OPTICAL SYSTEM AND METHOD AIMING LASER THROUGH THE ATMOSPHERE

The field of the invention is that of pointing laser systems of a target equipped with active imaging devices for identifying targets in a given environment, the target can be air or land and enslaving the pointing systems laser.

Generally, the active imaging uses its own light source, typically a pulsed laser. Thanks to the directivity of the transmission and the energies involved collecting a wide area signal even through a scattering medium. These characteristics particularly given this technology a significant weight for the security and defense. Photons emitted by a laser and reflected by different objects in a scene are collected by an imaging-receiver. The joint use of a pulsed laser and a time gate reception allows selection of a slice of space containing the target of interest.

Is concerned particularly pointing area systems laser energy directed applicant correcting effects of air turbulence on the free propagation of laser beams; turbulence disrupts the system and degrade the accuracy of performance and pointing stability. Further pursuing a moving target and simultaneous correction of optical disturbances introduced by the atmosphere require significant bandwidths servo bands (in the range of 1-2 kHz) to correct duration of disturbances characteristic of about 10 ms and need to cover a largest spatial domain as possible (about half a space), while satisfying operational requirements such as robustness, autonomy, mobility, deployment time, For applications requiring high performance (accuracy of the order of micro radian range of several kilometers), this correction involves having access to a measurement of the position of the target with a high angular resolution with sufficient frequency, to ensure first order compensation of the deformation of the wave surface (jitter phenomenon). Moreover, the illumination system must operate at a wavelength close to but different from that of the laser score. provide compensation to the first order of the deformation of the wave surface (jitter phenomenon). Moreover, the illumination system must operate at a wavelength close to but different from that of the laser score. provide compensation to the first order of the deformation of the wave surface (jitter phenomenon). Moreover, the illumination system must operate at a wavelength close to but different from that of the laser score.

There may be mentioned as other examples of the application, the implementation of optical communications in free space between a fixed ground station and an object flying in space or air space, or a wide area welding process, frequent case on shipyards for the assembly of large rooms and for which current solutions require the use of welding equipment in contact with or in close proximity of the components to be assembled.

There is now a solution implemented in telescopes to correct the effects associated with these atmospheric disturbances. The case of astronomical instruments, however, have different operational characteristics. Indeed, the object pointed is generally punctual and fixed (or moving very slowly), which is generally not the case of the targets envisaged with laser pointing systems. Furthermore operation day and night is required.

Accordingly, to this day remains a need for a laser with a target pointing system simultaneously giving satisfaction to all of the above requirements, in terms of accuracy, range and pointing stability, addressable field of space and system cost.

The proposed solution is based on optomechanical architecture in which the score is divided into two stages, one of said coarse and the other said end, the first ensuring the angular coverage and the second providing the ultimate accuracy. In addition, the gross score allows to implement an active imaging which allows the operation of the fine pointing.

More specifically, the invention relates to an optical pointing system laser of a target through the atmosphere. It is mainly characterized in that it comprises four optical channels:

- a means of passive imaging with an auxiliary camera adapted to obtain images of the target, and a coarse pointing control device connected to this camera,

- a means of illumination with a source of pulsed illumination and time synchronization means,

and in that the passive imaging system and illumination includes a first common optical device for coarse pointing,

- a pathway effector with a laser power source,

- a channel active imaging with:

o a synchronized high speed camera with the source of pulsed illumination by the time synchronization means,

o means to harmonize the high-speed camera with the laser power source, and

o a pointing control device end connected to the camera,

and in that the active imaging system and effector form a pair and contain

- a second common optical device for coarse pointing, first and second optical devices of coarse pointing being controlled by the coarse pointing control device or by the end pointing control device according to the operational phase in the firing sequence,

- a common optical device end pointing controlled by the fine pointing control device,

- a convergent optical device provided with focusing means,

and in that the coarse pointing control device is connected to the end pointing control device.

The converging optical device is preferably located between the common optical device for fine pointing and the second optical device for coarse pointing.

According to one characteristic of the invention, the optical pointing system comprises a first device of stacking of passive imaging system and illumination located between the first optical device for coarse pointing and the illumination laser source and a second device superposition of the active imaging channels and power located between the end pointing device and the power of laser source.

The optical pointing system optionally comprises other pairs of active imaging system and effector disposed in parallel; the pointing control device end of each channel active imaging is connected to the control device of the coarse pointing of the passive imaging path.

According to another characteristic of the invention, the pairs of active imaging system and effector are mounted on a frame in a predetermined pattern preferably straight, and the frame itself is mounted on a frame of the rotating device.

The system architecture of the invention allows the implementation of as many power lasers as necessary to achieve the desired effect.

It also helps to implement small-sized elements, easier to standardize so to get, which reduces the cost of the solution and allows great modularity of the system, so integration and maintenance easier.

The invention also relates to a tracking method of a target through the atmosphere by means of a pointing system as described above, characterized in that it comprises the following steps:

- guiding the first and each second coarse pointing device in a predetermined direction;

- when a target is present in the field of the auxiliary camera, hook and stabilize a coarse tracking loop;

- a target having been found and continued, the control of the first coarse pointing device and each second coarse pointing device is entrusted to the coarse pointing control device;

- lighting the illumination laser source;

- when the illumination is turned on, each high-speed camera provides a video stream to the fine pointing control device associated to hang and stabilize each fine tracking loop;

- each second coarse pointing device is then controlled by the pointing control device end of its pair, which therefore controls both the coarse pointing device and the pointing device end,

- where each second coarse pointing device is controlled by the pointing control device end of the pair considered, the coarse pointing control device only controls the first coarse pointing device,

- on the firing control system, light power lasers and track the target by the active imaging with the high-speed cameras and the end pointing devices and coarse so that each power laser source is pointing.

Other features and advantages of the invention will become apparent from reading the following detailed description, given by way of example and with reference to the accompanying drawings in which:

1 schematically shows an exemplary scoring system according to the invention, equipped with several pairs of active imaging system and effector,

2 shows a flowchart showing steps of the system operating method according to the invention,

3 schematically shows an exemplary scoring system according to the invention, mounted on a rotating assembly.

From one figure to another, the same elements are identified by the same references.

Is described in relation with Figure 1 an example of a target pointing laser optical system 100 through the atmosphere according to the invention. It has four channels:

- a means of passive imaging with a wide field camera 1 Auxiliary (e.g. about 3) adapted to obtain images of the target 100, and a device 2 for coarse pointing control connected to the camera, which is equipped a distance measuring device;

- a means of illumination with a source of high speed pulse illumination 5 operating in near-infrared band (SWIR: 0.8 μηπ μιτι-3) for example at a wavelength ensuring eye safety (1, 5μιτι) and having a smaller area than that of the large field camera (a few milliradians for example), and time synchronization means 1 1 of the high-speed camera 10i (the active imaging route described below) with the source illumination 5.

These passive imaging and illumination paths comprise a common first optical device 4 for coarse pointing, slaved to the instructions produced by the distance measuring from the images from the auxiliary camera 1.

The other two ways are:

- a pathway effector with a laser source 17-i power as said power train.

- a channel active imaging with:

o synchronized 10i camera with the illumination source 5 and having an equivalent field to that of the illumination source; Indeed illumination much larger than the imaging field is inefficient, much closer illumination that the imaging field will not provide sufficient uniformity.

o means the harmonization (not shown) of the high speed camera with the laser source, and o a pointing control device end 12-i connected to the camera and 10i which is equipped with a distance measuring device; 2 the coarse pointing control device is connected to the pointing control device end 12-i. These two pathways active imaging and effector form a pair and comprises:

o a second common optical device 14-i coarse pointing also slaved to the instructions produced by the distance measuring from the images from the auxiliary camera 1 and those of the high speed camera 10i as further discussed; the first and second optical devices of coarse pointing 4 and 14-i are identical and are controlled by the pointing control device 2 coarse,

o a common end 12 pointing device ; slaved to the instructions produced by the distance measuring device from the high camera from image 10-i cadence, positioned between the second coarse pointing device 14-i and the laser power source and controlled by the pointing control device end 12-ι,

o an optical device converge 15i provided with focusing means.

To correct atmospheric disturbances bandwidth equal to the frequency of Tyler atmosphere is of the order of 100 Hz, the performance target at the end pointing accuracy is of the order of micro-radian, and the bandwidth of the pursuit of kilohertz. typically can use the following for these performances.

The high speed 10i camera operates in the near infrared band (SWIR) to an upper frame rate in kilohertz e.g. 2 kHz; its resolution is at least 256x256 pixels. The pointing control device end 12-i and 16i end pointing device operate at rates adapted to that of the high speed camera.

The illumination source 5 provides a train of pulses of fluence generally greater than 10mJ, and operates at the wavelength 1 .5μιτι for eye safety reasons. It covers an equivalent field to that of the high-speed camera 10-i, a few mrad for example 5 mrad. To optimize the signal to noise ratio of the high speed camera, this beam is pulsed at a repetition rate synchronized with the rate frame of the high speed camera, using for example a synchronization clock January 1. This beam is typically pulsed at a whole multiple of the repetition rate frame rate of the high speed camera (CHC).

For example, the illumination source 5 may comprise an illumination laser provides an energy of the order of 250 millijoules per pulse whose duration is on the order of 500 nanoseconds, and be associated with a high speed camera having a time window opening on the order of the pulse duration of the illumination source with a spectral width filter of about ten nanometers. This illumination source architecture + high speed camera represents a suitable structure to meet the criteria of scope and size of objects to be treated.

Such illumination source 5 is described in EP 2 283 548. It transmits in a spectral range in the vicinity of 1 .5 μηι in a spectral window wavelength Δλ = ± 2 nm and delivers energy per pulse 250 mJ at a rate of 2kHz. This source is also coupled to an optical device (zoom) adjusts illuminated field at the target and the illumination distance, the field of view can vary from 1 .5 mrad to 5 mrad.

The auxiliary camera 1 operates for example in IR2 strip (3 μηι - 5 μιτι).

The 17-i power laser operates at a power up kilowatt to tens of kilowatts in near infrared (1 .07μηι example).

The cameras 1, 10-i, the illumination source 5 and the 17-i power source are preferably fixed.

coarse pointing of the devices 4 and 14-i have at least two degrees of freedom; typically they are optical heads with orientable mirror, with a four plane mirrors, two mirrors for a periscope or four mirrors for an optical carding.

16i end pointing device has at least two degrees of freedom; this is typically one or more mirrors placed on mounts provided with piezoelectric actuators or a glass plate placed on a frame provided with galvanometric actuator.

These coarse pointing devices 4 and 14-i may send a hemispherical field or a field in azimuth of 360 ° and in elevation from -10 ° to + 90 °, with or without restriction of the number of revolutions. Thus regardless of the trajectory of an object above the horizon, this object may be pointed to by the pointing system according to the invention.

The converging optical device 15i is provided with focusing means which cooperate with the second coarse pointing device 14-i and the pointing device 1 end 6i to form the image of the target 100 on the high-speed camera and 10i point 17-i power laser on the target 100. This is for example a parabolic mirror mounted on a triplet of linear actuators or a train of lenses mounted in a cam barrel.

So that the first optical device 4 coarse pointing is common to passive imaging system and illumination, is added first 3 of these two channels superimposing device (common to both channels) between the first coarse pointing device and the illumination laser source.

Similarly, for the second optical device 14 coarse pointing ; the pointing device and the end 16i convergent device 15i are common to active imaging system and effector is added a second device 13i superposition of these two channels (common to both channels) between the end pointing device and the power of laser source. It is advantageously located closer to the high-speed camera and 10i of the power source 17- |.

These superposition means are typically:

- a dichroic plate, or

- a diffraction grating used in reflection, or

- a holographic mirror as used in head-up displays, or

- a pierced mirror as described in WO2009077361 A1 and WO2009077360A1 patents. This device allows for the separation of laser channels of power and high speed active imaging independently wavelengths.

To ensure the total power needed by the system, while maintaining cost targets, robustness and maintainability, preferably using multiple laser sources of power. It then multiplies the pairs of active imaging system and effector, keeping only one channel of passive imaging and one way of illumination as shown in Figure 1 on which are also shown from 1 to N pairs active imaging system and effector with N> 2.

All lanes effector and active imaging have the same functional elements, but these elements can be made in different ways (eg, power, field, in pointing device technology ...). All high speed cameras 10i to 10 N of the active imaging channels are synchronized with one illumination source 5, that of the illumination path.

Each power laser beam 17-i (at 17 N ) is pointed towards the 100 target by its own coarse pointing devices 14-i (at 14 N ), pointing end 16 1 (16 N ) and converge 15i (15 N ).

A typical operating sequence is described below in connection with the flowchart of Figure 2 using the example of pointing sytem, ​​a system with multiple pairs of active imaging system and effector. In this figure the system states are represented in rectangles at right angles, the method steps in rounded corners in rectangles, and controls are given in French quotation marks "...".

In the initial state OFF, the optical laser pointer system is off or powered, all moving parts such as pointing devices are in the storage configuration, all control devices are off.

The START-UP step is to feed the system, run some startup tests, placing the moving parts in a "stand-by" configuration and initialize the control devices. It is triggered by the ignition control system "ON".

In the STANDBY state, the system is waiting. Since this state, an operator can run automated diagnostics, enter the System Setup mode, or continue operational sequence.

Step LOCK CP (Coarse Pointing) LOOP consists in directing the coarse pointing devices 4, 14-i to 14 N in a direction

predetermined or through an external target designation (DO Radar) or by performing a search pattern, particularly by means of the distance measuring device of the coarse control device 2 or by manual pointing of the operator. Following this prépointage:

- if a target is present in the auxiliary camera field 1 and recognized, a coarse tracking loop (LOOP CP) is suspended by the pointing control device 2 and stabilized coarse; the system switches to state TARGET LOCKED;

if no target allows the attachment, the system returns to standby after a delay set in the configuration.

This stage is triggered by the command "AIM", or by the loss of total hanging from a subsequent state.

In the state TARGET LOCKED, a 100 target was found and the system hung it successfully. All coarse pointing devices 4, 14-i (14 N ) and end 1 6i (1 6 N ) are controlled on the images from the auxiliary camera 1: all of the second coarse pointing devices 14-i (to 14 N ) are pointed at the target 100 simultaneously by the pointing control device 2 coarse.

Step ILLUM START / LOCK FP (Fine Pointing) LOOP is to turn on the illuminating laser source 5 and hang each end pointing loop. When the illumination is turned on, the pointing device end 16i (1 6 N ) of each pair of power track and active imaging is oriented in its accessible field until the target 100 is present in the field of the camera 10i high frame rate (10 N ) and recognized; fine tracking loop is then engaged by the pointing control device end 12-i (at 12 N ) by means of its distance measuring device and the high speed 10i camera (10 N ) synchronized with the illumination source 5.

In each channel power, control of the second coarse pointing device 14-i (14 N ) is then entrusted to the pointing control device end 12-i (at 12 N ) which becomes the master of the pointing control device coarse 2. this does therefore qu'élaborer control of coarse pointing devices based on instructions provided by

pointing end controls that control both the coarse pointing and the pointing end of their respective channels.

This stage is triggered by the arms control system "ARM" or by the loss of the fine tracking.

In ARMED state, the target is tracked through the active imaging. As indicated in the previous step, each power path is autonomous for control of the coarse pointing device 14-i (14 N ) and its end pointing device 16i (1 6 N). The route of passive imaging and therefore the first coarse pointing device 4 are controlled by the pointing control device coarse 2 to point the illuminator 5. In summary in this state, the device 2 for coarse pointing control receives score instructions for each second coarse pointing device from the corresponding end pointing control devices and develops the appropriate commands to the corresponding coarse pointing devices; he also always receives the video stream from the passive auxiliary camera (wide field), and develops control of the first coarse pointing device due to its deviation measurement.

It is this state that returns the system in case of security failure during shooting.

The step START HPL (High Power Laser) is to turn on each power laser source 17-i (at 17 N ). It is triggered by the fire control system "FIRE".

In FIRING state, each power source is turned on and laser pointing at the target 100 through the high-speed camera 10i (10 N ), the pointing device 1 end 6i (1 to 6 N ) and crude 14-i (14 N ) and the convergent device 15i (15 N ) of its path.

Step STOP HPL consists of cutting each power laser source 17-i (at 17 N ). It is triggered by the shooting stop control system "HOLD", by the expiration of a safety timer or by the loss of the auxiliary channel, which simultaneously cut all sources of power, or an interruption security system or by an interruption of the fine tracking that can cut only the relevant power train and back up an alarm.

We find the ARMED state as described above, wherein the illumination source is on and the control score for each pair 1 to N is provided by the pointing control device end 12-i (at 12 N ) respectively and checkpointing the pair 0 is provided by the pointing control device coarse 2

If security failure during firing, the system returns to the ARMED state.

Step STOP ILLUM./ RELEASE FP consists, in this order, to return control of the coarse pointing devices 4, 14-i (14 N ) to the coarse pointing control 2, disengaging the pointing end loops and cut the illuminator.

It is triggered by the control system of disarmament "DISARM", and then we found the TARGET LOCKED condition described above.

Step RELEASE CP LOOP is to release the coarse tracking to return to the STANDBY state. Coarse pointing devices 4, 14-i (at 14 N ) are placed on standby configuration.

It is triggered by the "RELEASE" command.

Step SHUT DOWN involves cutting power to the system, some run off tests, placing moving parts in a storage configuration.

It is triggered by the stop control system "OFF".

To ensure the combination of beams on the target (including power beams), supervision manages the geometry of the system with respect to its target to provide each path of correcting members so that each channel has the same point of the target or on the contrary, different pairs of active imagery and power channels aim different points (different impacts) to the same target.

To reduce the potential masking between the various pointing devices, masking all the more important as the number N of channels pairs is great, all channels is integrated into the same frame 201 shown Figure 3: This is typically of a standard container, optionally modified. It can be rotated about a vertical axis by means of a rotation device 202 of the frame according to one or more of its axes, for example permitting a clearance of -90 ° to + 90 ° with respect to the axis neutral system. This rotation device 202 may be a rotary table or a ball joint equipped with cylinders so as to swing the frame. Also this set of tracks is placed in a configuration minimizing the risk of masking given the evolution of the 100 with respect to the target system: pointing devices are advantageously arranged on the large midline 203 of the container roof. The turntable 202 and the implantation pattern pointing devices used to make the system operational in any direction accessible hemisphere. In this way, an operator can configure the system in the position where the masking will be removed in the direction of interest (towards the target).

While the invention has been described in connection with particular embodiments, it is obvious that it is not limited and it includes all the technical equivalents of the means described and their combinations if they within the scope of the invention.

CLAIMS

1. optical pointing system of a laser target (1 00) through the atmosphere, characterized in that it comprises four optical channels:

- a means of passive imaging with an auxiliary camera (1) capable of obtaining images of the target, and a device (2) coarse pointing control connected to the camera,

- a means of illumination with a pulsed source of illumination (5) and time synchronization means (1 1),

passive illumination and imaging paths having a common first optical device for coarse pointing (4) connected to the device (2) coarse pointing control,

- a pathway effector with a power laser source (1 7-i),

- a channel active imaging with:

o a high speed camera (1 0i) synchronized with the illumination source (5) by the time synchronization means (1 1),

o means to harmonize the high-speed camera (1 0i) with the power of laser source (1 7-i), and

o a device (1 2-i) fine pointing control associated with this high-speed camera,

and in that the active imaging system and effector form a pair (pair 1) and comprise

- a second common optical device (14-i) for coarse pointing, first (4) connected to the coarse pointing control device (2),

a common optical device for fine pointing (1 6i) controlled by the pointing control device end (1 2-i),

- a converging optical device (1 5-I) having focusing means,

and in that the coarse pointing control device (2) is connected to the end pointing control device (1 i-2).

optical target tracking system according to the preceding claim, characterized in that the convergent optical system (15-i) is located between the common optical device for fine pointing (1 6i) and the second optical device for coarse pointing (14 -i).

optical target tracking system according to one of the preceding claims, characterized in that it comprises a first superimposing device (3) passive imaging system and illumination located between the first optical device for coarse pointing (4) and the illumination laser source (5).

optical tracking system of a target according to one of the preceding claims, characterized in that it comprises a second superimposing device (13-i) active imaging channels and power located between the end pointing device ( June 1-i) and the power of laser source (17-i).

optical target tracking system according to one of the preceding claims, characterized in that it comprises other pairs of active imaging system and effector (pairs 1 to N) arranged in parallel and in that the coarse pointing control device (2) is connected to the fine pointing control device (12-1, 12N) to each channel active imaging.

optical target tracking system according to the preceding claim, characterized in that the pairs of active imaging system and effector are mounted on a frame (201) in a predetermined configuration, and in that the frame is him -even mounted on a device (202) of rotation of the frame.

System optical tracking of a target according to the preceding claim, characterized in that the configuration is rectilinear.

A method of tracking a target (100) through the atmosphere by means of a pointing system according to one of the preceding claims, characterized in that it comprises the following steps:

- guiding the first and each second coarse pointing device in a predetermined direction;

- when a target is present in the field of the auxiliary camera, hook and stabilize a coarse tracking loop;

- a target having been found and continued, the control of the first coarse pointing device and each second coarse pointing device is entrusted to the coarse pointing control device;

- lighting the illumination laser source;

- when the illumination is turned on, each high-speed camera provides a video stream to the fine pointing control device associated for hooking and stabilize each fine tracking loop;

- each second coarse pointing device is then controlled by the pointing control device end of its pair, which therefore controls both the second coarse pointing device and the pointing device end,

- where each second coarse pointing device is controlled by the pointing control device end of the pair considered, the coarse pointing control device only controls the first coarse pointing device,

- on the firing control system, light power lasers and track the target by the active imaging with the high-speed cameras and the end pointing devices and coarse so that each power laser source is pointing.

9. Method according to the preceding claim, characterized in that the coarse pointing direction is determined by an external target designation or by performing a search pattern, or by operator's manual score.