1:30pm  2:00pmKeynoteTopological and NonReciprocal Nanophotonics
Andrea ALU
The University of Texas at Austin, United States
In this talk, we will review our recent progress towards the concept, design and realization of magnetfree nonreciprocal photonic devices and arrays of them with strong topological protection, aimed at realizing reconfigurable, broadband isolators and circulators. We will discuss our approaches to design topological photonic metasurfaces based on spatiotemporal modulation, nonlinearities, and/or optomechanical interactions, and discuss our vision towards new transport phenomena for light, and new nanophotonic devices with enhanced nonreciprocal properties.
2:00pm  2:30pmInvitedUniversal SpinMomentum Locking of Light
Todd VAN MECHELEN, Zubin JACOB
Purdue University, United States
We show the existence of an inherent property of evanescent electromagnetic waves: spinmomentum locking, where the direction of momentum fundamentally locks the polarization of the wave. We trace the ultimate origin of this phenomenon to complex dispersion and causality requirements on evanescent waves. We demonstrate that every case of evanescent waves in total internal reflection (TIR), surface states, and optical fibers/waveguides possesses this intrinsic spinmomentum locking. We also introduce a universal righthanded triplet consisting of momentum, decay, and spin for evanescent waves. We derive the Stokes parameters for evanescent waves, which reveal an intriguing result—every fast decaying evanescent wave is inherently circularly polarized with its handedness tied to the direction of propagation. We also show the existence of a fundamental angle associated with TIR such that propagating waves locally inherit perfect circular polarized characteristics from the evanescent wave. This circular TIR condition occurs if and only if the ratio of permittivities of the two dielectric media exceeds the golden ratio. Our work leads to a unified understanding of this spinmomentum locking in various nanophotonic experiments and sheds light on the electromagnetic analogy with the quantum spinHall state for electrons.
2:30pm  3:00pmInvitedTopological Magnetoplasmons
Dafei JIN^{1,3}, Thomas CHRISTENSEN^{1}, Marin SOLJACIC^{1}, Ling LU^{1,2}, Xiang ZHANG^{3}, Liang FU^{1}, Nicholas X. FANG^{1}
^{1}Massachusetts Institute of Technology, United States; ^{2}Institute of Physics, Chinese Academy of Sciences, China; ^{3}University of California, Berkeley, United States
In this talk, we show that the historically studied twodimensional (2D) magnetoplasmon, which bears gapped bulk states and gapless oneway edge states near zero frequency, is topologically analogous to the 2D topological p+ip superconductor with chiral Majorana edge states and zero modes. We predict a new type of oneway edge magnetoplasmon at the interface of opposite magnetic domains, and demonstrate the existence of zerofrequency modes bounded at the peripheries of a hollow disk. Furthermore, we propose a twodimensional plasmonic platform – periodically patterned monolayer graphene – which hosts topological oneway edge states operable up to infrared frequencies. These findings can be readily verified in experiment, and can greatly enrich the topological phases in bosonic and classical systems.
3:00pm  3:15pmOralTopological Edge Modes in ParityTimeSymmetric Graphene Waveguide Arrays
Bing WANG
Huazhong University of Science and Technology, China
Topological edge states and paritytime (PT) symmetry have attracted intensive attention in waveguide arrays. A topological edge mode emerges at the interface between topological trivial and nontrivial structures, which are described by integervalued quantities. For example, the winding number is used to character the topology of onedimensional dimer chains. According to the ratio between intra and interlayer couplings, the winding number is either zero or unity separated by the spectral degeneracies, known as Dirac point. Such modes remain stable against disorders as the structure topology is not changed. On the other hand, the systems with gain and loss are nonHermitian. When the gainloss distribution is an odd function of position, the systems may possess all real or complex eigenvalues, corresponding to PT symmetric and broken phases. The two regions are divided by nonHermitian degeneracies, known as exceptional points (EPs). Here we shall investigate the topological edge modes of surface plasmon polaritons (SPPs) in a nonHermitian system composed of graphene dimer arrays with alternating gain and loss. The topological edge modes emerge when two topologically distinct graphene arrays are connected. The edge mode can exhibit global paritytime (PT) symmetry as all the modes present in the system maintain real propagation constants. The existence regions of the topological edge modes are related to the exceptional points (EPs), the degeneracies in the spectra. Thanks to the strong confinement of SPPs, the edge modes can be squeezed into a lateral width of ~λ/70. Moreover, we show such modes can be realized in lossy graphene waveguides without gain. The study provides a promising approach to robust light transport on deepsubwavelength scale.
3:15pm  3:30pmOralSurface PlasmonEnhanced Radiative Emission through Cascaded MetalDielectric Nanostructures
Sepideh GOLMAKANIYOON^{1,2}, Pedro Ludwig HERNANDEZMARTINEZ^{1,2,3}, Hilmi Volkan DEMIR^{2,3,4}, Xiao Wei SUN^{1,5}
^{1}School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore; ^{2}LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore; ^{3}Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore; ^{4}Department of Electrical and Electronics Engineering, Department of Physics, and UNAMInstitute of Materials Science and Nanotechnology, Bilkent University, Turkey; ^{5}Department of Electrical and Electronic Engineering, College of Engineering, South University of Science and Technology, China
Plasmonic nanostructures have been widely known for their notable capability to enhance the spontaneous emission of an electric dipole in their vicinity. It is well known that the decay rate of an emitting molecule in a vicinity of a metallic surface has been extremely modified due to a) dipole electric field coupling with the surface plasmon (SP) mode at the interface of metaldielectric at short distances and b) the mirror like behaviour of a metal surface at the large distances which leads to the dipole lifetime oscillations. While the radiative decay channel is mostly effected by the latter behaviour, the nonradiative decay rate is a dominant channel at the short distances (energy transfer zone). In other words, due to the availability of large optical density of states at the metallic surface, the radiative and nonradiative decay channels are dramatically modified. However, the enhancement cannot be realized for any desired emissive dipole as the existing plasmonic resonance frequency is limited to the wellknown plasmonic materials. Despite the fact that recent studies in metamaterial structures demonstrate a promising approach of tuning Purcell factor across the emission wavelength, the demonstrations still lack efficient radiative emission besides the complexity of their fabrication. Here we demonstrate theoretically and experimentally that the cascaded metaldielectric nanostructure results in a tuneable resonance frequency approach to obtain a maximum radiative decay rate for any desired dipole peak emission wavelength. Owing to the effective cascaded plasmonic modes coupling across the metaldielectric interfaces, the proposed design uniquely illustrates the ability to optimize the plasmonic nanostructure for 100% radiative transmission and 3fold radiative emission enhancement.
