Pancake lens ghosting mitigation
A near-eye display assembly includes an electronic display for providing image light, a circular polarizer disposed downstream of the electronic display for circularly polarizing the image light, and a pancake lens disposed downstream of the circular polarizer for conveying the image light to an eyebox of the near-eye display. The circular polarizer includes a quarter-wave waveplate disposed between the electronic display and the pancake lens, and spaced apart from the electronic display and the pancake lens, to additionally defocus ghost image artifacts at the eyebox.
1. A near-eye display assembly comprising:
an electronic display for providing image light;
a circular polarizer downstream of the electronic display for circularly polarizing the image light; and
a pancake lens downstream of the circular polarizer for conveying the image light to an eyebox;
wherein the circular polarizer comprises a first quarter-wave waveplate disposed between and spaced apart from the electronic display and the pancake lens; and
wherein the pancake lens comprises a pair of plano-convex lenses and a stack of a second quarter-wave waveplate and a reflective polarizer sandwiched between flat sides of the pair of plano-convex lenses.
2. The near-eye display assembly of claim 1 , wherein the circular polarizer is spaced apart from the electronic display and the pancake lens by air gaps.
3. The near-eye display assembly of claim 1 , wherein the circular polarizer is tilted w.r.t. an optical axis of the pancake lens.
4. The near-eye display assembly of claim 1 , wherein the circular polarizer has curved outer optical surfaces, wherein the circular polarizer has a substantially zero optical power for transmitted light.
5. The near-eye display assembly of claim 1 , wherein the first quarter-wave waveplate is disposed closer to the pancake lens than to the electronic display.
6. A near-eye display assembly comprising:
an electronic display for providing image light;
a circular polarizer downstream of the electronic display for circularly polarizing the image light; and
a pancake lens downstream of the circular polarizer for conveying the image light to an eyebox;
wherein the circular polarizer comprises a first quarter-wave waveplate disposed between and spaced apart from the electronic display and the pancake lens; and
wherein the pancake lens comprises a pair of plano-convex lenses with convex sides facing the electronic display, a second quarter-wave waveplate, and a reflective polarizer disposed downstream of the pair of plano-convex lenses.
7. The near-eye display assembly of claim 6 , wherein the first quarter-wave waveplate is disposed within 25% of the middle between the electronic display and the pancake lens.
8. The near-eye display assembly of claim 1 , wherein the first quarter-wave waveplate comprises an anti-reflective coating facing the pancake lens.
9. The near-eye display assembly of claim 8 , wherein the circular polarizer further comprises a linear polarizer upstream of and in contact with the first quarter-wave waveplate.
10. The near-eye display assembly of claim 8 , wherein the anti-reflective coating has reflectivities at wavelengths of red, green, and blue color channels differing by less than 50% of the reflectivity at the wavelength of the green color channel.
11. An optical assembly comprising a polarization stack and a pancake lens subassembly separated from the polarization stack by an air gap;
wherein the polarization stack comprises in sequence: an air-facing linear polarizer, a first quarter-wave waveplate in contact with the linear polarizer, and an air-facing anti-reflective coating on a surface of the first quarter-wave waveplate facing the pancake lens subassembly, wherein a transmission axis of the linear polarizer is disposed at 45 degrees w.r.t. an optic axis of the first quarter-wave waveplate; and
wherein the pancake lens subassembly comprises a first plano-convex lens having a partially reflective coating on its convex side facing the polarization stack.
12. The optical assembly of claim 11 , wherein the pancake lens subassembly further comprises in sequence: a second quarter-wave waveplate in contact with a flat side of the first plano-convex lens, a reflective polarizer having a transmission axis at 45 degrees w.r.t. an optic axis of the second quarter-wave waveplate, and a second plano-convex lens having a flat side in contact with the reflective polarizer.
13. The optical assembly of claim 11 , wherein the pancake lens subassembly further comprises:
a second plano-convex lens having a convex side facing towards the polarization stack;
a second quarter-wave waveplate; and
a reflective polarizer downstream of the second quarter-wave waveplate and in contact with a flat side of the second plano-convex lens, the reflective polarizer having a transmission axis at 45 degrees w.r.t. an optic axis of the second quarter-wave waveplate.
14. A method for coupling image light emitted by an electronic display to an eyebox of a near-eye display, the method comprising:
circularly polarizing the image light by a circular polarizer comprising a first quarter-wave waveplate spaced apart from the electronic display, to produce circularly polarized image light; and
conveying the circularly polarized image light to the eyebox by a pancake lens spaced by an air gap from the first quarter-wave waveplate;
wherein conveying the image light comprises propagating the image light in sequence through a first plano-convex lens, through a stack of a second quarter-wave waveplate and a reflective polarizer, and through a second plano-convex lens.
15. The method of claim 14 , wherein the circular polarizer is spaced apart from the electronic display by an air gap.
16. The method of claim 14 , further comprising disposing the first quarter-wave waveplate closer to the pancake lens than to the electronic display.