Tunable elastic dielectric metasurface lenses
Metasurfaces comprise an array of meta-atoms in a stretchable polymer. The dimensions and shapes of the meta-atoms and the spacing are varied to obtain desired optical properties. Any optical wavefront, for different wavelengths, illumination angles, and polarization states can be designed with proper design of the meta-atoms. As the metasurface is stretched, the distance between the meta-atoms changes, modifying the optical response, while the dimensions of the meta-atoms remains constant.
1. A method comprising: providing a metasurface lens having a focal length, the metasurface lens comprising: a plurality of dielectric scattering elements embedded in a flexible substrate, the plurality of dielectric scattering elements configured to control a phase and an amplitude of incident electromagnetic waves; and varying the focal length from a first focal length to a second focal length different from the first focal length, by applying a radial stretching force to the flexible substrate, thereby varying a spacing between adjacent scattering elements of the plurality of dielectric scattering elements.
2. The method of claim 1 , wherein the plurality of dielectric scattering elements have subwavelength dimensions.
3. The method of claim 2 , wherein the plurality of dielectric scattering elements comprises an array of amorphous Si pillars.
4. The method of claim 3 , wherein the flexible substrate is a transparent polymer.
5. The method of claim 4 , wherein the transparent polymer is polydimethylsiloxane.
6. The method of claim 5 , wherein the plurality of dielectric scattering elements further comprises a layer of aluminum oxide on a surface of each pillar of the array of amorphous Si pillars.
7. The method of claim 6 , wherein the amorphous Si pillars have a square cross-section.
8. The method of claim 7 , wherein a height of each pillar of the array of amorphous Si pillars is between 400 and 800 nm.
9. The method of claim 8 , wherein a width of each pillar of the array of amorphous Si pillars is between 50 and 400 nm.
10. The method of claim 9 , wherein the spacing is between 100 and 600 nm.
11. The method of claim 10 , wherein the height is 690 nm.
12. The method of claim 11 , wherein the spacing is 380 nm.
13. The method of claim 12 , wherein the width is between 100 and 200 nm.
14. The method of claim 13 , wherein the first focal length is 600 μm and the second focal length is 1400 μm.
15. The method of claim 13 , wherein varying the focal length is between 600 μm and 1400 μm.
16. The method of claim 13 , wherein the metasurface lens has a circular shape with a radius of 100 pm under no applied strain.
17. The method of claim 1 , where applying a stretching force is with a stretching ratio of 1+ε, and varying the focal length is by a factor of (1+ε) 2 , where ε is a real number.