Polarization-selective varifocal liquid lens

1. A varifocal liquid lens comprising first and second liquid lens components having an interface therebetween, the interface extending across a clear aperture of the varifocal liquid lens and having a curvature variable within a curvature range by applying a control signal;

wherein the first and second liquid lens components comprise first and second fluids, respectively, wherein at least one of the first or second fluids is birefringent, such that:

for a first light beam having a first polarization state, the first and second liquid lens components are index-matched, whereby the interface has a substantially zero optical power for the first light beam at any curvature of the interface within the curvature range; and

for a second light beam having a second polarization state orthogonal to the first polarization state, the first and second liquid lens components are index-mismatched, whereby the interface has a substantially non-zero optical power for the second light beam, the non-zero optical power depending on the curvature of the interface within the curvature range.

2. The varifocal liquid lens of claim 1 , wherein the first fluid is isotropic and has a first refractive index, and wherein the second fluid is anisotropic and has an ordinary refractive index and an extraordinary refractive index;

wherein the ordinary refractive index of the second fluid is matched to the first refractive index to within 0.05 or better.

3. The varifocal liquid lens of claim 1 , wherein the interface comprises an elastic membrane.

4. The varifocal liquid lens of claim 3 , wherein the elastic membrane comprises an electrically responsive polymer layer for changing a radius of curvature of the elastic membrane by applying an electric field to the electrically responsive polymer layer.

5. The varifocal liquid lens of claim 3 , wherein the elastic membrane is configured to change its radius of curvature by application of mechanical force to a perimeter of the elastic membrane.

6. The varifocal liquid lens of claim 1 , wherein the first and second fluids are immiscible, and wherein the interface comprises a boundary between the immiscible first and second fluids.

7. A near-eye display device comprising:

a polarization-selective display module for providing image light at a first polarization while propagating therethrough external light at a second, orthogonal polarization, wherein the image light carries an image to be displayed by the near-eye display device; and

a polarization-selective varifocal liquid lens in an optical path downstream of the polarization-selective display module, for focusing or defocusing the image light at the first polarization while propagating the external light at the second polarization substantially without focusing or defocusing, the polarization-selective varifocal liquid lens comprising a body filled with first and second fluids separated by an interface therebetween, the interface having a variable curvature across a clear aperture of the polarization-selective varifocal liquid lens;

wherein at least one of the first or second fluids is birefringent, such that a refractive index difference between the first and second fluids and resulting optical power of the interface is polarization-dependent.

8. The near-eye display device of claim 7 , further comprising a polarizer in an optical path upstream of the polarization-selective display module, for polarizing the external light to have the second polarization.

9. The near-eye display device of claim 7 , absent a varifocal lens in an optical path of the external light upstream of the polarization-selective display module.

10. The near-eye display device of claim 7 , wherein the polarization-selective display module comprises a polarization-selective pupil-replicating waveguide for expanding the image light at the first polarization across the clear aperture of the polarization-selective varifocal liquid lens.