Dark-state compensators for LC panels
View Patent ↗Described are various compensators for compensating for in-plate and out-of-plane retardances of LC panels in their dark states.
1. An optical component for compensating a reflective LC panel in an optical projection system, wherein the LC panel is operable to receive light on a forward pass and reflect the light on a reverse pass, the optical component comprising:
a first birefringent film having a first optic axis;
a second birefringent film having a second optic axis substantially orthogonal to the first optic axis;
wherein the optical component is disposed in the paths of the forward-pass light and the reverse-pass light and is operable to transform, on the forward pass, the polarization state of the forward-pass light from a first polarization to a second polarization, wherein the optical component is further operable to transform, on the reverse pass, the polarization state of the reverse-pass light from the LC panel from a third polarization to a fourth polarization;
wherein the retardances and respective orientations of the first and second films are configured to substantially compensate for a dark state of the reflective LC panel, such that, during the dark state, the first and fourth polarizations are substantially the same.
2. The optical component of claim 1 , wherein at least one of the first and second birefringent films is a uniaxial film.
3. The optical component of claim 1 , wherein at least one of the first and second birefringent films comprises a stretched polymer.
4. The optical component of claim 1 , wherein at least one of the first and second birefringent films is a low-elasticity organic film.
5. The optical component of claim 1 , wherein the first and second birefringent films are oriented relative to the LC panel to provide at least some compensation for field-of-view variations in an optical projection system in which the first and second films and the LC panel are used.
6. The optical component of claim 1 , wherein the difference between the respective retardances of the first and second birefringent films is substantially matched to the residual retardance of the LC panel in its dark state.
7. The optical component of claim 1 , wherein the first and second birefringent films have retardances that are substantially matched to each other.
8. The optical component of claim 1 , wherein the first and second birefringent films are positioned in a projection system with their optic axes oriented at ± 45° relative to an input light polarization.
9. The optical component of claim 1 , wherein the first and second birefringent films have a retardance value that is substantially matched to the retardance of the LC panel.
10. The optical component of claim 1 , wherein the birefringent film having the larger relative retardance is oriented with its optic axis substantially at 90° to the direction of the LC panel's dark-state residual retardance.
11. The optical component of claim 1 , wherein the component is oriented according to the formula
(
0
0
1
)
·
[
(
cos
(
2
·
θ
r
)
sin
(
2
·
θ
r
)
0
-
sin
(
2
·
θ
r
)
cos
(
2
·
θ
r
)
0
0
0
1
)
·
(
1
0
0
0
cos
(
2
·
π
·
Γ
r
λ
)
-
sin
(
2
·
π
·
Γ
r
λ
)
0
sin
(
2
·
π
·
Γ
r
λ
)
cos
(
2
·
π
·
Γ
r
λ
)
)
·
(
cos
(
2
·
θ
r
)
-
sin
(
2
·
θ
r
)
0
sin
(
2
·
θ
r
)
cos
(
2
·
θ
r
)
0
0
0
1
)
]
·
(
cos
(
2
·
ɛ
)
·
cos
(
2
·
ϕ
)
cos
(
2
·
ɛ
)
·
sin
(
2
·
ϕ
)
sin
(
2
·
ɛ
)
)
=
0
where φ and ε are the orientation and ellipticity angles describing the polarized state transformed from the input polarization by the LC layer panel, where Γr and θr are the in-plane retardance and orientation of the optical component, and where λ is the wavelength of the compensated light.
12. The optical component of claim 11 , wherein θr is chosen to be substantially unequal to 45 degrees.
13. The optical component of claim 1 , wherein the birefringent film having the smaller relative retardance is positioned closer to the associated LC panel.
14. The optical component of claim 1 , wherein the birefringent film having the larger relative retardance is positioned in an optical projection system as substantially aligned with an input light polarization.