Session Chair: Din Ping Tsai, National Taiwan University Session Chair: Jinghua Teng, Institute of Materials Research & Engineering, A*STAR
1:30pm - 2:00pm Keynote
Topological and Non-Reciprocal Nanophotonics
The University of Texas at Austin, United States
In this talk, we will review our recent progress towards the concept, design and realization of magnet-free non-reciprocal 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 spatio-temporal modulation, nonlinearities, and/or opto-mechanical interactions, and discuss our vision towards new transport phenomena for light, and new nanophotonic devices with enhanced non-reciprocal properties.
2:00pm - 2:30pm Invited
Universal Spin-Momentum Locking of Light
Todd VAN MECHELEN, Zubin JACOB
Purdue University, United States
We show the existence of an inherent property of evanescent electromagnetic waves: spin-momentum 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 spin-momentum locking. We also introduce a universal right-handed 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 spin-momentum locking in various nanophotonic experiments and sheds light on the electromagnetic analogy with the quantum spin-Hall state for electrons.
2:30pm - 3:00pm Invited
Dafei JIN1,3, Thomas CHRISTENSEN1, Marin SOLJACIC1, Ling LU1,2, Xiang ZHANG3, Liang FU1, Nicholas X. FANG1
1Massachusetts Institute of Technology, United States; 2Institute of Physics, Chinese Academy of Sciences, China; 3University of California, Berkeley, United States
In this talk, we show that the historically studied two-dimensional (2D) magnetoplasmon, which bears gapped bulk states and gapless one-way 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 one-way edge magnetoplasmon at the interface of opposite magnetic domains, and demonstrate the existence of zero-frequency modes bounded at the peripheries of a hollow disk. Furthermore, we propose a two-dimensional plasmonic platform – periodically patterned monolayer graphene – which hosts topological one-way 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 - 3:15pm Oral
Topological Edge Modes in Parity-Time-Symmetric Graphene Waveguide Arrays
Huazhong University of Science and Technology, China
Topological edge states and parity-time (PT) symmetry have attracted intensive attention in waveguide arrays. A topological edge mode emerges at the interface between topological trivial and non-trivial structures, which are described by integer-valued quantities. For example, the winding number is used to character the topology of one-dimensional 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 non-Hermitian. When the gain-loss 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 non-Hermitian degeneracies, known as exceptional points (EPs). Here we shall investigate the topological edge modes of surface plasmon polaritons (SPPs) in a non-Hermitian 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 parity-time (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 deep-subwavelength scale.
3:15pm - 3:30pm Oral
Surface Plasmon-Enhanced Radiative Emission through Cascaded Metal-Dielectric Nanostructures
Sepideh GOLMAKANIYOON1,2, Pedro Ludwig HERNANDEZ-MARTINEZ1,2,3, Hilmi Volkan DEMIR2,3,4, Xiao Wei SUN1,5
1School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore; 2LUMINOUS! Center of Excellence for Semiconductor Lighting and Displays, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore; 3Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore; 4Department of Electrical and Electronics Engineering, Department of Physics, and UNAM-Institute of Materials Science and Nanotechnology, Bilkent University, Turkey; 5Department 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 metal-dielectric 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 well-known 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 metal-dielectric 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 metal-dielectric interfaces, the proposed design uniquely illustrates the ability to optimize the plasmonic nanostructure for 100% radiative transmission and 3-fold radiative emission enhancement.