Masashi Miyata

Full-Color Subwavelength Printing with Gap-Plasmonic Optical Antennas.

Metallic nanostructures can be designed to effectively reflect different colors at deep-subwavelength scales. Such color manipulation is attractive for applications such as subwavelength color printing; however, challenges remain in creating saturated colors with a general and intuitive design rule. Here, we propose a simple design approach based on all-aluminum gap-plasmonic nanoantennas, which is capable of designing colors using knowledge of the optical properties of the individual antennas. We demonstrate that the individual-antenna properties that feature strong light absorption at two distinct frequencies can be encoded into a single subwavelength-pixel, enabling the creation of saturated colors, as well as a dark color in reflection, at the optical diffraction limit. The suitability of the designed color pixels for subwavelength printing applications is demonstrated by showing microscopic letters in color, the incident polarization and angle insensitivity, and color durability. Coupled with the low cost and long-term stability of aluminum, the proposed design strategy could be useful in creating microscale images for security purposes, high-density optical data storage, and nanoscale optical elements.

Multi-spectral plasmon induced transparency via in-plane dipole and dual-quadrupole coupling

We experimentally demonstrated an approach based on dipole and dual-quadrupole coupling to construct a planar metamaterial supporting multi-spectral plasmon induced transparency. The structure consists of two short silver wires (dipole) and two long silver wires (dual-quadrupole). The in-plane coupling between the dipole and the dual-quadrupole leads to two transmission windows even in the absorbance linewidth of the dipole. This phenomenon is well described and understood by numerical analyses and a classical oscillator model.

Excitation control of long-range surface plasmons by two incident beams

We demonstrate the excitation control of long-range surface plasmon polaritons (LRSPs) by experiments and simulations. We find that LRSPs and short-range surface plasmon polaritons can be selectively excited by two incident beams. This mechanism enables us to realize the excitation control of LRSPs using the phase difference or the intensity ratio between the two input signals. The excitation method analyzed here can be applied to active plasmonic devices based on LRSPs.

Gap Plasmon Resonance in a Suspended Plasmonic Nanowire Coupled to a Metallic Substrate

We present an experimental demonstration of nanoscale gap plasmon resonators that consist of an individual suspended plasmonic nanowire (NW) over a metallic substrate. Our study demonstrates that the NW supports strong gap plasmon resonances of various gap sizes including single-nanometer-scale gaps. The obtained resonance features agree well with intuitive resonance models for near- and far-field regimes. We also illustrate that our suspended NW geometry is capable of constructing plasmonic coupled systems dominated by quasi-electrostatics.

Mutual mode control of short- and long-range surface plasmons

A symmetric metal slab waveguide simultaneously supports two opposite types of propagation mode similar to a metal film: short-range surface plasmon (SRSP) like mode and long-range surface plasmon (LRSP) like mode. The strong field confinement of SRSP-like mode plays a crucial role for nano-optical integrated circuits in spite of short propagation length. In order to avoid the trade-off between field confinement and propagation length, we demonstrate selective mode excitation and mutual mode conversion for nanofocusing mediated by LRSP-like mode.

Colloidal quantum dot-based plasmon emitters with planar integration and long-range guiding.

We present an experimental demonstration of a quantum dot (QD)-based plasmon emitter controllably integrated in designed patterns on a thin metal film. The generation of surface plasmons polaritons (SPPs) from optically excited QDs on a thin metal film is experimentally demonstrated. Long-range, low-dispersion, two-dimensional isotropic guiding, as well as efficient coupling of the SPPs are also shown. The realization of planar, low loss and efficient plasmon emitter-waveguide integration will offer further development of plasmon circuits.

Field enhancement by longitudinal compression of plasmonic slow light

We propose a new approach for field enhancement by using plasmonic slow light (PSL), which is one of the phenomena unique to surface plasmon polariton (SPP). PSL shows a remarkably low group velocity and high field confinements beyond the diffraction limit. This phenomenon induces “longitudinal compression” of optical energy in nanoscale regions, resulting in a large field enhancement. The longitudinal compression by PSL opens a new dimension for field enhancement by SPP propagation. This approach will be applied to various prospective applications based on field enhancement in nanoplasmonics.

Promoted sulfurization of a single silver nanoparticle by plasmon resonance under white light illumination

We demonstrate the rapid spectral shift of the plasmon resonant peak from a single silver nanoparticle deposited on a dielectric-coated silver film in air under white light illumination. This shift occurs within several hours of white light illumination under the resonant condition of the metal–insulator–metal structure formed below the particle and is attributed to promoted sulfurization at the surface of the single silver nanoparticle resulting from the plasmonic heat generation. This thermal plasmonic effect will play a crucial role in the stability of plasmonic devices in the future.

Passive and active metasurface based on metal-insulator-metal structures

A metal-insulator-metal (MIM) structure is a fundamental plasmonic structure that has been studied widely since the early stage of plasmonics. It enables us to confine surface plasmon polariton (SPP) and concentrate light into nano-space beyond the diffraction limit. A finite-length MIM structure is considered to be a Fabry-Perot resonator of SPP as a nanocavity. Here, we review our recent studies about active metasurface based on a reconfigurable metal-air-metal (MAM) nanocavity which modify reflection or absorption spectra in scattering by changing a gap distance. Such reconfigurable MAM nanocavity becomes promising candidate for various applications such as plasmonic color or sky radiator from visible to infrared range.

Super long-range surface plasmon polaritons in a silver nano-slab waveguide

Long-range surface plasmon polariton (LRSP) with lower attenuation and longer propagation length than conventional surface plasmon polariton (SPP) on a single interface has been studied as new elements for integrated optical circuits. LRSP exhibits on a metal film bounded by dielectric and can be expected to edge closer to practical use due to the long propagation length. It is theoretically predicted that the propagation length of LRSP greatly increases as the lateral width of a metal film decreases. Such mode propagating in a metal slab waveguide with extremely long propagation length is named “super LRSP”. Here, we fabricate silver slab waveguide and observe the tendency of propagation properties of super LRSP.