GEOMETRIC PHASE IN-LINE SCANNING HOLOGRAPHY SYSTEM FOR TRANSMISSIVE OBJECT

Abstract

A geometric phase in-line scanning holography system for a transmissive object, includes: a polarization sensitive lens, which receives a linear polarization beam to generate a first spherical wave of right-sided circularly polarized light and a second spherical wave of left-sided circularly polarized light; a scan means for scanning the transmissive object by using an interference beam generated between the generated first and second spherical waves; a first beam splitter, which receives a beam having been transmitted through the transmissive object, so as to split the received beam into first and second output beams; first and second polarizers for polarizing the first and second output beams, respectively; and first and second photodetectors for detecting output beams having passed through the first and second polarizers.

Description

Claims

1. A geometric phase in-line scanning holography system for a transmissive object, comprising: a polarization sensitive lens which receives a linearly polarized beam to generate a first spherical wave of right-handed circularly polarized light having a negative focal distance and a second spherical wave of left-handed circularly polarized light having a positive focal distance;a scan means which scans the transmissive object by using an interference beam generated between the generated first and second spherical waves;a first beam splitter which receives a beam having been transmitted through the transmissive object and splits the received beam into first and second output beams;first and second polarizers which polarize the first and second output beams, respectively; andfirst and second photodetectors which detect output beams having passed through the first and second polarizers.

2. A geometric phase in-line scanning holography system for a transmissive object, comprising: a polarization sensitive lens which receives a linearly polarized beam to generate a first spherical wave of right-handed circularly polarized light having a negative focal distance and a second spherical wave of left-handed circularly polarized light having a positive focal distance;a scan means which scans the transmissive object by using an interference beam generated between the generated first and second spherical waves;a first beam splitter which receives a beam having been transmitted through the transmissive object and splits the received beam into first and second output beams;a second beam splitter which splits the first output beam into 1a and 1b output beams;a third beam splitter which splits the second output beam into 2a and 2b output beams;first and second polarizers which polarize the 1a and 1b output beams, respectively;third to fourth polarizers which polarize the 2a and 2b output beams, respectively; andfirst to fourth photodetectors which detect output beams having passed through the first to fourth polarizers.

3. A geometric phase in-line scanning holography system for a transmissive object, comprising: a polarization sensitive lens which receives a linearly polarized beam to generate a first spherical wave of right-handed circularly polarized light having a negative focal distance and a second spherical wave of left-handed circularly polarized light having a positive focal distance;a scan means which scans the transmissive object by using an interference beam generated between the generated first and second spherical waves;a first beam splitter which receives a beam having been transmitted through the transmissive object and splits the received beam into first and second output beams;a second beam splitter which splits the first output beam into 1a and 1b output beams;first and second polarizers which polarize the 1a and 1b output beams, respectively;a third polarizer which polarizes the second output beam; andfirst to third photodetectors which detect output beams having passed through the first to third polarizers.

4. The geometric phase in-line scanning holography system of claim 1, wherein the polarization sensitive lens includes a geometric phase lens.

5. The geometric phase in-line scanning holography system of claim 1, further comprising a light source-side polarizer which generates a linearly polarized beam from an input light source and provides the generated linearly polarized beam to the polarization sensitive lens.

6. The geometric phase in-line scanning holography system of claim 1, wherein the interference beam is defined by the following equation in the form of a geometric phase Fresnel zone plate: IGP−FZPx0,y0;z=cos2πfgpλ2fgp+zzx02+y02+2θwherein 1GP-FZP(x0,y0;z) represents the interference beam of the first and second spherical waves formed by the polarization sensitive lens, λ represents a wavelength of the beam used, fgp is a focal distance of the polarization sensitive lens, (x02+y02) represents a Cartersian coordinate system in which (x0,y0) is a plane orthogonal to an optical axis of the linearly polarized beam, z represents a distance from the focal position of the second spherical wave to the object, and θ represents a clockwise linearly polarized angle with respect to the polarization axis of the light source-side polarizer that generates the linearly polarized beam from the light source and provides the generated linearly polarized beam.

7. The geometric phase in-line scanning holography system of claim 6, further comprising a first lens which is installed between the polarization sensitive lens and the scan means and which adjusts a distance between focal points of the first and second spherical waves and images a pattern of a surface of the polarization sensitive lens to a surface of an object area, wherein the interference beam is defined by the following equation in the form of a geometric phase Fresnel zone plate: Ix0,y0;zimg=cos2πMimg2fgpλ2Mimg2fgp+zimgzimgMimg2x02+Mimg2y02+2θ+dc  orIx0,y0;zimg=cos2πMimg2fgpλzimg2−Mimg4fgp2Mimg2x02+Mimg2y02+2θ+dcwherein, I(x0, y0; zimg) represents the interference beam of the first and second spherical waves imaged on the object area by the first lens, Mimg represents the zooming-in or zooming-out ratio of the image by the first lens when imaging the pattern on the surface of the polarization sensitive lens to the surface of the object area, zimg represents the distance from the focal position of the second spherical wave to the object, 2M2imgfgp represents the distance between the focal points of the adjusted first and second spherical waves, and dc represents a dc bias component.

8. The geometric phase in-line scanning holography system of claim 6, further comprising a second lens which is installed between the polarization sensitive lens and the scan means and which has a same focal position as the second spherical wave and converting the second spherical wave into a plane wave, wherein the interference beam is defined by the following equation in the form of a linear Fresnel zone plate formed by interference between the first spherical wave and the plane wave: Ix0,y0;z=cosπλzx02+y02+2θ+dcwherein, I(x0, y0; z) represents the interference beam of the first spherical wave and the plane wave transferred by the second lens, z represents the distance from the focal position of the first spherical wave, to which a curvature is added by the second lens, to the object, and dc represents a direct current bias component.

9. The geometric phase in-line scanning holography system of claim 1, wherein the first beam splitter transmits a part of an incident beam and reflects a part of the incident beam to split the incident beam into two beams, and the second polarizer has a polarization direction rotated clockwise by 45 degrees with respect to a polarization direction of the first polarizer.

10. The geometric phase in-line scanning holography system of claim 2, wherein each of the beam splitters transmits a part of incident beam and reflects a part of the incident beam to split the incident beam into two beams, and the second to fourth polarizers have a polarization direction rotated clockwise by 45 degrees, 90 degrees, or 135 degrees with respect to a polarization direction of the first polarizer.

11. The geometric phase in-line scanning holography system of claim 1, further comprising an electronic processing unit which generates a complex hologram of the object by processing first and second current signals detected by the first and second photodetectors, wherein the first and second photodetectors generate the first and second current signals corresponding to intensities of the first and second output beams passing through the first and second polarizers, respectively.

12. The geometric phase in-line scanning holography system of claim 11, wherein the first and second current signals generated by the first and second photodetectors are defined by the following equation: I0dcx,y=∫Ox0,y0;z⊗cos2πfgpλ2fgp+zzx02+y02+dcdzIπ/2dcx,y=∫Ox0,y0;z⊗cos2πfgpλ2fgp+zzx02+y02+π2+dcdzwherein O(x0,y0;z) represents a three-dimensional image of the object as a three-dimensional distribution for transmittance of the object, ⊗ represents a convolution operation, λ represents a wavelength of the beam used, (x, y) represents a scan position of a scan beam designated by the scan means, fgp represents a focal distance of the polarization sensitive lens, (x02+y02) represents a Cartersian coordinate system in which (x0,y0) is a plane orthogonal to an optical axis of the linearly polarized beam, z represents a distance from the focal position of the second spherical wave to the object, and dc represents a dc bias component.

13. The geometric phase in-line scanning holography system of claim 11, wherein the electronic processing unit includes: first and second dc removal filters which remove a dc component, which is a direct current bias component, from the first and second current signals and input the first and second current signals, from which the dc component is removed, to an AD converter;the AD converter which converts the first and second current signals, from which the dc component is filtered, into digital signals;a signal processing unit which generates a complex hologram of the object from the converted digital signals;a storage unit which stores the complex hologram; anda scan control unit which generates a control signal for changing a position of the scan means whenever hologram processing is completed for an arbitrary position of the object.

14. The geometric phase in-line scanning holography system of claim 13, further comprising: a second beam splitter which is installed between the polarization sensitive lens and the scan means and which transmits a part of the incident interference beam to the scan means, and reflects a part of the incident interference beam and splits the incident interference beam into two beams; anda 1-R beam splitter, 1-R and 2-R polarizers, and 1-R and 2-R photodetectors which process the beam reflected by the second beam splitter and which are disposed to be symmetrical with the first beam splitter, the first and second polarizers, and the first and second photodetectors, respectively,wherein the electronic processing unit further includes 1-R and 2-R dc removal filters which use 1-R and 2-R current signals detected by the 1-R and 2-R photodetectors as first and second phase correction reference signals for compensating for phase fluctuation caused by vibration of the system and remove a dc component, which is a direct current bias component, from the first and second phase correction reference signals, respectively, andthe electronic processing unit converts the first and second phase correction reference signals, from which the dc component is removed, into digital signals to generate a complex hologram for phase correction, and corrects the phase fluctuation of the system by multiplying a complex conjugate of the complex hologram for the phase correction by the complex hologram of the object stored in the storage unit.

15. The geometric phase in-line scanning holography system of claim 2, further comprising an electronic processing unit which generates a complex hologram of the object by processing first to fourth current signals detected by the first to fourth photodetectors, wherein the first to fourth photodetectors generate the first to fourth current signals corresponding to intensities of the output beams passing through the first to fourth polarizers, respectively.

16. The geometric phase in-line scanning holography system of claim 15, wherein an nth current signal (Ipn (x, y)) generated by the first to fourth photodetectors is defined by the following equation: Ipnx,y=∫Ox0,y0;z⊗cos2πfgpλ2fgp+zzx02+y02+pndz, pn=0,π2,π,3π2wherein n={1,2,3,4}, pn is a shifted phase of a hologram signal generated by a photodetector designated as n, O(x0,y0;z) represents a three-dimensional image of the object as a three-dimensional distribution for transmittance of the object, ⊗ represents a convolution operation, λ represents a wavelength of the beam used, (x, y) represents a scan position of a scan beam designated by the scan means, fgp represents a focal distance of the polarization sensitive lens, (x02+y02) represents a Cartersian coordinate system in which (x0,y0) is a plane orthogonal to an optical axis of the linearly polarized beam, and z represents a distance from a focal position of the second spherical wave to the object.

17. The geometric phase in-line scanning holography system of claim 15, wherein the electronic processing unit includes: an AD converter which converts the first to fourth current signals into digital signals;a signal processing unit which generates a complex hologram of the object from the converted digital signals;a storage unit which stores the complex hologram; anda scan control unit which generates a control signal for changing a position of the scan means whenever hologram processing is completed for an arbitrary position of the object.

18. The geometric phase in-line scanning holography system of claim 15, further comprising: a fourth beam splitter which is installed between the polarization sensitive lens and the scan means and which transmits a part of the incident interference beam to the scan means, and reflects a part of the incident interference beam and splits the incident interference beam into two beams; and1-R to 3-R beam splitters, 1-R to 4-R polarizers, and 1-R to 4-R photodetectors which process the beam reflected by the fourth beam splitter and which are disposed to be symmetrical with the first to third beam splitters, the first to fourth polarizers, and the first to fourth photodetectors, respectively,wherein the electronic processing unit uses 1-R to 4-R current signals detected by the 1-R to 4-R photodetectors as first to fourth phase correction reference signals for compensating for phase fluctuation caused by vibration of the system, converts the first to fourth phase correction reference signals into digital signals to generate a complex hologram for phase correction, and corrects the phase fluctuation of the system by multiplying the complex hologram for the phase correction by the complex hologram of the object stored in the storage unit.