The Goos-Hanchen (GH) shifts of the wave reflected through a PT symmetric multilayer structure is investigated near the exceptional points and the CPA-laser points. We show that the shifts of reflections from different directions have same behaviors, although the reflections are direction-dependent, and the lateral shifts can be greatly enhanced near the exceptional points. Moreover, we predict that at the CPA-Laser points, the reflection and transmission as well as the corresponding shifts are all very large, reaching their negative or positive maxima. Additionally, one may realize the reversal of GH shift through the suitable adjustment of the incident angle and the layer numbers. Numerical simulations for Gaussian incident beams are provided, and reasonable agreement between the theoretical results and numerical simulations is found.

Laboratory of Artificial Intelligence Nanophotonics and Centre for Ultrahigh Bandwidth Devices for Optical Systems (CUDOS), School of Science, RMIT University, Melbourne, Victoria 3000, Australia

In optics, the possibility of manipulation of optical angular momentum at the nanoscale is of crucial importance for both fundamental research and many emerging applications. However, it is still fundamentally challenging to achieving on-chip angular momentum multiplexing due to the extrinsic nature of orbital angular momentum associated with a helical wavefront. Here we present an entirely new concept of nanoplasmonic multiplexing of angular momentum through the nonresonant angular momentum mode-sorting sensitivity by nanoring slit waveguides on tightly-confined plasmonic angular momentum modes, leading to on-chip angular momentum multiplexing of ultra-broadband light ranging from the visible to terahertz regions.

Based on Snell’s law, when electromagnetic waves are obliquely incident at an interface, reflected waves are in the opposite side of the incident waves with respect to the interface normal, which is called as normal reflection (or positive reflection). Here, we experimentally demonstrate negative reflection of electromagnetic waves that obliquely impinge on an anisotropic coding metasurface, in which the reflected and incident waves are in the same side of the surface normal. The anisotropic coding metasurface is composed of an array of ellipse-shaped coding particles, exhibiting powerful controls to electromagnetic waves with arbitrarily oblique incidence by adding compensation coding sequences to the original coding pattern. In addition to the negative reflections, the anisotropic coding metasurface also shows powerful abilities to convert the obliquely-incident spatial waves to surface waves with high efficiency. More importantly, two orthogonally polarized spatial waves are converted to two surface waves propagating in different directions, one of which is in the same side of the obliquely incident wave with respect to the surface normal, resulting in negative surface wave. Experimental results have good agreements to theoretical and numerical predictions for both negative reflections and negative surface waves.

Metamaterial is a kind of artificially structured material with optical properties that cannot be found in nature. This presentation covers the recent advances in the study of plasmonic metamaterials ranging from fundamental aspects to up-to-date applications. Special emphasis will be given on the new frontier of the metamaterial/plasmonic research, where nonlinear and quantum effects emerge together. 1. I will introduce an efficient model to describe the nonlocal and quantum nature of metallic electrons and show how the nonlocal effects can be used to enhance the nonlinear responses of plasmonic metamaterials; 2. I will show how judiciously structured metal surfaces can help transfer distinct properties of optical plasmons to much lower frequencies with greatly suppressed plasmonic losses. Based on this concept, I will discuss our recent experimental developments on spoof-plasmon-enabled invisibility dips and backward phase matching in nonlinear spoof plasmon waveguide.

The functionalities of traditional optical component are mainly based on the phase accumulation through the propagation length, leading to a bulky optical component like lens and waveplate. Plasmonic metasurfaces composed of two-dimensional (2D) artificial structures have attracted a huge number of interests due to their ability on controlling the optical properties including electromagnetic phase as well as amplitude at a subwavelength scale. They therefore pave a promising way for the development of flat optical devices and integrated optoelectronic systems. In this talk, several research topics for photonic applications based on metasurfaces will be performed and discussed: high efficiency anomalous beam deflection, highly dimensional holographic imaging, versatile polarization generation and analysis, multi-functional and tunable Metadevices, and engineering non-radiating anapole mode for the generation of toroidal dipole moment in free space.

This paper reports a new design of micro optofluidic chips in the application of plasmonic photocatalytic oxidization of Ammonium ions (NH₄⁺) dissolved in water under light illumination, Fig. 1. In this report, the Au nanoparticles (NPs) replaced the typically used catalyst in typical artificial nitrogen cycle. The micro optical fluidic chip (MOFC) reactor is good with high mass transfer rate that can enhance processing efficiency of chemical reaction [1]. The UV light transmittable construction material, e.g. glass, Polydimethylsiloxane (PDMS), or NOA81 [1], makes the MOFC perfectly suitable for photocatalytic reaction.

Typically, artificial nitrogen cycle processes via the wet air oxidization (WAO) method oxidize and eliminate the dissolved NH₄⁺ from water with temperature higher than 150 °C and high pressure. The plasmonic heating in metal nanostructures and localized high temperature under light illumination enhances chemical reactions [2-5]. In this study, the pre-deposited layer of (3-Aminopropyl)trimethoxysilane (APTMS) fixed various sized Au NPs on the inner walls of the flow channel, Fig. 2. The pink color in the lower chip is coming from the scattering light of the fixed Au nanoparticles with size of 20 nm. Only the area of the rectangle fluidic channel, 2 cm (W) × 3 cm (L) × 58 μm (H), deposited with APTMS layer can catch Au NPs, see SEM data in Fig. 3. No obvious depletion observed after the experiments of NH₄⁺ oxidization under alkaline conditions.

The MOFC reactor with or without fixed 20 nm Au nanoparticles presented oxidization of NH₄⁺ ions dissolved in water under light illumination, Fig. 1. Two array of profusion channels with 10 μm in width separated and limited the water flow-in speed from input-reservoir. External visible light supplied by halogen lamps illuminated the channel and induce surface plasmon resonances on Au nanoparticles. Two groups of experiments with various flow speed of test solution processed under alkaline condition with adding sodium hydroxide (NaOH). The pH adjustment increased the initial pH value to about 11.5 and supplied hydroxide ions (OH¯) for oxidization of NH₄⁺ ions in water.

The reserved NH₄⁺ ions in test solution after experiments with various water pumping flow speed was measured and depicted in Fig. 4. The experiments with fixed Au NPs had concentration of reserved NH₄⁺ smaller than that with no Au NPs after 1 hr of processing time. The Au nanoparticles presented plasmonic enhancement of the chemical catalytic oxidization of NH₄⁺ ions in water in the MOFC reactor.

In conclusion, the plasmonic oxidation of NH₄⁺ ions in water presented inside the MOFC reactor with Au NPs as photocatalyst. The MOFC reactor shows great potential for further investigation in the future.

Plasmonic systems exhibit a host of intriguing optical properties. In this talk I shall assert that the underlying source of this diversity is geometry: that is to say the shape of a plasmonic particle or the structure of a particular surface. I shall show how geometric complexity can be generated starting from simple structures such as waveguides and transforming them into more complex structures, then turning to transformation optics to understand how the properties of the complex structure relate to the simple one. Particular attention will be paid to singular structures which are known to act as harvesters of light and are responsible for the enhanced spectroscopic response that occurs in SERS experiments.

A new strategy aiming to achieve post-fabrication performance tuning capability for terahertz metamaterial absorber (MMA) was proposed. Different from conventional mechanical tuning methods (e.g. external stretching or bending), a more convenient tuning mechanism with build-in pneumatic actuator was adopted, in which the suspending membrane based pneumatic actuation mechanism integrated with microchannel network was designed, through which geometry of the metal structure sitting on the membrane (constructing the unit cell of MMA) can be changed. With respect to the applied positive or negative pressure, opposite membrane deflection as well as the induced geometry change in the metal structure can be obtained, thus achieving dual-side absorption peak tuning.

We experimentally demonstrate that the photonic gauge potential could efficiently control the frequency of light. The photonic gauge potential is introduced in the optical fiber communication system with phase modulators (PMs) under dynamic modulation by a sinusoidal radiofrequency (RF) signal. The value of the gauge potential is fully determined by the initial phase of the modulation. The frequency comb in the PM can be viewed as a Bloch mode in the frequency dimension. The main effect of photonic gauge potential is to shift the band structure of the frequency comb. The propagation of the frequency comb in the PM experiences diffraction-like behavior and can be artificially controlled by tailoring the band structure. The incident frequency comb generated by a mode-locked laser will undergo red and blue shifts as the direction of gauge potential is changed. When there are two PMs applied with opposite gauge potential, the frequency comb will experience negative refraction between the PMs. The spectrum undergoes blue shift through one PM and then red shift after another. The process is similar to what happens in discrete optical waveguides but for the lateral dimension of frequency. By varying the gauge potential through changing the modulation phase, we can obtain a widely expanded frequency comb under incidence of a single-frequency laser. As two PMs are used in the system and set with opposite gauge potential, the frequency is firstly expanded and then squeezed to its origin, similar to optical imaging by a perfect lens. The results are also holds for continuous spectra. The study paves a new way to manipulating the frequency of optical communication signals.

Light-induced pulling is of significant interests recently since it provides a new understanding of the light-matter interaction, which can be achieved by optical force or photophoretic force. For optical force, it comes from momentum exchange during the light-matter interaction, which has been widely utilized to manipulate microscopic objects mostly in vacuum or in liquids. While photophoretic force, coming from light-induced thermal effect, has emerged as a more effective way to transport light-absorbing particles in ambient gases. In all these cases, optical force and photophoretic force are used to manipulate objects independently, as working in different environments. In fact, optical force and photothermal force can come together in a subtle style. Here, by employing the synergy of optical force and photophoretic force, we propose and experimentally demonstrate a configuration which can drive a micron-size metallic plate moving back and forth on a tapered fiber with supercontinuum light in ambient air. Optical pulling and oscillation of the metallic plate are experimentally realized. The experiment results of light-induced oscillation will definitely trigger many future theoretical and experimental developments and extensive applications, of which typical example includes energy conversion from light energy to mechanical energy. Due to the extremely simple configuration, it can be used as a micro-transport system for a miniature chemical processing device called a lab-on-a-chip expediently. This study could offer a deeper understanding of a diversified light-matter interaction, open up new avenues for pluralistic optical manipulation including optical control and sensing, and inspire many researches on optical driving (e.g. light-driven motor).

1. Lu, H. Yang, L. Zhou, Y. Yang, S. Luo, Q. Li, and M. Qiu, Phys. Rev. Letters 118, 043601 (2017).