Plasmonic surface-scattering elements and metasurfaces for optical beam steering

Abstract

Systems and methods are described herein for an optical beam-steering device that includes an optical transmitter and/or receiver to transmit and/or receive optical radiation from an optically reflective surface. An array of adjustable plasmonic resonant waveguides is arranged on the surface with inter-element spacings less than an optical operating wavelength. A controller applies a pattern of voltage differentials to the adjustable plasmonic resonant waveguides. The pattern of voltage differentials corresponds to a sub-wavelength reflection phase pattern for reflecting the optical electromagnetic radiation. One embodiment of an adjustable plasmonic resonant waveguide includes first and second metal rails extending from the surface. The metal rails are spaced from one another to form a channel therebetween. An electrically-adjustable dielectric is disposed within the channel.

What is claimed is: 
     
         1 . An apparatus, comprising:
 a surface;   a plurality of adjustable plasmonic resonant waveguides to convey plasmons that extend from the surface and are arranged on the surface with inter-element spacings less than an optical operating wavelength of the apparatus.   
     
     
         2 . The apparatus of  claim 1 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises an electrically-adjustable dielectric and at least one plasmonic metal rail. 
     
     
         3 . The apparatus of  claim 2 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises two plasmonic metal rails spaced from one another to form a channel therebetween, wherein the electrically-adjustable dielectric is disposed within the channel between the two plasmonic metal rails. 
     
     
         4 . The apparatus of  claim 1 , wherein the surface comprises a dielectric substrate with an embedded optical reflector. 
     
     
         5 . The apparatus of  claim 1 , wherein the surface comprises a dielectric substrate with embedded optical reflectors underlying each of the adjustable plasmonic resonant waveguides. 
     
     
         6 . The apparatus of  claim 1 , wherein the surface comprises a plurality of optically reflective patches. 
     
     
         7 . The apparatus of  claim 1 , wherein an operational bandwidth includes a 905-nanometer wavelength and each of the adjustable plasmonic resonant waveguides extends from the surface to a height of approximately 400 nanometers. 
     
     
         8 . The apparatus of  claim 1 , wherein an operational bandwidth includes a 1550-nanometer wavelength and each of the adjustable plasmonic resonant waveguides extends from the surface to a height of approximately 700 nanometers. 
     
     
         9 . The apparatus of  claim 3 , wherein an operational bandwidth includes a 905-nanometer wavelength, and
 wherein the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides are spaced from one another by a channel width of between approximately 100 and 200 nanometers.   
     
     
         10 . The apparatus of  claim 3 , wherein an operational bandwidth includes a 1550-nanometer wavelength, and
 wherein the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides are spaced from one another by a channel width of between approximately 175 and 350 nanometers.   
     
     
         11 . The apparatus of  claim 3 , wherein the channel between the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides corresponds to a fundamental harmonic mode of frequencies within an optical operating bandwidth. 
     
     
         12 . The apparatus of  claim 11 , wherein each of the plasmonic metal rails extends from the surface to a height corresponding to the fundamental harmonic mode of frequencies within the optical operating bandwidth. 
     
     
         13 . The apparatus of  claim 11 , wherein each of the plasmonic metal rails extends from the surface to a height corresponding to a second order harmonic mode of frequencies within the optical operating bandwidth, such that two magnetic field antinodes can be realized within the channel between the surface and tops of the two plasmonic metal rails. 
     
     
         14 . The apparatus of  claim 3 , wherein the channel between the two plasmonic metal rails of each of the adjustable plasmonic resonant waveguides corresponds to a second order harmonic mode of frequencies within an optical operating bandwidth, such that two magnetic field antinodes can be realized within the electrically-adjustable dielectric between the two plasmonic metal rails. 
     
     
         15 . The apparatus of  claim 14 , wherein each of the plasmonic metal rails extends from the surface to a height corresponding to a fundamental harmonic mode of frequencies within the optical operating bandwidth. 
     
     
         16 . The apparatus of  claim 14 , wherein each of the plasmonic metal rails extends from the surface to a height corresponding to the second order harmonic mode of frequencies within the optical operating bandwidth, such that two magnetic field antinodes can be realized within the channel between the surface and tops of the plasmonic metal rails. 
     
     
         17 . The apparatus of  claim 3 , wherein each of the plasmonic metal rails of each of the adjustable plasmonic resonant waveguides extends from the surface to a height corresponding to a fundamental harmonic mode of frequencies within an optical operating bandwidth. 
     
     
         18 . A device, comprising:
 a converter to convert between electric power and optical electromagnetic radiation;   a surface to reflect the optical electromagnetic radiation;   a plurality of adjustable plasmonic resonant waveguides arranged on the surface with inter-element spacings less than an optical operating wavelength of the device to convey plasmons and selectively apply a sub-wavelength reflection phase pattern to the optical electromagnetic radiation.   
     
     
         19 . The device of  claim 18 , further comprising a controller to selectively apply a pattern of voltages to the plurality of adjustable plasmonic resonant waveguides,
 wherein the converter illuminates the adjustable plasmonic resonant waveguides arranged on the surface with optical electromagnetic radiation, and   wherein the pattern of voltages corresponds to a pattern of reflection phases of the plurality of adjustable plasmonic resonant waveguides to steer the reflected optical electromagnetic radiation.   
     
     
         20 . The device of  claim 18 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises:
 a first plasmonic metal rail extending to a first height from the surface;   a second plasmonic metal rail extending to a second height from the surface,
 wherein the first and second plasmonic metal rails are spaced from one another to form a channel therebetween; and 
   an electrically-adjustable dielectric disposed within at least a portion of the channel.   
     
     
         21 . The device of  claim 20 , wherein each of the plurality of adjustable plasmonic resonant waveguides further comprises:
 electrical contacts to receive an applied voltage differential to the first and second plasmonic metal rails,   wherein application of a first voltage differential to the first and second plasmonic metal rail corresponds to a first reflection phase, and   wherein application of a second voltage differential to the first and second plasmonic metal rail corresponds to a second reflection phase.   
     
     
         22 . The device of  claim 21 , wherein the plurality of adjustable plasmonic resonant waveguides are arranged in a one-dimensional array perpendicular to a length of the first and second plasmonic metal rails. 
     
     
         23 . The device of  claim 22 , wherein each of the first and second plasmonic metal rails extends between opposing edges of the surface. 
     
     
         24 . The device of  claim 20 , wherein the electrically-adjustable dielectric comprises a liquid crystal material. 
     
     
         25 . The device of  claim 20 , wherein the electrically-adjustable dielectric comprises an electro-optical polymer material. 
     
     
         26 . The device of  claim 20 , wherein the electrically-adjustable dielectric comprises silicon. 
     
     
         27 . The device of  claim 20 , wherein the electrically-adjustable dielectric comprises a chalcogenide glass. 
     
     
         28 . A method, comprising:
 conveying optical electromagnetic radiation to a reflective surface; and   adjusting a reflection phase for each of a plurality of adjustable plasmonic resonant waveguides to modify a reflection pattern of the conveyed optical electromagnetic radiation, wherein the adjustable plasmonic resonant waveguides are configured to convey plasmons and are arranged on the reflective surface with inter-element spacings less than an optical operating frequency of the adjustable plasmonic resonant waveguides.   
     
     
         29 . The method of  claim 28 , wherein the reflective surface comprises an optical reflector to reflect the conveyed optical electromagnetic radiation within an operational bandwidth that includes an optical operating wavelength. 
     
     
         30 . The method of  claim 29 , wherein the optical reflector comprises an electrically conductive reflector. 
     
     
         31 . The method of  claim 30 , wherein the electrically conductive reflector comprises a layer of metal. 
     
     
         32 . The method of  claim 30 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises an electrically-adjustable dielectric and at least one plasmonic metal rail. 
     
     
         33 . The method of  claim 32 , wherein each of the plurality of adjustable plasmonic resonant waveguides comprises two plasmonic metal rails spaced from one another to form a channel therebetween, wherein the electrically-adjustable dielectric is disposed within the channel between the two plasmonic metal rails. 
     
     
         34 . The method of  claim 33 , further comprising:
 selectively applying, via a controller, a pattern of voltage differentials to the plasmonic metal rails of each of the plurality of adjustable plasmonic resonant waveguides, wherein the pattern of voltage differentials corresponds to (i) a pattern of indices of refraction of the electrically-adjustable dielectric of each of the plurality of adjustable plasmonic resonant waveguides, and (ii) a reflection pattern of a wave of optical electromagnetic radiation incident on the plurality of adjustable plasmonic resonant waveguides.   
     
     
         35 . A method, comprising:
 adjusting a reflection phase for each of a plurality of adjustable plasmonic resonant waveguides to convey plasmons, wherein the adjustable plasmonic resonant waveguides are arranged on a reflective surface with inter-element spacings less than an optical operating frequency of the adjustable plasmonic resonant waveguides; and   conveying optical electromagnetic radiation reflected by the reflective surface to a receiver, wherein the optical electromagnetic radiation reflected by the reflective surface is modified by a reflection pattern corresponding to the reflection phases of each of the plurality of adjustable plasmonic resonant waveguides.   
     
     
         36 . The method of  claim 35 , further comprising:
 applying a pattern of voltages to the plurality of adjustable plasmonic resonant waveguides,   wherein the pattern of voltages corresponds to a pattern of reflection phases of the plurality of adjustable plasmonic resonant waveguides to steer the reflected optical electromagnetic radiation.   
     
     
         37 . The method of  claim 35 , wherein the reflective surface comprises a Bragg reflector comprising alternating low and high index dielectric materials. 
     
     
         38 . The method of  claim 35 , wherein the plurality of adjustable plasmonic resonant waveguides are arranged in a one-dimensional array.