Geometric phase in-line scanning holography system for transmissive object
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.
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; and
first and second photodetectors which detect output beams having passed through the first and second polarizers.
2 . The geometric phase in-line scanning holography system of claim 1 , wherein the polarization sensitive lens includes a geometric phase lens.
3 . 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.
4 . 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:
I
GP
-
FZP
(
x
0
,
y
0
;
z
)
=
cos
[
2
π
f
gp
λ
(
2
f
gp
+
z
)
z
(
x
0
2
+
y
0
2
)
+
2
θ
]
wherein I GP-FZP (x 0 , y 0 ; 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, f gp is a focal distance of the polarization sensitive lens, (x 0 2 +y 0 2 ) represents a Cartersian coordinate system in which (x 0 ,y 0 ) 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.
5 . The geometric phase in-line scanning holography system of claim 4 , 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:
I
(
x
0
,
y
0
;
z
img
)
=
cos
[
2
π
M
img
2
f
gp
λ
(
2
M
img
2
f
gp
+
z
img
)
z
img
(
M
img
2
x
0
2
+
M
img
2
y
0
2
)
+
2
θ
]
+
dc
or
I
(
x
0
,
y
0
;
z
img
)
=
cos
[
2
π
M
img
2
f
gp
λ
(
z
img
2
-
M
img
4
f
gp
2
)
(
M
img
2
x
0
2
+
M
img
2
y
0
2
)
+
2
θ
]
+
dc
wherein, I(x 0 , y 0 ; z img ) represents the interference beam of the first and second spherical waves imaged on the object area by the first lens, M img 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, z img represents the distance from the focal position of the second spherical wave to the object, 2M 2 img f gp represents the distance between the focal points of the adjusted first and second spherical waves, and dc represents a de bias component.
6 . The geometric phase in-line scanning holography system of claim 4 , 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:
I
(
x
0
,
y
0
;
z
)
=
cos
[
π
λ
z
(
x
0
2
+
y
0
2
)
+
2
θ
]
+
dc
wherein, I(x 0 , y 0 ; 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.
7 . 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.
8 . 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.
9 . The geometric phase in-line scanning holography system of claim 8 , wherein the first and second current signals
(
I
0
dc
(
x
,
y
)
,
I
π
/
2
dc
(
x
,
y
)
)
generated by the first and second photodetectors are defined by the following equation:
I
0
dc
(
x
,
y
)
=
∫
O
(
x
0
,
y
0
;
z
)
⊗
{
cos
[
2
π
f
gp
λ
(
2
f
gp
+
z
)
z
(
x
0
2
+
y
0
2
)
]
+
dc
}
dz
I
π
/
2
dc
(
x
,
y
)
=
∫
O
(
x
0
,
y
0
;
z
)
⊗
{
cos
[
2
π
f
gp
λ
(
2
f
gp
+
z
)
z
(
x
0
2
+
y
0
2
)
+
π
2
]
+
dc
}
dz
wherein O(x 0 ,y 0 ;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, f gp represents a focal distance of the polarization sensitive lens, (x 0 2 +y 0 2 ) represents a Cartersian coordinate system in which (x 0 ,y 0 ) 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.
10 . The geometric phase in-line scanning holography system of claim 8 , 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; and
a 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.