Apparatus and method for capturing fourier hologram

Patent metadata

Field	Value
Publication number	US-2018284694-A1
Application number	US-201815938834-A
Country	US
Kind code	A1
Filing date	Mar 28, 2018
Priority date	Mar 28, 2017
Publication date	Oct 4, 2018
Grant date	—

Abstract

An apparatus for capturing a Fourier hologram splits a coherent light source into an object beam and a reference beam, sets a distance of a virtual focal plane of a subject, generates spherical wave field data propagated from a point source of the virtual focal plane to a central coordinate plane of a spatial light modulator, generates a spherical wave field on a space from the spherical wave field data and the reference beam by the spatial light modulator, synthesizes an object wave field generated by reflecting the object beam by the subject and the spherical wave field with each other so that an interference pattern is formed on the image sensor face, captures the interference pattern formed on the image sensor face, and then performs Fourier transformation to calculate an object wave field formed on the focal plane of the subject.

First claim

What is claimed is:

1 . An apparatus for capturing a Fourier hologram, comprising:
a light source generating unit generating a coherent light source; a light source splitting unit splitting the coherent light source into an object beam and a reference beam; a phase generating unit generating spherical wave field data propagated from a point source of a virtual focal plane of a subject to a virtual coordinate plane on an optical path between a focal plane of the subject and an image sensor face and including a spatial light modulator generating a spherical wave field on a space using the reference beam and the spherical wave field data; a wave field synthesizing unit synthesizing an object wave field generated by reflecting the object beam by the subject and the spherical wave field with each other; an image capturing unit capturing an interference pattern formed on the image sensor face by the synthesized spherical wave field and object wave field; and a control unit performing Fourier transformation on an image of the interference pattern to calculate an object wave field formed on the focal plane of the subject and performing auto-focusing using an absolute value image of the calculated object wave field.

2 . The apparatus for capturing a Fourier hologram of claim 1 , wherein:
the control unit changes a position of the virtual focal plane for the purpose of the auto-focusing using a contrast value of the absolute value image of the calculated object wave field.

3 . The apparatus for capturing a Fourier hologram of claim 2 , wherein:
the control unit changes the position of the virtual focal plane on the basis of a comparison result between the contrast value of the absolute value image of the calculated object wave field and a contrast value of an absolute value image of the previously calculated object wave field.

4 . The apparatus for capturing a Fourier hologram of claim 2 , wherein:
the control unit changes a distance from the focal plane to the image sensor face by a set increment value and updates the increment value until the contrast value of the absolute value image of the calculated object wave field becomes maximum, and a distance from the position of the virtual focal plane to a central coordinate plane of the spatial light modulator that is virtually positioned is calculated on the basis of the distance from the focal plane to the image sensor face.

5 . The apparatus for capturing a Fourier hologram of claim 4 , wherein:
the control unit updates the increment value by a value obtained by dividing a difference between the contrast value of the absolute value image of the calculated object wave field and a contrast value of an absolute value image of the previously calculated object wave field by a set increment ratio.

6 . The apparatus for capturing a Fourier hologram of claim 1 , wherein:
the phase generating unit further includes: a spherical wave field data generator generating the spherical wave field data and outputting the spherical wave field data to the spatial light modulator; and a beam splitter making the reference beam split by the light source splitting unit incident to the spatial light modulator.

7 . The apparatus for capturing a Fourier hologram of claim 6 , wherein:
the phase generating unit further includes a filtering optical system removing noise from the spherical wave field.

8 . The apparatus for capturing a Fourier hologram of claim 1 , wherein:
the wave field synthesizing unit includes: a first beam splitter forming the spherical wave field and the object wave field on the image sensor face; and a second beam splitter transmitting the object beam to the subject and outputting the object wave field reflected from the subject to the first beam splitter.

9 . An apparatus for capturing a Fourier hologram, comprising:
a light source generating unit generating a coherent light source; a light source splitting unit splitting the coherent light source into an object beam and a reference beam; a phase generating unit generating spherical wave field data propagated from a point source of a virtual focal plane of a subject to a virtual coordinate plane on an optical path between a focal plane of the subject and an image sensor face and including a spatial light modulator generating a spherical wave field on a space using the spherical wave field data and the reference beam; a wave field synthesizing unit controlling paths of the spherical wave field and an object wave field generated by reflecting the object beam by the subject to form an interference pattern on the image sensor face; an image capturing unit capturing the interference pattern; and a control unit performing Fourier transformation on an image of the interference pattern to calculate an object wave field formed on the focal plane of the subject, capturing an absolute value image of the calculated object wave field, and controlling a position of the virtual focal plane depending on an input value from a user.

10 . The apparatus for capturing a Fourier hologram of claim 9 , wherein:
the phase generating unit further includes: a spherical wave field data generator generating the spherical wave field data and outputting the spherical wave field data to the spatial light modulator; and a beam splitter making the reference beam incident to the spatial light modulator.

11 . The apparatus for capturing a Fourier hologram of claim 10 , wherein:
the phase generating unit further includes a filtering optical system removing noise from the spherical wave field.

12 . The apparatus for capturing a Fourier hologram of claim 9 , wherein:
the wave field synthesizing unit includes: a first beam splitter forming the spherical wave field and the object wave field on the image sensor face; and a second beam splitter transmitting the object beam to the subject and outputting the object wave field reflected from the subject to the first beam splitter.

13 . A method for capturing a Fourier hologram by an apparatus capturing a Fourier hologram, comprising:
splitting a coherent light source into an object beam and a reference beam; setting a distance of a virtual focal plane of a subject; generating spherical wave field data propagated from a point source of the virtual focal plane of the subject to a virtual coordinate plane positioned on an optical path between a focal plane of the subject and an image sensor face; generating a spherical wave field on a space from the spherical wave field data and the reference beam through a spatial light modulator; synthesizing an object wave field generated by reflecting the object beam by the subject and the spherical wave field with each other so that an interference pattern is formed on the image sensor face; capturing the interference pattern; and performing Fourier transformation on an image of the interference pattern to calculate an object wave field formed on the focal plane of the subject.

14 . The method for capturing a Fourier hologram of claim 13 , further comprising:
performing auto-focusing using an absolute value image of the calculated object wave field.

15 . The method for capturing a Fourier hologram of claim 13 , wherein:
the performing of the auto-focusing includes changing a position of the virtual focal plane for the purpose of the auto-focusing using a contrast value of the absolute value image of the calculated object wave field.

16 . The method for capturing a Fourier hologram of claim 15 , wherein:
the changing includes: changing a distance from the focal plane to the ima

Assignees

• Electronics & Telecommunications Res Inst

Inventors

• Park Min-Sik

Classifications

• G03H2222/52

  Divergent beam · CPC title

• G03H1/2294

  Addressing the hologram to an active spatial light modulator · CPC title

• G03H1/0808

  Methods of numerical synthesis, e.g. coherent ray tracing [CRT], diffraction specific · CPC title

• G03H1/16 Primary

  using Fourier transform ({G03H1/10}, G03H1/12, G03H1/14 take precedence; analogue computers G06G, e.g. G06G7/19) · CPC title

• G03H1/0841

  Encoding method mapping the synthesized field into a restricted set of values representative of the modulator parameters, e.g. detour phase coding · CPC title