Session Chair: Wenshan Cai, Georgia Institute of Technology Session Chair: Zhiyuan Li, South China University of Technology
1:30pm - 2:00pm Invited
Light Manipulation with Metasurface and Meta-device
Din Ping TSAI
National Taiwan University, Taiwan
Artificial nano-structures have attracted a huge number of interests due to their ability on controlling the optical properties in demand. In this talk, two main approaches for light manipulation will be demonstrated: tailoring the fundamental responses in plasmonic metamaterials and controlling the electromagnetic phase as well as amplitude with flat metasurfaces. For the first part, different from prior published lectures, fundamental plasmon properties and potential applications in novel three dimensional vertical split-ring resonators (VSRRs) as the building block of metamaterial unit cell are designed and investigated. In the second part, two flat metasurfaces based meta-devices working in visible light will be performed in reflection: a multi-color meta-hologram and a versatile metasurface polarization generator (MPG). Beyond people’s imagination, acquiring polarization-controllable holographic images or multi-polarization generation by a single tiny component that can greatly decrease the complexity of design and might be applied on nanotechnology and integration of photonic integrated circuits.
2:00pm - 2:30pm Invited
Optical Antireflection without Index Match using Bi-Layer Metasurfaces
Los Alamos National Laboratory, United States
Fresnel reflection occurs at the surfaces of optical elements and components, resulting in detrimental effects in many optical systems. Minimizing optical reflection has long been pursued, through dielectric thin film coating with precisely matched refractive indices and thicknesses, or using surface relief structures that require complex fabrication processes. Here we show that bi-layer metallic metasurfaces can accomplish high-performance antireflection without involving any additional deposition of dielectric films. These metasurfaces are fabricated using lithographic patterning, reactive ion etching, and directional metal film deposition to create self-aligned resonant structures. Numerical simulations and experimental measurements show that excellent antireflection can be achieved for narrow-, dual-, or broad-band operation, by simply tailoring the geometry of the subwavelength pillars. This flexible antireflection scheme can be applied to substrates with arbitrary refractive indices and scalable to operate over a wide spectral range from terahertz to near-infrared. In addition, the use of metallic structures provides an opportunity to create multifunctional devices promising for many optoelectronic applications.
2:30pm - 3:00pm Invited
Non-volatile Phase-change Reconfigurable Photonic Devices and Metasurfaces
Qian WANG1, Guanghui YUAN2, Behrad GHOLIPOUR3, Edward T. F. ROGERS3,4, Kun HUANG1, Song Seng ANG1, Nikolay I. ZHELUDEV2,3, Jinghua TENG1
1Institute of Materials Research and Engineering, Agency for Science, Technology and Research (A*STAR), Singapore; 2Centre for Disruptive Photonic Technologies, Nanyang Technological University, Singapore; 3Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, United Kingdom; 4Instiute for Life Sciences, University of Southampton, United Kingdom
Current efforts in optical metasurfaces emerged various approaches to realize reconfigurable optical components using mechanical, electrical, or optical stimulus. Phase transition materials such as chalcogenide glasses (germanium-antimony-tellurium, GST) have particular promise for enabling reconfigurable devices due to fast response (nano second), low energy requirement (nJ energy level) and the large change of optical properties. We report here on recent advances in the development of versatile, planar optically-driven reconfigurable photonic devices and metasurfaces based on phase change material. The real-life applications of this technology include flat lenses, optical holograms, gray-scale photolithography mask, etc.
3:00pm - 3:15pm Oral
Nanoscale Optical Imaging of Graphene using s-SNOM
neaspec GmbH, Germany
Visualisation of the Dirac plasmons propagating along graphene was for the first time observed using the nea-SNOM infrared near-field microscope [1, 2].
Graphene plasmon interference mapping allows extraction of local material properties, e.g. conductivity, intrinsic doping, defects. Direct control of propagating surface plasmons on graphene with resonant antennas & conductivity patterns was also demonstrated using the same s-SNOM technology [3, 4].
During this presentation, photocurrent measurements on graphene, simultaneously recorded with optical and AFM images, will be to be shown . Furthermore, Mid-infrared probing of the conductivity dynamics in single and multi-layer graphene using ultrafast near-infrared excitation of electrons will be presented .
With more than 30 high impact articles published in the recent few years on the ‘flatland optics’, the neaSNOM is the best tool for nanoscale imaging and spectroscopy of the graphene.
 Z. Fei et al., Nature, 487 (2012) 82;
 J. Chen et al., Nature, 487 (2012) 77;
 P. A. Gonzales et al., Science 344 (2014), 1369;
 M. B, Lundeberg et al., Nature Mat. (2016);
 A. Woessner et al., Nature Comm. 7 (2016);
 M. Wagner et al., Nano Lett. 14 (2014) 4529.
3:15pm - 3:30pm Oral
High Q Toroidal Resonances and its Sensing Potential in Planar Metasurface
Manoj GUPTA1,2, Ranjan SINGH1,2
1Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore; 2Centre for Disruptive Photonic Technologies, The Photonics Institute, Nanyang Technological University, Singapore
Toroidal dipole can be viewed as circular head-to-tail arrangement of magnetic dipoles. Mirroring asymmetric Fano resonators result in excitation of toroidal resonances through interaction of anti-aligned magnetic dipoles. In planar metasurface, coupling of Fano resonators through toroidal moment indicates significant tailoring and the suppression of the radiative loss channel. The line width of toroidal resonance is smaller (high Q factor and high FoM) than that of Fano resonance, which has been demonstrated experimentally. We discover that the exponential decay of the Q factor of toroidal resonance mode occurs at half the rate of that in the Fano resonance as the asymmetry of the system is enhanced in planar metasurface. The complexity in fabrication of 3D metasurfaces poses difficulty in realization of the devices supporting toroidal dipole excitation, which limits to explore the exotic features of this phenomenon. Recent demonstrations by planar metasurfaces supporting toroidal dipole type excitations has once again enabled us to investigate less explored features of this member of multipole family. We have also exploited planar metasurfaces supporting toroidal resonances as a sensing platform for refractive index sensing of non-magnetic materials which can easily be spin coated on planar toroidal metasurface.