Patent ID: 11953686
Assignee: MICROSOFT TECHNOLOGY LICENSING, LLC
Field: Optics (Instruments)
Classification: CPC G | IPC G

Claim 13:
14. A mixed-reality optical display system providing a plurality of different focal lengths for planes into which images of virtual-world objects are displayable, comprising:
a source configured to generate light for virtual-world images, the virtual-world image light propagating on a light path from the source to an eye of a user of the mixed-reality display system;
first and second ferroelectric liquid crystal (FLC) modulators disposed along the light path, each of which is operatively coupled to the source to receive virtual-world image light, and each of which is switchable between first and second switched states;
a linear polarizer disposed along the light path between the source and the first FLC modulator and configured to impart a linearly polarized state to the virtual-world image light that is incident on the FLC modulator, wherein each switchable FLC modulator is configured as a half-wave plate that is aligned at zero degrees or 45 degrees with respect to a polarization axis of the linear polarizer depending on the switched state;
first and second birefringent lenses disposed along the light path downstream from the FLC modulator, each birefringent lens having an ordinary refractive index that is aligned with the polarization axis of the linear polarizer and an extraordinary refractive index that is orthogonal to the ordinary refractive index, wherein virtual-world image light incident on each birefringent lens having a state of polarization that is aligned with the ordinary refractive index is focused by the birefringent lens at a first focal length and virtual-world image light incident on each birefringent lens having a state of polarization that is aligned with the extraordinary refractive index is focused by each birefringent lens at a second focal length that is different from the first, wherein the first and second polarization modulators and first and second birefringent lenses are arranged in a stack through which the virtual-world image light propagates in series, the stack comprising the first polarization modulator, the first birefringent lens, the second polarization modulator, and the second birefringent lens;
a focal length controller operatively coupled to the pair of FLC modulators to switch each FLC modulator between the first and the second states, wherein in the first switched state of each FLC modulator, virtual-world image light exiting each FLC modulator and incident on the birefringent lens has a state of polarization that is aligned with the ordinary refractive index of the birefringent lens, and wherein in the second switched state of the FLC modulator, virtual-world image light exiting the FLC modulator has a state of polarization that is aligned with the extraordinary refractive index of the birefringent lens; and
a see-through optical combiner through which real-world objects are viewable by the user, the see-through optical combiner disposed on the light path downstream from the birefringent lens, and the see-through optical combiner being adapted to display the virtual-world object images which are superimposed over the views of real-world objects in first or second focal planes that are respectively associated with the first and second focal lengths;
wherein the stack of first and second polarization modulators and first and second birefringent lenses are operable by the focal length controller to provide four unique focal distances for the rendered virtual images, and
wherein the stack of first and second polarization modulators and first and second birefringent lenses are located on the HMD device outside the user's line of sight.