency is sufficient to capture beacon manifestation signals.

[0028] Thus, the invention relates to a system for identifying at least one beacon, the beacon integrating a device for emitting electromagnetic radiation at a wavelength of between 1000 and 1100 nanometers, the system comprising night vision binoculars or a scope integrating an image amplifier tube comprising:

[0029] ■ an input window configured to receive and transmit photons;

[0030] ■ a photocathode, fixed on an internal face of said input window, capable of converting photons transmitted by the input window into photoelectrons; the photocathode having a sensitivity spectrum defined as a function of the wavelength of the photons received by the photocathode and the quantum efficiency of the photocathode, that is to say the ratio between the number of photoelectrons generated and the number of photons received by the photocathode;

[0031] ■ an electron multiplier capable of multiplying photoelectrons into secondary electrons; and

[0032] ■ a phosphorescent screen transforming secondary electrons into photons.

[0033] The invention is characterized in that the image amplifier tube also comprises a diffraction grating placed between the input window and the photocathode so as to diffract the photons in said photocathode and to allow the photocathode to have a quantum efficiency:

[0034] ■ greater than 1% in an imaging wavelength range and;

[0035] ■ between 0.001 and 1% in a detection wavelength range, distinct from said image formation wavelength range, said detection wavelength range being at least between 1000 and 1100 nanometers; said image amplifier tube being configured to capture electromagnetic radiation emitted by said beacon in said detection wavelength range. The characteristic according to which the detection wavelength range is at least between 1000 and 1100 nanometers is to be understood in correlation with the wavelength of the beacon. Thus, according to this characteristic, the detection wavelength range of the photocathode corresponds at least to the emission wavelength range of the beacon, chosen between 1000 and 1100 nanometers.

[0036] The invention thus makes it possible to detect the beacons without degrading the images formed because the detection wavelength of the beacons is not included in the image formation wavelength range, for example between 450 nanometers and 900 nanometers.

[0037] In addition, the invention also improves the stealth of beacon wearers. Indeed, conventional night vision binoculars, which detect photons in the wavelength range between 450 nanometers and 900 nanometers, cannot pick up manifestation signals from beacons in the wavelength range between 1000 and 1100 nanometers, preferably between 1050 and 1075 nanometers. Preferably, the image amplifier tube is configured to pick up manifestation signals from the at least one beacon at a wavelength of 1064 nanometers.

[0038] Preferably, to obtain efficient detection in the detection wavelength range, the photocathode is formed from antimony and at least one alkali metal, such as NaKCs, SbNa KCs, SbNaK, SbKCs, SbRbKCs or SbRbCs alloys.

[0039] In addition to the image amplifier tube, the night vision binoculars or scope may also comprise a beacon activation device. Preferably, this beacon activation device is configured to emit an activation signal while the beacon comprises a module for receiving said activation signal so as to transmit the electromagnetic radiation at the wavelength between 1000 and 1100 nanometers in the form of a manifestation signal in response to the activation signal emitted by the activation device.

[0040] For example, the beacon activation device may consist of a radiofrequency transmitter or an optical transmitter, the beacon receiving module corresponding to an antenna or an optical receiver respectively. For an optical transmitter / receiver, the optical transmitter may be a laser diode with a wavelength between 1400 and 1800 nanometers, and the beacon receiving module may correspond to a photodiode capable of capturing a wavelength between 1400 and 1800 nanometers. Indeed, the transmission and reception of this activation signal in this wavelength range also ensures significant stealth for the beacon wearer.

[0041] Furthermore, to improve the detection range, the night vision binoculars or scope may be configured to observe a scene in which a specific observation area defined by the emission angle of said activation device and the viewing angle of the night vision binoculars or scope is placed, the detection of said beacon being carried out only in said specific observation area. Indeed, by aiming at a specific area of ​​the observation area, the emission angle of the activation device may be reduced in order to improve the range of the activation signal. Typically, it is possible to obtain detection of a beacon at more than three kilometers with this strategy.

[0042] Furthermore, the image amplifier tube may include a light gain regulation mechanism to adapt the output luminance of the tube. This function is called "auto-gating" in the English literature and makes it possible to limit saturation and increase dynamics for scenes with very strong variations in light intensity. This mechanism relies on the rapid detection of light variations to adjust, in a few milliseconds, the generation of photoelectrons and stabilize the brightness at the output of the image intensifier tube, typically between 6 and 12 candela / m 2 depending on the types of phosphorus used (green P43 or white P45).

[0043] The implementation of this light gain regulation mechanism is achieved by periodically adjusting the electrical potential of the photocathode. Thus, when a significant variation in brightness is detected at the output of the image intensifier tube, the light gain regulation mechanism intervenes to modify, in a few milliseconds, the duty cycle of the periodic voltage applied to the photocathode. This modification of the duty cycle makes it possible to adapt the number of photoelectrons generated by the photocathode which will then be multiplied by the electron multiplier. The voltage applied to the terminals of the electron multiplier will itself be adjusted to adapt the number of secondary electrons and, consequently, the output luminance of the tube. This principle of adaptation of electrical charges internal to the tube makes it possible not to exceed the predetermined luminance threshold.This threshold is, for example, an MOB threshold, an acronym for the expression “Maximum of Brightness” in Anglo-Saxon literature.

[0044] This dynamic amplification control not only protects the image intensifier tube from the risks associated with excessive light intensity, but also provides a better view of the observed scene by adapting the image resolution to the surrounding conditions, without saturation or visual glare. As a result, operators benefit from clearer and more stable night vision, even in the face of sudden light changes, which is crucial for applications such as military or surveillance operations.

[0045] However, the specific activation period at the photocathode of the light gain regulation mechanism induces phases in which the image amplifier tube cannot detect a beacon. To prevent the beacon from emitting a manifestation signal only outside the detection ranges of the image amplifier tube, the beacon can be configured to emit a signal for a significant duration and greater than the specific activation period of the light gain regulation mechanism.

[0046] However, this solution increases the consumption and therefore the size of the beacons. To solve this problem by asynchronous detection, the activation device can have a variable activation period. With this embodiment, the beacon can be detected when the specific activation period of the image amplifier tube coincides with the activation period of the activation device. This solution limits the necessary emission duration of the beacons but can cause a latency in the detection speed of the beacons, the time for the two activation periods to coincide.

[0047] To avoid this latency, synchronous detection can be achieved by connecting the activation device with the device for managing the specific activation period of the light gain regulation mechanism. In this embodiment, the activation device has an activation period synchronized with the specific activation period of the light gain regulation mechanism of the image amplifier tube. BRIEF DESCRIPTION OF THE FIGURES

[0048] The invention will be better understood from reading the following description, given solely by way of example, and drawn up in relation to the appended drawings, in which identical references designate identical or similar elements, and in which:

[0049] Figure 1 illustrates a schematic sectional view of a state-of-the-art night vision device;

[0050] Figure 2 illustrates the evolution of the quantum efficiency of the night vision device of Figure 1;

[0051] Figure 3 illustrates a perspective view of the night vision device of Figure 1;

[0052] Figure 4 illustrates a schematic view of a state-of-the-art beacon identification system implementing two night vision devices of Figure 1;

[0053] Figure 5 illustrates a schematic sectional view of a night vision device according to the invention;

[0054] Figure 6 illustrates the evolution of the quantum efficiency of the night vision device of Figure 5;

[0055] Figure 7 illustrates a schematic view of a system for identifying a beacon according to the invention implementing two night vision devices of Figure 5;

[0056] Figure 8 illustrates an example of images observed by night vision goggles incorporating two night vision devices of Figure 7;

[0057] Figure 9 illustrates four timing diagrams of asynchronous triggering of a beacon with the identification system of Figure 7; and

[0058] Figure 10 illustrates four timing diagrams of synchronous triggering of a beacon with the identification system of Figure 7.

[0059] DETAILED DESCRIPTION OF THE INVENTION

[0060] Figure 5 illustrates a night vision device 11 incorporating an image intensifier tube 13 according to the invention. As illustrated in Figure 1 of the prior art, the night vision device 11 is in the form of a goggle intended to be placed in front of a sensor, the eye of a user, or both eyes when two devices are juxtaposed to form night vision binoculars. This night vision device 11 incorporates several elements placed on the optical axis a1 of the sensor or the eye of the user in order to transform the image of the observed scene. More precisely, the goggle comprises, from the scene external to the sensor or the eye of the user, an objective 12, the image intensifier tube 13 of the invention and an eyepiece 14.

[0061] As described above, the objective 12 comprises one or more lenses for capturing the photons of the electromagnetic radiation of the observed scene. The eyepiece 14, similarly to the objective 12, comprises one or more lenses for capturing and incidentally viewing the photons of the light signal emitted by the image intensifier tube 13.

[0062] The image intensifier tube 13 comprises at least three separate elements integrated in an internal vacuum enclosure 24: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0063] As described above, the photocathode 16 is in the form of a semi-transparent photosensitive layer receiving the photons of the incident electromagnetic radiation, i.e. the photons transmitted by the objective 12. To do this, an input window 15 transmits the photons from the objective 12 onto the photocathode 16 while ensuring the hermeticity of an external wall 23 of the image intensifier tube 13.

[0064] The photocathode 16 is generally made in the form of a thin layer of metal or semiconductor applied to a layer of glass or a material transparent to light. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of the photons of the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by photoelectric effect, an emission of electrons.

[0065] More precisely, the photocathode 16 is fixed on a diffraction grating 30, itself fixed on an internal face of the entrance window 15.

[0066] The diffraction grating 30 is formed from a periodic arrangement of patterns, for example, notches, slits, recesses, notches or scratches, provided in the entrance window 15. A diffraction material is preferably placed between the patterns of the diffraction grating 30 of the entrance window 15 to form a flat surface for deposition of the photocathode 16. For example, the entrance window 15 may be made of glass, quartz or borosilicate glass. The patterns of the diffraction grating 30 of the entrance window 15 may be made by known etching techniques, such as holography, ion etching and / or diamond etching techniques.

[0067] The patterns are then preferably filled with a diffraction material whose optical refractive index n is different from that of the entrance window 15, such as for example EAI2O3 (n~1, 7), TiCh (n~2, 3-2, 6), Ta2O5 (n~2, 2), or HfCh. This diffraction material can be deposited by known physical vapor deposition techniques, such as sputtering, evaporation, or electron beam physical vapor deposition, also known by the acronym EBPVD for "electron beam physical vapor deposition" in the English literature.

[0068] The difference between the optical indices of the diffraction material present in said patterns and of the material of the entrance window 15 is preferably greater than or equal to 0.2.

[0069] The photocathode 16 is preferably made of a semiconductor material, preferably an alkaline compound based on antimony. Such an alkaline material may be chosen from the following materials: SbNaKCs, SbNa2K.Cs, SbNaK, SbKCs, SbRbKCs or SbRbCs. Preferably, the photocathode 16 is formed of antimony and sodium.

[0070] At the exit of the photocathode 16, the emitted electrons, called photoelectrons, are then subjected to a first electric field within a first acceleration zone 17 making it possible to direct the photoelectrons towards the electron multiplier 18. This first electric field is produced by applying a voltage between the photocathode 16 and the electron multiplier 18, typically a voltage of between 50 and 500 volts to guarantee a straight path for the electrons.

[0071] In addition to the first electric field created between the photocathode 16 and the electron multiplier 18, a second electric field is created between the two faces of the electron multiplier 18 by means of the electrodes placed on either side of the microchannel plate 25.

[0072] This electric field makes it possible to charge the internal semiconductor layer of the microchannels 25 so that the multiple collisions of the photoelectrons 28 in the microchannels 25 generate a large number of secondary electrons 29. This electric field also makes it possible, on the one hand, to accelerate the first secondary electrons 29 inside the microchannels 25, so that these first secondary electrons 29 collide again with the surface of the microchannels 25 producing in turn other secondary electrons 29, and so on generating by this physical process a large number of secondary electrons 29; and on the other hand to accelerate the secondary electrons 29 by supplying energy, in order to orient them from the entrance of the microchannels 25 to the exit of the microchannels 25. Typically, the photoelectrons 28 are multiplied by a factor of between 10 3 and 10 6in the electron multiplier 18. At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly towards the phosphorescent screen 20, within a second acceleration zone 19, under the effect of a third electric field generated between the electron multiplier 18 and the phosphorescent screen 20, typically an electric field generated by a voltage of between 4 and 10 kV.

[0073] The phosphorescent screen 20 makes it possible to transform the secondary electrons 29 into photons producing a luminous intensity. It is in the form of a phosphorescent layer or a layer of a luminophore material deposited on a substrate, conventionally made of glass.

[0074] At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, conventionally a network of optical fibers 21 possibly making it possible to return the image formed on the phosphorescent screen 20 to obtain a correct visualization of the observed scene.

[0075] To generate the three electric fields, electronic components 22 are conventionally arranged around the internal vacuum enclosure 24. The night vision system 11 thus formed therefore has optical elements, electronic components 22, and possibly a system for viewing the scene observed on the eyepiece 14.

[0076] As illustrated in Figure 6, the image intensifier tube 13 thus formed, with the association of the photocathode 16 and the diffraction grating 30, has a sensitivity spectrum with a quantum efficiency QE whose maximum is lower than the maximum quantum efficiency QE of an image intensifier tube 130 of the state of the art.

[0077] Furthermore, it is noted that the sensitivity spectrum is also wider. It is therefore possible to detect photons between 400 nanometers and 1064 nanometers, and no longer between 450 nanometers and 900 nanometers. More precisely, according to the invention, the image intensifier tube 13 thus formed has a quantum efficiency QE:

[0078] ■ greater than 1% in an imaging wavelength range and;

[0079] ■ between 0.001 and 1% in a range of detection wavelengths, distinct from said range of imaging wavelengths, the range of detection wavelengths being at least between 1000 and 1100 nanometers, preferably between 1050 and 1075 nanometers.

[0080] This range of detection wavelengths makes it possible to capture a manifestation signal Sm from at least one beacon B. Thus, as illustrated in Figure 7, the invention proposes to use night vision binoculars NVG, or a night vision goggle, integrating an image intensifier tube 13, as previously described, to capture a manifestation signal Sm from at least one beacon B in the range of detection wavelengths. Preferably, the beacon B emits a manifestation signal Sm at the precise wavelength of 1064 nanometers.

[0081] The beacon B may consist of an electronic box integrating a power supply and means for transmitting the manifestation signal Sm, for example an infrared diode.

[0082] Furthermore, the beacon B can emit a manifestation signal Sm permanently or in response to an activation signal Sa. Preferably, as illustrated in FIG. 7, the activation signal Sa can be emitted from the night vision binoculars NVG, or the night vision goggle. To do this, the night vision binoculars NVG, or the night vision goggle, incorporates an activation device 31.

[0083] The activation device 31 may consist of a tube integrating a power supply and means for transmitting the activation signal Sa. It should be noted that the power supply of the activation device 31 may be provided by the night vision binoculars NVG, or the night vision goggles, for example by the electronic components 22. The activation signal Sa may be luminous or radiofrequency. Thus, when the activation device 31 of the beacon B integrates a radiofrequency transmitter, the beacon B integrates an antenna and the manifestation signal Sm is transmitted only in response to the reception of the activation signal Sa. Alternatively, when the activation device 31 of the beacon B integrates an optical transmitter, for example a laser diode, the beacon B integrates an optical receiver, for example a photodiode, and the manifestation signal Sm is also transmitted only in response to the reception of the activation signal Sa.The laser diode and photodiode can be configured to operate at a wavelength between 1400 nanometers and 1800 nanometers, for example 1550 nanometers.

[0084] In order for beacon B to receive the activation signal Sa, it is necessary that the propagation range and propagation angle F31 of the activation device Sa be set so that the activation signal Sa reaches beacon B. Similarly, the power and propagation angle Fb of beacon B must be configured so that the manifestation signal Sm reaches the detection angle Fnvg of the night vision goggles NVG, or the night vision scope.

[0085] To increase the detection range of a B beacon, it is possible to reduce the propagation angle F31 of the activation signal Sa. It is also possible to use a propagation angle F31 of the activation signal Sa smaller than the viewing angle Fnvg of the night vision binoculars NVG, or of the night vision goggle. In this embodiment, the B beacons can only be detected on a specific observation zone Zp of the images observed by night vision binoculars NVG, or of the night vision goggle.

[0086] In the example of Figure 8, NVG night vision binoculars allow viewing binocular night images and, in these images, a specific central observation zone Zp allows the detection of B beacons.

[0087] Furthermore, the night vision binoculars NVG, or the night vision goggle, may incorporate a light gain regulation mechanism, also called "auto-gating" in the English literature, limiting the opening time of the image amplifier tube 13 to each specific activation period Pal of the light gain regulation mechanism. To prevent the beacon B from emitting a manifestation signal Sm only outside the detection ranges of the image amplifier tube 13, the beacon B may be configured to emit a signal for a significant duration and greater than the specific activation period Pal of the light gain regulation mechanism. Alternatively, with asynchronous detection as illustrated in FIG. 9, the activation device 31 may have a variable activation period P31.With this embodiment, the beacon B can be detected when the specific activation period Pal of the image amplifier tube 13 coincides with the activation period P31 of the activation device 31. Thus, on the last timing diagram of figure 9 relating to the detection of the image amplifier tube 13, the beacon B is not detected on the first two manifestation signals Sm emitted but it is detected on the last two manifestation signals Sm.

[0088] With synchronous detection as illustrated in Figure 10, the activation device 31 is connected with the device for managing the specific activation period Pal of the light gain regulation mechanism, for example by the electronic components 22. In this embodiment, the activation device 31 has an activation period P31 synchronized with the specific activation period Pal of the light gain regulation mechanism of the image amplifier tube 13. Thus, in this embodiment, on the last timing diagram of Figure 10 relating to the detection of the image amplifier tube 13, the beacon B is detected on the four manifestation signals Sm emitted.

[0089] Thus, the invention makes it possible to detect B beacons without degrading the images formed by the image amplifier tube 13 because the detection wavelength of the B beacons is not included in the image formation wavelength range, for example between 450 nanometers and 900 nanometers. In addition, the invention also improves the stealth of B beacon carriers because the detection wavelength of the B beacons is not detected by conventional night vision systems which capture photons in the wavelength range 1 between 450 nanometers and 900 nanometers.

Claims

CLAIMS 1. System for identifying at least one beacon (B), the beacon (B) incorporating a device for emitting electromagnetic radiation at a wavelength between 1000 nanometers and 1100 nanometers, the system comprising night vision binoculars (NVG) or a scope incorporating an image amplifier tube (13) comprising: ■ an input window (15) configured to receive and transmit the photons; ■ a photocathode (16), fixed on an internal face of said input window (15), capable of converting photons transmitted by the input window (15) into photoelectrons (28); the photocathode (16) having a sensitivity spectrum defined as a function of the wavelength of the photons received by the photocathode (16) and the quantum efficiency (QE) of the photocathode (16), that is to say the ratio between the number of photoelectrons (28) generated and the number of photons received by the photocathode (16); ■ an electron multiplier (18) capable of multiplying the photoelectrons (28) into secondary electrons (29); and ■ a phosphorescent screen (20) transforming the secondary electrons (29) into photons; characterized in that the image amplifier tube (13) also comprises a diffraction grating (20) placed between the input window (15) and the photocathode (16) so as to diffract the photons in said photocathode (16) and to allow the photocathode (16) to have a quantum efficiency (QE): ■ greater than 1% in an imaging wavelength range and; ■ between 0.001 and 1% in a detection wavelength range, distinct from said image formation wavelength range, said detection wavelength range being at least between 1000 nanometers and 1100 nanometers; the image amplifier tube (13) being configured to capture electromagnetic radiation emitted by said beacon (B) in said detection wavelength range.

2. System for identifying at least one beacon (B) according to claim 1, in which the photocathode (16) is formed from antimony and at least one alkali metal.

3. System for identifying at least one beacon (B) according to claim 1 or 2, in which the image amplifier tube (13) is configured to capture manifestation signals (Sm) from the at least one beacon (B) at a wavelength of between 1050 and 1075 nanometers, preferably 1064 nanometers.

4. System for identifying at least one beacon (B) according to one of claims 1 to 3, wherein the night vision binoculars (NV G) or the scope also comprises an activation device (31) for the beacon (B), configured to emit an activation signal (Sa), said beacon (B) comprising a module for receiving said activation signal (Sa) so as to transmit the electromagnetic radiation at the wavelength between 1000 nanometers and 1100 nanometers in the form of a manifestation signal (Sm) in response to the activation signal (Sa) emitted by the activation device (31).

5. System for identifying at least one beacon (B) according to claim 4, in which the activation device (31) of the beacon (B) consists of a radiofrequency transmitter, the reception module of said beacon (B) consisting of an antenna.

6. System for identifying at least one beacon (B) according to claim 4, in which the activation device (31) of the beacon (B) consists of an optical transmitter, the reception module of said beacon (B) consisting of an optical receiver.

7. System for identifying at least one beacon (B) according to claim 6, in which the optical transmitter is a laser diode with a wavelength between 1400 nanometers and 1800 nanometers, the receiving module of said beacon (B) consisting of a photodiode capable of capturing a wavelength between 1400 nanometers and 1800 nanometers.

8. System for identifying at least one beacon (B) according to one of claims 4 to 7, wherein the night vision binoculars (NVG) or the scope are configured to observe a scene (Sc) in which a specific observation zone (Zp) is placed, defined by the emission angle (F31) of said activation device (31) and the viewing angle (Fnvg) of the night vision binoculars (NVG) or the scope, the detection of said beacon (B) being carried out only in said specific observation zone (Zp).

9. System for identifying at least one beacon (B) according to one of claims 4 to 8, wherein the image amplifier tube (13) comprises a light gain regulation mechanism, the activation device (31) having a variable activation period (P31-1).

10. System for identifying at least one beacon (B) according to one of claims 4 to 8, in which the image amplifier tube (13) comprises a mechanism for regulating the light gain with a specific activation period (Pal), the activation device (31) having an activation period (P31-2) synchronized with said specific activation period (Pal) of the mechanism for regulating the light gain of said image amplifier tube (13).

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