Interactions between Plasmonic Nanoantennas and Vortex Beams.

The orbital angular momentum (OAM) of light offers a new degree of freedom for light-matter interactions, yet how to control such interactions with this physical dimension remains open. Here, by developing a numerical method enabling optical OAM simulations, we provide insights into complex plasmon behaviors with the physical dimension of OAM, and we prove in theory that plasmonic nanostructures can function as efficient antennas to intercept and directionally reradiate the power of OAM beams. The interplay between optical OAM and spin angular momentum (SAM) generates novel particle polarizations and radiations, which were inaccessible before. For arrayed nanoparticles, coherent surface plasmons with specific phase retardations determined by OAM of the beams enable directional power radiations, making a phased array antenna. These findings expand our knowledge of nanoplasmonics in the OAM area and are promising for quantum information processing and dynamic sensing of ultraweak biosignals.

All-optical frequency-dependent magnetic switching in metal-insulator-metal stub structures.

Many attempts to switch magnetization with optical pulses were based on free-space coupling schemes of circularly polarized light pulses, so-called all-optical helicity-dependent magnetic switching; however, waveguide coupling schemes are promising for on-chip all-optical magnetic switching. Metal-insulator-metal (MIM) stub structures provide a promising platform for highly integrated photonic circuits, thanks to their compact size, on-chip compatibility, and ease of fabrication. We found clockwise and counterclockwise ring-like modes in the MIM stub structure, which can act as effective magnetic fields with two opposite directions due to the inverse Faraday effect. Effective magnetic field spectra inside the MIM stub have dual resonant peaks at which the effective magnetic field intensity reaches its extreme values with opposite signs, corresponding to binary magnetic states. Switching between the binary magnetic states can be achieved by altering the optical pump frequency. The all-optical frequency-dependent magnetic switching in the MIM stub may provide a chip-compatible and ultracompact tool for ultrafast switching of magnetic order.

Analytical analysis of spectral sensitivity of plasmon resonances in a nanocavity.

Metallic nanocavities exhibit extremely high spectral sensitivity to geometrical variations and are promising for sensing applications. Here, the sensitivity of a cubic dimer cavity, to picometer gap variation, is analysed in a model, which takes into account the phase shift of scattering at the boundaries and the quantum tunnelling effect in the small gap limit. The resonance wavelengths are expressed in terms of the plasmon frequency, the medium dielectric function, and the geometry of the gap. The sensitivity of the resonance wavelength to the gap width variation is found to be as high as 1 nm pm-1. While the resonance wavelengths depend on the materials' dielectric functions, the sensitivity is found to scale universally as a function of gap distance. In the sub-nanometer regime, electron tunnelling across the gap starts to suppress the plasmonic field, setting the limit of sensitivity of such a dimer cavity. The results given by the analytical model are complemented by numerical simulations using Comsol. Our model reveals the origin and universal behaviours of the sensitivity of the cavity plasmon and provides guidance for the design of new sensitive rulers at the picometer scale.

Switchable plasmonic routers controlled by external magnetic fields by using magneto-plasmonic waveguides.

We analytically and numerically investigate magneto-plasmons in metal films surrounded by a ferromagnetic dielectric. In such waveguide using a metal film with a thickness exceeding the Skin depth, an external magnetic field in the transverse direction can induce a significant spatial asymmetry of mode distribution. Superposition of the odd and the even asymmetric modes over a distance leads to a concentration of the energy on one interface which is switched to the other interface by the magnetic field reversal. The requested magnitude of magnetization is exponentially reduced with the increase of the metal film thickness. Based on this phenomenon, we propose a waveguide-integrated magnetically controlled switchable plasmonic routers with 99-%-high contrast within the optical bandwidth of tens of THz. This configuration can also operate as a magneto-plasmonic modulator.

Magnetic Fano resonance-induced second-harmonic generation enhancement in plasmonic metamolecule rings.

The "artificial magnetic" resonance in plasmonic metamolecules extends the potential application of magnetic resonance from terahertz to optical frequency bypassing the problem of magnetic response saturation by replacing the conduction current with the ring displacement current. So far, the magnetic Fano resonance-induced nonlinearity enhancement in plasmonic metamolecule rings has not been reported. Here, we use the magnetic Fano resonance to enhance second-harmonic generation (SHG) in plasmonic metamolecule rings. In the spectra of the plasmonic metamolecule, an obvious Fano dip appears in the scattering cross section, while the dip does not appear in the absorption cross section. It indicates that at the Fano dip the radiative losses are suppressed, while the optical absorption efficiency is at a high level. The largely enhanced SHG signal is observed as the excitation wavelength is adjusted at the magnetic Fano dip of the plasmonic metamolecule rings with stable and tunable magnetic responses. We also compare the magnetic Fano dip with the electric case to show its advantages in enhancing the fundamental and second harmonic responses. Our research provides a new thought for enhancing optical nonlinear processes by magnetic modes.

Transport properties of a single plasmon interacting with a hybrid exciton of a metal nanoparticle-semiconductor quantum dot system coupled to a plasmonic waveguide.

The transport properties of a single plasmon interacting with a hybrid system composed of a semiconductor quantum dot (SQD) and a metal nanoparticle (MNP) coupled to a one-dimensional surface plasmonic waveguide are investigated theoretically via the real-space approach. We considered that the MNP-SQD interaction leads to the formation of a hybrid exciton and the transmission and reflection of a single incident plasmon could be controlled by adjusting the frequency of the classical control field applied to the MNP-SQD hybrid nanosystem, the kinds of MNPs and the background media. The transport properties of a single plasmon interacting with such a hybrid nanosystem discussed here could find applications in the design of next-generation quantum devices, such as single-photon switching and nanomirrors, and in quantum information processing.

Actively phase-controlled coupling between plasmonic waveguides via in-between gain-assisted nanoresonator: nanoscale optical logic gates.

The development of nanoscale optical logic gates has attracted immense attention due to increasing demand for ultrahigh-speed and energy-efficient optical computing and data processing, however, suffers from the difficulty in precise control of phase difference of the two optical signals. We propose a novel conception of nanoscale optical logic gates based on actively phase-controlled coupling between two plasmonic waveguides via an in-between gain-assisted nanoresonator. Precise control of phase difference between the two plasmonic signals can be performed by manipulating pumping rate at an appropriate frequency detuning, enabling a high contrast between the output logic states "1" and "0." Without modification of the structural parameters, different logic functions can be provided. This active nanoscale optical logic device is expected to be quite energy-efficient with ideally low energy consumption on the order of 0.1 fJ/bit. Analytical calculations and numerical experiments demonstrate the validity of the proposed concept.

Nonlinearity of surface-plasmon polaritons in sub-wavelength metal nanowires.

We investigate the nonlinear propagation of surface plasmon polaritons guided on gold nanowires surrounded by silica glass. Based on the Lorentz reciprocity theorem, we derive a formula for the complex nonlinear susceptibility, and study its dependence on waveguide parameters and wavelength for the fundamental mode. Depending on these parameters both positive and negative signs of the real and imaginary parts of the nonlinear coefficient are predicted. This implies that nanowires exhibit the property of saturable absorption or optical limiting as well as positive and negative nonlinear phase shifts. The physical origin of this phenomenon is discussed.

Plasmonic phase modulator based on novel loss-overcompensated coupling between nanoresonator and waveguide.

We present that surface plasmon polariton, side-coupled to a gain-assisted nanoresonator where the absorption is overcompensated, exhibits a prominent phase shift up to π maintaining the flat unity transmission across the whole broad spectra. Bandwidth of this plasmonic phase shift can be controlled by adjusting the distance between the plasmonic waveguide and the nanoresonator. For a moderate distance, within bandwidth of 100 GHz, the phase shift and transmission are constantly maintained. The plasmonic phase can be shift-keying-modulated by a pumping signal in the gain-assisted nanoresonator. A needed length in our approach is of nanoscale while already suggested types of plasmonic phase modulator are of micrometer scale in length. The energy consumption per bit, which benefits from the nano size of this device, is ideally low on the order of 10 fJ/bit. The controllable plasmonic phase shift can find applications in nanoscale Mach-Zehnder interferometers and other phase-sensitive devices as well as directly in plasmonic phase shift keying modulators.

Study on the vibration displacement distribution of a circular ultrasonic motor stator.

In this paper is presented a theoretical consideration on the stator's displacement distribution, which is one of the most important problems in defining the structure of a circular ultrasonic motor stator. The results are compared with ones obtained utilizing a holographic interferometer, a laser vibrometer and FEM (finite element method) simulation. They are in good agreement with each other.

High-power soliton-induced supercontinuum generation and tunable sub-10-fs VUV pulses from kagome-lattice HC-PCFs.

We theoretically study a novel approach for soliton-induced high-power supercontinuum generation by using kagome lattice HC-PCFs filled with a noble gas. Anomalous dispersion and broad-band low loss of these fibers enable the generation of two-octave broad spectra by fs pulses, with high coherence and high spectral peak power densities up to five orders of magnitude larger than in standard PCFs. In addition, up to 20% of the output radiation energy forms a narrow UV/VUV band, which can be tuned by controlling the pressure in the range from 350 nm to 120 nm. In the temporal domain this corresponds to sub-10-fs UV/VUV pulses with pulse energy of few tens of microJ, caused by the formation of a high-order soliton emitting non-solitonic radiation.

Guiding properties and dispersion control of kagome lattice hollow-core photonic crystal fibers.

Dispersion properties, loss and optimum design of kagome lattice hollow-core photonic crystal fibers filled with argon are studied for the purpose of possible applications in ultrafast nonlinear optics. As will be shown numerically and by using an approximate analytical formula these fibers exhibit anomalous dispersion for visible or UV wavelengths both for a 1-cell-core as well for a 3-ring-core which can be controlled by the gas pressure and do not suffer from high loss. It is shown that while the loss is mainly influenced by the strut thickness of the kagome lattice the group velocity dispersion is almost independently controlled by the core size. These results demonstrate that kagome lattice hollow fibers have a promising potential in ultrashort pulse delivering of high-energy pulses and in several interesting applications in ultrafast nonlinear optics.