To realize small footprint and high speed nanoelectronics, the plasmonics based tunneling electrons have been shown as a potential technology. In general, surface plasmons have been demonstrated that they are able to be directly excited by tunneling electrons in different ways including scanning tunneling microscopes (STMs), metal–insulator–metal junctions using vacuum or metal oxides or molecular tunneling barriers. The direct excitation of plasmons by tunneling electrons is attractive because, on the one hand, there is no background light generated, and on the other hand this approach is feasible to develop fast devices (on the timescale of quantum tunneling) as no slow electron–hole recombination processes are required.

In this talk we will report our recent development of theoretical frameworks to model and simulate the direct excitation of plasmons based on tunneling electrons with respect to different metallic and graphene plasmonic structures. First the directional excitation of electrical-plasmon propagating surface plasmons on a periodic 1D Au cavity by a STM will be addressed [1]. Second thanks to electron tunneling in self-assembled monolayers (SAM), the on-chip molecular electronic plasmon sources consisting of tunnel junction 2nm-layer of SAM sandwiched between two metallic electrodes that excite plasmons will be discussed in detail [2]. Third, by using 2nm-metal oxide layer in MIM junction, we will demonstrate that on-chip electronic-plasmonic transducers can be achieved to efficiently generate, manipulate and transfer plasmons [3]. Last, we will demonstrate that the graphene is potentially a highly efficient material for tunneling excitation of plasmons because of its narrow plasmon linewidths, strong emission, and large tunability in the mid-IR wavelength regime [4].

Efficient manipulation of surface waves, such as surface plasmon polaritons (SPP), is a vital issue in various nanophotonic applications, such as plasmonic circuitry.  In plasmonic devices, SPP sources and launchers have important roles, which are required not only to generate directionally propagating SPPs efficiently, but also to be able to shape the distribution of the SPP field. Here, we present simple approaches to realizing versatile directional excitation and wavefront shaping of SPPs based on metasurfaces consisting of a special type of Δ-shaped plasmonic optical nanoantennas (Δ-POAs). We first demonstrate the special radiation properties of the Δ-POAs, including the directionality of SPP excitation and the phase control mechanism. Then, by using such Δ-POAs to compose metasurfaces, we present two approaches that can realize effective and versatile control of the SPP wavefront. We first propose a general method that can control the complex excitation ratio of any two linearly independent SPP modes just by controlling the incident polarization state of the incident light. With this method, an efficient dual-function SPP launcher is realized, which can achieve both tunable directional SPP excitation at an arbitrary wavelength and the unidirectional SPP excitation over an ultra-broad bandwidth. Then, we present a simple method to generate unidirectionally propagating SPP beams with arbitrary amplitude and phase profiles. As an example, a high-order Hermite–Gauss SPP beam generator is designed and realized, validated by near-field characterization.

Nonequilibrium hot carriers near the interfaces of semiconductors and metals play a crucial role in catalysis, chemical reactions, water splitting as well as optoelectronic processes. In addition to excitation by light, such hot carriers can also be generated due to quantum mechanical effects in tunnel junctions. The tunnelling behavior is extremely sensitive to the immediate property change of a medium placed in the tunnel path, which holds great opportunities for the development of tunnelling-based devices for the dynamical control of plasmons or the detections of environmental changes with high sensitivity. Here we will discuss hot-electron excitation in electrically-driven plasmonic nanorod metamaterials and their applications for light emission and gas sensing, including hydrogen and oxygen gases. Electrically-driven plasmonic nanorod metamaterials comprise a fertile platform merging photonics, electronics and chemistry, opening up opportunities for developing electron tunnelling-based nanoscale devices for light generation and modulators and chemical sensing.

Tailoring the geometry and arrangement of metasurface structures yields a complete control of the reflection/transmission amplitude, phase, and polarization states. Few-layer metasurfaces can overcome the issues of high-loss and fabrication challenge in bulk metamaterials and weak coupling in single-layer metasurfaces. Furthermore, the coupling among layers results in functionalities beyond the individual constituent metasurfaces. Here we show that bi-layer metallic metasurfaces can realize narrow-, dual-, and broadband antireflection in THz and mid-IR spectral ranges, through tailoring the dispersion of the constituent metasurfaces. We also show tri-layer metasurfaces can be used to enable broadband conversion of linear polarization accompanied with a control of phase spanning the full 2p range. Based on this property, we demonstrate highly efficient flat lenses in the THz and microwave frequency ranges.

Optical spin-Hall effect (OSHE) is a spin-dependent transport phenomenon of light. Although being discovered decades ago, OSHEs are usually extremely weak and in uncontrollable manner owning to the inability to fully control the spin-orbit coupling [1]. Recently, the development of metasurfaces open a new way for control the spin-dependent splitting of light beam by using a single sheet metamaterials [2-3]. However, these previous works on OSHE only demonstrated simple and symmetric splitting of the two spins [1-3], far from the capability to generate independent OSHEs, which can then work coherently together for more flexible and tunable functionalities. Here, we present a plasmonic metasurface consisting of an array of nano-slots with tailor-made orientation profiles to generate independent surface plasmon polariton (SPP) patterns on the metasurface with the two incident spins [4]. For example a “cross” pattern for one spin and a “triangle” pattern for another as incidence. With such flexible control of OSHEs, we also demonstrate that it is possible to make the two spins work coherently together by controlling the relative phase between the two polarizations, which allows us to play motion pictures, for example, to write a letter “b” with a series of picture frames. Our work may stimulate more applications in near-field optics, such as optical integrated circuits, tip-free near-field scanning optical microscopy, and plasmonic tweezers to trap and move micron size particles.

Abrupt modifications of the fields across an interface can be engineered by depositing an array of sub-wavelength resonators specifically tailored to address local amplitude, phase and polarization changes. Physically, ultrathin nanostructure arrays (δ≪λ), also called ‘‘optical metasurfaces’’, control light by engineering artificial boundary conditions of Maxwell’s equations. Metasurfaces have been implemented to obtain various sorts of optical functionalities, ranging from the basic control of the transmission and reflection of light, to the control of the radiation patterns for comprehensive wavefront engineering and holography. In this presentation, we will discuss recent works on free standing visible (GaN based) and mid-infrared (Si-based) metasurfaces.  We will explain which physical mechanisms are utilized for the design of efficient ultrathin planar optical components and show that these conditions are connected with the well-known Kerker conditions already proposed for isolated scatterers. Similar principles can be used to design various other optical metasurfaces, e.g. flat lenses, phase plates, waveplates, helical wavefront generators, and holograms. Rectangular, elliptical, or other asymmetrical hole shapes can be used to impart birefringence to different light polarisations, as required in waveplates or polarisation beam splitters. We will conclude our presentation with a discussion on the concept of conformal boundary optics: an analytical method based on novel, first-principle derivations that allows us to engineer transmission and reflection at will for any interface geometry and any given incident wave.

By designing an ultrathin metasurface, which consists of spatially variant plasmonic structures with engineered geometric Berry phase, it is shown that spin-orbit coupling of light can be utilized to manipulate the SAM dependent focusing of light or the optical vortex beam and rotate the orbital angular momentum of light. More recently, we also demonstrated that the spin dependent metasurface can be applied to design highly efficient optical holograms The metasurface hologram offers the unique opportunity of creating high quality holographic optical patterns with high spatial resolution and broad angle of view, which have important impact in the areas including holographic displays, beam shaping, data storage, optical trapping, optical tweezers and so on.

In nonlinear optical regime, we also provided proof for the first time of the existence of nonlinear geometrical Berry phase in a third harmonic generation process by using a plasmonic nanocross with spatially variant orientation angle. The nonlinear geometric Berry phase is 4θ, where θ is the orientation angle of the nanocross with respect to the x-axis. This nonlinear phase can be continuously tuned by from zero to 2π by simply rotating the in plane orientation angle of the meta-atom.

I will report some of the most recent developments in engineering and manipulating light-matter interactions, via the artificially constructed metamaterials of ultrathin thickness compared to the wavelength. In particular, the low-dimension and high-frequency scaling may promise a lot more interesting applications, while the challenges in design principle and fabrication capability will become critical limits. Nano-patterned surfaces to modulate and structure novel light behavior will be studied and the following advanced functionalities will be discussed, e.g., farfield super-resolution imaging, 3D meta-hologram, dynamic OAM generation, plasmonic high-resolution prints, etc. Our work paves a roadmap to design sophisticated and advanced optical devices, with low dimension, miniaturization, randomness, and scaled-up capability.

Achieving multiple diversified functionalities in a single flat device is crucial for electromagnetic (EM) integration, but available efforts suffer the issues of device thickness, low-efficiency and restricted functionalities. Here we describe a general strategy to design high-efficiency bifunctional devices based on meta-surfaces composed by anisotropic meta-atoms with polarization-dependent phase responses. Based on the derived general criterions, we design and fabricate two bifunctional meta-devices, working in reflection and transmission modes, respectively, that can realize two distinct functionalities with very high efficiencies (~90% in reflection geometry and ~72% in transmission one). Microwave experiments, including both far-field and near-field characterizations, are performed to demonstrate the predicted effects, which are in excellent agreement with numerical simulations. Our findings can motivate the realizations of high-performance bifunctional meta-devices in other frequency domains and with different functionalities, which are of crucial importance in EM integration.

In this talk, I will present quantum plasmonics and its applications in integrated optofluidics for fundamental life sciences and precision medicine.  First, I will introduce a quantum plasmonic nanoscope that allows non-invasive optical imaging of quantum biological electron-transfer (QBET) dynamics in live cells. The quantum nanoscope is designed to capture the real-time QBET imaging of enzymes using Plasmon Resonance Energy Transfer (PRET) mechanism and quantized plasmon quenching dips in resonant Rayleigh scattering spectra.  Second, I will discuss the important role of nanoplasmonics in integrated molecular diagnostic systems (iMDx) for personalized precision medicine. The iMDx comprises three key elements of precision medicine on chip: (1) ultrafast multiplexed photonic PCR for the early detection of DNA and RNA biomarkers in blood, (2) signal amplifications of protein markers, and (3) a self-contained sample preparation from whole blood on chip, which allows a sample-to-answer readout platform.  Microphysiological analytics platforms (MAPs) are also created as innovative solutions in pathogenesis life science, personalized drug discovery, and therapeutics.  In particular, the real-time imaging of formation and dynamics of pathogenesis in mini-brains MAP and pancreatic islets MAP will be discussed along with the vision of preventive medicine via precision engineering medicine.