Dynamic draft for Fresnel lenses
A lens includes an optically transparent substrate having a first lens surface and a second lens surface opposite to the first lens surface. The first lens surface includes a plurality of Fresnel structures. A respective Fresnel structure of the plurality of Fresnel structures includes a slope facet and a draft facet. The draft facet is characterized by a draft angle. The draft angle of the respective Fresnel structure is based on a distance of the respective Fresnel structure from a center of the lens.
1. A lens, comprising:
an optically transparent substrate having a first lens surface and a second lens surface opposite to the first lens surface, wherein:
the first lens surface includes a plurality of Fresnel structures;
a respective Fresnel structure of the plurality of Fresnel structures includes a slope facet and a draft facet, wherein the draft facet is characterized by a draft angle;
the draft angle of the respective Fresnel structure is based on a distance of the respective Fresnel structure from a center of the lens;
the optically transparent substrate has a central portion and a peripheral portion that is distinct from the central portion and is located around the central portion;
the first lens surface for the central portion of the lens is defined by a Fresnel surface profile;
the second lens surface for the central portion of the lens is defined by a smooth surface profile;
the first lens surface for the peripheral portion of the lens has a convex shape and is defined by a Fresnel surface profile; and
the second lens surface for the peripheral portion of the lens has a concave shape and is defined by a Fresnel surface profile.
2. The lens of claim 1 , wherein:
the plurality of Fresnel structures includes a first Fresnel structure and a second Fresnel structure;
the draft facet of the first Fresnel structure has a first draft angle; and
the draft facet of the second Fresnel structure has a second draft angle that is distinct from the first draft angle.
3. The lens of claim 1 , wherein:
the lens is configured to focus light impinging on the first lens surface.
4. The lens of claim 1 , wherein:
the draft angle of the respective Fresnel structure is selected, based on the distance of the respective Fresnel structure from the center of the lens, to reduce interaction of light impinging on the first lens surface and the draft facet of the respective Fresnel structure.
5. The lens of claim 1 wherein the first lens surface for the peripheral portion of the lens is connected to the first lens surface for the central portion of the lens, and the second lens surface for the peripheral portion of the lens is connected to the second lens surface for the central portion of the lens.
6. The lens of claim 1 wherein:
the peripheral portion of the lens corresponds to one or more portions of a convex-concave lens.
7. The lens of claim 1 wherein:
the central portion of the lens corresponds to one or more portions of a plano-convex lens.
8. The lens of claim 7 , wherein:
the peripheral portion of the lens corresponds to one or more portions of a convex-concave lens; and
a convex surface of the peripheral portion of the lens extends from a planar surface of the central portion of the lens.
9. The lens of claim 7 , wherein:
the peripheral portion of the lens corresponds to one or more portions of a convex-concave lens; and
a concave surface of the peripheral portion of the lens extends from a planar surface of the central portion of the lens.
10. The lens of claim 1 , wherein:
the central portion of the lens corresponds to one or more portions of a convex-convex lens.
11. The lens of claim 1 wherein:
the second lens surface is defined by a polynomial that includes a convex surface for the central portion of the lens and a concave surface for the peripheral portion of the lens; and
the first lens surface is defined by a polynomial that includes a convex surface for the central portion of the lens and a convex surface for the peripheral portion of the lens.
12. A display device, comprising:
the lens of claim 1 ; and
an array of light emitting devices coupled with the lens for outputting light through the lens.
13. The display device of claim 12 , wherein the display device is a head-mounted display device.
14. The display device of claim 13 , wherein the array of light emitting devices is configured to output light and transmit the light through the lens toward an eye of a user when the display device is worn on a head of the user.