Electromagnetic Wave Broadband Angular Selectivity

Technology #16896

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Inventors
Professor Marin Soljacic
Department of Physics, MIT
External Link (www.rle.mit.edu)
Professor John Joannopoulos
Department of Physics, MIT
External Link (ab-initio.mit.edu)
Professor Steven Johnson
Department of Mathematics, MIT
External Link (math.mit.edu)
Ivan Celanovic
Institute for Soldier Nanotechnologies, MIT
Yichen Shen
Department of Physics, MIT
Dexin Ye
Department of Physics, Zhejiang University
Managed By
Christopher Noble
MIT Technology Licensing Officer - Clean and Renewable Energy
Patent Protection

Methods and apparatus for broadband angular selectivity of electromagnetic waves

PCT Patent Application WO 2015-178982

Methods and apparatus for broadband angular selectivity of electromagnetic waves

US Patent Pending US 2016-0252652
Publications
Optical Broadband Angular Selectivity
Science, 28 Mar 2014: Vol. 343, Issue 6178, pp. 1499-1501
Metamaterial Broadband Angular Selectivity
Physical Review B, 15 Sept. 2014, 90, 125422
Broadband Angular Selectivity of Light at the Nanoscale: Progress, Applications, and Outlook
Applied Physics Review, 3, 011103 (2016)

Applications

An angularly dependent material-system can be used in solar energy conversion, privacy protection, and high signal-to-noise detectors.

Problem Addressed

In currently known angularly selective systems, the transmission of light depends on the light frequency. This material-system decouples the frequency and the viewing angle, so that there is transparency throughout the visible spectrum at one angle and reflection at every other angle.

Technology

The material-system is achieved through two separate approaches.  Both operate under the following principles: all dielectrics have a Brewster Angle, angle of incidence at which light is completely transmitted, and the location of the bandgap scales proportionally to the periodicity of the quarter-wave stack (i.e. the bandgap can be controlled by stacking layers of quarter-wavelength thickness). Therefore, the effective bandgap can be enlarged by stacking quarter-wave stacks with various periodicities together and if all of these layers have the same Brewster Angle then the entire stack will theoretically transmit all frequencies of light incident at a particular angle. The first approach is photonic crystals that consist of only isotropic materials. This approach consists of 84 layers of Silicon dioxide (SiO2) and Tantalum pentoxide (Ta2O5) fabricated with Bias Target Deposition (BTD) technique and fused on a silica wafer. The sample is transparent to p-polarized incident light at the angular window of transparency (55o±8o), and behaves like a mirror at all other incident angles over the entire visible spectrum. For s-polarized, light the sample behaves like a mirror at all angles, but this can be overcome with a mirror and polarization "flipper". In the first approach, the Brewster angle is limited to angles >45o and is not very tunable. This is overcome in the second approach which consists of isotropic and anisotropic layers, which can be made out of polymers (PET and PMMA) or metamaterials (Rogers R3010 panel and polypropylene). The second approach used only 12 periods of layers to demonstrate the concept. This angularly selective system can change the form of waves from a point source to plane waves and increase the resolution of systems like GPS and Radar that currently rely on interactive wave propogation. This method can also be implemented for systems that have Brewster angle analogs, such as acoustic and elastic waves.

Advantages

  • Ability to transmit light independent of frequency for one incident angle
  • Tunable transmission angle