SELF-REFERENCE HOLOGRAPHIC IMAGING SYSTEM

• US 20150293498A1
• Filed: 10/28/2013
• Published: 10/15/2015
• Est. Priority Date: 10/30/2012
• Status: Active Grant

• Current Assignee: Centre National De La Recherche Scientifique, IMMM, Institut des Molécules et Matériaux du Mans
• Original Assignee: Centre National De La Recherche Scientifique, IMMM, Institut des Molécules et Matériaux du Mans
• Inventors: Picart, Pascal, Malek, Mokrane
• Granted Patent: US 10,120,334 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G03H 1/0011 for security or authentication holograms on information-bearing cards B42D25/328; testing papers with holograms G07D7/0032
• CPC Class Codes: G03H 1/0443 Digital holography, i.e. recording holograms with digital recording means holobject computation G03H1/0866
• CPC Class Codes: G03H 1/265 Angle multiplexing; Multichannel holograms G03H1/268 takes precedence
• CPC Class Codes: G03H 1/28 superimposed holograms only
• CPC Class Codes: G03H 2001/005 in microscopy, e.g. digital holographic microscope [DHM] microscopes G02B21/00; digital holography G03H1/0866
• CPC Class Codes: G03H 2001/0447 In-line recording arrangement
• CPC Class Codes: G03H 2001/045 Fourier or lensless Fourier arrangement
• CPC Class Codes: G03H 2001/0458 Temporal or spatial phase shifting, e.g. parallel phase shifting method
• CPC Class Codes: G03H 2001/266 Wavelength multiplexing
• CPC Class Codes: G03H 2225/12 2D SLM
• CPC Class Codes: G03H 2225/32 Phase only
• CPC Class Codes: G03H 2227/03 Means for moving one component G03H1/0476, G03H2001/2695 take precedence

Abstract

A system for recording a digital hologram of an object comprises: a coherent source intended to illuminate the object and thus produce a wave diffracted by the object; and a digital sensor intended to record the digital hologram of the object. It furthermore comprises a spatial phase modulating assembly able to produce in the plane of the sensor a plurality of duplicates of the wave diffracted by the object, the duplicates being offset from each other but overlapping partially, these duplicates forming on the sensor a digital hologram of the object, this hologram being what is referred to as a self-reference hologram.

Claims

1. A system for recording a digital hologram of an object, comprising:

a partially coherent or coherent source intended to illuminate the object and thus produce a wave diffracted by the object; and

a digital sensor intended to record the digital hologram of the object, characterized in that it furthermore comprises a spatial phase modulating assembly consisting of;

a spatial phase modulator located between the object and the sensor, associated with

a first image-forming device able to form the image A″

of the object at a distance Δ

z1 from the spatial phase modulator; and

a second image-forming device able to form;

the image of the plane of the spatial phase modulator in a plane located at a non-zero distance Δ

z2 from the plane of the sensor; and

the image A′

of the image A″

of the object, in a plane located at a distance Δ

z′

from the plane of the sensor,

this modulating assembly being able to produce in the plane of the sensor a plurality of duplicates of the wave diffracted by the object, said duplicates being offset from each other but overlapping partially, these duplicates forming on the sensor a digital hologram of the object, this hologram being what is referred to as a self-reference hologram.

2. The system for recording a digital hologram as claimed in claim 1, wherein the spatial phase modulator is a periodic grating.

3. The system for recording a digital hologram as claimed in claim 1, wherein the modulating assembly is able to produce 4 duplicates in the plane of the sensor.

4. The system for recording a digital hologram as claimed in claim 1, wherein the source is spatially and/or temporally partially coherent.

5. The system for recording a digital hologram as claimed in claim 1, wherein the partially coherent or coherent source is a multi-wavelength source.

6. The system for recording a digital hologram as claimed in claim 5, wherein the object being intended to be illuminated in a preset direction, it comprises a multi-wavelength source with an illumination direction that is different for each wavelength.

7. The system for recording a digital hologram as claimed in claim 1, wherein the object is intended to be illuminated in transmission or in reflection.

8. The system for recording a digital hologram as claimed in claim 1, further comprising means for modifying the direction of illumination of the object and thus is able to record, for various illumination directions, one hologram per illumination direction.

9. The system for recording a digital hologram as claimed in claim 1, further comprising means for engendering a rotation of the object about a given axis, thus making it possible to record, for various angles of rotation, one hologram per angle of rotation.

10. The system for recording a digital hologram as claimed in claim 1, wherein the sensor is a CCD or CMOS camera.

11. The system for recording a digital hologram as claimed in claim 1, wherein the first image-forming device comprises a cube beam splitter.

12. The system for recording a digital hologram as claimed in claim 11, wherein the first image-forming device furthermore comprises a lens and/or a microscope objective.

13. The system for recording a digital hologram as claimed in claim 11, wherein the second image-forming device comprises the same cube beam splitter.

14. A numerical method for reconstructing the image of an object from a hologram of the object obtained by a recording system as claimed in claim 1, which comprises steps of:

calculating, by discrete Fourier transform or DFT, the spatial frequency spectrum of the hologram, comprising a main spectral lobe and secondary spectral lobes; and

digitally filtering the spectral lobes,

wherein at least two lobes are filtered,

the main lobe; and

at least one secondary lobe,

and in that it comprises steps of;

from the filtered main lobe, calculating, in the plane of the sensor, the modulus of the complex amplitude of the wave diffracted by the object during the recording;

for each filtered secondary lobe, calculating, by inverse DFT, in the plane of the sensor, the spatial derivative of the optical phase of the wave diffracted by the object in a direction set depending on the phase modulation of the modulator during the recording;

integrating these spatial derivatives in order to obtain in the plane of the sensor the optical phase of the wave diffracted by the object; and

combining the modulus of the complex amplitude and the optical phase to obtain in the plane of the sensor the complex wave diffracted by the object.

15. The numerical method for reconstructing the image of the object as claimed in claim 14, further comprising a step of numerically focusing the image of the object.

16. A computer program product, said computer program comprising:

code instructions allowing the steps of the reconstructing method as claimed in claim 14 to be carried out when said program is executed on a computer.

17. A digital system for reconstructing the image of an object from a hologram obtained by a recording system as claimed in claim 1, which comprises means for implementing numerical method for reconstructing the image of an object from a hologram of the object obtained by a recording system as claimed in claim 1, which comprises steps of:

calculating, by discrete Fourier transform or DFT, the spatial frequency spectrum of the hologram, comprising a main spectral lobe and secondary spectral lobes; and

digitally filtering the spectral lobes,

characterized in that at least two lobes are filtered,

the main lobe; and

at least one secondary lobe,

and in that it comprises steps of;

from the filtered main lobe, calculating, in the plane of the sensor, the modulus of the complex amplitude of the wave diffracted by the object during the recording;

for each filtered secondary lobe, calculating, by inverse DFT, in the plane of the sensor, the spatial derivative of the optical phase of the wave diffracted by the object in a direction set depending on the phase modulation of the modulator during the recording;

integrating these spatial derivatives in order to obtain in the plane of the sensor the optical phase of the wave diffracted by the object; and

combining the modulus of the complex amplitude and the optical phase to obtain in the plane of the sensor the complex wave diffracted by the object.

18. A digital system for reconstructing the image of an object from a hologram obtained by a recording system as claimed in claim 1, comprising implementing means being a computer equipped with a computer program product, said computer program comprising:

code instructions allowing a numerical method for reconstructing the image of an object from a hologram of the object obtained by a recording system as claimed in claim 1, to be carried out when said program is executed on a computer, which method comprises steps of;

calculating, by discrete Fourier transform or DFT, the spatial frequency spectrum of the hologram, comprising a main spectral lobe and secondary spectral lobes; and

digitally filtering the spectral lobes,

characterized in that at least two lobes are filtered,

the main lobe; and

at least one secondary lobe,

and in that it comprises steps of;

from the filtered main lobe, calculating, in the plane of the sensor, the modulus of the complex amplitude of the wave diffracted by the object during the recording;

for each filtered secondary lobe, calculating, by inverse DFT, in the plane of the sensor, the spatial derivative of the optical phase of the wave diffracted by the object in a direction set depending on the phase modulation of the modulator during the recording;

integrating these spatial derivatives in order to obtain in the plane of the sensor the optical phase of the wave diffracted by the object; and

combining the modulus of the complex amplitude and the optical phase to obtain in the plane of the sensor the complex wave diffracted by the object.

19. A holographic imaging system that comprises a recording system as claimed in claim 1, and a digital system for reconstructing the image of an object from a hologram obtained by a recording system as claimed in claim 1, which comprises means for implementing a numerical method for reconstructing the image of an object from a hologram of the object obtained by a recording system as claimed in claim 1, which comprises steps of:

calculating, by discrete Fourier transform or DFT, the spatial frequency spectrum of the hologram, comprising a main spectral lobe and secondary spectral lobes; and

digitally filtering the spectral lobes,

characterized in that at least two lobes are filtered,

the main lobe; and

at least one secondary lobe,

and in that it comprises steps of;

from the filtered main lobe, calculating, in the plane of the sensor, the modulus of the complex amplitude of the wave diffracted by the object during the recording;

for each filtered secondary lobe, calculating, by inverse DFT, in the plane of the sensor, the spatial derivative of the optical phase of the wave diffracted by the object in a direction set depending on the phase modulation of the modulator during the recording;

integrating these spatial derivatives in order to obtain in the plane of the sensor the optical phase of the wave diffracted by the object; and

combining the modulus of the complex amplitude and the optical phase to obtain in the plane of the sensor the complex wave diffracted by the object.