High quality factor non-uniform metasurfaces
High quality factor electromagnetic metasurfaces are provided. The metasurface is configured to have in plane guided-mode resonances (e.g., corresponding to waveguide modes or the like). Coupling features are included in the metasurface that are configured to couple free-space radiation to the guided mode resonances. The resulting structures have a high-Q response to free-space radiation and can be used for various applications, such as beam splitting, beam steering, and beam focusing or defocusing.
1. An apparatus comprising:
an electromagnetic metasurface having metasurface features disposed conformally on a surface of a substrate, wherein adjacent metasurface features of the electromagnetic metasurface are spaced apart by less than an operating wavelength of the apparatus;
wherein the metasurface features of the electromagnetic metasurface support one or more in-plane guided mode resonances; and
a pattern of coupling features superposed on the metasurface features and configured to couple free-space radiation to a selected at least one of the in-plane guide mode resonances.
2. The apparatus of claim 1 , wherein the metasurface features include one or more waveguides, and wherein the guided mode resonances correspond to waveguide modes of at least one of the waveguides.
3. The apparatus of claim 2 , wherein the coupling features include a periodic longitudinal perturbation of the at least one of the waveguides.
4. The apparatus of claim 2 , wherein the at least one of the waveguides is a photonic crystal waveguide.
5. The apparatus of claim 1 , wherein a quality factor Q of the selected at least one of the in-plane guided mode resonances is 100 or more.
6. The apparatus of claim 1 , wherein the metasurface features have at least one sub-wavelength dimension.
7. The apparatus of claim 1 , wherein the electromagnetic metasurface is a phase gradient metasurface.
8. The apparatus of claim 1 , wherein the electromagnetic metasurface is configured as a beam steering device.
9. The apparatus of claim 1 , wherein the electromagnetic metasurface is configured as a beam splitting device.
10. The apparatus of claim 1 , wherein the electromagnetic metasurface is configured as a beam focusing or defocusing device.
11. The apparatus of claim 1 , wherein a material of the metasurface features is selected from the group consisting of: silicon, lithium niobate, gallium phosphide, gallium arsenide, aluminum nitride, indium phosphide, III-V semiconductors, and diamond.
12. The apparatus of claim 1 , wherein the surface of the substrate is planar.
13. The apparatus of claim 1 , wherein the surface of the substrate is curved.