EP0058592B1 - Dispositif optique transformateur de Fourier, et corrélateur optique mettant en oeuvre ce dispositif optique transformateur de Fourier - Google Patents

Dispositif optique transformateur de Fourier, et corrélateur optique mettant en oeuvre ce dispositif optique transformateur de Fourier Download PDF

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Publication number
EP0058592B1
EP0058592B1 EP82400164A EP82400164A EP0058592B1 EP 0058592 B1 EP0058592 B1 EP 0058592B1 EP 82400164 A EP82400164 A EP 82400164A EP 82400164 A EP82400164 A EP 82400164A EP 0058592 B1 EP0058592 B1 EP 0058592B1
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EP
European Patent Office
Prior art keywords
optical
medium
plane
lens
fourier transformer
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Expired
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EP82400164A
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German (de)
English (en)
French (fr)
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EP0058592A1 (fr
Inventor
Laurence Pichon
Jean-Pierre Huignard
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Thales SA
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Thomson CSF SA
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    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06E—OPTICAL COMPUTING DEVICES; COMPUTING DEVICES USING OTHER RADIATIONS WITH SIMILAR PROPERTIES
    • G06E3/00—Devices not provided for in group G06E1/00, e.g. for processing analogue or hybrid data
    • G06E3/001—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements
    • G06E3/003—Analogue devices in which mathematical operations are carried out with the aid of optical or electro-optical elements forming integrals of products, e.g. Fourier integrals, Laplace integrals, correlation integrals; for analysis or synthesis of functions using orthogonal functions

Definitions

  • the invention relates to the field of optical correlation which makes it possible to obtain the function of correlation of one image by another.
  • Such systems make it possible, for example, to recognize a graphic in a given pattern.
  • a device described in the article published in "APPLIED OPTICS", volume 15, No. 6 of June 1976, pages 1418 to 1424 includes a source, a modulating object, a lens and optical means ensuring the illumination of a plane by a distribution of light amplitudes Fourier transform of the optical modulation created by this object.
  • These optical means comprise an interaction medium receiving the pumping beam emerging from a lens.
  • a reflector is formed on one side of the interaction medium, which is a Pockels Readout Optical Modulator (PROM), to reflect the pumping beam, which therefore crosses the PROM twice. This reflector is also used to deflect the beam emerging from the PROM towards the plane where the Fourier transform of the optical modulation created by this object is projected.
  • PROM Pockels Readout Optical Modulator
  • the system according to the invention implements the reproduction of a wave front of complex morphology emerging from a modulating object, generated by interference in an interaction medium of an optical wave. incident having this wavefront with a pumping wave.
  • This interference occurs in a photoexcitable interaction medium with three-dimensional index variation whose physical characteristics and in particular the refractive index are spatially modulated by a network of fringes resulting from the incident wavefront wave. ⁇ Oz and pumping wave.
  • the cited document considers a PROM (Pockels Readout Optical Modulator) interaction medium using a longitudinal electro-optical effect whose spatial resolution is limited by the thickness of the material.
  • This PROM interaction medium is, in fact, produced by a thin layer of electro-optical material covered with an insulating layer and comprising transparent electrodes deposited on its front and rear faces.
  • electrodes being deposited on the lateral faces of the electro-optical crystal.
  • a known optical correlator system is described in the French patent application published on May 8, 1981 under No. 2,468,947.
  • a system of interference fringes representing the diffraction pattern obtained is recorded on a photosensitive support. from two parallel coherent beams, on the path of which have been interposed two objects with non-uniform transparency, after focusing by a lens.
  • This photosensitive support is read by one of the beams and one obtains in the focal plane of a second lens a distribution of intensity characteristic of the correlation product between the two objects; when one wants to find a graphic in a given pattern, the image obtained is formed of peaks indicating the presence and the position of this graphic in the considered motif.
  • the photosensitive support is a continuously recyclable medium, that is to say writable without development and erasable at will.
  • parasitic phase distortions induced by the optical components and, for the input of the data, by photographic transparencies or by electro-optical transducers.
  • this filter remains valid whatever the translation of the transparency in the object plane, this filter is positioned in the Fourier plane.
  • the Fourier transformer system of the invention compensates for these distortions in a simpler way. It uses, in fact, a wavefront conjugate of the incident wavefront which, at each point, is isomorphic of it. This conjugate wavefront, by reverse return, is modulated a second time by the object. But because of the reverse path, there is compensation for the modulation deformations of the outward path. It is the same for the deformations due to the aberrations of the lens: they are compensated.
  • the optical correlator system which includes the Fourier transformer system, allows a significant gain on the signal / noise ratio of the correlation peak. This is made equivalent to that resulting from an inconsistent illumination.
  • the subject of the invention is an optical Fourier transformer device, comprising a point source of coherent radiation disposed at the focal point of a converging lens, means for positioning a modulating object in the collimated beam emerging from this lens and optical means. ensuring the illumination of a plane by a distribution of light amplitudes transformed by Fourier of the optical modulation created by this object, these optical means comprising a photo-excitable medium of interaction with index variation receiving collimated beam via this object and a pumping beam, characterized in that this interaction medium with three-dimensional index variation is an electro-optical crystal comprising electrodes arranged on its lateral faces at the terminals of which a voltage is applied so as to use an electro- transverse optics, this pumping beam coming from this source; a plane reflector being arranged to reflect in normal incidence and towards this medium the radiation which emerges therefrom in the direction of propagation of this pumping beam, this radiation having a conjugate wavefront and isomorphic to the wavefront of the collimated beam of so as to compensate for the
  • the invention further relates to a double diffraction optical correlator comprising a first Fourier transformer device, a photo-excitable interaction medium with index variation which comprises electrodes arranged on its lateral faces at the terminals of which is applied a voltage arranged to receive simultaneously the radiation emerging from this first transformer device and another radiation contained in a reference beam and a second Fourier transformer intended to project into an image plane an illumination representative of the correlation function of the two patterns of a modulating object introduced into this first Fourier transformer device, characterized in that this first optical Fourier transformer device is an optical Fourier transformer device as described above.
  • the system according to the invention implements the reproduction of a wave front of complex morphology emerging from a modulating object, generated by interference in an interaction medium of an incident optical wave before this front of wave with a pumping wave.
  • this interference occurs in a photoexcitable interaction medium 2 with variation of three-dimensional incide whose physical characteristics and in particular the refraction incide, are spatially modulated by a network of fringes resulting from the incident wavefront wave ⁇ 2 and pumping wave Fp.
  • ⁇ 2 * has characteristics isomorphic to those of ⁇ 2 and follows the same optical path but in the opposite direction; ⁇ 2 * returns to the object from which ⁇ 2 emanates.
  • the return of the wave ⁇ 2 is performed in real time at time rd'êt strata network near which can range from 10- 3 to 10- 12 seconds.
  • the interactive medium 2 consists, for example, of a photoconductive electro-optical material such as bismuth-silicon oxide (BSO). It could also be an oxide such as bismuth-germanium oxide (BGO). These two oxides are particularly suitable for the invention because they are very sensitive in the range of wavelengths commonly used which constitutes the field of visible light waves. In addition one can obtain single crystals of sufficient dimensions having good optical qualities.
  • This medium is polarized at the voltage Vo.
  • the incident wave ⁇ 2 comes from a beam focused at a source point S.
  • This source point is located at the focus of a spherical lens L1.
  • the wave front which is spherical ⁇ 0 becomes linear ⁇ 1 .
  • the light beam collimated by the lens L 1 is then modulated by the non-linearly transparent object 1. This is located in the focal plane Po of the lens, or object plane.
  • the forward path through the lens L 1 and the transparent object 1 creates parasitic phase distortions of the waves ⁇ 1 and ⁇ 2 . These distortions are due to the aberrations of the lens Li and to the deformations relating to the support of the transparent object.
  • the return path through the same transparent object and lens L i makes it possible to compensate for these defects due to a parasitic phase modulation of the wave fronts. It also makes it possible to double the contrast of the amplitude modulation due to the object.
  • Figure 3 a parallel ray after being modulated by a transparent object consisting of two patterns A and B is focused by a spherical lens L inside a interaction medium 10 located in the focal plane thereof.
  • this medium there is recording of the algebraic sum of the Fourier transforms, that is to say spectra of two two-dimensional functions which represent the transmittances of the two transparent object patterns A and B.
  • this medium is located in the focal plane of L or Fourier plane.
  • the spectra of the space signals are symmetrical with respect to the zero frequency. But this is a symmetry in the plane and no longer only on an axis. If we translate the transparent object of Ax in an object plane, the spectrum remains unchanged in the Fourier plane, indeed the Fourier transform is invariant in translation.
  • the medium 10 therefore records the superposition of fringes of different steps, the average step being equal to ⁇ 1 2sin ⁇ where ⁇ 1 war the optical wavelength of the incident beams which interfere, and the half-angle between these beams.
  • the interference fringes resulting from the superposition of these beams which illuminate A and B, after the focusing operated by the lens L, are therefore recorded in an interaction medium 10 consisting for example of an electro-optical material polarized by a electric field obtained by means of a voltage source Vo. Its orientation is such that the electric field produces a transverse electro-optical effect.
  • the spatial variations in light intensity existing in this plane P F are instantly reflected in the plate by spatial variations in the refractive index.
  • the thickness of the crystal must be equal to or greater than the width of the diffraction zone.
  • a thickness can be defined which is clearly greater than the wavelength of the beams so that the recording in the slide can be considered as three-dimensional. It is a superposition of arrays of surfaces. When the width of the blade is not too large, these surfaces can be assimilated to planes perpendicular to the plane of the figure.
  • Their pitch p and the inclination ⁇ with respect to an axis normal to the plane P F and in the plane of the figure depend on the angle of the interfering rays, their wavelength ⁇ 1 and the refractive angle n crystal 10.
  • the usable materials must be photosensitive and electro-optical such as bismuth-silicon oxide or bismuth-germanium oxide.
  • the beam F R is, for example, deflected by a conventional acousto deflector -optical or mechanical. It is here, returned by a semi-transparent plate in the direction of the medium 10.
  • a conventional acousto deflector -optical or mechanical It is here, returned by a semi-transparent plate in the direction of the medium 10.
  • the parallel reading beam F R may have a wavelength A 2 different from that of the source beam which is modulated by A and B.
  • a color filter 5 is then inserted between the medium 10 and the lens L 2 so that 'it only lets through the part of the emerging beam of wavelength ⁇ 2 . Indeed it is necessary to eliminate the part of the emerging beam of wavelength ⁇ 1 .
  • the beam emerging from the interaction medium 10 has undergone a reflection on the interference strata of this medium.
  • This wave beam is therefore assigned a horizontal polarization. Indeed, the interference strata are perpendicular to the direction of the applied field. If a polarizer 6 is inserted in this emerging beam, a better signal / noise ratio is obtained by promoting the transmission of the polarized waves.
  • the beam modulated by the object patterns A and B is the conjugate return beam emerging from the medium 2. This beam then passes through the lens L i .
  • the lens L in FIG. 3 therefore becomes the lens Li in FIG. 2.
  • This device in FIG. 2 makes it possible to perform an optical correlation. It incorporates the Fourier transformer of Figure 1.
  • the wavefront return beam ⁇ 0 * which is reflected on the semi-transparent plate is a beam modulated in amplitude by the object 1 which includes two patterns; A and B in FIG. 3.
  • There is both compensation for the aberrations of the lens Li effecting the transform of Fourier, and distortions induced by the data entry device which operates here by transmission.
  • the discriminating power in the source plane of the correlator is weak. There are speckles due to the use of coherent light. To improve the signal / noise ratio, averaging is carried out by supposing the intensities of a certain number of images; each image is obtained with an identical transparent object, but with a different speckle shape.
  • This averaging can be achieved by moving the source beam F s along a straight line Si S z , the reference beam F R being moved synchronously to strike the medium 10 at the same point as the input source beam S ' i and S ' z .
  • These displacements can be obtained by any acousto-optical, electro-optical deflection device or even by the mechanical displacement of a lens or end of optical fiber.
  • FIG. 4 illustrates this possibility of displacement of the ends of two single-mode optical fibers 20 and 21.
  • the light beam coming from a laser 22 is split by the interposition of a semi-transparent plate 23 into two components which after focusing by two lenses L 3 and L 4 propagate in these fibers 20 and 21.
  • the ends of these two fibers are moved synchronously by two motor 24 and 25 controlled by a generator 26, the component of the beam flowing in the fiber 20 is collimated by a lens L 5 to give the reference beam F R.
  • FIG. 5 A simpler electro-optical configuration is indicated in FIG. 5.
  • the source So remains fixed and the fictitious translation of So, from Si to S 2 obtained using an acousto-optical tank arranged to deflect the return beam which is modulated by the object, for example in the object plane.
  • the aberrations induced by the lens Li are compensated rigorously only for the point S ' o .
  • the fictitious points Si and S 2 are in the vicinity of S o and it can be considered that the residual distortions induced by the lens L i remain low.
  • the beam F R must move as in the previous case.
  • Another way to improve the signal-to-noise ratio is to attenuate the low spatial frequencies of the object transparency spectrum. This can be achieved by considering a pumping beam Fp of intensity lower than that of the object beam. Only the high spatial frequencies are retained in the conjugate wave front, which corresponds to a reinforcement of the contours of the transparent object.
  • the optical correlator system of FIG. 2 was produced with a first monocrystalline plate 2 of bismuth-silicon oxide.
  • This blade has a surface of 30 x 30 square millimeters and a thickness of 3 millimeters.
  • the second blade is also a monocrystalline bismuth-silicon oxide blade. It has a surface of 2 x 10 square millimeters and a thickness of 1 millimeter. These blades are polarized with a voltage Vo of gold dre of 2000 volts.
  • the transparent object has a surface of 25 ⁇ 25 square millimeters.
  • T is the time taken by the source point S to move from Si to Sz, here distant by 5 millimeters, if the time of registration of the space charge field in the crystal BSO 10 (bismuth-silicon oxide) remains ), T is, for example, equal to 1 second and ⁇ to 1 millisecond.
  • this optical correlator system provides a new solution to the problems posed by any coherent optical correlation device. It allows operation at the limits of diffraction with optical components of reduced quality, in particular the spherical lens Li.
  • the signal / noise ratio can be made equivalent to that resulting from incoherent lighting.
  • the main applications concern, for example, target tracking or robotics.

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  • Physics & Mathematics (AREA)
  • Mathematical Physics (AREA)
  • Engineering & Computer Science (AREA)
  • Theoretical Computer Science (AREA)
  • Nonlinear Science (AREA)
  • Optics & Photonics (AREA)
  • General Physics & Mathematics (AREA)
  • Holo Graphy (AREA)
EP82400164A 1981-02-06 1982-01-28 Dispositif optique transformateur de Fourier, et corrélateur optique mettant en oeuvre ce dispositif optique transformateur de Fourier Expired EP0058592B1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8102410A FR2499735A1 (fr) 1981-02-06 1981-02-06 Dispositif optique transformateur de fourier et correlateur optique mettant en oeuvre ce dispositif optique transformateur de fourier
FR8102410 1981-02-06

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EP0058592A1 EP0058592A1 (fr) 1982-08-25
EP0058592B1 true EP0058592B1 (fr) 1985-07-10

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EP82400164A Expired EP0058592B1 (fr) 1981-02-06 1982-01-28 Dispositif optique transformateur de Fourier, et corrélateur optique mettant en oeuvre ce dispositif optique transformateur de Fourier

Country Status (5)

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US (1) US4514038A (enrdf_load_stackoverflow)
EP (1) EP0058592B1 (enrdf_load_stackoverflow)
JP (1) JPS57148720A (enrdf_load_stackoverflow)
DE (1) DE3264603D1 (enrdf_load_stackoverflow)
FR (1) FR2499735A1 (enrdf_load_stackoverflow)

Families Citing this family (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4556950A (en) * 1983-09-02 1985-12-03 Environmental Research Institute Of Michigan Incoherent optical processor
GB2154092A (en) * 1984-02-07 1985-08-29 Standard Telephones Cables Ltd Optical correlator
EP0182509B1 (en) * 1984-11-14 1992-04-08 Nortel Networks Corporation Two-dimensional optical information processing apparatus
US4695973A (en) * 1985-10-22 1987-09-22 The United States Of America As Represented By The Secretary Of The Air Force Real-time programmable optical correlator
US4723222A (en) * 1986-06-27 1988-02-02 The United States Of America As Represented By The Secretary Of The Air Force Optical correlator for analysis of random fields
US4932741A (en) * 1988-07-20 1990-06-12 Grumman Aerospace Corporation Optical correlator system
JPH0830830B2 (ja) * 1988-09-07 1996-03-27 セイコー電子工業株式会社 光学的相関処理装置
IT1232051B (it) * 1989-03-24 1992-01-23 Cselt Centro Studi Lab Telecom Dispositivo per la correlazione fra fasci ottici
US5107351A (en) * 1990-02-16 1992-04-21 Grumman Aerospace Corporation Image enhanced optical correlator system
US5233554A (en) * 1990-09-10 1993-08-03 United Technologies Corporation Programmable optical correlator
FR2681988A1 (fr) * 1991-09-27 1993-04-02 Thomson Csf Laser de puissance a deflexion.
FR2696014B1 (fr) * 1992-09-18 1994-11-04 Thomson Csf Miroir à conjugaison de phase.
FR2755516B1 (fr) 1996-11-05 1999-01-22 Thomson Csf Dispositif compact d'illumination
ES2147714B1 (es) * 1998-11-26 2001-04-01 Univ Madrid Politecnica Transformador de fourier de señales opticas en el dominio temporal, basado en redes de difraccion en fibra.
FR2819061B1 (fr) * 2000-12-28 2003-04-11 Thomson Csf Dispositif de controle de polarisation dans une liaison optique

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2362466A1 (fr) * 1976-08-19 1978-03-17 Thomson Csf Cellule d'enregistrement holographique, memoire et dispositif de calcul optique utilisant une telle cellule
FR2468947A1 (fr) * 1979-11-05 1981-05-08 Thomson Csf Systeme de correlation optique en temps reel

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Publication number Publication date
FR2499735A1 (fr) 1982-08-13
FR2499735B1 (enrdf_load_stackoverflow) 1985-02-08
US4514038A (en) 1985-04-30
EP0058592A1 (fr) 1982-08-25
DE3264603D1 (en) 1985-08-14
JPS57148720A (en) 1982-09-14

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