Controlling light with plasmonic metasurfaces

Valente, João (2016) Controlling light with plasmonic metasurfaces. University of Southampton, Faculty of Physical Sciences and Engineering, Doctoral Thesis, 184pp.

Record type: Thesis (Doctoral)

Abstract

Nanostructured membrane plasmonic metasurfaces have exciting mechanical properties and enable new approaches to dynamic control of optical radiation. In this thesis I report:

The first realization of a photonic metasurface that can be reconfigured by application of electric current and magnetic field. In an artificial chevron nanowire structure, fabricated on an elastic nanomembrane, the Lorentz force drives reversible transmission changes on application of a fraction of a volt when the structure is placed in a fraction-of-Tesla magnetic field. The change of optical characteristics of the structure is underpinned by nanoscale movements of the nanowires and associated changes of their plasmonic spectra. I show that magneto-electro-optical modulation can be driven to hundreds of thousands of cycles per second promising applications in magneto-electro-optical modulators and field sensors at nano-Tesla levels. Stimulation-induced transmission changes reaching 45% have been observed in this structure at the telecommunications wavelength of 1550 nm.

The photonic metasurface activated by the Lorentz force as a material structure exhibiting a giant reciprocal magneto-electro-optical effect that manifests itself as strong changes of optical properties of the metamaterial in response to simultaneous application of external electric and magnetic fields and does not depend on reversal of the propagation direction of the wave. This new effect is fundamentally different from the Faraday, Cotton-Mouton and the polar, longitudinal and transversal magneto-optical Kerr effects. From our experimental data we can estimate the order of magnitude of the effect as χ(3)/n = 10^-4, where n is the refractive index and χ(3) is a component of the dielectric tensor of the medium.

The first auxetic materials with a negative Poisson's ratio that have micro- and nanoscale periodicity. These planar auxetic structures possess the distinct mechanical property of expanding laterally upon being stretched. Fabricated by structuring nanoscale plasmonic films supported by dielectric nanomembranes, these materials exhibit negative Poisson's ratios between -0.3 and -0.5 under uniaxial tension or compression. In contrast to conventional materials, stretching or compression of auxetics provides an opportunity where both the aspect ratio of the unit cell and its corresponding optical anisotropy (or isotropy) can in principle remain unchanged. Infrared and optical spectra of these structures show plasmonic resonances, indicating that such materials could act as novel nanomechanical light modulators.

The first nanofabrication method for ultrathin free-standing gold metasurfaces with identical optical properties for opposite directions of illumination. These metasurfaces enable coherent control of light with light. Due to deeply subwavelength thickness of the free-standing plasmonic metasurface and its symmetry with respect to the light propagation direction, the light-matter interaction of such a metasurface can be controlled by placing it in a standing wave and changing the position of the metasurface relative to the nodes of the standing wave. Coherent control of absorption of light with up to THz bandwidth and down to single photon intensities for applications from all-optical logical operations to image processing has been demonstrated.

In summary, this thesis introduces novel solutions for controlling light with plasmonic metasurfaces by exploiting mechanical reconfiguration of nanomembrane metamaterials and coherent control of light with light on metasurfaces. These complementary approaches can be applied to various metamaterials, enabling the development of electrically, magnetically and optically controlled active metadevices for optoelectronics, nanophotonics and plasmonics.