Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N3/00—Scanning details of television systems; Combination thereof with generation of supply voltages
  • H04N3/02—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only
  • H04N3/08—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only having a moving reflector
  • H04N3/09—Scanning details of television systems; Combination thereof with generation of supply voltages by optical-mechanical means only having a moving reflector for electromagnetic radiation in the invisible region, e.g. infrared
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B26/00—Optical devices or arrangements for the control of light using movable or deformable optical elements
  • G02B26/08—Optical devices or arrangements for the control of light using movable or deformable optical elements for controlling the direction of light
  • G02B26/10—Scanning systems
  • G02B26/108—Scanning systems having one or more prisms as scanning elements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
  • H04N25/48—Increasing resolution by shifting the sensor relative to the scene

Definitions

• the invention relates to the field of infrared detection, more particularly to detection by infrared cameras using, as detectors, two-dimensional mosaics of elementary photosensitive cells.
• the object of the invention is a micro-scanning device intended in particular for such infrared observation cameras.
• Detectors with a two-dimensional mosaic made up of a large number of photosensitive cells have the advantage, compared to
• a detection strip is made up of a very limited number of elementary cells, at least on one dimension, requiring the adapted scanning of a
• the two-dimensional detectors constitute real electronic retinas, and the image of the scene projected on the detector having in this case dimensions equivalent to those of the detector.
• the photosensitive cells of such mosaics are separated by non-sensitive zones which overall represent a large percentage of the total surface of the detector. For example, on a 128 x 128 mosaic of sensitive cells in the 3-5 ⁇ m band, the sensitive areas
• the video signal supplied by two-dimensional detectors, is only obtained after multiplexing and reading charges delivered by the cells, proportional to the light flux received in a given infrared spectral band (for example in the 3-5 ⁇ or 8-12 ⁇ m band corresponding to atmospheric transmission windows).
• the multiplexing and the reading of the charges are carried out conventionally through charge transfer circuits CCD (initials of Charge Coupled Device, in English terminology) or CID (Charge Injection Circuit) made up of charge integration and transfer zones whose dimensions cannot be reduced arbitrarily.
• the invention aims to obtain spatial continuity of the detection surface of a two-dimensional detector, making it possible to increase the number of pixels in the final image formed from a video signal delivered by the detector, while overcome the disadvantages of the vibratory systems of the prior art.
• the present invention proposes to carry out a mono or bidirectional microscanning using an assembly of thin blades, animated by a uniform rotational movement around an axis perpendicular to the convergent light beam coming from the scene observed.
• the invention relates to a microscan device for periodically deflecting the direction of a convergent light beam, characterized in that it comprises an even number of optical blades 2 to 2 parallel associated dp so as to constitute an assembly of polygonal section around an axis of symmetry, perpendicular to the mean direction of the converging light beam.
• the invention also relates to an infrared camera comprising such a micro-scanning device.
• FIG. 2 an embodiment of the device according to the invention applied to a monodirectional microscan, this device being seen in section along a plane perpendicular to its axis of symmetry;
• FIG. 3 an example of opto-electronic organization of an infrared camera with two-dimensional detector according to the invention;
• This solution implements a polygonal refractive prism, such as that referenced 1 in Figures la and lb which represent it in horizontal section, respectively, according to a first and a second angular position.
• a polygonal refractive prism such as that referenced 1 in Figures la and lb which represent it in horizontal section, respectively, according to a first and a second angular position.
• Such a prism is described in the work of G. GAUSSORGUES entitled “The infrared thermography ", published by LAVOISIER (TEC and DOC).
• a parallel beam FE coming from the scene to be observed, passes through a converging lens 2, of center 0, which forms a converging conjugate beam FC thereof, projected at a focal point occupying a position Po.
• An average radius Rm of the beams FE then FC, defining their mean direction, is coincident with the optical axis AOP A 'shown in phantom.
• the converging beam FC penetrates into the polygonal prism 1 and emerges from this prism according to a beam of the same convergence which finally focuses on a detection strip 3, placed precisely in the focusing plane of the lens 2-prism assembly 1.
• the prism 1 is constituted by a refractive material cut according to a regular polygon comprising an even number of plane facets, for example 8 facets referenced 11 to 18.
• each pair of opposite facets, such as 11 and 15 constitutes a blade with plane and parallel faces which does not modify the convergence of an incident beam.
• the effect used to perform a large amplitude scan, shown in FIG. 1b, is the offset of the optical path of a light ray caused by the crossing of a blade with parallel faces inclined with respect to this ray.
• the angle> . is defined as the angular difference between the optical axis AA ', and the normal to the opposite facets crossed by the converging beam.
• the external beam FE which finally converges on the bar 3 is then inclined by an angle G and the beam FC, conjugated with FE, virtually converges at a point which then occupies a position P .. different from the position P.
• the mean radius Rm is no longer confused with the optical axis AA r .
• each elementary cell of the bar "sees" juxtaposed areas of space forming a strip of space called the "line" of the image of the observed scene.
• a complete image of the observed scene is thus scanned by the bar.
• the passage of the beam FC on an edge of the prism 1 separating two facets causes a discontinuity of the scanning which returns at the beginning of the image by passing from a pair of blades to the next, such as M-15 and 12 - 16 in FIG. .
• the invention exploits this same possibility of obtaining a lateral deflection of a convergent beam by crossing an optical element with parallel faces and inclined with respect to the mean axis of this beam. But in order to cause only an angular scan of very low amplitude, also called microbay, opposite to the previous type of scan, the invention implements an assembly composed of thin blades. The thickness of these blades is very small compared to that of the prism 1 crossed, in order to greatly reduce the factor e of the formulas (I) and (II) and therefore to reduce the amplitude of the optical deflection obtained by the same amount.
• the plates are made of a material transparent to the converging beam to be deflected, at least in a spectral band covering at least the range of sensitivity of the detector used in the main application envisaged below.
• the assembly generally has a polygonal configuration such as that shown in horizontal section, by way of example in FIG. 2.
• the polygonal assembly 20 is formed of 8 identical thin blades 21 to 28 of thickness _, with rectangular, planar and parallel external faces.
• the traces of two successive blades form in the plane of the figure a dihedral with an apex angle equal to 135 °, so as to form an octagon overall, the sides of which are formed by thin blades 21 to 28 two by two opposite, and whose axis of symmetry A is perpendicular to the plane of the figure.
• this assembly 20 When this assembly 20 is driven by a uniform rotational movement around the axis _X, it causes a lateral deviation ⁇ x d focal point of the converging beam FC.
• the expressions of ⁇ x, introduced previously, are still applicable in the case of the deviation obtained using the thin-blade assembly 20. More precisely, the thickness e used in the expressions I or II is then equal to the sum of the thicknesses of the two opposite blades traversed, such as the blades 21 and 25 of FIG. 2.
• this equivalent blade representing a fraction of the thickness of the large amplitude scanning prism 1, described with reference to FIGS. 1 a and 1 b, by example a few percent, the amplitude of the lateral deviation, proportional to the thickness crossed according to formulas I or II, will be reduced in the same proportions.
• the arbitrarily as small as desired thickness of the blades of the assembly 20 according to the invention allows a sweep of amplitude almost as reduced as desired.
• FIG. 3 represents an example of an opto-electronic organization of an infrared camera with a two-dimensional detector equipped with a micro-scanning device according to the invention.
• the same references designate the same objects as in the previous figures.
• a parallel beam F coming from the observed scene is made convergent according to a beam FC and projected onto an infrared detector 31, of the two-dimensional mosaic type, by passing through a focusing lens 2.
• a polygonal microscan assembly 33 according to the invention composed of six thin blades in the example shown, is interposed in the path of the convergent beam FC, that is to say between the focusing lens 2 and the detector 31, the axis of symmetry ⁇ of the assembly 33 being perpendicular to the direction of the converging beam FC.
• the assembly 33 is driven in rotation by the action of a motor M, the speed of rotation being linked to the multiplexing times (integration, transfer and reading) of the charges released in the detector 31 in proportion to the light flux received and multiplexed conventionally in a CCD circuit integrated into the detector 31.
• the reading rate is managed by a sequencer 32 which also adjusts the speed of rotation of the motor M through an angular encoder 34.
• the signal formed by the multiplexed charges, at the output of the detector 31, is processed in a circuit 35 which delivers, in connection with this sequencer 32 a video signal SV according to a TV standard adapted to a display monitor (not shown).
• the rotation of the polygonal assembly 33 gives the FE beam, as explained above, a movement of horizontal microscanning in one direction Dx on the detector 31.
• a micro-sweep in two directions for example in the directions Dx and Dy indicated in FIG. 3, an alternative embodiment of the polygonal assembly according to the invention is described below with reference to FIGS. 4 and 5.
• FIG. 4 illustrates a schematic representation of the beginnings of the first and of the second row of photosensitive cells, C .., ⁇ TO ' ⁇ 13' ⁇ 21 ' C 22' C 23 of a two-dimensional mosaic detector comprising nxp cells
• Cij distributed over a matrix of n rows and p columns, i varying from 1 to n, and j from 1 to p.
• the cells represented have for example a square shape of 25 ⁇ m on a side and are separated, according to the horizontal direction Dx, from 100 ⁇ m and, according to the vertical direction Dy, from 70 ⁇ m.
• Dx horizontal direction
• Dy vertical direction
• the additional cells C. .. ... VS .. . ,- , CC. ..,.
• the microlines, such as Ml and M2 are scanned identically 2 N times per rotation of an assembly with 2 N identical blades forming N pairs of blades opposite two by two.
• a bidirectional microscan assembly according to the invention is, globally, approximately like the monodirectional assembly 3 shown in FIG. 3.
• these assemblies have been shown in FIG. 5, in section along a plane passing through the axis of rotation ___ of FIG. 3 and the median lines of a couple of opposing blades.
• the traces of the blades of the unidirectional microscan assembly 33 appear in dotted lines and that of a bidirectional microscan assembly 50 appear in solid lines.
• the thin blades of the assembly 50, such as 51 and 54 have a prismatic profile with an angle at the apex A, the interior faces of these blades, such as FI. and F4.
• the converging beam FC from the focusing lens 2 has also been shown in section. It is well known to the laws of light propagation that the passage from a light ray to through a slightly prismatic plate with an angle at the apex A, such as 51 or 54, causes an angular deviation approximately equal to (n-1) A. This angular deviation results, for the focal point P5 of the convergent beam, by a vertical offset A y of approximate value:
• l being the distance between the prismatic plate and the focal point
• n the refractive index of the optical material constituting the plate.
• the prismatic angles are different from one pair of blades opposite to another, the vertical offset produced by each of these couples, successively intercepting the converging beam during the rotation of the assembly j is different and the corresponding scanned microline s 'is shifted by as much.
• the different values of the prismatic angles can form a progression such that the successive shifts of the corresponding microlines form a progression of constant pitch.
• an assembly comprising N pairs of opposite blades, ie 2N blades, causes the scanning of N microlines when each of the N couples consists of prismatic blades of the same angle at the top, this angle being different from one couple to the other.
• the N microlines are scanned twice at each rotation of the assembly since the same pair of opposite prismatic blades causes the same offset twice per rotation, the blades coming to the beam converge in a certain order and an inverted order for two positions of the assembly angularly separated by 180 °.
• angles at the top of the 3 pairs of blades of assembly 50 are, respectively, 0 ° (blades of constant thickness), A 0 and 2A °, two additional microlines are created since a couple opposite blades, such as 51 and 54, causes the same microline offset twice per rotation, respectively (nl) A (1 1 + 1 4 ) and (nl) A (_ 4 + l.).
• angles at the top of the prismatic plates being very small, a few degrees at most, the distortion on the scanning which results from the prismatic effect, caused by the presence of a variable deflection of a light ray as a function of the thickness crossed by this radius, remains negligible.
• the assembly of the thin blades can be achieved by any known means, for example by gluing or by fusion between two machined flanges;
• the offset ⁇ y shown in FIG. 5 can also be achieved by assembling thin blades with flat and parallel faces such as the blades of the assembly 33 but with different values of inclination of the blades relative to the axis ⁇ , l the angle of inclination of a pair of opposite blades being identical and the different values of the angles forming a progression such that the successive shifts of the Corresponding microlines form a constant step progression.

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• Physics & Mathematics (AREA)
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• Electromagnetism (AREA)
• Toxicology (AREA)
• General Physics & Mathematics (AREA)
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Cited By (6)

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Citations (7)

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• 1991
  • 1991-11-08 FR FR9113811A patent/FR2683639B1/fr not_active Expired - Fee Related
• 1992
  • 1992-11-06 EP EP93900234A patent/EP0611454A1/de not_active Withdrawn
  • 1992-11-06 WO PCT/FR1992/001039 patent/WO1993009463A1/fr not_active Application Discontinuation

Patent Citations (7)

Non-Patent Citations (1)

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