Crystalline waveguides and wearable devices containing the same

1 . A head mounted display, comprising:

a head mounted display frame;

a first eyepiece supported by the frame, the first eyepiece comprising a first substrate composed of a crystalline, transparent material having crystallographic axes in a first orientation with respect to the frame, the first substrate having a first surface and a second surface opposite the first surface, the first eyepiece further comprising a first in-coupling element comprising a grating on the first surface, and a first out-coupling element comprising a grating on the first surface and/or a grating on the second surface; and

a second eyepiece comprising a second substrate composed of the crystalline, transparent material having crystallographic axes in a second orientation with respect to the frame different from the first orientation, a second in-coupling element on either surface of the second substrate, and a second out-coupling element on either surface of the second substrate.

2 . The head mounted display of claim 1 , wherein for both the first orientation and the second orientation, a first crystallographic axis of the crystallographic axes is oriented perpendicular to the surface of the respective substrate and a second crystallographic axis of the crystallographic axes is oriented in a plane of the second substrate.

3 . The head mounted display of claim 1 , wherein an optic axis of the crystalline, transparent material in the first eyepiece is parallel to an optic axis of the crystalline, transparent material in the second eyepiece.

4 . The head mounted display of claim 1 , wherein a thickness of the first substrate varies across the first substrate.

5 . The head mounted display of claim 1 , wherein the crystalline, transparent material is selected from the group consisting of LiNbO 3 , SiC, and LiTaO 3 .

6 . The head mounted display of claim 5 , wherein the crystalline, transparent material is a birefringent material.

7 . The head mounted display of claim 1 , wherein at least one of the first and second in-coupling elements and the first and second out-coupling elements comprise multiple materials with different indices of refraction.

8 . The head mounted display of claim 1 , wherein:

the first surface supports a layer of a first dielectric material that extends over the first in-coupling element and the first out-coupling element, the first dielectric material having a refractive index of 1.5 or less;

the second surface supports a layer of a second dielectric material that extends over the second in-coupling element and the second out-coupling element, the second dielectric material having a refractive index of 1.5 or less;

or both.

9 . The head mounted display of claim 1 , further comprising an adhesive layer on edges of at least one of the first and second eyepieces, the adhesive layer configured to absorb visible light.

10 . The head mounted display of claim 1 , wherein at least one of the first and second in-coupling elements and the first and second out-coupling elements is etched into the surface of the first and second substrates, respectively.

11 . An article comprising:

a wafer composed of a crystalline, transparent material having crystallographic axes in a first orientation with respect to a surface of the wafer, a thickness of the wafer varying across the surface of the wafer such that for a cross-sectional profile of the wafer, the thickness increases monotonically from edges of the wafer to a location of maximum thickness away from the edges; and

a plurality of optical elements comprising a grating on the surface of the wafer and spaced apart from each other, each grating corresponding to a portion of the wafer for singulation into a component for an eyepiece for a head mounted display, each portion having the same thickness profile.

12 . The article of claim 11 , further comprising a respective optical element for each grating in a corresponding portion of the wafer.

13 . An eyepiece comprising:

a transparent, crystalline substrate composed of a material having a refractive index greater than 2.2, the substrate extending in a plane and having a thickness in a direction perpendicular to the plane that varies along a first direction in the plane and along a second direction in the plane substantially perpendicular to the second direction;

an in-coupling element comprising a grating supported by a first surface of the substrate; and

an optical element comprising a grating supported by the first surface and/or a second surface of the substrate opposite the first surface.

14 . The eyepiece of claim 13 , wherein the optical element is a combined pupil expander, an exit pupil expander, or an orthogonal pupil expander.

15 . The eyepiece of claim 13 , wherein the eyepiece corresponds to portion of a spherical or rotational symmetric aspherical surface.

16 . The eyepiece claim 13 , wherein the eyepiece is coated in an absorptive adhesive material.

17 . The eyepiece of claim 13 , wherein a difference between a maximum thickness and a minimum thickness is in a range of 1 to 500 nm.

18 . The eyepiece of claim 13 , wherein a total length in the plane spanning the in-coupling element and optical element is in a range of 60-70 mm.

19 . The eyepiece of claim 13 , wherein the substrate is configured to guide light in at least one of the following ranges: 455 nm+/−30 nm, 530 nm+/−30 nm, or 635 nm+/−30 nm.

20 . The eyepiece of claim 13 , wherein at least one of the in-coupling element and the optical element comprise two or more materials with different indices of refraction.