SYSTEM FOR IDENTIFYING AT LEAST ONE TAG

Abstract

A system for identifying at least one beacon (B) comprising night vision binoculars or a telescope 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 in said photocathode and to enable the photocathode to exhibit a quantum efficiency (QE): – greater than 1% in an image formation 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 1050 nanometers and 1075 nanometers; the image intensifier tube being configured to capture electromagnetic radiation emitted by said beacon in said second detection wavelength range. Figure for the abridged version: Fig 5

Description

Title of the invention: SYSTEM FOR IDENTIFYING AT LEAST ONE BEACON Scope of the invention

[0001] The technical field of the invention relates to beacon identification systems using night vision binoculars or night vision goggles, particularly in low-light conditions. The beacons can be worn by individuals, animals, vehicles, or placed in strategic locations.

[0002] The invention finds a particularly advantageous application in the military field. Indeed, for friend or foe identification on a military operational terrain, also known by the Anglo-Saxon acronym IFF for "Identification Friend or Foe," beacons can be worn by soldiers. In this context, the invention allows a soldier equipped with a scope or binoculars to reliably and discreetly identify friendly forces. Thus, this system makes it possible to prevent friendly fire incidents and optimize coordination between friendly units, while offering a response capability adaptable to various operational scenarios. Prior art

[0003] 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 classically presented in the form of a pair of glasses 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 goggles, also known by the Anglo-Saxon acronym NVG for "Night Vision Goggle".

[0004] This night vision device 110 incorporates several elements positioned on the optical axis 1a of the sensor or the user's eye, in order to transform the image of the observed scene. More specifically, the telescope comprises, from the perspective of the scene outside the sensor or the user's eye, an objective lens 12, an image intensifier tube 130, and an eyepiece 14. The objective lens 12 conventionally comprises one or more lenses for capturing the photons of the electromagnetic radiation from the observed scene. The eyepiece 14, similarly to the objective lens 12, comprises one or more lenses for capturing and, incidentally, viewing the photons of the light signal emitted by the image intensifier tube 130.

[0005] The image intensifier tube 130 comprises at least three distinct elements: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0006] The photocathode 16 is in the form of a semi-photosensitive layer transparent receiving the photons of the incident electromagnetic radiation, i.e. the photons transmitted by the objective 12. To do this, an entrance window 15 transmits the photons from the objective 12 onto the photocathode 16 while ensuring the airtightness of the external wall 23 of the image intensifier tube 130.

[0007] The photocathode 16 is generally made in the form of a thin layer of metal or semiconductor deposited on a layer of glass or a light-transparent material. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of photons from the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by the photoelectric effect, the emission of electrons, called photoelectrons.

[0008] These photoelectrons are then subjected to a first electric field within a first acceleration zone 17, allowing the photoelectrons to be directed towards the electron multiplier 18. This first electric field is achieved 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 of the electrons.

[0009] The electron multiplier 18, also called an electron amplifier, conventionally 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-language literature. It is made of a resistive or dielectric material plate with a thickness typically between 0.2 and 1 millimeter.

[0010] The microchannels 25 of this wafer have an axis of revolution a2 inclined at an angle a3 of a few degrees, typically between 4 and 12 degrees, with respect to the normal to the surface of the electron multiplier 18, so as to induce multiple collisions of the photoelectrons 28 in the microchannels 25.

[0011] 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 outlet of the electron multiplier 18 by means of the electrodes placed on either side between the inlet and outlet of the microchannel wafer 25.

[0012] This electric field charges the internal semiconductor layer of the microchannels 25, so that the multiple collisions of photoelectrons 28 in the microchannels 25 generate a large number of secondary electrons 29. This electric field also accelerates 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 accelerates the electrons secondary 29 by energy input, in order to direct them from the entrance of the microchannels 25 to the exit of the microchannels 25. Typically, the photoelectrons 28 are multiplied by a factor between 102 and 104 in the electron multiplier 18.

[0013] At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly in the direction of the phosphorescent screen 20, within a second acceleration zone 19, under the effect of a third electric field generated between the output of the electron multiplier 18 and the phosphorescent screen 20, typically an electric field generated by a voltage between 4 and 10 kV.

[0014] The phosphorescent screen 20 transforms the secondary electrons 29 into photons that produce light intensity. It is in the form of a phosphorescent layer or a layer of a phosphor material deposited on a substrate, typically glass. At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, typically an optical fiber array 21, optionally allowing the image formed on the phosphorescent screen 20 to be inverted to obtain a correct view of the observed scene.

[0015] 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 visualization system of the scene observed on the eyepiece 14.

[0016] A night vision system 110 currently available on the market typically captures and amplifies photons over a range of X-ray wavelengths between 450 nanometers and 900 nanometers. More precisely, the operational X-ray wavelength range of a night vision system 110 is primarily determined by the sensitivity spectrum of the photocathode 16.

[0017] As illustrated in [Fig.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 Anglo-Saxon acronym QE for "Quantum Efficiency", i.e. 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 prior art night vision system 110, the quantum efficiency QE is classically greater than 1% between 450 nanometers and 900 nanometers and less than 0.001% outside this range of operational X wavelengths.

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

[0019] For example, as described in document EP 0 560 470, a system Identification friend or foe (IFF) 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 as taught in EP 0 560 470. In this example, the NVG night vision goggles are associated with a beacon B activation device. This activation device generates an Sa signal that activates the beacon B, causing it to produce a manifestation signal Sm detectable by the NVG night vision goggles. To achieve this, the beacon B can use an infrared diode that flashes within the operational X-ray wavelength range of the NVG night vision goggles when 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 X wavelength range of the night vision system 110. However, the detection of a B beacon in the operational X wavelength range 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 on the field of operations leads to a decrease in the stealth of the carriers of B beacons because the opponents / enemies may be equipped with NVG night vision binoculars which also allow the detection of the manifestation signal Sm emitted by the B beacons because the NVG night vision binoculars are practically all sensitive in the X wavelength range between 450 nanometers and 900 nanometers.

[0023] There is therefore a need to improve the prior art beacon identification systems in order to guarantee image quality and preserve the stealth of beacon bearers. Description of the invention

[0024] The invention proposes to address this technical problem by using night vision binoculars or a telescope incorporating a tube with an extended operational wavelength range so as to achieve the detection of beacons outside the wavelength range used to form the images of the scene.

[0025] More specifically, the invention arises from an observation that the use of a diffraction grating intercalated 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 1050 nanometers and 1075 nanometers.

[0026] The invention therefore proposes to use beacons emitting a manifestation signal between 1050 nanometers and 1075 nanometers associated with night vision binoculars or a telescope incorporating an image intensifier tube operating in a first range of wavelengths, called the image formation wavelength range, to observe the scene and in a second range of wavelengths, called the detection wavelength range, to detect the beacons.

[0027] Indeed, although the quantum efficiency is not sufficient in the detection wavelength range between 1050 nanometers and 1075 nanometers to form an image of the scene, this quantum efficiency is sufficient for detecting 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 between 1050 nanometers and 1075 nanometers, the system comprising night vision binoculars or a telescope integrating an image intensifier tube comprising: - an input window configured to receive and transmit photons; - a photocathode, fixed on an internal face of said entrance window, capable of converting photons transmitted through the entrance 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; - an electron multiplier capable of multiplying photoelectrons into secondary electrons; and - a phosphorescent screen transforming secondary electrons into photons.

[0029] The invention is characterized in that the image-amplifying 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 exhibit quantum efficiency: - greater than 1% in a range of image formation wavelengths 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 1050 nanometers and 1075 nanometers; said image amplifier tube being configured to capture electromagnetic radiation emitted by said beacon in said second detection wavelength range.

[0030] 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 range of image formation wavelengths, for example between 450 nanometers and 900 nanometers.

[0031] Furthermore, the invention also improves the stealth of beacon wearers. Indeed, conventional night-vision goggles, which detect photons in the wavelength range between 450 nanometers and 900 nanometers, cannot capture the beacon manifestation signals in the wavelength range between 1050 nanometers and 1075 nanometers. Preferably, the image intensifier tube is configured to capture manifestation signals from at least one beacon at a wavelength of 1064 nanometers.

[0032] Preferably, to obtain efficient detection in the detection wavelength range, the photocathode is formed based on antimony and at least one alkali metal, such as NaKCs, SbNa KCs, SbNaK, SbKCs, SbRbKCs or SbRbCs alloys.

[0033] In addition to the image intensifier tube, the night vision binoculars or telescope may also include a beacon activation device. Preferably, this beacon activation device is configured to emit an activation signal, while the beacon includes a receiver module for said activation signal so as to transmit electromagnetic radiation at a wavelength between 1050 nanometers and 1075 nanometers in the form of a manifestation signal in response to the activation signal emitted by the activation device.

[0034] For example, the beacon activation device may consist of a radio frequency transmitter or an optical transmitter, with the beacon's receiving module corresponding respectively to an antenna or an optical receiver. For an optical transmitter / receiver, the optical transmitter may be a laser diode with a wavelength between 1400 nanometers and 1800 nanometers, and the beacon's receiving module may be a photodiode capable of capturing a wavelength between 1400 nanometers and 1800 nanometers. Indeed, the transmission and reception of this activation signal in this wavelength range also ensures significant stealth for the beacon wearer.

[0035] Furthermore, to improve the detection range, the night vision binoculars or telescope can be configured to observe a scene in which a specific observation zone is located, defined by the emission angle of the activation device and the viewing angle of the night vision binoculars or telescope. Detection of the beacon is then performed only within this specific observation zone. Indeed, by targeting a specific area within the observation zone, the emission angle of the activation device can be reduced to improve the range of the activation signal. Typically, it is possible to detect a beacon at a distance of more than three kilometers using this strategy.

[0036] Furthermore, the image intensifier tube may include a light gain regulation mechanism to adapt the tube's output luminance. This function, referred to as "auto-gating" in the English-language literature, limits saturation and increases dynamic range for scenes with very strong variations in light intensity. This mechanism relies on the rapid detection of light variations to adjust, within milliseconds, the generation of photoelectrons and stabilize the brightness at the output of the image intensifier tube, typically between 6 and 12 candela / m², depending on the type of phosphor used (green P43 or white P45).

[0037] This light gain regulation mechanism is implemented 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, within milliseconds, the duty cycle of the periodic voltage applied to the photocathode. This modification of the duty cycle allows the number of photoelectrons generated by the photocathode to be adjusted, which are then multiplied by the electron multiplier. The voltage applied across the terminals of the electron multiplier is itself adjusted to adapt the number of secondary electrons and, consequently, the output luminance of the tube.

[0038] This principle of adapting internal electrical charges within the tube makes it possible not to exceed the predetermined luminance threshold. This threshold is, for example, a MOB threshold, an acronym for "Maximum of Brightness" in English-language literature.

[0039] 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 glare. As a result, operators benefit from clearer and more stable night vision, even in the face of sudden changes in light, which is crucial for applications such as military or surveillance operations.

[0040] However, the specific activation period at the photocathode of the light gain control mechanism induces phases in which the image intensifier tube cannot detect a beacon. To prevent the beacon from emitting a signal only outside the detection ranges of the image intensifier tube, the beacon can be configured to emit a signal for a longer duration than the specific activation period of the light gain control mechanism.

[0041] However, this solution increases power consumption and therefore the size of the beacons. To resolve this problem through 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 intensifier tube coincides with the activation period of the activation device. This solution limits the required transmission time of the beacons but may introduce latency in the beacon detection speed, while the two activation periods are being synchronized.

[0042] To avoid this latency, synchronous detection can be achieved by connecting the activation device with the activation period management device specific to the light gain control mechanism. In this embodiment, the activation device has an activation period synchronized with the specific activation period of the light gain control mechanism of the image intensifier tube. Brief description of the figures

[0043] The invention will be better understood upon reading the following description, given solely by way of example, and carried out in conjunction with the accompanying drawings, in which identical reference numerals designate identical or analogous elements, and in which:

[0044] Fig. 1 illustrates a schematic cross-sectional view of a prior art night vision device;

[0045] Fig. 2 illustrates the evolution of the quantum efficiency of the night vision device of Fig. 1;

[0046] [Fig.3] illustrates a perspective view of the night vision device of [Fig.1];

[0047] Figure [Fig. 4] illustrates a schematic view of a prior art beacon identification system implementing two night vision devices from Figure [1]

[0048] Figure 5 illustrates a schematic cross-sectional view of a night vision device according to the invention;

[0049] Fig. 6 illustrates the evolution of the quantum efficiency of the night vision device of Fig. 5;

[0050] Fig. 7 illustrates a schematic view of a beacon identification system according to the invention implementing two night vision devices of Fig. 5;

[0051] Fig. 8 illustrates an example of images observed by night vision goggles incorporating two night vision devices from Fig. 7;

[0052] Figure 9 illustrates four asynchronous triggering timing diagrams of a beacon with the identification system of [Fig. 7]; and

[0053] Fig. 10 illustrates four timing diagrams of synchronous triggering of a beacon with the identification system of Fig. 7. Detailed description of the invention

[0054] 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 pair of glasses intended to be placed in front of a sensor, the user's eye, or both eyes when two devices are placed side-by-side to form night vision binoculars. This night vision device 11 incorporates several elements positioned on the optical axis 1a of the sensor or the user's eye in order to transform the image of the observed scene. More specifically, the glasses comprise, from the perspective of the scene outside the sensor or the user's eye, a lens 12, the image intensifier tube 13 of the invention, and an eyepiece 14.

[0055] As described above, the objective 12 comprises one or more lenses for capturing photons from the electromagnetic radiation of the observed scene. The eyepiece 14, similarly to the objective 12, comprises one or more lenses for capturing and incidentally visualizing photons from the light signal emitted by the image intensifier tube 13.

[0056] The image intensifier tube 13 comprises at least three distinct elements integrated in an internal vacuum enclosure 24: a photocathode 16, an electron multiplier 18, and a phosphorescent screen 20.

[0057] As described previously, the photocathode 16 is in the form of a semi-transparent photosensitive layer receiving photons from the incident electromagnetic radiation, i.e. the photons transmitted by the lens 12. To do this, an entrance window 15 transmits the photons from the lens 12 onto the photocathode 16 while ensuring the airtightness of an external wall 23 of the image intensifier tube 13.

[0058] The photocathode 16 is generally made in the form of a thin layer of metal or semiconductor deposited on a layer of glass or a light-transparent material. The material of the photocathode 16 is chosen according to its sensitivity to the image of the observed scene. The interaction of photons from the incident electromagnetic radiation of the observed scene with the photocathode 16 produces, by the photoelectric effect, the emission of electrons.

[0059] More specifically, the photocathode 16 is fixed on a diffraction grating 30, itself fixed on an inner face of the entrance window 15.

[0060] The diffraction grating 30 is formed by a periodic arrangement of motifs, by Examples include notches, grooves, recesses, notches, or scratches made 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 deposition surface for the photocathode 16. For example, the entrance window 15 can be made of glass, quartz, or borosilicate glass. The patterns of the diffraction grating 30 of the entrance window 15 can be produced by known etching techniques, such as holography, ion etching, and / or diamond etching.

[0061] The patterns are then preferentially filled with a diffraction material whose optical refractive index n is different from that of the entrance window 15, such as Al2O3 (n~1, 7), TiO2 (n~2, 3-2, 6), Ta2O5 (n~2,2), or HfO2. 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-language literature.

[0062] 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.

[0063] The photocathode 16 is preferably made of a semiconductor material, preferably an alkali compound based on antimony. Such an alkali material may be chosen from the following materials: SbNaKCs, SbNa2KCs, SbNaK, SbKCs, SbRbKCs, or SbRbCs. Preferably, the photocathode 16 is made of antimony and sodium.

[0064] 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 allowing the photoelectrons to be directed towards the electron multiplier 18. This first electric field is made by applying a voltage between the photocathode 16 and the electron multiplier 18, typically a voltage between 50 and 500 volts to guarantee a straight path of the electrons.

[0065] 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 wafer 25.

[0066] This electric field charges the internal semiconductor layer of the microchannels 25 so that the multiple collisions of photoelectrons 28 in the microchannels 25 generate a large number of secondary electrons 29. This electric field also accelerates 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 direct them from the entrance of the microchannels 25 to the exit of the microchannels 25. Typically, the photoelectrons 28 are multiplied by a factor between 103 and 106 in the electron multiplier 18. At the exit of the microchannels 25, these secondary electrons 29 are then moved linearly in the direction of 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 between 4 and 10 kV.

[0067] The phosphorescent screen 20 allows the secondary electrons 29 to be transformed into photons producing a light intensity. It is in the form of a phosphorescent layer or a layer of a luminophoric material deposited on a substrate, conventionally glass.

[0068] At the output of the phosphorescent screen 20, the image formed is transmitted to the eyepiece 14 by optical means, classically a network of optical fibers 21 allowing possibly to turn the image formed on the phosphorescent screen 20 to obtain a correct visualization of the scene observed.

[0069] 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 visualization system of the observed scene on the eyepiece 14.

[0070] As illustrated in [Fig.6], the image intensifier tube 13 thus formed, with the association of the photocathode 16 and the diffraction grating 30, exhibits a sensitivity spectrum with a quantum efficiency QE whose maximum is less than the maximum quantum efficiency QE of an image intensifier tube 130 of the prior art.

[0071] Furthermore, it is observed that the sensitivity spectrum is also more extensive. It is therefore possible to detect photons between 400 nanometers and 1064 nanometers, and no longer between 450 nanometers and 900 nanometers.

[0072] More specifically, according to the invention, the image intensifier tube 13 thus formed exhibits a quantum efficiency QE: - greater than 1% in a range of image formation wavelengths and; - between 0.001 and 1% in a detection wavelength range, distinct from said image formation wavelength range, the detection wavelength range being at least between 1050 nanometers and 1075 nanometers.

[0073] This range of detection wavelengths makes it possible to capture an Sm manifestation signal from at least one B beacon. Thus, as illustrated in [Fig. 7], the invention proposes using NVG night vision binoculars, or night vision goggles, incorporating an image intensifier tube 13, as previously described, to capture an Sm manifestation signal from at least one B beacon within the detection wavelength range. Preferably, the B beacon emits an Sm manifestation signal at the precise wavelength of 1064 nanometers.

[0074] The beacon B may consist of an electronic box integrating a power supply and means for emitting the manifestation signal Sm, for example an infrared diode.

[0075] Furthermore, the beacon B can emit a manifestation signal Sm continuously or in response to an activation signal Sa. Preferably, as illustrated in [Fig. 7], the activation signal Sa can be emitted from the NVG night vision binoculars, or the night vision scope. To this end, the NVG night vision binoculars, or the night vision scope, incorporates an activation device 31.

[0076] The activation device 31 may consist of a tube incorporating a power supply and means for emitting the activation signal Sa. It should be noted that the power supply for the activation device 31 may be provided by the NVG night vision goggles, or the night vision scope, for example by the electronic components 22.

[0077] The activation signal Sa can be light or radio frequency. Thus, when the activation device 31 of the beacon B incorporates a radio frequency transmitter, the beacon B incorporates an antenna and the manifestation signal Sm is emitted only in response to the reception of the activation signal Sa.

[0078] Alternatively, when the activation device 31 of the beacon B incorporates an optical emitter, for example a laser diode, the beacon B incorporates an optical receiver, for example a photodiode, and the manifestation signal Sm is also emitted only in response to the reception of the activation signal Sa. The laser diode and the photodiode can be configured to operate at a wavelength between 1400 nanometers and 1800 nanometers, for example 1550 nanometers.

[0079] In order for the beacon B to receive the activation signal Sa, it is necessary that the propagation range and the propagation angle F31 of the activation device Sa be set so that the activation signal Sa reaches the beacon B. In the same way, the power and the propagation angle Fb of the beacon B must be configured so that the manifestation signal Sm reaches the detection angle Fnvg of the NVG night vision binoculars, or the night vision scope.

[0080] To increase the detection range of a beacon B, 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 that is smaller than the viewing angle Fnvg of the NVG night vision binoculars or night vision scope. In this embodiment, the B beacons can only be detected within a specific observation area Zp of the images viewed by the NVG night vision binoculars or night vision scope.

[0081] In the example of [Fig.8], NVG night vision binoculars allow binocular night images to be viewed and, in these images, a specific central observation zone Zp allows the detection of B beacons.

[0082] Furthermore, NVG night vision binoculars, or night vision goggles, may incorporate a light gain regulation mechanism, also called "auto-gating" in the English-language literature, limiting the opening time of the image intensifier 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 intensifier tube 13, the beacon B can be configured to emit a signal for a longer duration than the specific activation period Pal of the light gain regulation mechanism.

[0083] Alternatively, with asynchronous detection as illustrated in [Fig. 9], the activation device 31 can have a variable activation period P31. In this embodiment, the beacon B can be detected when the specific activation period Pal of the image intensifier tube 13 coincides with the activation period P31 of the activation device 31. Thus, in the last timing diagram of [Fig. 9] relating to the detection of the image intensifier tube 13, the beacon B is not detected on the first two emitted manifestation signals Sm but is detected on the last two manifestation signals Sm.

[0084] With synchronous detection as illustrated in [Fig. 10], the activation device 31 is connected with the specific activation period management device Pal of the light gain regulation mechanism, for example by 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 intensifier tube 13. Thus, in this embodiment, on the last timing diagram of [Fig. 10] relating to the detection of the image intensifier tube 13, the beacon B is detected on the four manifestation signals Sm emitted.

[0085] 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, by for example, between 450 nanometers and 900 nanometers. In addition, the invention also improves the stealth of B-beacon wearers because the detection wavelength of B-beacons is not detected by conventional night vision systems that capture photons in the X-ray wavelength range between 450 nanometers and 900 nanometers.

Claims

Demands

1. A system for identifying at least one beacon (B), the beacon (B) incorporating a device for emitting electromagnetic radiation at a wavelength between 1050 nanometers and 1075 nanometers, the system comprising night vision goggles (NVGs) or a telescope incorporating an image intensifier tube (13) comprising: - an input window (15) configured to receive and transmit photons; - a photocathode (16), fixed on an internal face of said entrance window (15), capable of converting photons transmitted by the entrance 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 photoelectrons (28) into secondary electrons (29); and - a phosphorescent screen (20) transforming secondary electrons (29) into photons; characterized in that the image intensifier 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 enable the photocathode (16) to exhibit a quantum efficiency (QE): - greater than 1% in a range of image formation wavelengths 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 1050 nanometers and 1075 nanometers; the image intensifier tube (13) being configured to capture electromagnetic radiation emitted by said beacon (B) in said second detection wavelength range.

2. A system for identifying at least one beacon (B) according to claim 1, wherein the photocathode (16) is formed based of antimony and at least one alkali metal.

3. Identification system for at least one beacon (B) according to claim 1 or 2, wherein the image intensifier tube (13) is configured to capture manifestation signals (Sm) from at least one beacon (B) at a wavelength of 1064 nanometers.

4. Identification system for at least one beacon (B) according to any one of claims 1 to 3, wherein the night vision goggles (NVG) or binoculars also comprise a beacon (B) activation device (31), configured to emit an activation signal (Sa), said beacon (B) comprising a receiver module for said activation signal (Sa) so as to transmit electromagnetic radiation at the wavelength between 1050 nanometers and 1075 nanometers in the form of a manifestation signal (Sm) in response to the activation signal (Sa) emitted by the activation device (31).

5. Identification system for at least one beacon (B) according to claim 4, wherein the activation device (31) of the beacon (B) consists of a radio frequency transmitter, the receiving module of said beacon (B) consisting of an antenna.

6. Identification system for at least one beacon (B) according to claim 4, wherein the activation device (31) of the beacon (B) consists of an optical transmitter, the receiving module of said beacon (B) being constituted by an optical receiver.

7. Identification system for at least one beacon (B) according to claim 6, wherein the optical emitter is a laser diode with a wavelength between 1400 nanometers and 1800 nanometers, the receiving module of said beacon (B) being made up of a photodiode capable of capturing a wavelength between 1400 nanometers and 1800 nanometers.

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

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

10. Identification system for at least one beacon (B) according to any one of claims 4 to 8, wherein the image intensifier tube (13) includes a light gain regulation mechanism 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 light gain regulation mechanism of said image intensifier tube (13).

Images