Depolarization element and projection type display device
View Patent ↗A depolarization element includes high depolarization for light beams having coherence and plural wavelengths and also provides a projection type display device capable of reducing speckle noise. Unit regions, each formed of m regions (m≧4) having different phase differences generated for incident light, are disposed, and two regions extracted from the m regions have at least one combination of regions being different in area. When plural light beams having different wavelengths are incident, the composition of the Stokes vectors of the light beams emitted from the respective m regions is made nearly zero by setting the areas of the respective m regions and the generated phase differences, whereby the light beams having coherence and plural wavelengths can be converted so as to have the polarization state of natural light.
1. A depolarization element comprising:
birefringence material layers including birefringence materials; and
unit regions, each formed of m regions (m≧4) having different phase differences generated for incident linearly-polarized light, wherein:
two regions, extracted from the m regions, has at least one combination of regions being different in area;
a polarization state of the light that includes two or more light beams being different is changed; and
when the area of the unit region is 1, i is an integer of 1 to m, the area of the i-th region is Ai, the phase difference generated for the light incident on the i-th region is δi, the angle between the polarization direction of the incident linearly-polarized light and the optical axis of the birefringence material is θ, the following expressions are satisfied
[
Mathematical
expression
28
]
Ai
(
1
-
2
sin
2
δ
i
2
sin
2
2
θ
)
≤
0.0707
(
9
a
)
Ai
sin
2
δ
i
2
sin
4
θ
≤
0.0707
(
9
b
)
Ai
sin
δ
i
sin
2
θ
≤
0.0707
.
(
9
c
)
2. The depolarization element according to claim 1 , wherein the m is fallen within a range from 4 to 8.
3. The depolarization element according to claim 1 , wherein
the light includes a light beam having a wavelength of 440 nm and a light beam having a wavelength of 650 nm.
4. The depolarization element according to claim 3 , wherein
the light includes a light beam having a wavelength of 532 nm.
5. The depolarization element according to claim 4 , wherein
the light includes a light beam having a band of 440 to 650 nm.
6. The depolarization element according to claim 1 , wherein:
the optical axes of the birefringence materials are aligned in the same direction; and
the thicknesses of the birefringence material layers of the m regions are different from each other (a layer having a thickness of zero is included).
7. The depolarization element according to claim 6 , wherein
the thicknesses of the m regions are different from each other while having a nearly equal level difference.
8. The depolarization element according to claim 1 , wherein
the angle between the polarization direction of the linearly-polarized light and the optical axis direction of the birefringence material is approximately 45° and the following expressions are satisfied
[
Mathematical
expression
29
]
Ai
cos
δ
i
≤
0.1
(
17
a
)
Ai
sin
δ
i
≤
0.1
.
(
17
b
)
9. A projection type display device comprising:
a light source section having at least one light source emitting coherent light;
an image light generating section for generating image light by modulating the light emitted from the light source section;
a projection section for projecting the image light; and
a depolarization element, disposed in the optical path of the light emitted from the light source section, including:
birefringence material layers including birefringence materials; and
unit regions, each formed of m regions (m≧4) having different phase differences generated for incident linearly-polarized light, wherein:
two regions, extracted from the m regions, has at least one combination of regions being different in area;
a polarization state of the light that includes two or more light beams being different is changed; and
when the area of the unit region is 1, i is an integer of 1 to m, the area of the i-th region is Ai, the phase difference generated for the light incident on the i-th region is δi, the angle between the polarization direction of the incident linearly-polarized light and the optical axis of the birefringence material is θ, the following expressions are satisfied
[
Mathematical
expression
30
]
Ai
(
1
-
2
sin
2
δ
i
2
sin
2
2
θ
)
≤
0.0707
(
9
a
)
Ai
sin
2
δ
i
2
sin
4
θ
≤
0.0707
(
9
b
)
Ai
sin
δ
i
sin
2
θ
≤
0.0707
.
(
9
c
)
10. The projection type display device according to claim 9 , further comprising:
a rocking control section for oscillating the disposed depolarization element.