Optical scanning holography system
An optical scanning holography system includes a polarization-sensitive lens configured to receive a linearly polarized beam and generate a first spherical wave of right-handed circular polarized light having a negative focal length and a second spherical wave of left-handed circular polarized light having a positive focal length, a first polarizer configured to pass only a beam component therethrough in a predetermined polarization direction among components of the generated first and second spherical waves, a scanning unit configured to scan an object by using an interference beam generated between the first and second spherical waves passing through the first polarizer, and a first photodetector configured to detect a beam reflected from the object.
1. A geometric phase in-line scanning holography system, comprising:
a polarizer configured to convert an input beam into a linearly polarized beam;
a collimator configured to receive the linearly polarized beam from the polarizer and expand the linearly polarized beam;
a single polarization-sensitive lens configured to simultaneously generate, from the expanded linearly polarized beam, a first spherical wave of right-handed circular polarization having a negative focal length located on a source side of the single polarization-sensitive lens, and a second spherical wave of left-handed circular polarization having a positive focal length located on an object side of the single polarization-sensitive lens;
wherein the negative focal length and the positive focal length are formed along a single optical path;
a scanning unit configured to scan an object by using an interference beam formed by superposition of the first spherical wave and the second spherical wave along the single optical path;
a light integrator configured to spatially integrate light reflected from the object scanned by the interference beam;
a first beam splitter configured to receive the spatially integrated light from the light integrator and to split the spatially integrated light into a first output beam and a second output beam;
a second beam splitter configured to split the first output beam into a 1a th output beam and a 1b th output beam;
a third beam splitter configured to split the second output beam into a 2a th output beam and a 2b th output beam;
first, second, third, and fourth polarizers respectively arranged to polarize the 1a th , 1b th , 2a th , and 2b th output beams, wherein polarization directions of the first to fourth polarizers are rotated 0°, 45°, 90°, and 135°, respectively, relative to one another; and
first, second, third, and fourth photodetectors configured to respectively detect the 1a th , 1b th , 2a th , and 2b th output beams passing through the first to fourth polarizers and generate corresponding detection signals,
wherein an electronic processor is configured to combine the detection signals to obtain a complex hologram of the object based on geometric-phase interference of the first spherical wave and the second spherical wave.
2. The geometric phase in-line scanning holography system of claim 1 , wherein the single polarization-sensitive lens is a geometric phase lens.
3. The geometric phase in-line scanning holography system of claim 1 , wherein the interference beam has a form of a geometric phase Fresnel zone plate and is defined by a following equation,
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
]
where λ is a wavelength of a used beam, f gp is a focal length of the single polarization-sensitive lens, (x 0 2 +y 0 2 ) is a Catharsian coordinate system having a plane orthogonal to an optical axis of the linearly polarized beam as (x 0 ,y 0 ), z is a distance from a focal point of the second spherical wave to the object, and θ is an angle linearly polarized clockwise with respect to a polarization axis of a light source side polarizer that generates and provides the linearly polarized beam from a light source.
4. The geometric phase in-line scanning holography system of claim 1 , wherein the electronic processor is configured to generate the complex hologram of the object by processing a first current signal and a second current signal detected by the first photodetector and the second photodetector respectively,
wherein the first photodetector and the second photodetector generate the first current signal
I
0
dc
(
x
,
y
;
z
)
and the second current signal
I
π
/
2
dc
(
x
,
y
;
z
)
respectively, as represented by following equations in correspondence with intensities of the first output beam and the second output beam passing through the first polarizer and the second polarizer respectively,
I
0
dt
(
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
+
π
2
]
+
dc
}
dz
where O(x 0 ,y 0 ;z) is a three-dimensional distribution of the reflectance of the object and is a three-dimensional image of the object, ⊗ is a convolution operation, λ is a wavelength of a used beam, (x,y) is a scan position of a scan beam designated by the scanning unit, f gp is a focal length of the single polarization-sensitive lens, z is a distance from a focal point of the second spherical wave to the object, and dc is a DC bias component.