Atsushi Yokoo

Self-repair of ordered pattern of nanometer dimensions based on self-compensation properties of anodic porous alumina

The self-repair of an ordered pattern of nanometer dimensions based on the self-compensation properties of anodic porous alumina is demonstrated. In a pretextured pattern formed on Al using the nanoindentation process with an array of convexes, the deficiency sites of the pattern were found to be compensated automatically during the anodization. Combining the self-compensation properties of the pore configuration of the anodic porous alumina with the preparation of a replica of the compensated porous structure allowed us to develop a process which has the capability of self-repairing the imperfections in the starting pattern. It was confirmed that deficiencies in the starting pattern could be repaired automatically in the Ni pattern regenerated using the self-compensated anodic porous alumina as a template.

Photonic Band Gap in Anodic Porous Alumina with Extremely High Aspect Ratio Formed in Phosphoric Acid Solution

Two-dimensional (2D) photonic crystals were fabricated using anodic porous alumina with a highly ordered air-hole array of triangular lattice with a high aspect ratio of over 200. The transmission properties of the obtained ordered air-hole array in the alumina matrix exhibited a stop band in the spectrum which corresponds to the band gap in 2D photonic crystals.

Movable high-Q nanoresonators realized by semiconductor nanowires on a Si photonic crystal platform.

Subwavelength semiconductor nanowires have recently attracted interest for photonic applications because they possess various unique optical properties and offer great potential for miniaturizing devices. However, realizing tight light confinement or efficient coupling with photonic circuits is not straightforward and remains a challenge. Here we show that a high-Q nanocavity can be created by placing a single III–V semiconductor nanowire with a diameter of under 100 nm in a grooved waveguide in a Si photonic crystal, by means of nanoprobe manipulation. We observe very fast spontaneous emission (91 ps) from nanowires accelerated by the strong Purcell enhancement in nanocavities, which proves that very strong light confinement can be achieved. Furthermore, this system enables us to move the nanocavity anywhere along the waveguide. This configuration provides a significant degree of flexibility in integrated photonics and permits the addition and displacement of various functionalities of III–V nanocavity devices in Si photonic circuits.

Monocrystalline 2-Adamantylamino-5-Nitropyridine (AANP) – a Novel Organic Material for Laser Raman Converters in the Visible and Near-IR

We have open up new nonlinear-laser potential in polar C15H19N3O2 (AANP) single crystal. At room temperature under one-micron picosecond laser excitation high-order stimulated Raman scattering (SRS) and self-sum-frequency generation effects in this organic material were observed. All their registered lasing components were identified and put in relation with the SRS-active vibration modes (ωSRS ≈1280 cm-1). The investigated crystal is classified a as promising χ(2)+χ(3) medium for laser-frequency converters and Raman lasers in the visible and near-IR.

Ideally Ordered Metal Hole Arrays with High Aspect Ratios Prepared from Anodic Porous Alumina

Metal hole arrays with submicrometer dimensions were fabricated by a two-step molding process that uses anodic porous alumina with ideally ordered hole configurations as a starting material. The obtained metal (Ni) hole arrays had geometrical structures identical to those of the original. Transmission spectra of Ni hole array membranes show the band-pass characteristic in the visible range. The cut-off wavelength in the long-wavelength region is dependent on the hole size.

All-optical switching by use of cascading of phase-matched sum-frequency generation and difference-frequency generation processes

We have investigated proposed all-optical switching by use of cascading of phase-matched sum-frequency-generation (SFG) and difference-frequency-generation (DFG) processes. The switching operation is accomplished by both a π phase change and an amplitude change of the signal field in SFG–DFG processes. We theoretically confirmed that the proposed switch requires the least operation power of any switch that uses cascading SFG–DFG processes. The switching characteristics have been numerically clarified, and the experimental full-switching characteristics when a bulk-type periodically poled LiNbO3 is used correspond to the numerical analysis. An ultrafast all-optical switch with low switching power and small size can be expected from use of waveguide-type devices.

Fabrication of GaAs hole array as a 2D-photonic crystal and their application to photonic bandgap waveguide

A two dimensional (2D) GaAs hole array with a high aspect ratio was successfully fabricated by dry etching techniques using a highly ordered alumina membrane as a mask. The reflection spectra of the GaAs hole array shows characteristics of the photonic bandgap (PBG) calculated by using the 2D triangular lattice structure. Various defect lines were formed etching in the GaAs hole array using focused ion beam. The defect-type PBG waveguide was experimentally demonstrated.

63-nm-pitch pit pattern fabrication on polycarbonate surface by direct nano-printing

The authors show that surface deformation of polycarbonate is successfully achieved by direct nano-printing. Using the replication technique, it is possible to fabricate a nano-CD ROM with a storage density of over 185 Gbits/in/sup 2/ directly from a master mold.

Design for ultrahigh-Q position-controlled nanocavities of single semiconductor nanowires in two-dimensional photonic crystals

Using finite-difference time-domain simulation, we show that ultrahigh-Q nanocavities can be obtained through the manipulation of a single semiconductor nanowire (NW) inside a slot in a line defect of a two-dimensional photonic crystal. By controlling the design and its lattice parameters of the photonic crystal, we have achieved a quality factor Q larger than 106 and a mode volume Vc smaller than 0.11 μm3 (1.25 of a cubic wavelength in the NW) for a cavity peak in the telecommunication band. This design is useful for realizing a position-controlled cavity in a photonic crystal. Here, we also discuss the small dependence of the Q-factor, the Vc, and the cavity peak in relation to the position of the NW inside the slot and the potential application to the cavity quantum electrodynamics using the embedded-emitter NW.

Organic photonic crystal band edge laser fabricated by direct nanoprinting

In this paper, we employed direct nanoprinting on an organic amorphous layer to realize a PhC band edge laser. A 2D-PhC pattern with pitch of 400 nm was succesfully transferred to the surface of an organic amorphous layer, and laser oscillation was confirmed. In addition, we found that the lasing threshold can be controlled by controlling the press condition. As far as we know, this is first organic PhC band edge laser fabricated by transferring a PhC pattern directly onto an organic amorphous layer from the mold. We can utilize the direct nanoprinting to exploit the advantage of PhC band edge laser, that is, single mode oscillation with a simple device structure.