Tunable dielectric metasurface for beam steering
A metasurface includes a plurality of Bragg mirrors, each having a defect cavity therein, arrayed in a grid. A heat source is provided for each of the plurality of Bragg mirrors. Each heat source is positioned to selectively modulate heat applied to its respective Bragg mirror and to impart a different phase shift via the applied heat from the heat source.
1. A metasurface, comprising:
a plurality of Bragg mirrors, each having a defect cavity therein, arrayed in a grid; and
a heat source for each of the plurality of Bragg mirrors, each heat source positioned to selectively modulate heat applied to its respective Bragg mirror and to impart a different phase shift via the applied heat from the heat source.
2. The apparatus of claim 1 , wherein the heat source is a gold heater.
3. The apparatus of claim 1 , wherein each Bragg mirror comprises a first plurality of alternating layers of silicon (Si) and silicon nitride (Si 3 N 4 ), and a second plurality of alternating layers of Si and Si 3 N 4 , the first and second plurality of alternating layers disposed on either side of the defect cavity.
4. The apparatus of claim 3 , wherein the defect cavity comprises Si.
5. The apparatus of claim 3 , wherein the defect cavity comprises alternating layers of Si and Si 3 N 4 , tapering a Bragg mirror period of the cavity from a first distance equivalent to a period of the first plurality of alternating layers to a second distance smaller than the first distance.
6. The apparatus of claim 1 , wherein each Bragg mirror comprises a first plurality of alternating layers of silicon (Si) and diamond like carbon (DLC), and a second plurality of alternating layers of Si and DLC, the first and second plurality of alternating layers disposed on either side of the defect cavity.
7. The apparatus of claim 6 , wherein the defect cavity comprises Si.
8. The apparatus of claim 6 , wherein the defect cavity comprises alternating layers of Si and DLC, tapering a Bragg mirror period of the cavity from a first distance equivalent to a period of the first plurality of alternating layers to a second distance smaller than the first distance in a plurality of cavity layers.
9. The apparatus of claim 1 , wherein the plurality of Bragg mirrors is suspended between silicon supports over a substrate, and wherein the plurality of Bragg mirrors has a pitch therebetween of about 1.5 microns, and including an air gap between adjacent Bragg mirrors and an air gap between Bragg mirrors and substrate.
10. An apparatus, comprising:
a substrate; and
a plurality of pillars connected to the substrate at each end thereof, disposed end to end and supported by support structures on the substrate, separated from each other and from the substrate by air gaps, and arrayed in a grid;
each pillar comprising:
a pair of Bragg mirrors having a defect cavity therebetween; and
a heat source positioned to selectively modulate heat applied to its respective defect cavity and to impart a different phase shift via the applied heat from the heat source.
11. The apparatus of claim 10 , wherein each Bragg mirror comprises a first plurality of alternating layers of silicon (Si) and silicon nitride (Si 3 N 4 ), and a second plurality of alternating layers of Si and Si 3 N 4 , the first and second plurality of alternating layers disposed on either side of the defect cavity.
12. The apparatus of claim 11 , wherein the defect cavity comprises Si.
13. The apparatus of claim 11 , wherein the defect cavity comprises alternating layers of Si and silicon nitride Si 3 N 4 , tapering a Bragg mirror period of the cavity from a first distance equivalent to a period of the first plurality of alternating layers to a second distance smaller than the first distance.
14. The apparatus of claim 10 , wherein each Bragg mirror comprises a first plurality of alternating layers of silicon (Si) and diamond like carbon (DLC), and a second plurality of alternating layers of Si and DLC, the first and second plurality of alternating layers disposed on either side of the defect cavity.
15. The apparatus of claim 14 , wherein the defect cavity comprises Si.
16. The apparatus of claim 14 , wherein the defect cavity comprises alternating layers of Si and DLC, tapering a Bragg mirror period of the cavity from a first distance equivalent to a period of the first plurality of alternating layers to a second distance smaller than the first distance.
17. A method of beam steering, comprising:
providing an array of beam steering pillars, each pillar having a pair of Bragg mirrors surrounding a defect cavity; and
thermally changing a refractive index of the cavities in a pattern to induce beam steering through constructive and destructive interference of reflected light from the beam steering pillars.
18. The method of claim 17 , wherein thermally changing comprises heating each pillar of the array of beam steering pillars with an independent heat source for each of the pillars, each independent heat source heating its pillar cavity to a determined temperature to impart a phase shift of light entering the pillar via the applied heat from the heater.
19. The method of claim 17 , wherein thermally changing comprises applying a pattern of temperatures to the array of beam steering pillars to change the refractive constant of each cavity in a sawtooth pattern to induce a pattern dependent beam steering angle.
20. The method of claim 17 , wherein thermally changing allows a beam steering of −30 to 30 degrees.