Laser communication device and method for optically aligning two laser communication devices

Abstract

A laser communication device (1, 1A, 1B) comprising a sight (10) and a laser unit (20) carried by the sight, the sight being an observation and / or fire control sight, and the laser unit comprising: a laser emitter (21) arranged to emit an original laser beam (F) along a line of sight (L); and an optical module (23) arranged to selectively modify the divergence of the original laser beam so as to obtain a useful laser beam (F'') capable of adopting a beacon state in which the useful laser beam is broadened along the line of sight, and a communication state in which said useful laser beam is collimated along said line of sight. FIGURE IN ABRIDGED DIAGRAM: Fig. 4

Description

Title of the invention: Laser communication device and method for optically aligning two laser communication devices

[0001] The present invention relates to the field of wireless communications, and more particularly to a laser communication device and a method of optical alignment between two laser communication devices.

[0002] BACKGROUND OF THE INVENTION

[0003] In the field of military communications, there is a growing need for high-speed, reliable and secure wireless communication to exchange large amounts of data between two terminals.

[0004] Traditional wireless communication using radio frequencies suffers from several drawbacks: - rapid attenuation of the radio signal depending on the distance separating the terminals; - limited available communication frequencies; and - radio signal easily picked up, intercepted and jammed by an enemy transmitter / receiver.

[0005] Laser wireless communication offers an interesting alternative in that, by nature, it is not subject to the disadvantages of radio frequency communication (little or no attenuation of a laser signal with a low-diverging beam, no bandwidth constraint, difficult interception and jamming...).

[0006] However, laser wireless communication relies on transmitters / receivers which need to be aligned with a greater or lesser degree of precision.

[0007] A laser communication device comprising a laser emitter with sufficient divergence to receive a signal that incorporates information enabling the laser communication device to point to the signal emitter is known from document EP 4 078 853. Such a laser communication device requires a high-power laser emitter, resulting in a large size and mass for the communication device and posing an eye safety risk for personnel in the vicinity of said communication device.

[0008] Another laser communication device is known, comprising a laser emitter with low divergence, which is optimal for limiting the size and mass of the communication device. However, such a laser emitter does not allow for the function of receiving a signal incorporating information so that the laser communication device can point the signal emitter, so that it It is necessary to equip said signal transmitter and communication device with physical beacons to allow their optical alignment.

[0009] SUBJECT OF THE INVENTION

[0010] The invention therefore aims to provide a communication device that at least partially overcomes the aforementioned drawbacks. Summary of the invention

[0011] To this end, a laser communication device is proposed comprising a sight and a laser unit mounted on the sight. The sight is an observation and / or fire control sight, and the laser unit comprises:

[0012] - a laser emitter arranged to emit an original laser beam along a line of targeted; and

[0013] - an optical module arranged to selectively modify the beam divergence original laser so as to obtain a useful laser beam capable of adopting a beacon state in which the useful laser beam is broadened along the line of sight, and a communication state in which said useful laser beam is collimated along said line of sight.

[0014] The optical module thus enables the laser unit to perform both a beacon function and a communication function, and therefore allows the laser communication device to be free of physical beacons.

[0015] Furthermore, mounting such a laser unit on a sight makes it possible to obtain a laser communication device at a lower cost.

[0016] According to a particular embodiment of the invention, the optical module is a liquid lens with variable focal length.

[0017] In particular, the laser unit includes an optical amplifier arranged between the laser emitter and the optical module to amplify the original laser beam before modifying its divergence via said optical module.

[0018] In particular, the sight is an optronic sight.

[0019] The invention also relates to a laser communication system comprising at minus two such laser communication devices.

[0020] In particular, the laser communication devices are identical.

[0021] The invention also relates to a method for aligning the laser units of such a communication system, comprising: • an initial alignment of the laser units based on data exchanged by radio frequency between the laser communication devices; • a second alignment of the laser units based on the useful laser beams of the laser communication devices in beacon mode; and • a third alignment of the laser units based on the useful laser beams of the laser communication devices in the communication state.

[0022] In particular, the first alignment comprises the following steps:

[0023] a) exchange between the radio frequency data communication devices, enabling each communication device to estimate in real time a position and velocity of the other communication device; and

[0024] b) alignment of laser units via sights from estimated positions and velocities.

[0025] In particular, the second alignment comprises the following steps:

[0026] c) while the useful laser beams of the communication devices are in beacon state, variable pointing of the line of sight of the laser unit of one of the communication devices around the estimated position of the other of the communication devices until a detection of the useful laser beam of said other communication device;

[0027] d) stopping the variable pointing and estimating by calculation the position of the other communication device;

[0028] e) application of an offset by the communication device to its line of sight from the position estimated in step d); and

[0029] f) repeating steps c) to e) reversing the roles of the communication devices until the lines of sight of said communication devices are sufficiently aligned to be controlled via their useful laser beams in the beacon state.

[0030] In particular, the third alignment comprises the following steps:

[0031] g) while the useful laser beams of the communication devices are in the communication state, variable pointing of the line of sight of the laser unit of one of the communication devices around the estimated position of the other of the communication devices until detection of the useful laser beam of said other communication device;

[0032] h) stopping the variable pointing and estimating by calculation the position of the other communication device;

[0033] i) application of an offset by the communication device on its line of sight from the position estimated in step d); and

[0034] j) repeating steps g) to i) reversing the roles of the communication devices until the lines of sight of said communication devices are sufficiently aligned to be slaved via their laser beams useful to the communication state. Brief description of the drawings

[0035] The invention will be better understood in the light of the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying drawings, among which:

[0036] [Fig-1] [Fig. 1] is a view illustrating two buildings each comprising a communication device according to the invention;

[0037] [Fig.2] [Fig.2] is a schematic view of the laser unit of the devices illustrated communication in [Fig.1];

[0038] [Fig.3A] [Fig.3A] is a schematic view of the useful laser beam exiting the laser unit illustrated in [Fig.2] via the optical module, the useful laser beam being in the beacon state, ;

[0039] [Fig.3B] [Fig.3B] is a view identical to [Fig.3A], in which the useful laser beam is in the communication state.

[0040] [Fig.4] [Fig.4] is a schematic view of an optical alignment method for laser units of the communication devices illustrated in [Fig.1]; DETAILED DESCRIPTION OF THE INVENTION

[0041] With reference to [Fig. 1], the invention is described in application to two buildings A, B or ships, each comprising: • a communication device 1 enabling wireless communication between said two buildings A, B; and • a control unit UC of the communication device 1 connected to said communication device 1.

[0042] The following description relates to one of the communication devices 1, the communication devices 1 being identical here but also being different. The two communication devices 1 are distinguished in Figures 1 and 4 by the addition of the letters A, B.

[0043] The communication device 1 includes an observation and / or fire control sight 10, and a laser unit 20 carried by the sight 10.

[0044] The sight 10 is here an optronic sight, such as those marketed by Safran Electronics & Defense under the name Vigy or Paseo, and comprises, in a manner known per se, a base 11, a rotating body 12 pivotally mounted on the base 11 about a bearing axis Z, and an optronic unit 13 pivotally mounted on the rotating body 12 about a site axis X perpendicular to the bearing axis Z. The rotating body 12 is driven in rotation about the bearing axis Z by first drive means, and the optronic unit 13 is driven in rotation about the site axis X by second drive means. The first drive means comprise a first electric motor (not shown) which is arranged inside the base 11 and which allows rotation of the The first drive means include a rotating body 12 around the axis in the Z-axis, ranging from 0 degrees to 360 degrees. The second drive means include a second electric motor (not shown) arranged inside the rotating body 12, which allows rotation of the optronic unit 13 around the axis in the C-axis, ranging, for example, from -20 degrees to +85 or even 90 degrees in elevation relative to the plane perpendicular to the axis in the Z-axis and including the axis in the X-axis. The first and second drive means are controlled by the control unit UC.

[0045] With reference to [Fig.2], the laser unit 20 comprises: • a laser emitter 21 arranged to selectively emit an original laser beam F along a line of sight L; • a high-power optical amplifier 22 arranged downstream of the laser emitter 21 to amplify the original laser beam F so as to obtain, at the output of the optical amplifier 22, an amplified laser beam F'; and • An optical module 23 arranged downstream of the optical amplifier 22 to selectively modify the divergence of the amplified laser beam F' so as to obtain, at the output of the optical module 23, a useful laser beam F” that can adopt a beacon state in which the useful laser beam F' is broadened along the line of sight L ([Fig. 3A]), and a communication state in which said useful laser beam F” is collimated along said line of sight L ([Fig. 3B]). The divergence of the useful laser beam F” is here between 2 and 5 mrad (milliradians) in the beacon state, and is less than 0.5 mrad in the communication state.

[0046] The optical module 23 here comprises a variable focal length liquid lens: the liquid lens has a focal length that can be changed via an electrical signal and is positioned in a first position in which the useful laser beam F” is in beacon mode and in a second position in which the useful laser beam F” is in communication mode. The laser unit 20 and in particular the optical module 23 are controlled by the control unit UC.

[0047] A method for optically aligning the laser units 20 of the two communication devices IA, IB will now be detailed with reference to [Fig.4].

[0048] In a first step 100, the communication devices IA, IB regularly exchange data via radio frequency, allowing each communication device IA, IB to estimate in real time the position and velocity of the other communication device IA, IB. Based on these estimates, the control units UC of the communication devices IA, IB command in real time the first and second drive means of the sights 10 in order to perform an initial alignment of the laser units 20 based on the geographic target designation. It is understood that this initial alignment includes real-time pointing of the device AI communication to the IB communication device, but also real-time pointing from the IB communication device to the AI ​​communication device. It should be noted that the estimation of the positions of the AI, IB communication devices is subject to errors, so that the first alignment is said to be crude in that it does not allow each of the AI, IB communication devices to lock onto the useful laser beam F” of the other of the AI, IB communication devices, whether said useful laser beam F” is in the communication state or in the beacon state.

[0049] In a second step 200, the optical modules 23 of the communication devices IA, IB are controlled so that the useful laser beams F” generated by the laser units 20 are in a beacon state. The first and second drive means of the sight 10 of the communication device IA are then controlled to perform a variable sweep or offset of the line of sight of its laser unit 20 around the estimated position of the communication device IB, which remains slaved to the geographic target designation of said communication device IA. The sweep is, for example, a sweep in one or more spirals.

[0050] In parallel, the control unit UC of the communication device IB implements, via its control unit UC, a process of detecting the useful laser beam F” in the beacon state of the communication device IA.

[0051] As soon as the control unit UC of the communication device IB detects the useful laser beam F” in the beacon state of the communication device IA, or when the scan time of the viewfinder 10 of the communication device IA has reached a predetermined duration, the communication device IA ceases its scan and the communication device IB implements, via its control unit UC, a process for calculating the position of the communication device IA relative to its line of sight. Based on this calculated position, the communication device IB applies an offset to its line of sight tending to reduce its pointing error towards the communication device IA.

[0052] This second step 200 is repeated by reversing the roles of the AI, IB communication devices until the lines of sight of said AI, IB communication devices are sufficiently aligned to lock onto their useful laser beams F” in the beacon state, that is to say, said lines of sight define an angle less than half the divergence of the useful laser beam F’’ in the communication state, i.e., here an angle less than 0.25 mrad. It should be noted that the scanning of the AI, IB communication devices will be adapted according to the typology of the position estimation errors of said AI, IB communication devices.

[0053] It is understood that the second step 200 allows a second alignment of the laser units 20 of the communication devices IA, IB on the basis of the useful laser beams F” in the beacon state.

[0054] In a third step 300, the optical modules 23 of the laser units 20 of the communication devices IA, IB are controlled so that the useful laser beams F” generated by said laser units 20 are in the communication state. The first and second drive means of the sights 10 of the communication device IA are then controlled to perform a variable sweep or offset of the line of sight of its laser unit 20 around the estimated position of the communication device IB, which remains locked to the useful laser beam F” in the beacon state of said communication device IA. The sweep is primarily performed in azimuth.

[0055] In parallel, the control unit UC of the communication device IB implements, via its control unit UC, a process of detecting the useful laser beam F” in the communication state of the communication device IA.

[0056] As soon as the control unit UC of the communication device IB detects the useful laser beam F” in the communication state of the communication device IA, the communication device 1A ceases its scanning and the communication device IB implements, via its control unit UC, a process to calculate the position of the communication device IA relative to its line of sight. Based on this calculated position, the communication device IB applies an offset to its line of sight tending to reduce its pointing error towards the communication device IA.

[0057] This third step 300 is repeated by reversing the roles of the communication devices IA, IB until the lines of sight of said communication devices IA, IB are sufficiently aligned to lock onto their useful laser beams F” in the communication state, that is to say, said lines of sight define an angle well below half the divergence of the useful laser beam F” in the communication state, i.e., here an angle less than 0.02 mrad. It should be noted that the scanning of the communication devices IA, IB will be adapted according to the type of errors in calculating the positions of said communication devices IA, IB. It should also be noted that this angle value of 0.02 mrad can be adjusted up or down depending on the desired range and data rate of the communication between the communication devices IA, IB.

[0058] It is understood that the third step 300 allows a third alignment of the laser units 20 of the communication devices IA, IB on the basis of the useful laser beams F” in the communication state.

[0059] It is also understood that the principle of the third step 300 is substantially identical to that of the second step 200, the third alignment of the laser units 20 being carried out on the basis of the useful laser beams F” in the communication state and not in the beacon state as is the case for the second alignment.

[0060] It is further understood that at the end of the third step 300, the laser units 20 are sufficiently aligned to allow data exchange between building A and building B, this data being transmitted via the useful laser beams F” in the communication state generated by the laser units 10 of the communication devices IA, IB. In the communication state, the useful laser beams F” of the laser units 10 are collimated, which makes the data exchanges particularly robust to jamming and guarantees their discretion if the frequency band of the useful laser beams F' ' is chosen outside the visible range.

[0061] Of course, the invention is not limited to the embodiment described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0062] The optical amplifier 22 is optional.

[0063] Although the optical module 23 includes a variable focal length liquid lens, it may also include a solid lens mounted on a wheel or carousel type rocker or other allowing the lens to be positioned in the optical path and / or removed.

[0064] Although the invention is described here in application to two buildings A, B, it can also be applied to any fixed or mobile carrier, whether land-based or maritime.

Claims

Demands

1. Laser communication device (1, IA, IB) comprising a sight (10) and a laser unit (20) carried by the sight, the sight being an observation and / or fire control sight, and the laser unit comprising: - a laser emitter (21) arranged to emit an original laser beam (F) along a line of sight (L); and - an optical module (23) arranged to selectively modify the divergence of the original laser beam so as to obtain a useful laser beam (F”) capable of adopting a beacon state in which the useful laser beam is broadened along the line of sight, and a communication state in which said useful laser beam is collimated along said line of sight.

2. Laser communication device (1, IA, IB) according to claim 1, wherein the optical module is a variable focal length liquid lens (23).

3. Laser communication device (1, IA, IB) according to any one of the preceding claims, wherein the laser unit (20) includes an optical amplifier (22) arranged between the laser emitter (21) and the optical module (23) to amplify the original laser beam (F) before modifying its divergence via said optical module.

4. Laser communication device (1, IA, IB) according to any one of the preceding claims, wherein the sight (10) is an optronic sight.

5. Laser communication assembly comprising at least two laser communication devices (1, IA, IB) according to any one of the preceding claims.

6. Laser communication assembly according to claim 5, wherein the laser communication devices (1, IA, IB) are identical.

7. Method for aligning the laser units (20) of a laser communication set according to claim 5 or 6, comprising: • a first alignment (100) of the laser units on the basis of data exchanged by radio frequency between the laser communication devices (IA, IB); • a second alignment (200) of the laser units on the basis of the useful laser beams (F”) of the laser communication devices in the beacon state; • a third alignment (300) of the laser units on the basis of the useful laser beams (F”) of the laser communication devices in the communication state.

8. Alignment method according to claim 7, wherein the first alignment (100) comprises the following steps: a) exchange between the laser communication devices (AI, IB) of radio frequency data enabling each of the laser communication devices (AI, IB) to estimate in real time a position and velocity of the other of the laser communication devices; and b) alignment of the laser units (20) via the sights (10) from the estimated positions and velocities;

9. Alignment method d according to claim 7 or 8, wherein the second alignment (200) comprises the following steps: c) while the useful laser beams (F”) of the communication devices (IA, IB) are in the beacon state, variable pointing of the line of sight of the laser unit of one of the communication devices around the estimated position of the other of the communication devices until detection of the useful laser beam of said other communication device; d) stopping the variable pointing and estimating by calculation the position of the other of the communication devices; e) applying an offset by the communication device to its line of sight from the position estimated in step d);and f) repetition of steps c) to e) reversing the roles of the communication devices until the lines of sight of said communication devices 1 A, IB are sufficiently aligned to be slaved via their useful laser beams F” to the beacon state.;

10. An alignment method according to any one of claims 7 to 9, wherein the third alignment (300) comprises the following steps: (g) while the useful laser beams (F”) of the communication devices (IA, IB) are in the communication state, variable pointing of the line of sight of the laser unit of one of the communication devices around the estimated position of the other of the communication devices up to detection of the useful laser beam of said other communication device; h) stopping the variable pointing and estimating by calculation the position of the other communication device; i) application of an offset by the communication device on its line of sight from the position estimated in step d); and j) repetition of steps g) to i) reversing the roles of the communication devices until the lines of sight of said communication devices IA, IB are sufficiently aligned to be slaved via their useful laser beams F” to the communication state.