Polarization modulation wheel
View Patent ↗A polarization switch provides substantially ideal binary polarization switching over a broad range of wavelengths using a polarization modulation wheel having at least one retarder stack that transforms polarization. Using the polarization modulation wheel in a polarization system provides a high throughput polarization switch and operates over a wide range of incidence angles while providing substantially continuous and smooth polarization output for each component for any selected polarization basis set. The polarization modulation wheel is well-suited for stereoscopic polarized projection applications.
1. A polarization modulator operable to temporally modulate incoming linearly polarized light on a light path, comprising:
a polarization wheel located on the linearly polarized light path, the polarization wheel having a first circular arc and a second circular arc,
wherein at least one of the first circular arc and the second circular arc comprises a multi-layer retarder stack filter having a plurality of linear retarders.
2. The polarization modulator of claim 1 , wherein the retarder stack filter has substantially negligible retardation.
3. The polarization modulator of claim 1 , wherein the retarder stack filter has a circular basis vector.
4. The polarization modulator of claim 1 , wherein the retarder stack filter rotates the linearly polarized light by a predetermined angle regardless of the angular position of the polarization wheel.
5. The polarization modulator of claim 1 , wherein the retarder stack filter has substantially constant phase difference between right and left hand polarization within a visible light spectrum.
6. The polarization modulator of claim 1 , wherein the first circular arc comprises a first retarder stack filter and the second circular arc comprises a second retarder stack filter.
7. The polarization modulator of claim 6 :
wherein the first retarder stack filter rotates the linearly polarized light by a first predetermined angle when illuminated by the linearly polarized light, regardless of the angular position of the first circular arc,
wherein the second retarder stack filter rotates the linearly polarized light by a second predetermined angle when illuminated by the linearly polarized light, regardless of the angular position of the second circular arc,
wherein the first predetermined angle is orthogonal to the second predetermined angle.
8. The polarization modulator of claim 6 :
wherein the first retarder stack filter is a θ degree polarization state rotator, and
wherein the second retarder stack filter is a (θ−90) degree polarization state rotator.
9. The polarization modulator of claim 8 :
wherein the first retarder stack filter is a +45 degree polarization state rotator, and
wherein the second retarder stack filter is a −45 degree polarization state rotator.
10. The polarization modulator of claim 1 , wherein the polarization state of light on the light path exiting the first circular arc is orthogonal to the polarization state of light on the light path exiting the second circular arc.
11. The polarization modulator of claim 1 , wherein the first and second circular arcs each provide halves of the polarization wheel.
12. The polarization modulator of claim 1 , wherein the first circular arc transforms the polarization state of input polarized light by 90 degrees, and the second circular arc does not transform the polarization state of the input polarized light.
13. The polarization modulator of claim 2 , wherein the first circular arc and the second circular arc each comprise a substantially dispersionless retarder material.
14. The polarization modulator of claim 13 , wherein the substantially dispersionless retarder material comprises one of cyclic-olefin-copolymer (COC) and polycarbonate.
15. The polarization modulator of claim 1 , further comprising a quarter wave retarder on the light path following the polarization wheel, the quarter wave retarder being oriented at +45 degrees with respect to the state of polarization emanating from the first circular arc, and oriented at −45 degrees with respect to the state of polarization emanating from the second circular arc.
16. The polarization modulator of claim 1 , wherein the retarder stack filter comprises a Finite Infinite Response (FIR) filter, and is operable to generate at least N+1 spatially offset light pulses in response to a linearly polarized light impulse input.
17. The polarization modulator of claim 1 , wherein the polarization wheel further comprises an antireflective coating.
18. A stereoscopic projection system, comprising:
a projector subsystem; and
a polarization modulator subsystem,
the polarization modulator subsystem being operable to temporally modulate projected images from the projector subsystem into orthogonal polarization states,
wherein the polarization modulator subsystem comprises:
a polarization wheel having a first circular arc and a second circular arc, wherein the first circular arc comprises a first multi-layer retarder stack filter having a first plurality of linear retarders, and wherein the second circular arc comprises a second multi-layer retarder stack filter having a first plurality of linear retarders.
19. The stereoscopic projection system of claim 18 , further comprising a controller adapted to control the position of the polarization wheel in synchronization with the projected images from the projector subsystem.
20. The stereoscopic projection system of claim 18 , wherein a linear polarizer is located in a light path between the projector subsystem and the polarization modulator subsystem.
21. The stereoscopic projection system of claim 18 :
wherein the first retarder stack filter is a θ degree polarization state rotator, and
wherein the second retarder stack filter is a (θ−90) degree polarization state rotator.
22. The stereoscopic projection system of claim 21 :
wherein the first retarder stack filter is a +45 degree polarization state rotator, and
wherein the second retarder stack filter is a −45 degree polarization state rotator.
23. The stereoscopic projection system of claim 18 , wherein a projection lens is located in a light path after the polarization wheel.
24. The stereoscopic projection system of claim 18 , wherein a projection lens is located in a light path between the projection subsystem and the polarization modulation subsystem.
25. The stereoscopic projection system of claim 18 , further comprising a quarter wave retarder on the light path following the polarization wheel, the quarter wave retarder being oriented at +45 degrees with respect to the state of polarization emanating from the first circular arc, and oriented at −45 degrees with respect to the state of polarization emanating from the second circular arc.
26. The polarization modulator of claim 18 , wherein the first retarder stack filter comprises a Finite Infinite Response (FIR) filter, and is operable to generate at least N+1 spatially offset light pulses in response to the linearly polarized light impulse input.