Gravity sag compensation in fluid-filled lenses
Examples include a device including a fluid lens having a membrane, a substrate, and a fluid at least partially enclosed between the membrane and the substrate. The membrane may have a spatial variation in at least one membrane parameter along a particular direction, that may compensate for gravity sag in the membrane of the fluid lens when the device is worn by a user. Examples also include related methods and systems.
1. A device comprising a fluid lens, wherein the fluid lens comprises:
a membrane;
a substrate; and
a fluid located within an enclosure formed at least in part by the membrane and the substrate; wherein:
the fluid lens is an adjustable fluid lens having a maximum optical power, a minimum optical power, and a mid-range optical power located between the maximum optical power and the minimum optical power;
the membrane has a spatial variation in at least one membrane parameter along a particular direction that compensates for gravity sag in the membrane when the fluid lens is adjusted to the mid-range optical power;
the at least one membrane parameter includes a membrane thickness; and
the membrane thickness has a linear variation with height with the membrane thickness being greater in a lower portion of the membrane when the device is worn by a user in a standing position.
2. The device of claim 1 , wherein the device is a head-mounted device.
3. The device of claim 1 , wherein the device is an ophthalmic device configured to be used as eyewear, an augmented reality device, or a virtual reality device.
4. The device of claim 1 , wherein the fluid lens is sized for use with a human eye, and the fluid lens has a diameter, width, or analogous dimension of between approximately 20 mm and approximately 80 mm.
5. The device of claim 1 , wherein the at least one membrane parameter includes the membrane thickness and at least one of a membrane composition, a membrane elastic constant, or a membrane tension.
6. The device of claim 1 , wherein the membrane thickness has a generally linear variation in membrane thickness extending across the membrane along the particular direction, wherein the particular direction is a vertical direction when the device is worn by the user.
7. The device of claim 1 , wherein the at least one membrane parameter includes an elastic constant of the membrane.
8. The device of claim 7 , wherein the elastic constant is an elastic modulus of the membrane.
9. The device of claim 1 , wherein the at least one membrane parameter includes a membrane composition.
10. The device of claim 9 , wherein the membrane includes a membrane polymer, and the membrane composition includes a degree of cross-linking within the membrane polymer.
11. The device of claim 9 , wherein the membrane includes a membrane polymer and an additive, and the membrane composition includes a weight percentage of the additive within the membrane.
12. The device of claim 1 , wherein the device further includes:
a peripheral structure disposed around a periphery of the membrane;
at least one membrane attachment attached to the peripheral structure; and
at least one support structure configured to engage with a respective membrane attachment of the at least one membrane attachment, wherein:
the fluid lens is configured such that movement of the at least one membrane attachment relative to the substrate adjusts an optical property of the fluid lens;
the membrane is an elastic membrane; and
the at least one membrane parameter includes an elastic tension within the membrane.
13. The device of claim 12 , wherein each of the at least one support structure provides a guide path for a respective membrane attachment of the at least one membrane attachment,
wherein each respective membrane attachment is moveable along the guide path to adjust the optical property of the lens.
14. The device of claim 1 , further comprising an edge seal, wherein the edge seal is configured to retain the fluid between the substrate and the membrane, and wherein
the substrate is an optically transparent substrate,
the membrane is an optically transparent membrane, and
the fluid includes an optically transparent liquid.
15. A method, comprising:
forming a membrane having a spatial variation in at least one membrane parameter along a particular direction; and
assembling a device, the device including a fluid lens comprising the membrane,
wherein:
the fluid lens is an adjustable fluid lens having a maximum optical power, a minimum optical power, and a mid-range optical power located between the maximum optical power and the minimum optical power;
the spatial variation in the at least one membrane parameter along the particular direction compensates for gravity sag in the membrane of the fluid lens membrane when the fluid lens is adjusted to the mid-range optical power;
the at least one membrane parameter includes a membrane thickness; and
the membrane thickness has a linear variation with height with the membrane thickness being greater in a lower portion of the membrane when the device is worn by a user in a standing position.
16. The method of claim 15 , wherein
the spatial variation in the at least one membrane parameter along the particular direction includes a variation in an elastic constant of the membrane along the particular direction, and
assembling the device includes configuring the fluid lens so that the elastic constant of the membrane is generally greater within the lower portion of the fluid lens.
17. The method of claim 15 , wherein
the at least one membrane parameter includes a membrane thickness, and
assembling the device includes configuring the fluid lens so that the membrane thickness is generally greater within the lower portion of the fluid lens.
18. The method of claim 15 , wherein the at least one membrane parameter further includes at least one of:
a membrane composition;
a treatment temperature of the membrane; or
a lens fluid absorption of the membrane.