WO2007045638A1

WO2007045638A1 - Dual-laser-scanning optical device having multiple adjustable parameters

Info

Publication number: WO2007045638A1
Application number: PCT/EP2006/067461
Authority: WO
Inventors: Alexandre Paleologue
Original assignee: Commissariat A L'energie Atomique
Priority date: 2005-10-18
Filing date: 2006-10-16
Publication date: 2007-04-26
Also published as: FR2892206A1; FR2892206B1

Abstract

The invention relates to a dual-laser-scanning optical device having multiple adjustable parameters and consisting of two continuously-rotating wedges, each rotating wedge comprising two counter-rotating prisms which are disposed consecutively on the path of the laser beam. According to the invention, the following parameters can be adjusted: a1, a2, a3, a4, i.e. the angles at the top of the prisms of the two wedges (25, 26); ?1, ?2, ?3, ?4, i.e. the speed of rotation of the prisms of the two wedges (25, 26); n1, n2, n3, n4, i.e. the indices of the prisms of the two wedges (25, 26); and ß1, ß2, i.e. the angles formed between the two prisms of each wedge (25, 26) in a plane that is perpendicular to the axis of the beam.

Description

MULTI-PARAMETRABLE LASER DOUBLE SCAN OPTICAL DEVICE

DESCRIPTION

TECHNICAL AREA

The invention relates to a multiparameter optical device for double laser scanning.

STATE OF THE PRIOR ART

In the optical field of active detection and non-contact distance measurement, it may be necessary to use laser optical double-scanning devices, each of these scans being obtained mechanically and electronically with a given scanning pattern, for example television type scan. The document referenced [1] at the end of the description thus describes a scanning method that makes it possible to increase the field of view (FOV) of a focal plane array camera (FPA) by rotating optical prisms in front of the optics of the camera. the camera, these two prisms rotating with continuous rotational speeds, and opposite, around a common axis. This method makes it possible to obtain a non-uniform speed of movement of the line of sight (LdV). In this process four images taken in different directions of the line of sight are linked together in a large image resulting in a field of view significantly increased in two directions. The referenced document [2] describes the use of a diasporameter to perform a simple scan in a telemetry device and its application to an obstacle detection system. As illustrated in FIG. 1, this device comprises a laser source 10 emitting a beam 11, this source being controlled in pulses, along a line of sight (Δ) for measuring the distance separating this laser source 10 from a target 12 reflecting back echoing at least a portion of the energy received to the laser source 10. A mono-element receiver

(lens 13, interference filter 14, photodiode 15) of the energy thus returned (reflected ray 22) and means 16 for determining said distance generate a control signal of the laser source 10. A diasporameter 17, provided with two prisms 18 and 19 animated opposite rotation speeds in directions about said axis (Δ), prints the beam 11 a deflection variable in time so that it describes a determined scanning pattern in a plane perpendicular to said axis (Δ) . This beam 11 scans the target 12 according to the configuration of a scanning figure. A polarization splitter cube 20 associated with a quarter wave plate 21 makes it possible to use a common transmission / reception optics with separation on the polarization of the light. In this device the diasporameter 17 is used in transmission and reception. The inventor however envisages the possibility of using two diasporameters: one in emission, the other in reception, these two diasporameters then operating in phase, which makes this solution complex.

Diasporameters are well-known optical systems. But they are little used because they generate large chromatic aberrations broadband and geometric deformation effects at the edge of the field marked convergent beam.

Scanning devices of the field of view using a pointing laser (detection, or illumination of an object) of the prior art can also use two-axis mirrors driven. But this imposes large mirror sizes and therefore binding requirements (mass, volume, power) in terms of motorization. In addition, these devices are not of zero moment of inertia, which imposes mechanical correction systems both heavy and complex.

The double-scanning devices of the known art have the drawbacks of being cumbersome, complex to implement and having low scanning speeds and low fields.

The object of the invention is to overcome these disadvantages by proposing a multiparameter optical device for double-scanning laser.

STATEMENT OF THE INVENTION

The invention relates to a multiparameter optical double laser scanning device, characterized in that it comprises two diasporameters in continuous rotation, each diasporameter consisting of two counter-rotating prisms arranged consecutively on the path of a laser beam, and in that the following parameters are adjustable:

α1, α2, α3, α4: angles at the apex of the prisms of the two diasporameters, ω1, ω2, ω3, ω4: rotational speeds of the prisms of the two diasporameters,

- ni, n2, n3, n4: prism indices of the two diasporameters,

- βl, β2: angles that form between them the vertices of the two prisms of each diasporameter in a plane perpendicular to the axis of the beam.

In an advantageous embodiment, the device of the invention further comprises means for coupling to a passive mirror telescope, for example of the Infra-Red type, an active detector, and possibly a passive detector.

In an advantageous embodiment the two diasporameters are arranged between a laser source followed by a lens and the telescope through a first semi-transparent plate and a first lens. A second semi-transparent plate, disposed between the two diasporameters, is associated with an active detector via a third lens. The first semi-transparent plate is associated with a passive detector and a second lens.

The device of the invention further comprises:

electronic means for controlling the laser source; electronic control means for the two diasporameters; electronic control means of the active detector, these different control means being connected to each other. It thus comprises:

electronic control means for the passive sensor,

electronic means for processing the passive signal; electronic means for processing the signal received by the active detector;

electronic means for storing and processing the data received from these electronic processing means.

The device of the invention has many advantages:

The scanning rate is solely related to the rotational speed of the prisms of the two diasporameters.

- This device has no imbalance: the residual moment of inertia is zero.

- The size of this device is reduced. Compared to the device of the known art described in the referenced document [2], the device of the invention has the following advantages:

It includes a double diasporameter and no longer a single diasporameter or two diasporameters in phase: the adjustment parameters are therefore more numerous. The realizable reasons are also more numerous. The FOV obtained is more important.

- The detection used is a matrix detection, and no longer a monoelement detection: it results a direct position information in the FOV, in addition to the distance information.

- The coupling with the passive infrared telescope is simple, while the document referenced [2] does not offer clever coupling with such a telescope.

The device of the invention when coupled with a passive infrared telescope can advantageously be used in exo-atmospheric interceptor vehicles (altitude greater than 120 km), these vehicles then having infrared detection capabilities and capabilities distance measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a device of the prior art.

FIGS. 2A, 2B and 2C illustrate the device of the invention, which comprises two diasporameters, as well as the scanning patterns obtained at the output of each diasporameter.

FIGS. 3A to 5D illustrate various scanning patterns obtained with the device of the invention illustrated in FIG. 2A. FIG. 6 illustrates the device of the invention associated with a passive infrared telescope. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

FIG. 2A illustrates the multi-parametric optical dual-scanning laser device of the invention, which comprises two continuous diasporameters 25 and 26 in continuous rotation arranged in the path of a laser beam. The optical and kinematic characteristics of these two diasporameters 25 and 26 differ, thus offering a large range of scanning patterns of the field of view and the field of laser illumination, as illustrated in FIGS. 2B.

(scan pattern 27) and 2C (scan pattern 28).

The scanning speeds of the two diasporameters 25 and 26 are limited only by the rotational speeds ωl, ω2, ω3 and ω4 that can be achieved with motors in continuous rotation. The scan rate obtained can therefore be quite interesting.

The fact of using two diasporameters 25, 26 consecutive makes it possible to generate completely original scanning figures. FIG. 2B corresponds to the scanning pattern obtained at the output of the first diasporameter 25. FIG. 2C corresponds to the scanning pattern obtained at the output of the second diasporameter 26.

The scanning pattern illustrated in FIG. 3C can be adapted in real time by part of the following adjustment parameters:

- ωl, ω2, ω3, ω4: rotational speeds of the prisms of the two diasporameters 25 and 26, - βl and β2: angles that form between them the two prisms of each diasporameter 25 or 26 when viewed in a plane perpendicular to the line of sight. There are therefore 14 adjustment parameters including six variables in real time in total to control the two diasporameters 25 and 26 of the device of the invention.

FIGS. 3A to 5D illustrate different types of scanning patterns generated with the double diasporameter 25, 26.

Figure 3A illustrates the line of sight ("one of sight" or LOS) of the first diasporameter 25 ("diasporameter 1") in the image plane (plane (oy, oz)).

FIG. 3B illustrates the course of the line of sight of the second diasporameter 26 ("diasporameter 2") in the image plane.

FIG. 3C illustrates the overall output of the line of sight (within a few steps) of the two diasporameters 25 and 26, mounted one behind the other.

FIG. 3D illustrates the overall output of the line of sight (complete course) of the two diasporameters 25 and 26 mounted one behind the other, the pattern of the first diasporameter 25 superimposed, for each position, on the pattern of the second diasporameter 26 which ends up giving the course illustrated in this 3D figure.

FIGS. 4A to 4D and 5A, 5B and 5D illustrate paths similar to those illustrated on FIGS. Figures 3A to 3D for different scanning patterns.

The device of the invention thus offers the possibility of performing the double-scanning of a field of view and a field illuminated by a laser according to 14 parameters, some of these parameters can be added in real time.

The device of the invention is purely rotary, the prisms of the two diasporameters 25, 26 operating in counter rotation. This device is therefore extremely compact and has a moment of inertia resulting zero. It is also possible, thanks to the 14 adjustment parameters, to optimize the complete system either by maximizing the field of view, by maximizing the scanning speed, or by driving the line of sight on a predetermined pattern.

FIG. 6 illustrates the multiparameter optical double scanning laser device of the invention with coupling to a passive infrared telescope with mirror 32, enabling photons to be collected and focused on a passive detector 36 which aims to converting said photons into electrons to make an electronic 2D image.

The two diasporameters 25 and 26 are arranged between a laser source 30 followed by a lens 31, and the passive telescope 32, through a first semi-transparent plate 33 and a first lens 34.

The first semi-transparent plate 33 is associated with a passive detector 36 and a second lens 37. A second semi-transparent plate 40 disposed between the two diasporameters 25 and 26 associated with an APD detector (avalanche photodiode) 41, called "active detector", via a third lens 42, makes it possible to direct the afocal beam towards this active detector 41.

The telescope 32 adapted to the Infra-Red (operating between 3 .mu.m and 12 .mu.m, ie covering the infra-red medium and far) or adapted to any other wavelength of interest to the user

(UV / VIS ...) is conventionally composed of two mirrors; a primary mirror Ml and a secondary mirror M2. But any other type of telescope combination is conceivable (Cassegrain, three mirrors ...) This catadiotric telescope 32, associated with the afocal dioptric objective (of a few degrees maximum), allows to realize the image of a scene:

(i) on the passive detector 36 after crossing the lenses 34 and 37, allowing the focusing of the beam, and of the semi-transparent plate 33,

(ii) on the active detector 41 through the second semi-transparent plate 40 and the focusing lens 42. The passive detector 36 is a device for converting the photon energy of the scene into discretized electrical energy through the pixels who compose it. This detector 36 is said to be "passive" in that it uses no other information than that contained in the scene seen through the telescope 32. Thanks to the second semi-transparent plate 40, the afocal beam is diverted to the "active" channel. This beam then passes through the diasporameter 26, the first semi-transparent plate 33 and the lenses 34 and 42 allowing (as for the passive detector) the focusing on the active detector 41. This channel is said to be "active" because it uses a additional information to that of the scene which is the light emitted by the laser 30 and reflected by the object (scene) that one seeks to image or detect.

The laser source 30 emits an optical pulse that propagates:

(i) through the first lens 31 to enter the telescope 32,

(ii) through the first diasporameter 25 which gives an elementary scanning pattern,

(iii) through the semi-transparent plate 40 which deflects the beam towards the second diasporameter 26 which gives the field extension by a second scanning pattern,

(iv) through the first semi-transparent plate 33 which returns the beam to the telescope 32 to illuminate the object in the scene. The scene (object) reflects the laser light that starts again (with an angular scattering pattern) towards the telescope 32.

Note that the active detector 41 is placed between the two diasporameters 25 and 26 through the use of a semi-transparent plate 40. The second diasporameter 26 has, in effect, the objective of propagate the elementary pattern found at the output of the first diasporameter 25 over the entire field of view thanks to its own scanning. The field of view is slightly enlarged (and can be optimized in this sense) which allows to have a larger detection space.

The "passive" path is not strictly necessary for detection. Indeed, using a 2D APD detector (two-dimensional) avalanche photodiode matrix, we would have a 3D information (x, y and distance for each pixel). The addition of a 2D infra-red detector (or another wavelength) simply allows to have information

2D richer (many more pixels available for passive sensors than for APD type detectors

(avalanche photodiode)) and thereby improve multi-spectral detection processes ...

The afocal objective makes it possible, moreover, to make the magnification independent of the position of the object:

(i) deflect and arrange the optical beam without fear of convergence and field problems,

(ii) to work with the diasporameter 25 and 26 in parallel beam which simplifies the possible optical correction systems.

As illustrated in FIG. 6, the device of the invention also comprises:

electronic control means 45 for controlling the laser 30, electronic control means 46 for controlling the two diasporameters 25 and 26,

electronic means 47 for controlling the active detector 41, these various control means being connected to one another.

It also includes:

electronic control means 50 for controlling the passive detector 36, electronic means 51 for processing the passive infra-red signal,

electronic means 52 for processing the signal LIDAR received by the active detector 41,

electronic means 53 for storing and processing data received from these electronic processing means 51 and 52.

Such a global scanning device concept associated with a passive infrared telescope 32 allows considerable volume and mass gain compared to an upstream mirror device.

The use of an afocal lens in the optical combination of an Infra-Red telescope 32 allows:

a significant reduction in the size, volume and mass of the optics, to overcome the constraints of geometric aberrations related to the diasporameters 25 and 26.

The device of the invention makes it possible to solve the following technical problem: to carry out a scanning of the elementary FOV (FOV or "Field of View" or field of view which is the field that an optical instrument sees instantaneously, that is to say under scanning) of a passive sensor 36 (itself extended to the FOR or "Field of Regard" or field of view which corresponds to the part of the space swept by the instrument) by a laser beam (source 30) of low divergence coupled to an APD matrix detector 41 (avalanche diode), with a minimum of space, compatible with embedded systems, and high scan rates.

The device of the invention is weak field (less than 2 ° X2 °), and almost monochromatic (illumination with laser). The second defect of the diasporameters 25 and 26, which is chromatic aberration, is thus arranged.

The device of the invention does not create any disturbance on the carrier, for example a land vehicle (tank turret, armored vehicle ...), or an airplane, a drone, a satellite ..., unlike a mirror system whose imbalance must be compensated.

By judicious choice of the prisms (refractive index, apex angle), it may slightly increase the initial field of view of the telescope ^¬ infra red 32 while covering the same field with one illuminator laser through the second rotating wedge 26.

Example of realization

In a concrete example of embodiment, the following adjustment parameters are used: speeds of rotation of the diasporameters 25 and 26: ω1, ω2, ω3, ω4 = from a few ° / s to a few tens of ° / s, prism indices of the two diasporameters 25 and 26: n1, n2, n3, n4 = 1 at 5 (depending on the choice of glasses),

opening angles of the prisms of the two diasporameters 25 and 26: α1, α2, α3, α4 = a few ° to some ten °, - angles at the apex of the prisms of the two diasporameters 25 and 26: β1, β2 = 0 to 180 °.

REFERENCES

[1] Article titled "Step scan method to enlarge the field-of-view of a focal plane array of cameras by continuously rotating optical elements" by Michael Assel and Jocken Barth (Infrared Technology and Application, SPIE 2004, vol 5406, pages 755-764 )

[2] US 5,359,403

Claims

1. A multi-parametric laser double-scanning optical device, characterized in that it comprises two diasporameters in continuous rotation, each diasporameter consisting of two counter-rotating prisms arranged consecutively in the path of this laser beam, and in that the following parameters are adjustable: α1, α2, α3, α4: apex angles of the prisms of the two diasporameters (25, 26),

- ωl, ω2, ω3, ω4: rotational speeds of the prisms of the two diasporameters (25, 26),

- ni, n2, n3, n4: prism indices of the two diasporameters (25, 26),

- βl, β2: angles that form between them the two prisms of each diasporameter (25, 26) in a plane perpendicular to the axis of the beam.

2. Device according to claim 1 comprising means for coupling to a mirror telescope (32), and an active detector (41).

3. Device according to claim 2, wherein the telescope (32) is an infrared telescope.

4. Device according to claim 2 comprising a passive sensor (36).

5. Device according to claim 2, wherein the two diasporameters (25, 26) are arranged between a laser source (30) followed by a lens and the telescope (32) through a first semi-transparent plate (33). ) and a first lens (34).

6. Device according to claim 5, wherein a second semi-transparent plate (40), disposed between the two diasporameters (25, 26), is associated with an active detector (41) via a third lens (42).

7. Device according to claim 5, wherein the first semi-transparent plate (33) is associated with a passive sensor (36) and a second lens (37).

8. Device according to claim 7 comprising:

electronic means (45) for controlling the laser source (30),

- Electronic means (46) for controlling the two diasporameters (25 and 26), - electronic means (47) for controlling the active detector (41), these different control means being interconnected.

9. Device according to the claim comprising: electronic control means (50) for controlling the passive detector (36), electronic passive signal processing means (51), electronic means (52) for processing the signal received by the active detector (41),

electronic means (53) for storing and processing data received from these electronic processing means (51 and 52).

Apparatus according to any one of the preceding claims, which is used in an exo-atmospheric interceptor vehicle.