Device applications of metafilms
Professor Mark Brongersma, Geballe Laboratory for Advanced Materials, USA
Many conventional optoelectronic devices consist of thin, stacked films of metals and semiconductors. In this presentation, I will demonstrate how one can improve the performance of such devices by nano-structuring the constituent layers at length scales below the wavelength of light.
The resulting metafilms and metasurfaces offer opportunities to dramatically modify the optical transmission, absorption, reflection, and refraction properties of device layers. This is accomplished by encoding the optical response of nanoscale resonant building blocks into the effective properties of the films and surfaces. To illustrate these points, I will show how nanopatterned metal and semiconductor layers may be used to enhance the performance of solar cells, photodetectors, and enable new imaging technologies. I will also demonstrate how the use of active nanoscale building blocks can facilitate the creation of active metafilm devices.
Dielectric Huygens metasurfaces – fundamentals and applications
Professor Dragomir Neshev, Australian National University, Australia
The concept of Huygens metasurfaces has recently emerged as a powerful platform for complete manipulation of light properties, including phase, amplitude, polarisation, and even colour. Their operation is based on the interference of the electric and magnetic dipolar responses of the constituent metasurface elements, called meta-atoms, such that they can only scatter in forward direction, while back-scattering is inhibited. Dielectric Huygens metasurfaces stand out as a prominent example, due to their negligible optical losses and easy fabrication. Such dielectric metasurfaces are composed of small high-refractive-index nano-particles, which exhibit Mie-type resonances of both electric and magnetic origin and comparable strength. By designing the geometry of the individual meta-atoms it is possible to exactly match the spectral position of these resonances, thus enabling unitary transmission through the Huygens metasurface, while simultaneously being able to control the phase of transmitted light in the full range of 0-2π.
This talk will review the fundamental designs and principles of operation of such dielectric metasurfaces, as well as will overview the plethora of their functionalities, including frequency selectivity, wavefront shaping, and polarization control. In particular, we demonstrate experimentally beam shaping in complex holographic shapes with near unity transmission efficiency. We further utilise our Huygens metasurfaces for generation of beams carrying orbital angular momentum, including vortex and vectors beams with azimuthal/radial polarisations operating over a broad spectral range. Finally, we will present some of their recent applications in nonlinear light sources, biosensing, and quantum optics.
Silicon-based metasurfaces for near-infrared optics
Professor Jason Valentine, Vanderbilt University, USA
Absorption loss continues to be one of the primary impediments to the application of plasmonic metamaterials and metasurfaces at optical frequencies. Dielectric metamaterials offer one potential solution to this issue by eliminating ohmic loss, allowing the realization of highly transparent materials. As with their plasmonic counterparts, manipulation of the unit cell structure of all-dielectric metasurfaces also offers a means to engineer a wide variety of optical functionalities.
In this talk, I will discuss our recent experimental efforts to demonstrate silicon-based metasurfaces within the telecommunications band. I will talk about how simple unit cell geometries allow these metasurfaces to be scaled to large areas using self-assembly based patterning techniques. Importantly, defects in such materials are found to have little effect on the performance of the surfaces. On the other hand, I will discuss how more complicated unit cells can be used to realize wavefront control as well as high quality factor resonances. The high-Q resonances can be used for sensing and the large local field enhancement within the silicon unit cells results in a third harmonic conversion enhancement factor of 105 with respect to an unstructured silicon slab. Such surfaces could potentially be applied for all-optical switches in the future.
Active graphene-integrated plasmonic metasurfaces and their applications: from motion detection to polarization control of infrared light
Professor Gennady Shvets, The University of Texas at Austin, USA
Plasmonic metasurfaces enhance light-matter interaction by focusing light into extremely subwavelength dimensions. These carefully designed structures have been used in extremely thin optical component which can mold the wavefront, with exciting applications in optical lenses, beam steering, and biosensing applications. Adding dynamic tunability to these devices opens up the possibility for new application in single pixel detection and 3D imaging as well as optical modulators and switches. However the existing approaches for designing active optical devices in infrared, are either slow or have small refractive index change. Integrating plasmonic metasurfaces with single-layer graphene (SLG) opens exciting opportunities for developing active plasmonic devices because the amplitude and phase of the transmitted and reflected light can be rapidly modulated by injecting charge carriers into graphene using field-effect gating. I will describe our recent experimental results demonstrating strong phase modulation of mid-infrared light. The phase shifting due to electric gating of the SLG was measured using a Michelson interferometer, and further utilized to demonstrate an electrically controlled (i.e. no moving parts) interferometry capable of measuring distances with sub-micron accuracy. Because of the potentially nanosecond-scale measurement time, active metasurfaces represent a promising platform for ultra-fast standoff detection. Finally, we demonstrate that, by the judicious choice of a strongly anisotropic metasurface, the graphene-controlled phase shift of light can be rendered polarization-dependent, thereby modulating the polarization state (e.g., the ellipticity) of the reflected light. These results pave the way for novel high-speed graphene-based optical devices and sensors such as polarimeters, ellipsometers, and frequency modulators.