Broadband achromatic polarization-insensitive metalens with anisotropic nanostructures
Polarization-insensitive metasurfaces using anisotropic nanostructures are disclosed. These anisotropic structures allow for an accurate implementation of phase, group delay, and group delay dispersion, while simultaneously making it possible to realize a polarizationinsensitive, diffraction-limited and achromatic metalens for wavelength, e.g., λ=from about 460 nm to about 700 nm. The approach of polarization-insensitivity can be also applied for other metasurface devices with applications in, e.g., imaging and virtual or augmented reality.
1. An optical device, comprising:
a metasurface including a plurality of anisotropic nanoscale elements defining an optical profile that focuses a broadband incident light beam to a diffraction limited spot;
wherein the optical profile is insensitive to a polarization state of the broadband incident light beam and tailorable according to wavelengths of the incident light; and
wherein the broadband incident light beam includes a plurality of wavepackets, and the optical profile includes a phase term that specifies parameters of the anisotropic nanoscale elements such that the wavepackets are transmitted towards the diffraction limited spot.
2. The optical device of claim 1 , wherein each of the anisotropic nanoscale elements includes multiple nanostructures.
3. The optical device of claim 2 , wherein the anisotropic nanoscale elements offer a freedom to impart an additional π phase shift by a 90-degree rotation without changing dispersion, wherein the dispersion corresponds to phase delay changes with wavelengths.
4. The optical device of claim 2 , wherein lengths and widths of the nanostructures of anisotropic nanoscale elements vary to tune the phase term, a group delay term and a group delay dispersion term to impart the tailorable optical profile with wavelengths.
5. The optical device of claim 2 , wherein the anisotropic nanoscale elements are made of TiO 2 , GaN, Si 3 N 4 , SiO 2 , Al 2 O 3 or other lossless optical glasses in the visible spectrum.
6. The optical device of claim 1 , wherein each of the anisotropic nanoscale elements is aligned either substantially parallel or substantially perpendicular to a neighboring one of the anisotropic nanoscale elements.
7. The optical device of claim 1 , wherein the optical profile includes a group delay term that specifies parameters of the anisotropic nanoscale elements such that the wavepackets arrive at the diffraction limited spot simultaneously.
8. The optical device of claim 7 , wherein the group delay term is a first order derivative term of the optical profile.
9. The optical device of claim 1 , wherein the optical profile includes a group delay dispersion term specifies parameters of the anisotropic nanoscale elements such that the wavepackets arriving at the diffraction limited spot have an identical width in a time domain.
10. The optical device of claim 9 , wherein the group delay dispersion term is a second order derivative term of the optical profile.
11. The optical device of claim 1 , wherein the wavelengths of the incident light are within a visible spectrum.
12. An optical device, comprising:
a metasurface including a plurality of anisotropic nanoscale elements defining an optical profile that focuses a broadband incident light beam to a diffraction limited spot;
wherein the optical profile is insensitive to a polarization state of the broadband incident light beam and tailorable according to wavelengths of the incident light;
wherein each of the anisotropic nanoscale elements includes multiple nanostructures; and
wherein lengths and widths of the nanostructures of anisotropic nanoscale elements vary to tune a phase term, a group delay term and a group delay dispersion term to impart the tailorable optical profile with wavelengths.
13. The optical device of claim 12 , wherein the anisotropic nanoscale elements offer a freedom to impart an additional π phase shift by a 90-degree rotation without changing dispersion, wherein the dispersion corresponds to phase delay changes with wavelengths.
14. The optical device of claim 12 , wherein the anisotropic nanoscale elements are made of TiO 2 , GaN, Si 3 N 4 , SiO 2 , or Al 2 O 3 .
15. The optical device of claim 12 , wherein the broadband incident light beam includes a plurality of wavepackets, and the optical profile includes the group delay dispersion term that specifies parameters of the anisotropic nanoscale elements.
16. An optical device, comprising:
a metasurface including a plurality of anisotropic nanoscale elements defining an optical profile that focuses an incident light beam to a diffraction limited spot,
wherein each set of neighboring anisotropic nanoscale elements of the plurality of anisotropic nanoscale elements includes two anisotropic nanoscale elements, a long axis of each of the two anisotropic nanoscale elements aligned either substantially parallel or substantially perpendicular to each other;
wherein the optical profile is insensitive to a polarization state of the incident light beam; and
wherein the metasurface is achromatic from a wavelength of 460 nm to 700 nm.
17. The optical device of claim 16 , wherein:
each of the anisotropic nanoscale elements includes multiple nanostructures; and
varying lengths and widths of the nanostructures of anisotropic nanoscale elements tune a phase term, a group delay term and a group delay dispersion term to impart the optical profile with wavelengths.
18. The optical device of claim 16 , wherein:
each of the anisotropic nanoscale elements includes multiple nanostructures; and
the anisotropic nanoscale elements offer a freedom to impart an additional π phase shift by a 90-degree rotation.
19. The optical device of claim 16 , wherein the incident light beam includes a plurality of wavepackets, and the optical profile includes a phase term that specifies parameters of the anisotropic nanoscale elements such that the wavepackets are transmitted towards the diffraction limited spot.
20. The optical device of claim 16 , wherein the incident light beam includes a plurality of wavepackets, and the optical profile includes a group delay dispersion term that specifies parameters of the anisotropic nanoscale elements.