Variable-focus virtual image devices based on polarization conversion
Example display devices include a waveguide configured to propagate visible light under total internal reflection in a direction parallel to a major surface of the waveguide. The waveguide has formed thereon an outcoupling element configured to outcouple a portion of the visible light in a direction normal to the major surface of the waveguide. The example display devices additionally include a polarization-selective notch reflector disposed on a first side of the waveguide and configured to reflect visible light having a first polarization while transmitting the portion of the visible light having a second polarization. The example display devices further include a polarization-independent notch reflector disposed on a second side of the waveguide and configured to reflect visible light having the first polarization and the second polarization, where the polarization-independent notch reflector is configured to convert a polarization of visible light reflecting therefrom.
1. A display device, comprising:
a wave-guiding device interposed between a first switchable lens assembly and a second switchable lens assembly,
wherein the wave-guiding device comprises:
one or more cholesteric liquid crystal (CLC) layers each comprising a plurality of chiral structures, wherein each chiral structure comprises a plurality of liquid crystal molecules that extend in a layer depth direction and are successively rotated in a first rotation direction, wherein arrangements of the liquid crystal molecules of the chiral structures vary periodically in a lateral direction perpendicular to the layer depth direction such that the one or more CLC layers are configured to Bragg-reflect incident light; and
one or more waveguides formed over the one or more CLC layers and configured to propagate visible light under total internal reflection (TIR) in a direction parallel to a major surface of the waveguide and to optically couple visible light to or from the one or more CLC layers.
2. The display device of claim 1 , wherein the one or more waveguides are interposed between a polarization-selective notch reflector and a polarization-independent notch reflector, wherein the polarization-selective notch reflector is configured to reflect visible light having a first polarization while transmitting visible light having a second polarization, and wherein the polarization-independent notch reflector is configured to reflect visible light having the first polarization and visible light having the second polarization.
3. The display device of claim 2 , wherein the one or more CLC layers serve as the polarization-selective notch reflector.
4. The display device of claim 2 , wherein the polarization-selective notch reflector comprises one or more CLC layers.
5. The display device of claim 4 , wherein each of the one or more CLC layers of the polarization-selective notch reflector comprises a plurality of chiral structures,
wherein each of the chiral structures comprises a plurality of liquid crystal molecules that extend in a layer depth direction by at least a helical pitch and are successively rotated in a first rotation direction,
wherein the helical pitch is a length in the layer depth direction corresponding to a net rotation angle of the liquid crystal molecules of the chiral structures by one full rotation in the first rotation direction, and
wherein arrangements of the liquid crystal molecules of the chiral structures vary periodically in a lateral direction perpendicular to the layer depth direction.
6. The display device of claim 2 , wherein the polarization-selective notch reflector is configured to preserve a polarization of visible light reflecting therefrom, and wherein the polarization-independent notch reflector is configured to convert a polarization of visible light reflecting therefrom.
7. The display device of claim 2 , further comprising a first quarter-wave plate interposed between the polarization-independent notch reflector and the waveguide.
8. The display device of claim 7 , further comprising a second quarter-wave plate interposed between the second switchable lens and the polarization-selective notch reflector.
9. The display device of claim 1 , wherein the first switchable lens and the second switchable lens have optical powers having opposite signs when activated.
10. The display device of claim 1 , wherein the first switchable lens assembly comprises a Pancharatnam-Berry (PB) lens and the second switchable lens assembly comprises a second Pancharatnam-Berry (PB) lens.