Metasurface-based active retroreflector
View Patent ↗An optoelectronic device apparatus using active, frequency-selective metasurfaces to achieve retroreflection at a pre-determined single frequency and optionally provide signal modulation on the reflected light beam. The apparatus may use several active, frequency-selective metasurfaces to replace traditional optical lens and mirrors.
1. A retroreflector apparatus for processing an optical beam incident thereon, comprising:
an upper metasurface separated from a lower metasurface by an optically transparent region therebetween, the optically transparent region configured to pass the incident optical beam between the upper metasurface and the lower metasurface;
the upper metasurface having a plurality of sub-wavelength scale resonators formed thereat, the upper metasurface configured to spatially modify a local phase of an optical beam passing therethrough to shape a wavefront thereof on a lower metasurface;
the lower metasurface disposed above a frequency-selective reflector and having a plurality of sub-wavelength scale resonators formed thereat, the lower metasurface configured to spatially modify a local phase of an optical beam passing therethrough to the reflector and to focus a reflected optical beam on the focal plane of the upper metasurface;
the upper metasurface configured, in response to an electric voltage imparted thereto, to spatially modify a local phase or a transmitted intensity of the reflected optical beam passing therethrough to provide a frequency-selective retroreflected optical beam.
2. The apparatus of claim 1 , wherein the optically transparent region separating the upper metasurface from the lower metasurface comprises an optically transparent substrate.
3. The apparatus of claim 2 , wherein the optically transparent substrate comprises an upper surface having formed thereupon the upper metasurface, and a lower surface having formed thereupon the lower metasurface.
4. The apparatus of claim 1 , wherein the optically transparent region separating the upper metasurface from the lower metasurface comprises an air gap.
5. The apparatus of claim 1 , wherein the upper metasurface is embedded within an optically transparent substrate having a refractive index adapted in response to the electric voltage so as to spatially modify the local phase of the optical beam passing through the upper metasurface.
6. The apparatus of claim 5 , wherein the electro-optic film comprises transparent conductive oxides such as indium tin oxide (ITO), fluorine doped tin oxide (FTO), aluminum doped zinc oxide, and gallium doped zinc oxide (AZO/GZO) operating in the epsilon near zero region.
7. The apparatus of claim 1 , wherein the optically transparent substrate comprises a polymer film having embedded therein the upper metasurface, wherein an electric voltage imparted to the electro-optic film adapts a refractive index thereof to spatially modify the local phase of the optical beam passing through the upper metasurface.
8. The apparatus of claim 2 , wherein the optically transparent substrate comprises a semiconductor having embedded therein the upper metasurface, wherein an electric voltage imparted to the electro-optic film adapts a refractive index thereof to spatially modify the local phase of the optical beam passing through the upper metasurface.
9. The apparatus of claim 1 , wherein the optically transparent region imparts a separation distance between the upper metasurface and lower metasurface that allows the transmitted beam to be focused on the lower metasurface.
10. The apparatus of claim 2 , wherein the reflector comprises at least one of a frequency selective mirror, a frequency selective grating, and a frequency selective metamaterial.
11. The apparatus of claim 1 , wherein the plurality of sub-wavelength scale resonators comprises an array of sub-wavelength scale resonators with identical or different shapes, sizes, and orientations to control spatially varying phase response and transmitted intensity.
12. The apparatus of claim 1 , wherein the plurality of sub-wavelength scale resonators comprises an array of spatially non-uniform sub-wavelength scale resonators to increase the operating bandwidth of the metasurfaces.
13. The apparatus of claim 1 , wherein the plurality of sub-wavelength scale resonators comprises an array of sub-wavelength scale resonators including sub-wavelength scale resonators of a first shape and sub-wavelength scale resonators of a second shape to exploit the geometrical symmetry induced optical resonances for energy-efficient active retroreflection.
14. The apparatus of claim 1 , wherein the plurality of sub-wavelength scale resonators comprises an array of sub-wavelength scale resonators including sub-wavelength scale resonators of a first pattern period and sub-wavelength scale resonators of a second pattern period to effectively control the operating bandwidth of the retroreflection.
15. The apparatus of claim 1 , wherein the electric voltage imparted thereto is configured for modulation in accordance with a data signal.
16. The apparatus of claim 15 , wherein the data signal conveys any of an identification code, a location code, a static message, and a surveillance data stream.
17. A surveillance communications apparatus, comprising:
a signals receiver and encoder configured to encode received signals information to provide thereby an encoded data signal; and
a retroreflector, comprising:
an upper metasurface separated from a lower metasurface by an optically transparent region therebetween, the optically transparent region configured to pass an incident optical beam between the upper metasurface and the lower metasurface;
the upper metasurface having a plurality of sub-wavelength scale resonators formed thereat, the upper metasurface configured to spatially modify a local phase of an optical beam passing therethrough to shape a wavefront thereof on a lower metasurface;
the lower metasurface disposed above a frequency-selective reflector and having a plurality of sub-wavelength scale resonators formed thereat, the lower metasurface configured to spatially modify a local phase of an optical beam passing therethrough to the reflector and to focus a reflected optical beam on the focal plane of the upper metasurface; and
the upper metasurface configured, in response to an electric voltage imparted thereto, to spatially modify a local phase or a transmitted intensity of the reflected optical beam passing therethrough to provide a frequency-selective retroreflected optical beam;
wherein the electric voltage is modulated in accordance with the encoded data signal.
18. The apparatus of claim 17 , wherein the optically transparent region separating the upper metasurface from the lower metasurface comprises at least one of an air gap and an optically transparent substrate, the optically transparent substrate having an upper surface having formed thereupon the upper metasurface, and a lower surface having formed thereupon the lower metasurface.
19. The apparatus of claim 17 , wherein the upper metasurface is embedded within an optically transparent substrate having a refractive index adapted in response to the electric voltage so as to spatially modify the local phase of the optical beam passing through the upper metasurface.
20. The apparatus of claim 19 , wherein the plurality of sub-wavelength scale resonators comprises an array of sub-wavelength scale resonators with shapes, sizes, and orientations selected to control spatially varying phase response and transmitted intensity.