USOO5926295A United States Patent (19) 11 Patent Number: 5,926,295 Charlot et al. (45) Date of Patent: Jul. 20, 1999 54) HOLOGRAPHIC PROCESS AND DEVICE 4,602,844 7/1986 Sirat et al. ............................. 350/3.83 USING INCOHERENT LIGHT 4,976,504 12/1990 Sirat et al. .. ... 350/3.73 5,011,280 4/1991 Hung.............. ... 356/345 75 Inventors: Didier Charlot, Paris; Yann Malet, 5,081,540 1/1992 Dufresne et al. ... ... 359/30 Saint Cyr l’Ecole, both of France 5,081,541 1/1992 Sirat et al. ...... ... 359/30 5,216,527 6/1993 Sharnoff et al. ... 359/10 73 Assignee: Le Conoscope SA, Paris, France 5,223,966 6/1993 Tomita et al. .......................... 359/108 5,291.314 3/1994 Agranat et al. ......................... 359/100 21 Appl. No.: 08/681,926 22 Filed: Jul. 29, 1996 Primary Examiner Jon W. Henry Attorney, Agent, or Firm Michaelson & Wallace; Peter L. Related U.S. Application Data Michaelson; John C. Pokotylo 62 Division of application No. 08/244.249, filed as application 57 ABSTRACT No. PCT/FR92/01095, Nov. 25, 1992, Pat. No. 5,541,744. An optical device for generating a signal based on a distance 30 Foreign Application Priority Data of an object from the optical device. The optical device includes a first polarizer, a birefringent crystal positioned Nov. 27, 1991 FR France ................................... 91. 14661 optically downstream from the first polarizer, and a Second 51) Int. Cl. .............................. G03H 1/26; G01B 9/021 polarizer arranged optically downstream from the birefrin 52 U.S. Cl. ................................... 359/30; 359/11; 359/1; gent crystal. The Second polarizer creates a pair of inter 359/495; 359/501; 356/345; 356/360 ferograms by adjusting a phase of the light. Two outputs are 58 Field of Search .................................... 359/30, 11, 1, generated by Separately integrating an amount of light of at 359/495, 494, 497, 501; 356/345, 360 least a part of each of the pair of interferograms. Finally, the two outputs are combined Such that the Signal, depending 56) References Cited only on the distance between the object and the optical System, is obtained. U.S. PATENT DOCUMENTS 4,124.278 11/1978 Grinberg et al. ....................... 359/250 38 Claims, 6 Drawing Sheets 32 -1N-N PROCESSOR U.S. Patent Jul. 20, 1999 Sheet 1 of 6 5,926,295 FIG. f. O 32 ? 35 -1N-N 5 -1N 36 12 - S - 33 34 U.S. Patent Jul. 20, 1999 Sheet 2 of 6 5,926,295 FIC, 7 U.S. Patent Jul. 20, 1999 Sheet 3 of 6 5,926,295 DETECTOR 52 FIG. 9 a a w CENTER 5 ||" |/|Y: || 2-1 U.S. Patent Jul. 20, 1999 Sheet 4 of 6 5,926,295 FIC. 1 1 100 130 P v-ap 112 133-1 34 N-N-1 13 132 U.S. Patent Jul. 20, 1999 Sheet S of 6 5,926,295 O N N YN CO N?) n1) N-N-1 N a 3 R S.3-a 2 2 N5 O va s n Nr. 3 U.S. Patent Jul. 20, 1999 Sheet 6 of 6 5,926,295 5,926.295 1 2 HOLOGRAPHIC PROCESS AND DEVICE The interference pattern obtained which represents the USING INCOHERENT LIGHT conoscopic hologram of a point is called Gabor Zone lens. Indeed, the conoscopic hologram of a point recorded at This application is a divisional of our patent application the wavelength ) is similar to the hologram of the same Ser. No. 08/244,249 filed on Oct. 6, 1994 now U.S. Pat. No. point recorded with coherent light (Gabor holography) at an 5,541,744, which was a national Stage of International equivalent wavelength eq given by: Application No. PCT/FR92/01095, filed Nov. 25, 1992. BACKGROUND OF THE INVENTION The present invention describes an improved holographic proceSS and a device using incoherent light. The French Patent Publication No. FR-A-2641091 The principle of incoherent holography and its application describes Some improvements to the System described in to distance measurements have been described in U.S. Pat. U.S. Pat. No. 4,602,844. Still other improvements are No. 4,602,844. This patent describes an optical system described in the French Patent Publication Nos. FR-A- (named “Conoscopic Apparatus) including a birefringent 15 2646251 and FR-A-2646252. uniaxial crystal and two polarizers which permit the holo Until now, to recover the shape of the object, it was gram of a point in incoherent light to be optically formed. proposed to record the holograms on a CCD array or linear If a ray of light impinges on the crystal, the birefringent CCD array, to then digitize the obtained signal, and to properties of the crystal causes the incident light to be split numerically process the digitized signal. The numerical data into two light beams having perpendicular polarizations. process consists mainly of a Fourier transform. The first light beam (ordinary ray) propagates inside the The systems described in the above mentioned documents crystal at a velocity Vo (index of refraction No) independent have a great interest. However, the known Systems which of the propagation direction. The Second light beam include numerical data processing have a limited measure (extraordinary ray) propagates inside the crystal at a Velocity ment time because of the time consumed by the numerical 25 data processing. In addition the quantity of light needed to Ve (index of refraction Ne) which is a function of the achieve a given signal to noise ratio (on which depends the propagation direction. further precision) is proportional to the Square root of the At the first order of approximation on the incidence angle, number of detectors. the two light beams follow the same geometrical path in the The object of present invention is to improve the existing crystal. However, because the two light beams do not devices and to SuppreSS their disadvantages. propagate at the same Velocity, they are out of phase with each other at the exit face of the crystal. SUMMARY OF THE INVENTION The polarizer placed after the crystal will permit the The present invention obtains the above mentioned ordinary and extraordinary vibrations to recombine Such that objects by providing a proceSS including Steps of the phase of the resulting wave is coded in the form of an 35 creating a point hologram by means of an optical device interference Figure. including a crystal and 2 polarizers positioned upstream and The polarizer placed before the crystal permits two rays of downstream the crystal; the same intensity to be obtained Such that a maximum Separately recording the System outputs corresponding to contrast is obtained at the output. two different polarizations, and For a Small incident angle 0, and with a crystal of length 40 L., whose crystallographic optical axis is parallel to the combining these two recordings to give a signal which is optical axis of the System, the phase difference between the function of the distance between the point and the optical ordinary and extraordinary rays induced by passing through System. the crystal is: In a preferred embodiment of the present invention, the 45 combination of the two recordings of the device is based on 1 1 (1) the ratio between a difference and a Sum of the recordings. Acis = *z,ZE 7.)Zo The present invention also concerns a device to imple ment the above described process. BRIEF DESCRIPTION OF THE DRAWINGS where 50 Others characteristics, goals and advantages of the present invention will be clarified in the detailed description of the annexed Figures, given for non limitative examples. The amplitude of the wave in the observation plane is the FIG. 1 is a schematic which represents the structure of a Sum of the ordinary and extraordinary amplitudes. The 55 first device in accordance with present invention. intensity recorded at a point Q (x, y, o) is proportional to: FIGS. 2 to 6 represent interference patterns recorded by a (4a) detector. FIG. 7 represents signal output curves given after pro 60 cessing the Signals recorded by detectors. (4b) FIG. 8 represents a preferential output curve. depending on whether the two polarizers have the same FIG. 9 represents an alternative embodiment of a detec handineSS or not. tion device in accordance with the present invention. In these relationships, I(P) is the intensity of the wave FIG. 10 represents some curves obtained with the detec coming from the object point P(x0,y0,z), onto the detector, 65 tion device of FIG. 9. i.e., this one which should be recorded without the cono FIGS. 11, 12 and 13 represent alternative devices in Scopic part. accordance with the present invention. 5,926.295 3 4 FIG. 14 represents an intensity mask which may be used Moreover, a comparison of the results of the FIGS. 2, 4, in the present invention. and 5 show that, when F increases and Z is fixed, the center FIG. 15 represents a device having autofocus properties in position of the Gabor Zone moves away from the center of accordance with the present invention. the detector 50. The representations given on FIGS. 2 to 6 correspond to DETAILED DESCRIPTION one of the two used polarizations. The interference patterns First Example recorded with the Second polarization are complementary with those illustrated on FIGS. 2 to 6. A first example of the present invention is described referring to FIG. 1. General Information About Processing The optical axis of device 10 is referenced as 12. The device 10 contains: FIG. 7 represents the relationship of the ratio between the a conoscopic System 30 including: difference and sum of the values (S) successively obtained a birefringent crystal 31, and by photodetector 50 by the valve action 38 based on the 15 distance Z for respective F values of 0, 1, 2, 3, 4.