Optronic diffraction detection device and vehicle equipped with such an optronic device

Abstract

Optronic detection device (1), comprising: an optronic sensor (3) comprising a matrix of photosensitive elements (E); a filtering matrix (4) comprising at least first filters (B1) transparent to a first wavelength range and second filters (B2) transparent to a second wavelength range, the first filters (B1) and the second filters (B2) being distributed in a regular pattern each facing one of the photosensitive elements (E); an optical system (5) extending in front of the filtering matrix (4). The optical system (5) comprises at least one diffraction grating (6) arranged so that any incident radiation coming from an external point source strikes one of the first filters (B1) and one of the second filters (B2). Vehicle comprising such a device. FIGURE OF THE ABSTRACT: Fig. 1

Description

Title of the invention: Optronic diffraction detection device and vehicle equipped with such an optronic device

[0001] The present invention relates to the field of detection of optical phenomena and more particularly to an optronic detection device usable for example for the self-protection of military vehicles and the guidance of missiles.

[0002] BACKGROUND OF THE INVENTION

[0003] An optronic detection device generally comprises an optronic sensor and an optical system arranged in front of the optronic sensor. The optronic sensor comprises a matrix of photosensitive elements commonly called pixels (from the English picture elements) delivering a signal proportional to the energy transmitted by the light radiation which strikes them.

[0004] Threat detection for the self-protection of military vehicles is based on the detection of threats, such as missiles, from optical phenomena linked for example to the ejection of gases by the missile nozzle. It is understood that to increase the chances of survival of the vehicle and to be able to trigger countermeasures, it is necessary to detect the missile as early as possible, that is to say even when the missile is very far away. This therefore presupposes being able to detect a very localized optical phenomenon in the landscape and to distinguish it from natural optical phenomena such as the sun or a solar pool. The principle is roughly the same for the guidance of missiles towards a target.

[0005] Early detection of threats / targets depends directly on the signal-to-noise ratio or SNR provided by the optronic sensor (the more the signal has an intensity greater than that of the noise, the easier it is to detect).

[0006] The classification of the detected phenomena (natural phenomena vs threats / targets) is carried out according to a bi-spectral ratio or BSR, that is to say that the optronic detection device is arranged to provide a signal in two spectral bands and the classification depends on the intensity ratio of the signals in each of the bands. For this purpose, it is known to place, in front of the optronic sensor, a bi-spectral filtering matrix comprising first filters allowing light radiation to pass in a first wavelength band and second filters allowing light radiation to pass in a second wavelength band. The first filters and the second filters are arranged in a Bayer type pattern so that a first part of the photosensitive elements is struck by the light radiation in the first wavelength band and a second part of the photosensitive elements is struck by light radiation in the second wavelength band.

[0007] Furthermore, to be effective, optronic detection devices must have a relatively small instantaneous field of view (FOV) to have a sensitivity and resolution suitable for detection. However, the narrower the field of view, the smaller the area covered by the electronic device.

[0008] Optronic detection devices are therefore designed to have an orientable line of sight. We then speak of total field of observation or FOR from the English field of regard to designate the maximum area covered by the optronic device by orienting its line of sight.

[0009] This architecture has two weaknesses: - the interpolation necessary for calculating the bi-spectral ratio because this interpolation tends to locally reduce the intensity of the signal in the interpolated parts of the image, interpolated parts which risk being drowned in noise when the signal / noise ratio is low, particularly at the detection limit (distant threat / target or small dimensions). - the refresh rate of the total field of observation must be as high as possible but depends directly on the speed of movement of the line of sight.

[0010] The only way to address the first weakness is to optimize the interpolation algorithm.

[0011] One way to overcome the second weakness is to use a larger optronic sensor, fixedly mounted on the vehicle (so-called strapdown mounting). However, this is accompanied by a disadvantage that did not exist with optronic devices with a steerable line of sight. Indeed, a threat heading towards collision with the threatened vehicle always presents itself in the same orientation relative to the threatened vehicle. When it is distant, the light radiation emitted by the threat only strikes one filter of the bi-spectral filtering matrix and can only be detected by the photosensitive element located behind this filter if the light radiation corresponds to the wavelength band of this filter.This problem does not occur with an optronic device with a steerable line of sight because the line of sight scans the vehicle's environment (the light radiation from the threat will successively hit several filters in the filtering matrix, and therefore the photosensitive elements behind it).

[0012] SUBJECT OF THE INVENTION

[0013] The invention aims in particular to improve the detection capabilities of an optronic detection device. Summary of the invention

[0014] For this purpose, according to the invention, an optronic detection device is provided, comprising: - a frame, - an optronic sensor comprising a matrix of photosensitive elements; - a filtering matrix extending in front of the optronic sensor and comprising at least first filters transparent to a first wavelength range and second filters transparent to a second wavelength range, the first filters and the second filters being distributed in a regular pattern on a surface of the filtering matrix each facing one of the photosensitive elements; - an optical system extending in front of the filter matrix;

[0015] The optical system comprises at least one diffraction grating arranged so that any incident radiation from an external point source strikes one of the first filters and one of the second filters.

[0016] Thus, thanks to the diffraction grating, the light radiation coming from each point of the observed scene will arrive on two photosensitive elements each corresponding to a wavelength band. Expressed in a more technical way, the barycenter of the point spread function (describing the response of the optronic sensor to a point source of radiation - this function is commonly called PSF from the English point spread function), also called spatial impulse response, is not on a single photosensitive element but on two photosensitive elements arranged behind one of the first filters and one of the second filters respectively. Consequently, the risk of a lack of detection is low even if the line of sight is fixed. In addition, there is no longer any need for interpolation between the two wavelength bands because the information acquired in the two wavelength bands correspond to the same element of the observed scene.

[0017] According to optional characteristics, used individually or in whole or in part in combination: - the diffraction grating is carried by a blade; - the diffraction grating is arranged at one end of the optical system neighbor of the filter matrix; - the optical system comprises at least a first group at the input of the optical system and a second group at the output of the optical system and the diffraction grating between the two groups; - the diffraction grating is arranged near the first group; the diffraction grating is arranged near the second group; the diffraction grating is arranged at one end of the optical system neighbor of the filter matrix; the optical system comprises at least one scanning plate; the scanning plate carries the diffraction grating.

[0018] The invention also relates to a vehicle having a structure on which such an optronic device is fixed, the optronic device being fixed in position relative to said structure.

[0019] Other characteristics and advantages of the invention will emerge from reading the following description of particular and non-limiting embodiments of the invention. Brief description of the drawings

[0020] Reference will be made to the accompanying drawings, among which:

[0021] [Fig-1] is a schematic view of an optronic detection device according to a first embodiment, in section along the optical axis thereof, in a version mounted on a vehicle;

[0022] [Fig.2] is a view similar to [Fig.l] of an optronic device according to a second embodiment;

[0023] [Fig.3] is a view similar to [Fig.l] of an optronic device according to a third embodiment;

[0024] [Fig.4] is a view similar to [Fig.l] of an optronic device according to a fourth embodiment;

[0025] [Fig.5] is a view similar to [Fig.l] of an optronic device according to a fifth embodiment;

[0026] [Fig.6] is an enlarged view of zone VI of [Fig.5];

[0027] [Fig.7] is a view similar to [Fig.l], partial, of an optronic device according to a variant of the fifth embodiment;

[0028] [Fig.8] is a partial schematic top view of a filtering matrix according to a first embodiment;

[0029] [Fig.9] is a view similar to [Fig.8] showing different possible offsets on this filter matrix;

[0030] [Fig. 10] is a partial schematic top view of a filtering matrix according to a second embodiment;

[0031] [Fig. 11] is a partial schematic top view of a filter matrix according to a third embodiment;

[0032] [Fig. 12] is a partial schematic top view of a filter matrix according to a fourth embodiment;

[0033] [Fig. 13] is a schematic sectional view of a diffraction plate used in this optronic detection device, according to a first embodiment;

[0034] [Fig. 14] is a schematic sectional view of a diffraction plate according to a second embodiment;

[0035] [Fig. 15] is a partial schematic top view of an optronic sensor used in the optronic detection device according to the invention;

[0036] [Fig. 16] is a schematic sectional view showing the diffraction effect obtained by the invention;

[0037] [Fig. 17] is an enlarged view of area XVII of [Fig. 16]. DETAILED DESCRIPTION OF THE INVENTION

[0038] With reference to [Fig.l], the optronic detection device according to the invention, generally designated 1, is mounted on a vehicle V.

[0039] The optronic device 1 comprises a frame 2, an optronic sensor 3, a filtering matrix 4 and an optical system 5.

[0040] The frame 2 is fixed to a structure of the vehicle V to be immobile relative to it (so-called strapdown mounting).

[0041] The optronic sensor 3 is fixed to the frame 3 and comprises, in a manner known per se, a matrix of photosensitive elements E (see [Fig. 15]).

[0042] The filtering matrix 4 extends in front of the optronic sensor 3 and comprises, in a manner known per se, first filters B1 transparent to a first wavelength range and second filters B2 transparent to a second wavelength range. The first filters B1 and the second filters B2 are distributed in a regular pattern on a surface of the filtering matrix 4, each facing one of the photosensitive elements E ([Fig. 15]). The pattern is, for example, a BAYER-type checkerboard. The first filters B1 here allow the blue MWIR wavelength band ([3.6 pm; 4.1 pm]) to pass and the second filters B2 here allow the red MWIR wavelength band ([4.5 pm; 4.9 pm]) to pass.

[0043] The optical system 5 extends in front of the filtering matrix 4 and here comprises, along an optical axis, a first group of lenses 5.1 arranged at the entrance of the optical system 5 and a second group of lenses 5.2 arranged at the exit of the optical system 5 to direct the incident light radiation towards the optronic sensor 3 and form an image thereon. This arrangement is known in itself and will not be detailed further here.

[0044] The optical system 5 further comprises at least one diffraction grating 6 arranged so that any incident radiation coming from a point source strikes one of the first filters B1 and one of the second filters B2. The shift thus produced on the filtering matrix 4 is illustrated in Figures 16 and 17.

[0045] The diffraction grating may be arranged to cause an offset of any odd number of filters, in one direction or another: - along the X axis (lines) of the filtering matrix (arrows Dl, D2 of [Fig.9]); and / or - along the Y axis (columns) of the filtering matrix (arrows D3, D4 of [Fig.9]); and / or - along any axis of the filtering matrix (arrows D5, D6 of [Fig.9]).

[0046] The shifts D1 and D3 are rectilinear shifts of one filter; the shift D2 is a rectilinear shift of three filters in a straight line; the shift D4 is a rectilinear shift of seven filters in a straight line; the shifts D5 and D6 are L-shaped shifts of three filters. Other shift values ​​are of course possible.

[0047] It is understood that the light radiation coming from each point of the scene will arrive on a filter B1 and a filter B2 and therefore on two photosensitive elements E each corresponding to a band of wavelengths. In other words, the barycenter of the point spread function (or spatial impulse response) is therefore not on a single photosensitive element E but on two photosensitive elements E arranged behind one of the first filters B1 and one of the second filters B2 respectively.

[0048] In the first embodiment shown in [Fig. 1], the diffraction grating 6 is carried by a blade 60 positioned close to the lens group 5.2 at the output of the optical system 5.

[0049] For photosensitive elements E of dimension 15 pm, the diffractive equation of the diffractive grating 6 is for example 0.0036X for an offset along the X axis of the filtering matrix 4 (we recall that the optical phase is defined modulo 2ir and that X is the slope of the straight line defining the surface of the diffractive grating 6, a straight line that is folded every 2ir jump to obtain a sawtooth surface profile such as that visible in [Fig. 13]). The diffractive equation of the diffractive grating 6 is for example 0.0036Y for an offset along the Y axis of the filtering matrix 4.

[0050] According to a first embodiment of the blade 60, shown in [Fig. 13], the blade 60 is made of germanium and has a surface provided with reliefs forming the diffraction grating 6.

[0051] According to a second embodiment of the plate 60, shown in [Fig. 14], the plate 60 is a phase plate incorporating local modifications of the refractive index distributed and arranged in the thickness of the plate 60 to form the diffraction grating 6.

[0052] In the second embodiment of the optronic device, shown in [Fig.2], the diffraction grating 6 is carried by a blade 60 positioned at the output of the optical system 5 near the filtering matrix 6.

[0053] For photosensitive elements E of dimension 15 pm, the diffractive equation of the diffractive grating 6 is for example 0.035X for an offset along the X axis of the filtering matrix 4. The diffractive equation of the diffractive grating 6 is for example 0.035Y for an offset along the Y axis of the filtering matrix 4.

[0054] In the third embodiment shown in [Fig.3], the diffraction grating 6 is carried by a blade 60 positioned close to the first group of lenses 5.1.

[0055] For photosensitive elements E of dimension 15 pm, the diffractive equation of the diffractive grating 6 is for example 0.0066X for an offset along the X axis of the filtering matrix 4. The diffractive equation of the diffractive grating 6 is for example 0.0066Y for an offset along the Y axis of the filtering matrix 4.

[0056] In the fourth embodiment shown in [Fig.4], the diffraction grating 6 is carried by a 90° reflecting plate 5.3 positioned between the two groups of lenses 5.1 and 5.2.

[0057] For photosensitive elements E of dimension 15 pm, the diffractive equation of the diffractive grating 6 is for example 0.0029X for an offset along the X axis of the filtering matrix 4. The diffractive equation of the diffractive grating 6 is for example 0.0029Y for an offset along the Y axis of the filtering matrix 4.

[0058] In the fifth embodiment shown in Figures 5 and 6, the diffraction grating 6 is carried by a blade 60 positioned as in the first embodiment and the optical system 5 comprises at least one scanning blade 7 positioned close to the first group of lenses 5.1. The scanning blade 7 is a blade with flat and parallel faces, mounted to pivot about its central axis forming an acute angle with the optical axis of the optical system 5 to have two extreme positions shown respectively in solid line and in dot-and-dash line in [Fig.6]. The scanning blade 7 is arranged to shift the line of sight by a few sensitive elements in such a way that the optronic detection device does not have a blind zone.

[0059] For photosensitive elements E of dimension 15 pm, the angle between the central pivot axis of the scanning blade 7 and the optical axis of the optical system 5 is approximately 2.16°.

[0060] It is possible to produce the diffractive beam directly on the scanning blade 7. In such a case, the scanning blade is inclined by 2.11° and the diffractive equation is 0.0058X (or Y as the case may be)

[0061] In the variant of the fifth embodiment shown in [Fig. 7], the scanning blade 7 is positioned in the second lens group 5.2. The angle between the central pivot axis of the scanning blade 7 and the optical axis of the optical system 5 is approximately 1.12°.

[0062] Of course, the invention is not limited to the embodiments described but encompasses any variant falling within the scope of the invention as defined by the claims.

[0063] In particular, the optronic detection device according to the invention may have a structure different from that described.

[0064] Instead of a checkerboard distribution as shown in Figures 8 and 9, the first filters and the second filters can be distributed in rows as in [Fig. 10], in columns or diagonally. The filter matrix can further comprise, in addition to the first filters and the second filters, third filters transparent to a third wavelength (see [Fig. 11] with a distribution of the filters by diagonals for example), or even fourth filters transparent to a fourth wavelength (see [Fig. 12] with a distribution of the filters by rows for example) or more.

[0065] The first wavelength band may be separated from the second wavelength band as in the example described, or the two wavelength bands may be joined. For example, one could have: the first wavelength band corresponding to the MWIR band and the second wavelength band corresponding to the SWIR band; or the first wavelength band corresponding to the MWIR band and the second wavelength band corresponding to the LWIR band; or the first wavelength band corresponding to the SWIR band and the second wavelength band corresponding to the LWIR band. It will be noted, however, that the optronic device of the invention is not limited to infrared detection applications but may also be arranged to operate in other domains and for example in the visible domain.

[0066] The optical system may comprise a single lens group or more than two lens groups.

[0067] The diffractive grating 6 can be produced directly on a lens of the optical system 5.

[0068] The sweeping blade 7 is optional.

Claims

Claims

1. Optronic detection device (1), comprising: - a frame (2), - an optronic sensor (3) comprising a matrix of photosensitive elements (E); - a filtering matrix (4) extending in front of the optronic sensor (3) and comprising at least first filters (B1) transparent to a first wavelength range and second filters (B2) transparent to a second wavelength range, the first filters (B1) and the second filters (B2) being distributed in a regular pattern on a surface of the filtering matrix (4) each facing one of the photosensitive elements (E); - an optical system (5) extending in front of the filtering matrix (4); characterized in that the optical system (5) comprises at least one diffraction grating (6) arranged so that any incident radiation coming from an external point source strikes one of the first filters (B1) and one of the second filters (B2).

2. Device according to claim 1, in which the diffraction grating (6) is carried by a blade.

3. Device according to claim 1, wherein the diffraction grating (6) is arranged at one end of the optical system (5) adjacent to the filter matrix (4).

4. Device according to claim 1, wherein the optical system comprises at least a first group at the input of the optical system and a second group at the output of the optical system and the diffraction grating (6) is between the two groups.

5. Device according to claim 4, wherein the diffraction grating (6) is arranged in proximity to the first group.

6. Device according to claim 4, wherein the diffraction grating (6) is arranged near the second group.

7. Device according to claim 1, wherein the optical system (5) comprises at least one scanning blade (7).

8. Device according to claim 7, wherein the scanning blade (7) carries the diffraction grating (6). 10

9. Vehicle (V) having a structure on which is fixed an optronic device (1) according to any one of the preceding claims, the optronic device (1) being fixed in position relative to said structure.

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