Dynamic wide gamut color generation using highly lossy metal-based metal-dielectric-metal structure


Broadband Ag/SiO2/Fe/TiO2 ultrathin planar absorber with a wide acceptance angle from visible to near-infrared regions


Wireless data transmission in the 560-GHz band utilizing terahertz wave generated through photomixing of a pair of distributed feedback lasers injection-locking to a Kerr micro-resonator soliton comb


Determining the Optical Geometry of a Gold Semi-Shell under the Kretschmann Configuration

Dielectric nanoparticles coated with metals (half-shell or semi-shell structures) have attracted attention as potential composite plasmonic nanomaterials with large optical anisotropy and absorption cross-sections. Structures approximately 100 nm in size can excite plasmons in the visible and near-infrared ranges, highlighting their distinct optical properties. This study employed metal semi-shell structures (metal: gold, dielectric: silica) in the Kretschmann configuration to experimentally and numerically demonstrate the optical determination of single-structure orientations through a finite-difference time-domain method. Gold semi-shell structures were fabricated through deposition and etching. These structures were removed from their substrate in ultrapure water and randomly dropped onto a thin gold substrate. In the single structure, we experimentally observed changes in the scattering light spectrum based on the optical geometry of the gold semi-shell at wavelengths ranging from 530 to 700 nm. The obtained results closely resembled those of a simulation and confirmed the presence of eigenmodes in the orientation through electric field analysis. These observations allow for the cost-effective and rapid determination of the orientations of numerous structures that are approximately 100 nm in size, solely through optical methods. This technique is a valuable development for measurement applications in nanostructure orientation control and functionality enhancement.


Carrier conversion from terahertz wave to dual-wavelength near-infrared light for photonic terahertz detection in wireless communication


Improvement of Optical Confinement for Terahertz Vertical-Cavity Surface-Emitting Laser with Square-Lattice Photonic Crystal Structure


Terahertz wireless communication in a 560-GHz band using a Kerr micro-resonator soliton comb


Ultra-thin deep ultraviolet perfect absorber using an Al/TiO2/AlN system


Experimental confirmation of self-imaging effect between guided light and surface plasmon polaritons in hybrid plasmonic waveguides

We fabricated a hybrid plasmonic device using self-imaging effect between guided light and surface plasmon polaritons in the hybrid plasmonic waveguide. The hybrid plasmonic device was fabricated by evaporating gold on the part of the silicon waveguide. Self-imaging was generated at the gold-covered section in the waveguide. Self-imaging of guided light and surface plasmon polaritons in hybrid plasmonic waveguides affect the output intensity of the hybrid plasmonic waveguide. The length of the hybrid plasmonic waveguide changes self-imaging conditions. We confirmed that the output intensity was affected by the length of the hybrid plasmonic waveguide. These findings contribute to the development of hybrid plasmonic devices and potentially improve integration density of hybrid photonic integrated circuits.


Numerical finite difference time domain calculation for extreme enhancement of magneto optical effect at ultraviolet wavelength using Ni subwavelength grating on SiO2/Ni structure


Design of AlN-subwavelength grating for deep ultraviolet wavelength reflector operating at 244 nm of wavelength


Highly reflective visible color filter based on a double layer TiO2 subwavelength structure


Low-Background Tip-Enhanced Raman Spectroscopy Enabled by a Plasmon Thin-Film Waveguide Probe


Optical detection for magnetic field using Ni-subwavelength grating on SiO2/thin-film Ag/glass structure

An optical sensor for magnetic field detection using Ni-subwavelength grating (SWG) on SiO/Ag-thin-film/glass substrates was experimentally developed on the basis of the re-radiation condition of surface-plasmon-polaritons (SPPs) at Ag surfaces. The fabricated sample showed two dips in the reflection spectra associated with SPP excitation, and the optical response exhibited good agreement with that simulated by the finite-difference time-domain method. The reflectivity at one of the dip wavelengths varied minimally with the application of the magnetic field, whereas that at the other dip wavelength significantly decreased owing to the large electric field overlap of SPP with the magnetized Ni-SWG. As a result, a magnetic field on the order of a few mT could be detected with a simple normal-incidence optical system.


Design of a hybrid plasmonic waveguide device using a trench structure


Magnetically tunable visible reflectivity utilizing the electron accumulation in indium-tin-oxide waveguide layer with subwavelength grating


GaN-Based High-Contrast Grating for Refractive Index Sensor Operating BlueViolet Wavelength Region


Femtosecond laser self-assembly for silver vanadium oxide flower structures

Flower-like silver vanadium oxide (SVO) micropatterns were realized by femtosecond laser in situ writing from its precursor. Self-assembled petals irradiated by a femtosecond laser were observed standing on the substrate along the scanned routine assisted by the formation of silver seeds and plasmonic-mediated effects. By controlling the concentration of ammonium monovanadate and the laser exposure time, a different thickness of petals was manipulated from ∼100 nm to micrometers. The SVO products were confirmed AgVO, AgVO, and part of AgVO by x-ray diffraction (XRD) measurement. Photon-driven self-assembly for in situ fabrication of microstructures looks to be an effective and facile technique for SVO and other functional compounds.


Ni subwavelength grating/SiO2/Ag based optical magnetic field sensor with normal incident geometry


Dual-wavelengths filter operating at visible wavelength region using subwavelength grating on waveguide structure


Highly Sensitive Refractive Index Sensor Using Dual Resonance in Subwavelength Grating/Waveguide With Normally Incident Optical Geometry


Optical magnetic field sensor based on guided mode resonance with Ni subwavelength grating/ waveguide structure


Size-dependent plasmonic resonance of rectangular resonator coupled with plasmonic waveguide

In this study, we propose and investigate a rectangular resonator coupled with metal/insulator/metal-(MIM)-type plasmonic waveguides (PWGs) for application in strain or refractive index sensors. Two types of resonance modes due to different propagation directions of the surface plasmon polaritons in the rectangular resonator are analyzed through numerical simulation. The proposed device is realized by placing a rectangular resonator on MIM-type PWGs fabricated on a glass substrate, and the experimental transmission spectra of this device are found to be in good agreement with the results of numerical simulation. Two types of resonance modes with different amounts of shift are clearly observed. The change of 10 nm in the size of the rectangular resonator is detected by using the resonance mode.


Design optimization and resonance modes of a plasmonic sensor based on a rectangular resonator

In this paper, we propose a plasmonic nanosensor based on a metal/insulator/metal plasmonic waveguide with a rectangular resonator. The proposed nanosensor can be used for mechanical strain and thermal stress sensing. We investigated the plasmonic resonance modes based on a standing wave model in the rectangular resonator. In addition, the plasmonic resonances of the rectangular resonator were numerically investigated using the finite-difference time-domain method. The bonding and anti-bonding modes of the plasmonic resonator can be expressed using the mechanical model of coupled harmonic oscillators.


Highly sensitive magnetic field sensor with normal-incidence geometry using Ni-based bilayer subwavelength periodic structure operating in visible-wavelength region


MEMS plasmonic switch with stripe plasmonic waveguide


High-sensitivity refractive index sensor with normal incident geometry using a subwavelength grating operating near the ultraviolet wavelength


Ultraviolet polarizer with a Ge subwavelength grating


Resonance modes in unbalanced Mach-Zehnder interferometers embedded in plasmonic waveguides

We proposed an unbalanced Mach-Zehnder interferometer (MZI) by using Metal/Insulator/Metal PWGs for optical modulation or sensor devises. Transmission spectra of the MZI were calculated by Finite difference time domain method. We observed an interference pattern and transmission dips in calculated transmission spectra of an unbalanced MZI. An interference pattern is due to different path length of an unbalanced MZI. The Transmission dips are due to resonance in unbalanced MZI. Standing wave was appeared when the wavelength of the gap plasmon mode is equal to the integral multiple of PWG length of resonance area. Therefore, an unbalanced MZI in plasmonic waveguides serves as a ring resonator.


Hybrid plasmonic-photonic crystal formed on gel-immobilized colloidal crystal via solvent substitution

Gel-immobilized colloidal crystals were prepared to obtain hybrid plasmonic-photonic crystals, in which electric field enhancement to a greater extent than that due to localized surface plasmons (LSP) alone was expected due to coupling between LSP and the photonic band. Polystyrene colloidal crystals immobilized by the N-(hydroxymethyl)acrylamide gel were immersed in an aqueous dispersion of gold nanoparticles (AuNPs). Then, the gel-immobilized colloidal crystals were picked out and immersed in an ionic liquid mixture. The surfaces of the gel-immobilized colloidal crystals immersed in the AuNP dispersion were observed via scanning electron microscopy after this solvent substitution. The lattice spacing of the colloidal crystal varied as the composition of the ionic liquid mixture was changed. The composition was determined so that the photonic band gap wavelength coincided with the LSP wavelength. Further, the reflection spectra were measured. Thus, we successfully prepared a hybrid plasmonic-photonic crystal.


Theoretical investigation of polarization control in ultraviolet wavelength region using eigenmode within subwavelength grating


Fabrication of peelable thin films containing crescent-shaped split-ring resonators for three-dimensional optical metamaterials

In this paper, we propose peelable thin films containing crescent shaped split-ring resonators (SRRs) that can be utilized for the fabrication of three-dimensional (3D) metamaterials. The SRRs were two-dimensionally fabricated by nanosphere lithography with closely packed polystyrene nanospheres in a large area prepared by electrostatic adsorption. The SRR monolayer film, which had macroscopic dimensions of over 10 × 10 mm2 (area) and a thickness of about 230 nm, was then obtained by using a separation technique. Once the SRR monolayer films were fabricated, multi-layered metamaterials were obtained via repetition of a simple stacking procedure. In this case, we fabricated a 4-layered SRR film with the same relative orientation for each layer. In order to investigate the optical characteristics of these multi-layered SRR films, transmission spectra for normal incident light were measured. The transmission spectra demonstrate that our multi-layered metamaterials operate in the near-infrared region.


Gap plasmon excitation in plasmonic waveguide using Si waveguide

Plasmonic waveguides have attracted considerable attention for application in highly integrated optical circuits since they can confine light to areas smaller than the diffraction limit. In this context, in order to realize a highly integrated optical circuit, we fabricate and evaluate the optical characteristics of a poly(methyl methacrylate) junction positioned between Si and plasmonic waveguides. For the plasmonic waveguide, we employ a gap plasmonic waveguide in which the energy of the plasmonic wave can be confined in order to reduce the scattering loss at the junction. By experimental measurement, we determine the coupling efficiency between the Si and gap plasmonic waveguides and the propagation length at the gap plasmonic waveguide to be 52.4% and 11.1 m, respectively. These values agree with those obtained by the three-dimensional finite-difference time-domain simulation. We believe that our findings can significantly contribute to the development of highly integrated optical circuits.

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Design optimization and fabrication of Mach-Zehnder interferometer based on MIM plasmonic waveguides

We proposed and designed a compact unbalanced Mach-Zehnder interferometer (MZI) based on metal/insulator/metal (MIM) plasmonic waveguides for ultrafast optical signal processing. The MZI was fabricated by a lithography technique and we provide, for the first time experimental evaluation of the transmission performance of the MZI using MIM PWGs. The experimental results were in good agreement with the numerical simulations. The proposed structure could be considered as a key device for on-chip optical integrated circuits.


Highly polarized emission from a GaN-based ultraviolet light-emitting diode using a Si-subwavelength grating on a SiO2 underlayer


Preparation of Large-area Controllable Patterned Silver Nanocrystals for High Sensitive and Stable Surface-enhanced Raman Spectroscopy

Chemical Research in Chinese Universities


Pulsed-laser-deposited TiO2 nanocrystalline films supporting Au nanoparticles for visible-light-operating plasmonic photocatalysts

Applied Physics. A, Materials Science & Processing


Nanostrucure for Hybrid Plasmonic-Potonic Crystal Formed on Gel-Immobilized Colloidal Crystal Observer by AFM after Drying

Aiming at fabrication of hybrid plasmonic-photonic crystals, gel-immobilized colloidal crystals made of a polystyrene colloidal suspension and an N-(Hydroxy methyl)acrylamid-based gel were immersed into an aqueous dispersion of gold nanoparticles. Atomic force microscope (AFM) observations have been performed for the gel-immobilized colloidal crystals with gold nanoparticles deposited on their surfaces. In the present study, the diameter of a colloidal sphere was c.a. 190 nm. The diameter of a gold nanoparticle was the same as in a preliminary study, c.a. 40 nm. Various immersion times up to two hours were tested. Surface of a sample of 2 hr immersion has been observed. Prior to the AFM observation, the sample was dried in a desiccator for 18 hrs. We have identified a face-centered cubic {111} structure of a colloidal crystal of nearly close packing. Nanoparticles isolated with one another have been observed on the surface of gel-immobilized crystal, which can be regarded as gold nanoparticles from their sizes.

Bulletin of the Chemical Society of Japan


Optical characteristics of rounded silver nanoprisms


NEMS技術を利用した可変プラズモンデバイスの開発

NEMS技術を利用した可変プラズモンデバイスの開発

IEEJ Transactions on Sensors and Micromachines

電気学会論文誌E (センサ・マイクロマシン部門誌)


剥離可能な分割リング共振器フィルムの作製

剥離可能な分割リング共振器フィルムの作製

PMMA薄膜上にナノスフィアリソグラフィ法で作製したSRRを配置させた「SRRフィルム」を作製し，その積層膜作製や凸構造を持つ基板上への堆積実験を行った．

電気学会論文誌E (センサ・マイクロマシン部門誌)


Influence of low-contrast subwavelength grating shape on polarization characteristics of GaN-based light-emitting diode emissions


Heterojunction of poly (o-toluidine) and silicon nanowires

A nanostructured poly (o-toluidine)/silicon nanowires (NPOT/SiNWs) heterojunction has been fabricated with a low cost and simple techniques, where NPOT has been in situ polymerized upon SiNWs synthesized by chemical etching of a silicon wafer. The morphology of SiNWs before and after deposition of NPOT has been examined by scanning electron microscope (SEM). The chemical composition of NPOT has been investigated by Fourier transform infrared (FTIR), ultraviolet-visible (UV-visible) spectroscopy, and X-ray diffraction (XRD) techniques. NPOT morphology has also been examined by SEM before being deposited on the SiNWs. I-V measurements of the device have been made at room temperature under dark conditions. The heterojunction diode parameters such as turn-on voltage, reverse saturation current (I0), ideality factor (), barrier height (B) and series resistance (Rs) have been determined from the I-V curves using Schottky equations. The device shows promising characteristics as a candidate for producing heterojunction diodes.


Self-imaging confirmed in plasmonic channel waveguides at visible wavelengths


Optical Characterization of the Antigen Antibody Thin Layer Using the Whispering Gallery Mode

We immobilized an antibody (anti--Galactosidase) on a polystyrene microsphere by using a covalent bond, and observed the resonance peaks in the scattered light intensity spectra related to the whispering gallery mode (WGM) excitation of the microsphere. The amount and the optical parameters, i.e., thickness and refractive index, of anti--Galactosidase on the sphere surface were evaluated based on an absorbance measurement and a resonance peak shift measurement, respectively. Moreover, we measured the variation of the WGM spectra depending on the concentration of the enzyme solution (-Galactosidase), which allowed us to optically evaluate the thickness and the refractive index of the antigen antibody layer from the shift of the WGM spectra peak.


Polarized emission characteristics of UV-LED with subwavelength grating


Cross-Sectional Optimization of Whispering-Gallery Mode Sensor With High Electric Field Intensity in the Detection Domain

Optimal cross-sectional shapes for whispering-gallery mode sensors with prescribed emission wavelengths and resonance modes are generated through topology optimization based on the finite element method. The sensor is assumed to detect the state of the domain surrounded by the sensor. We identified the integral of the square of the electric field intensity over the detection domain and the quality factor (Q factor), which should be maximized, as key values for the sensor sensitivity, representing the detection limit for the relative permittivity change of the test object. Based on this, the integral of the square of the electric field intensity over the detection domain and the Q factor are studied as the optimization targets. In our numerical study, their optimal configuration characteristics are identified and analyzed. The resulting device has a small radius, a small detection domain and a concave shape with a center located next to the detection domain. We also succeeded in performing simultaneous optimization of the integral of the square of the electric field intensity over the detection domain and the Q factor.

IEEE Journal of Selected Topics in Quantum Electronics


Research on the fabrication and property of hydrophobic antireflective infrared window

We proposed a facile approach for rapid and maskless production of zinc sulfide microstructure used as antireflective and hydrophobic surface by direct laser interference ablation. This surface could improve the infrared transmittance from 75% to 92%; and the problem of bad film adhesion, corrosion resistance, and the thermal expansion mismatch in the antireflective coating membrane were solved. By this method a quick and simple fabrication, and a large-area production as well as the hydrophobic properties with a contact angle of 145° can be realized. Hence this approach can have future broad applications in areas of optoelectronics, solar energy, aerospace, and infrared guidance etc.


Fabrication of microelectrodes based on precursor doped with metal seeds by femtosecond laser direct writing

Silver (Ag) seeds for assisting femtosecond laser direct writing (FsLDW) were employed in the fabrication of microelectrodes (MEs). Pattern-controllable and size-tunable MEs can be easily constructed by introducing Ag seeds to the ion precursor solution in the process of laser-induced photoreduction of the Ag ions. The fabrication process is stable under sufficient material supply, and the applied laser power is reduced to one-tenth of that without Ag seeds. Finally, as a representative application, an organic field effect transistor (OFET) was fabricated, based on this laser-fabricated Ag ME. The OFET exhibited good photoelectric properties, and achieved an on off ratio of 200.


Characteristics of nano-plasmonic resonators with a gap structure

Applied Physics. A, Materials Science & Processing


Electrically driven plasmon chip: Active plasmon filter

We have developed an electrically driven plasmon chip, i.e., an active plasmon filter, consisting of a metallic subwavelength grating modulated by a nano-electro-mechanical system (NEMS) type actuator. The device shifts the plasmon resonance wavelength and the transmittance when an electrical signal is applied. The fabricated filter shows resonance wavelength shifts of 60nm with a bias voltage of less than 10 V. A rigorous numerical calculation confirms the origin of the surface plasmon resonance and qualitatively explains the effect. Such NEMS optical devices offer rapid voltage-controlled plasmonic tuning of 20 MHz, opening up applications in agile sensing and nanoscale object trapping using actively tailored optical hot spots.


Resonance-based integrated plasmonic nanosensor for lab-on-chip applications

An integrated plasmonic resonator was proposed and analyzed. The detection performance of our device has been numerically verified by finite-difference time-domain simulations. The spectral sensitivity obtained was found to be 700 nm/RIU , where RIU is the refractive index unit. Our proposed sensor was found to have a detection limit in the order of 10 -6 RIU . The plasmonic sensor could be fabricated using focus ion beam milling. Our design leads to an ultra-compact sensor suitable for on-chip sensing applications associated with a high sensitivity. For biosensing, the proposed sensor could have the ability for a specific capture of biomolecules at the sensor surface that enables for quantification of the biomolecules.


Complex third-order nonlinear optical susceptibility spectrum of a CdS film coat on a silver nanoparticle

We have fabricated a CdS-coated Ag nanoparticle using the reverse micelle method and observed the nonlinear optical response of the scattered light intensity caused by an individual particle. In addition, we succeeded in obtaining the complex third-order nonlinear susceptibility χ(3) spectrum near the energy band edge of the CdS film by comparing the experimental result and the result of the Mie calculation that considered the optical Kerr effect of the CdS. At ħωi = 2.43 eV, the χ(3) of the CdS was (1.1 + i0.6) × 10-17m2/V2. We conjecture that an increase in the carriers in the interband transition of the CdS originates from the increase in the χ(3) of the CdS at ħωi > 2.4eV.


Fabrication and evaluation of photonic metamaterial crystal


Electrical Characterization of Nanopolyaniline/Porous Silicon Heterojunction at High Temperatures

Nanopolyaniline/p-type porous silicon (NPANI/PSi) heterojunction films were chemically fabricated via in situ polymerization. The composition and morphology of the nanopolymer were confirmed using Fourier transform infrared, scanning electron microscopy, UV-visible, and transmission electron microscopy techniques. The results indicated that the polymerization took place throughout the porous layer.The I-V measurements, performed at different temperatures, enabled the calculation of ideality factor, barrier height, and series resistance of those films. The obtained ideality factor showed a nonideal diode behavior.The series resistance was found to decrease with increasing temperature.


Characteristics of Double-Plasmonic-Racetrack Resonator to Increase Quality Factor


Dependence of LC resonance wavelength on size of silver split-ring resonator fabricated by nanosphere lithography

We fabricated silver split-ring resonators (SRRs) using nanosphere lithography and measured the LC resonance wavelength of single isolated SRRs in optical wavelength range. The SRRs' sizes decreased when smaller polystyrene spheres were used as templates, and their LC resonance wavelength decreased to 721 nm. The LC resonance wavelength corresponding to the observed properties of the SRRs was calculated using the LC circuit model; we confirmed that the observational and calculated results agreed well. The LC resonance frequency of a miniaturized SRR with a constant shape was also calculated. For SRRs of the shape that we fabricated, the estimated short-wavelength limit was 426 nm.


Surface Plasmon Polariton grating coupler on the Ti diffused LiNbO3 channel waveguide

World Academy of Science, Engineering and Technology


Sterilization effect of UV light on Bacillus spores using TiO(2) films depends on wavelength.

UV light and photocatalysts such as titanium dioxide (TiO(2)) and silver (Ag) are useful for disinfection of water and surfaces. However, the effect of UV wavelength on photocatalytic disinfection of spores is not well understood. Inactivation of Bacillus spores has been examined using different UV wavelengths and TiO(2) or TiO(2)/Ag composite materials. The level of UVA disinfection of Bacillus anthracis and Bacillus brevis vegetative cells increased with the presence of the TiO(2) and Ag photocatalysts, but had little effect on their spores. B. brevis spores were slightly more sensitive to UVB and UVC than the spores of B. atrophaeus. Photocatalytic sterilization against spores was strongest in UVC and UVB and weakest in UVA. The rate of inactivation of Bacillus spores was significantly increased by the presence of TiO(2), but was not markedly different from that induced by the presence of Ag. Therefore, TiO(2)/Ag plus UVA can be used for the sterilization of vegetative cells, while TiO(2) and UVC are effective against spores.

The Journal of Medical Investigation : JMI


Experimental demonstration of plasmonic racetrack resonators with a trench structure


Design of Plasmonic Racetrack Resonators with a Trench Structure

The authors present a plasmonic racetrack resonator with a trench structure. The depth of the structure and the length of the racetrack straightaways both significantly influence the characteristics of the plasmonic racetrack resonator. The optimum depth of the structure and length of the straightaways have been numerically evaluated by the finite-difference time-domain method. The quality factor of the plasmonic racetrack resonator is 38. As compared to the output intensity of a plasmonic ring resonator with a trench structure, the output intensity of the proposed plasmonic racetrack resonator is greater by one order of magnitude.


Characteristics of Coupled Plasmon Modes in Asymmetric Layered System


Additional effects of silver nanoparticles on bactericidal efficiency depend on calcination temperature and dip-coating speed.

There is an increasing interest in the application of photocatalytic properties for disinfection of surfaces, air, and water. Titanium dioxide is widely used as a photocatalyst, and the addition of silver reportedly enhances its bactericidal action. However, the synergy of silver nanoparticles and TiO(2) is not well understood. The photocatalytic elimination of Bacillus atrophaeus was examined under different calcination temperatures, dip-coating speeds, and ratios of TiO(2), SiO(2), and Ag to identify optimal production conditions for the production of TiO(2)- and/or TiO(2)/Ag-coated glass for surface disinfection. Photocatalytic disinfection of pure TiO(2) or TiO(2) plus Ag nanoparticles was dependent primarily on the calcination temperature. The antibacterial activity of TiO(2) films was optimal with a high dip-coating speed and high calcination temperature (600°C). Maximal bacterial inactivation using TiO(2)/Ag-coated glass was also observed following high-speed dip coating but with a low calcination temperature (250°C). Scanning electron microscopy (SEM) showed that the Ag nanoparticles combined together at a high calcination temperature, leading to decreased antibacterial activity of TiO(2)/Ag films due to a smaller surface area of Ag nanoparticles. The presence of Ag enhanced the photocatalytic inactivation rate of TiO(2), producing a more pronounced effect with increasing levels of catalyst loading.


Study the Effect of Phenylenediamine Compounds on the Chemical Polymerization


Visible near-infrared light scattering of single silver split-ring structure made by nanosphere lithography

We succeeded in making a silver split-ring (SR) structure of approximately 130 nm in diameter on a glass substrate using a nanosphere lithography technique. The light scattering spectrum in visible near-infrared region of a single, isolated SR was measured using a microscope spectroscopy optical system. The electromagnetic field enhancement spectrum and distribution of the SR structure were simulated by the finite-difference time-domain method, and the excitation modes were clarified. The long wavelength peak in the light scattering spectra corresponded to a fundamental LC resonance mode excited by an incident electric field. It was shown that a single SR structure fabricated as abovementioned can operate as a resonator and generate a magnetic dipole.


The optical characteristics of planar bilayered metallic prisms

Applied Physics. A, Materials Science & Processing


Fabrication of Organic Spin-on-Glass Microring Resonator with a Narrow Gap between a Microring Resonator and a Waveguide Using Nanoimprint Lithography

A microring resonator with a narrow gap between a waveguide and a microring resonator has been fabricated by using nanoimprint lithography. An organic spin-on-glass has been used as the material for the microring resonator. The outer diameter of the microring resonator is 20 m and the coupling gap between the straight waveguide and the microring resonator is 40 nm. The filtering characteristics of the microring resonator have been evaluated using a metal halide lamp. The free spectral range is 3.9 nm and the $Q$-factor is 310. The structure of the microring resonator with a narrow gap can be used as a fundamental component of optical devices.

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


PLASMONIC RACETRACK RESONATOR FOR APPLICATION TO PHOTONIC INTEGRATED CIRCUITS AT SUB-WAVELENGTH

Journal of Nonlinear Optical Physics & Materials


Nonlinear trimer resonators for compact ultra-fast switching

We propose and numerically verify a scheme for compact optical modulation which can enable complex directional switching of signals in integrated micro-optical circuits within hundreds of femtoseconds. The scheme is based on a trimer comprised of two identical silica whispering gallery mode (WGM) microresonators spaced by a central non-linear WGM resonator. The non-linear resonator is in the form of a silica cylinder with a thin coating of an ultrafast Kerr nonlinear material (a J-aggregate of cyanine dye). Using a two-dimensional finite-difference time-domain method and realistic material and structural parameters, we investigated the near-field coupling from a waveguide to the trimer and the subsequent switching process. In our scheme the sandwiched central control resonator has a resonant frequency that is mismatched to that of the input and output resonators. Therefore the optical energy is coupled from the waveguide into only the primary resonator in linear operation. However, for control light intensities of more than approximately 10(-2) W/microm the effective index and hence eigenfrequency of the central resonator can be shifted to match that of its neighbors and hence the optical energy can be redirected.


Linear and Nonlinear Optical Phenomena of Metallic Nanoparticles

IEEE Journal of Selected Topics in Quantum Electronics


Characteristics of Surface Plasmons in Silver Nanorods

We have calculated the optical responses of a variety of nano size silver particles, i.e., a column, a hexahedron, an ellipse, and an ellipsoidal rod, by using the finite-difference time-domain method. For a pair of ellipsoidal rods, we have found a suitable distance for the gap between the rods for transferring the energy of longitudinal (L) and transverse (T)-mode plasmons. We have also investigated the suitable configuration of an ellipsoidal rod array with a bend for changing the plasmon propagation direction and the mode from the L-mode to the T-mode.


Characteristics of gap plasmon waveguide with stub structures

We found that metal-dielectric-metal plasmon waveguides with a stub structure, i.e. a branch of the waveguide with a finite length, can function as wavelength selective filters of a submicron size. It was found that the transmission characteristics of such structures depend on the phase relationship between the plasmon wave passing through the stub and the one returning to the waveguide from the stub. We also propose structures with a lossless 90 degrees bend in a plasmon waveguide, utilizing a stub structure. Furthermore, we present a functional stub structure, e.g., a 1:1 demultiplexer and a wavelength selective demultiplexer.


Numerical and experimental investigation of wedge tip radius effect on wedge plasmons


Nonlinear Optical Response of a CdS-Coated Ag Particle

In this paper, we present an experimental observation of the optical nonlinear characteristics of a CdS-coated Ag particle at room temperature. By using sub-picosecond pulses generated by a tunable optical parametric amplification system, we confirm that the light intensity scattered by the particle considerably decreases with an increase in the incident light intensity at a photon energy higher than the energy corresponding to the interband absorption edge of CdS. The nonlinear phenomena presented in this paper are observed in an event in which localized surface plasmons enhance the two-photon absorption in CdS and cause the valence electrons to be excited into the conduction band of CdS and to further move to a higher energy band of Ag without additional energy supply.


Characteristics of light intensity enhancement of a silver nanoprism with rounded corners


Electric field enhancement effect of nano gap of silver prism


Characteristics of an Optical Filter Composed of Two Vertically Coupled Microring Resonators

We have numerically evaluated the filtering characteristics of two vertically coupled microring resonator filters. In this evaluation we used the finite-difference time-domain method as the numerical analysis method. The structure we designed allows only a specific wavelength to pass. The filtering characteristics of this structure can be altered by changing the layout of the microring resonator. By using this structure the interval between peak wavelengths at a specific wavelength in the output spectrum can be increased. Specifically, the interval between peak wavelengths can be increased from 20nm to 40nm at wavelengths near 1.46μm.


Optical Amplifier Using Nonlinear Nanodefect Cavity in Photonic Crystal

We have proposed a new optical amplifier in a photonic crystal. The amplifier consists of a nonlinear nanodefect cavity and a cross waveguide. The input-output characteristics have been simulated for the amplifier with three- or four-port cross waveguide in a two-dimensional photonic crystal by the finite-difference time-domain method. In the amplifier, a signal light can be amplified by an energy transfer from a control light to the signal light at the nonlinear nano-defect cavity. The calculated amplification factor of the amplifier was $2.33imes 10^{4}$. When optical transistor was used with an amplifier with a three-port cross waveguide in a two-dimensional photonic crystal, the calculated switching rate, the on-off ratio and the amplification factor of the transistor were 12 Gbit/s, $1.95imes 10^{5}$ and $2.29imes 10^{4}$, respectively. The transistor can work well even under a low power input in the signal port and can be utilized as a small amplifier and an optical sensor with a fast response.

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Fabrication and Optical Evaluation of Silica Microsphere Coated with J-Aggregates

We have fabricated a micrometer-sized nonlinear optical resonator consisting of a silica microsphere coated with J-aggregates of 1,1'-diethyl-2,2'-cyanine iodide in a thin silica film by a sol-gel process. The sphere diameter was 4.5 µm and the film thickness was estimated to be approximately 100 nm by scanning electron microscopy. The coating on the sphere was characterized by the fluorescence of the J-aggregates and the detection of whispering gallery modes (WGM) in the fluorescence spectrum. The optical evaluation of the sphere was performed in the attenuated-total-reflection configuration. We confirmed that the resonances in the scattering spectrum were due to WGMs, on the basis of a comparison of the experimentally obtained peak positions for coated and noncoated spheres, to those obtained using Mie's theory. The positions of the scattering peaks and the values of the full-width at half-maximum in the scattering spectrum for the coated sphere differ from those of the noncoated sphere.


Self-modulation of scattering intensity from a silica sphere coated with a sol-gel film doped with J-aggregates


New plasmon waveguides composed of twin metal wedges with a nano gap


Numerical analysis of coupled wedge plasmons in a structure of two metal wedges separated by a gap


Preparation of Nano- and Microparticles through Self-Assembly of Azobenzene-Pendent Ionomers

アゾベンゼンを側鎖として含むアイオノマーを合成し，自己組織化によってナノ/マイクロ粒子を調製した．アゾベンゼン含量とNaOH水溶液の濃度を変化させることによって粒子サイズを制御できることが明らかとなった．


Filtering Characteristic of a Microring Resonator with a Gap

ギャップが一つある場合と2つある場合のマイクロリング共振器と導波路を組み合わせた構造での光フィルタ特性を数値解析した．その結果，ギャップを持つマイクロリング共振器では，ギャップがないマイクロリングでは2つ以上を組み合わせしなければ実現できない，自由スペクトル領域の拡大や透過帯域の平坦化が実現できることが分かった．

Electronics and Communications in Japan (Part II: Electronics)


Composite domain control for surface plasmon resonance

We developed a method of composite domain control (CDC) for plasmon resonance as an application of multilayered domain control (MLDC). A distinctive characteristic of CDC is the utilization of dielectric and metal particles. Its structure is similar to that fabricated by the sol-gel method. It is considerably thinner than that prepared by MLDC. In addition, it is possible to conveniently and exactly adjust the plasmon resonance utilizing CDC because it combines the characteristics of MLDC. Accordingly, CDC is a conventional method that is more effective than MLDC. Moreover, CDC is suitable in manufacturing with regard to stress reduction, miniaturization, and cost of the products.


Two-dimensionally localized modes of a nanoscale gap plasmon waveguide

We report numerical analysis and experimental observation of two dimensionally localized plasmonic modes guided by a nanogap in a thin metal film. Dispersion, dissipation, and field structure of these modes are analyzed using the finite-difference time-domain algorithm. The experimental observation is conducted by the end-fire excitation of the proposed gap plasmon waveguides and detection of the generated modes using their edge scattering and charge coupled device camera imaging. Physical interpretation of the obtained results is presented and origins of the described modes are discussed.


Multilayered domain control for surface plasmon resonance

Metal particles are utilized to study surface plasmon resonance. They are regulated in terms of their dimensions to control surface plasmon resonance, and sealed with a dielectric material. In this study, we applied a method of domain growth to form particles. It is an advantage in manufacturing because the entire process is carried out in a sputtering system. We describe a method of multilayered domain control (MLDC), illustrating it with Au, Ag and Cu for particles and SiO2 for dielectric layers in this paper. A remarkable feature of MLDC is its intensification of surface plasmon resonance. Moreover, this intensification enables base metals to substitute for noble metals.

Japanese Journal of Applied Physics, Part 2 (Letters)


Microscopic and Macroscopic Investigation of Localized Surface Plasmons on Ag Nanoparticles Embedded in Porous TiO2 Glass


Nonlinear Optical Response of a Metal Circular Cylinder Coated with a Kerr Material: Numerical Simulations

The Journal of the Korean Physical Society


Characteristics of Whisperng Galley Modes in Single Dielectric Spheroid: Dependence on the Direction of Incident Light


Theoretical and experimental investigation of strongly localized plasmons on triangular metal wedges for subwavelength waveguiding

ナノサイズのウェッジ型プラズモン導波路において，局在プラズモンが伝搬できることをFDTD数値シミュレーションとNSOMの実験で初めて示した．頂上が40度の銀のウェッジ型プラズモン導波路をFIB加工で作製し，エンドファイヤーカップリングでプラズモンを励起し，ウェッジに沿って伝搬する局在プラズモンの近接場光の分布をNSOMで観測した．実験結果から得られた局在プラズモンの伝搬距離が，数値シミュレーションによる値と良く一致していることを示した．


ギャップのあるマイクロリング共振器のフィルタ特性解析

ギャップのあるマイクロリング共振器のフィルタ特性解析

The Transactions of the Institute of Electronics, Information and Communication Engineers C

電子情報通信学会論文誌(C)


Characteristics of Whispering Gallery Modes in Single Dielectric Spheroid Excited by Gaussian Beam

We hav enumerically analyzed a coupling between a Gaussian light and speroids by using a finite-difference time-domain method.There exists a complex whispering gallery mode in a speroids. The characteristics of the complex whispering gallery mode are similar to those produced from a combination of several WGM's.

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Light Intensity Enhancement and Optical Nonlinear Response due to Localized Surface Plasmons in Nanosize Ag Sphere

金属微小球を非線形光学材料でコートした構造の非線形光学応答を計算できる拡張ミー散乱理論に基づき，ナノサイズの銀微小球にCdSでコートした構造において生じる非線形光学特性の計算機シミュレーションを行った．微小球サイズ，コート膜厚が光スイッチ·光双安定現象に与える影響についてシミュレーションし，線形応答時における光強度増強度の微小球サイズ，コート膜厚依存性が局在プラズモンを利用した非線形光学応答に大きく関わっていることを明らかにした．


Mg添加GaN中のMgの熱活性化過程を二次イオン質量分析法とファンデアポー配置によるホール効果測定にて評価した．熱処理によりMg添加GaN層から脱離した水素の量と当該層の層のホール移動度，ホールキャリア濃度と抵抗率測定から，Mg添加GaN中の水素の脱離エネルギーは2成分観測された．一つは，0.8-1.5eV，もう一つは0.2-0.5eVである．前者はGaN中でMgの不活性化に関連していると思われ，後者はMg添加GaN中での正孔キャリアの電気的補償機構の不活性化に関連していると思われる．


Fabrication and optical characterization of a TiO2 thin film on a SiO2 micro-sphere

ゾルゲル法により直径10μmのシリカ微小球上に均質性が高い酸化チタン薄膜を作製することに成功した．さらに全反射減衰配置下では，偏光の違いにより球に励起される光学モードの特性が異なることを利用し，作製した膜の厚さと屈折率をそれぞれ65nmと2.4と決定した．直径10μm以下の微小球上の薄膜について，光学的な方法で求めることができる事を実験的に成功したのは世界ではじめてである．


Experimental evaluation of reflectance of surface plasmon polaritons at metal step barrier

ガラス基板状に銀薄膜を作製し表面プラズモンポラリトン(SPP)が金属ステップに入射した場合の反射率を実験により世界ではじめて直接的に求めた．単純な金属ステップに対してSPPの反射率は5%程度と小さい事を示した．


Evaluation of band-gap energies and characterization of nonradiative recombination centers of film and bulk GaN crystals

バルクと薄膜のGaN試料に対してバンドギャップ近辺における光熱分光スペクトルを測定し，バンド端吸収に対応した光吸収スペクトルを得た．不純物の種類や濃度の異なる薄膜試料についても測定し，光熱分光法により容易にGaNのバンドギャップエネルギを求めることができること，不純物をドープした試料ではhν<Egの領域で光吸収量が増大すること，またその領域のスペクトルに複数のピークが観測されその由来は非発光再結合準位であることを示した．


Optical switching due to whispering gallery modes in dielectric micro-spheres coated by a Kerr material

高屈折率(n=2.52)の誘電体微小球に光カー媒質をコートした球をプリズム上に配置した構造にて，プリズム側から球へ入射する光を信号光，空気側プリズム表面に平行に球へ入射する制御光とすると，制御光により光カー媒質の屈折率を変化させ，球特有の光学モードであるウィスパリングギャラリーモードの励起条件を変えることが可能であることを数値計算により示した．この時制御光は信号光をコントロールすることができるので，ミクロンサイズの光スイッチング素子の可能性を示す結果が得られた．


Optical filtering by microring resonators

高屈折率材料としてシリコンを，利用する波長として光通信帯域を想定し，スラブ型の微細直線導波路と円筒型の直径2μm程度の2つのリング型光共振器を組み合わせ，その光学特性を数値計算により求めた．2つのリングの直径や間隔をうまく設計する事で，これまでより2桁以上小さな面積にて光通信用に向いた特性を有する波長選択性の光学フィルタの構築が可能である事を示した．


Numerical studies of optical switching and optical bistability phenomena of nano- or meso-size spheres

We propose the use of numerical calculations of the optical response of nonlinear Kerr-spheres, modifying the Mie theory. As a numerical example, we use a CuCl sphere coated with a Kerr-nonlinear sphere, taking into account the excitation of the Z3-exciton. The results clearly show that optical bistable and/or optical switching devices can be realized on a nano- and meso-size scale when the real part of the dielectric constant of CuCl is negative.

ミー散乱理論を拡張し，ナノサイズの負誘電率微小球に光カー媒質による薄膜をコートした構造の非線形光学応答を求める計算手法を世界ではじめて開発した．まず，負誘電率微小球としてCuCl(Z3励起子によって負誘電率を示す波長を用いる)，光カー媒質としてCdSを想定し，コート外部の電界強度が入射光強度に対して最も強くなる構造を決定した．次に，その構造にてコート外部の電界強度の入射光強度に対する応答特性を求めたところ，光スイッチングや光双安定現象といった非線形光学応答が観測され，将来サブミクロンからナノメートルのサイズの非線形光学デバイスが開発できる可能性を示した．


Optical Switching Phenomena of Kerr Nonlinear Micro-Sphere due to Near-Field Coupling: Numerical Analysis

We calculated linear and nonlinear responses of a Kerr nonlinear microsphere sandwiched by two prisms using the excitation of whispering gallery modes due to near-field coupling. As numerical calculations, the finite-difference time-domain method that takes into account the Kerr nonlinear effect was used. We dealt with two types of spheres, i.e., the Kerr-material sphere and the dielectric sphere coated by the Kerr material. It was found that the optical switching phenomena are induced in such spheres. The switching results from the fact that the variations of the refractive index of the nonlinear spheres affect the excitation condition of the whispering gallery modes.

半導体のように屈折率が高い(n=2.52)誘電体微小球(直径1μm)に光カー媒質をコートした球をプリズム上に配置した全反射減衰構造にて，プリズム側からの光入射により球特有の光学モードであるウィスパリングギャラリーモードを利用すると，屈折率を変化によるモード励起条件変化を誘起することが可能であり，自己光スイッチング現象生ずることを数値計算シミュレーションにより示した．このように小さな誘電体微小球の光スイッチング現象の数値計算に成功したのは世界ではじめてである．ミクロンサイズの光スイッチング素子を実現する可能性があることを示す結果が得られた．


Temperature dependence of the thermal conductivity and phonon scattering time of a bulk GaN crystal

We have measured photothermal signals of a bulk GaN crystal by the photothermal divergence (PTD) method in the temperature range from 110 K to 370 K. The thermal conductivity and the scattering time of phonons contributing to the thermal conductivity have been evaluated from the phototherinal signals. A phonon-defect interaction has been expected to play a crucial role in determining the thermal properties of the sample employed here in the above temperature range.

バルクGaN試料に対して温度と励起光の変調周波数をパラメータとした光熱分光測定をおこない，GaNの熱伝導率とフォノン散乱時間の温度依存性を求めた．これまで信じられていたGaNの熱伝導率(室温で1.2W/cmK)よりも，大きな値(1.7W/cmK)であることを示した．また，フォノンの散乱時間の温度依存性から，測定に用いた試料には不純物が多く含まれていることが分かり，良質のGaNではさらに熱伝導率が大きくなる可能性を示唆した．


Lifetime of Optical Modes in Two Dimensionally Ordered Spheres

基板上に置かれた2次元配列の誘電体微小球中を伝搬する光学モードのライフタイムを，全反射減衰配置での光入力の場合と球内部から光が発生する場合について，有限差分時間領域法による数値計算シミュレーションにより求めた．全反射減衰配置で容易に観測·励起されるモードは基板の影響を受けやすく寿命が短い事，TEとTMの偏光では寿命が異なりTM偏光では基板の影響を受けやすいことを示した．

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Interaction of Light with Ordered Dielectric Spheres: Finite-Difference Time-Domain Analysis

有限差分時間領域法を用いて，誘電体微小球を配列させたフォトニック結晶にガウス光を入射した場合の結晶内部での光の伝播の状況や反射·透過特性を求めた．平面波入力ではわからなかった，結晶内部での光の拡散の状況を視覚的に明らかにした．


Numerical Analysis of optical modes in Two-dimensionally ordered polystyrene spheres in Attenuated Total Reflection Geometry

ガラスプリズム基板上の直径2μmのポリスチレン微小球からなるフォトニック結晶に対する角度スキャン全反射信号スペクトルを，有限差分時間領域法によるシミュレーションで再現するとともに，観測されたモードどのように球内部を伝搬しているのかを視覚的にあきらかにした．


Finite-Difference Time-Domain Analysis on Nonlinear Fabry-Perot Resonator in Optical Waveguide Geometry

非線形性の飽和と非線形感受率の虚部を考慮して3次の非線形光学現象を計算できる有限差分時間領域法を開発し，スラブ型光導波路中に光カー媒質からなるファブリペロー共振器を配置した場合の光双安定特性を計算した．非線形性の飽和があった場合に，非線形ファブリペロー共振器がより安定に動作することを示した．


Optical Switching Due to Local Kerr Nonlinearity in Attenuated Total Reflection Geometry

3次の非線形光学材料であるポリジアセチレンをコアとする対称三層スラブ型光導波構造に，全反射減衰配置でビーム広がりを考慮したガウス型の光ビームにより導波モードを励起すると，条件によっては光スイッチング現象が生ずることをシミュレーションにより明らかにした．そこで必要な入射光強度は10kW/cm2より小さく，非線形屈折率定数も10-14m2/V2以下と十分実験可能な領域にあることを示した．入射光の広がり角の調整などにより，空間的な位相関係を最適な状態にすれば，非常に低い入射光強度で光スイッチ現象が得られる可能性があることを示した．


Determination of the Second-Order Nonlinear Optical Susceptibility of GaN Films on Sapphire

メーカフリンジ法にて，サファイア基板上のGaN試料の2次の非線形光学定数を求めた．これまで，GaN試料では無視されていたGaN薄膜内部での光干渉の効果を考慮しなければ正しい定数を求めることができないのを明らかにし，2次の非線形光学定数χ(2)として，zxx成分は14.7pm/V，xzx成分は14.4pm/V，zzz成分は29.7pm/Vと求めた．


Optical modes in two-dimensionally ordered dielectric spheres

直径5μmのポリスチレン微小球をガラス基板上に2次元的に配列させたフォトニック構造にて，色素レーザを光源とする全反射減衰法による光学モード励起実験を行った．伝播速度が速いものと遅い2つのタイプの導波型光学モードが観測した．伝播速度の違いと屈折率分布状況より考察を行い，速いタイプはチャネル導波路を直線的に伝搬する導波モード，遅いタイプは球の表面近くを周り込みながら隣の球へと伝搬する型の導波モードと解釈できること示した．


Optical Pulse Narrowing Due to Electronic Nonlinearity of PDA Films in ATR Geometry

ポリジアセチレン薄膜をコアとするスラブ型対称三層構造の導波モードを，パルスレーザを用いて全反射減衰配置にて励起し，反射光角度依存パターンの入射光強度依存性を観測したところ，入射光強度が大きい場合に反射光空間パターンが非対称に狭くなる現象を観測した．パルスレーザのパルス時間幅は150ps程度で繰り返し周波数は802Hzであり熱効果を排除できるので，コアの電子的効果に基づく屈折率変化によりこの現象が観測できたと考えられる．


Interaction of Near-Field Light with Ordered Polystyrene Spheres: Experimental Studies

ガラス基板上に作製された2次元配列ポリスチレン微小球(直径2μm)の光学モード励起実験を全反射減衰法にて行った．その結果，伝搬モードを励起しやすい配置とそうでない配置がある事，伝搬モードには速度の異なるものが多数存在する事，伝搬せず局在型のモードが存在することが分かった．有限差分時間領域法によるシミュレーションで，入射角度により伝搬速度の異なる伝搬モードが励起される，実験結果と一致する結果を得た．


Real-time observation of the dielectric constant variation of evaporated polydiacetylene films during photopolymerization and photochromic transitions

固相のまま光重合やフォトクロミック変化を起こすことで知られるPDA-C4UC4について，光重合やフォトクロミック変化の間にPDA膜の光学定数，膜厚がどのよう変化するかをATR法によって明らかにした．このことにより各色相の状態が明確にわかるようになった．Ag膜の上の真空蒸着したPDA膜の光学定数値は配向膜のそれにほぼ等しい値となることがわかった．さらに，400nm-1400nmの波長域でのPDAの光学定数値を垂直反射法で決めることに成功した．


Optical constants and growth mode of Ni films deposited on evaporated Al, Ag and Cu films

Ni/Al(AlOx·Al), Ni/Ag, Ni/Cu(CuOx·Cu)の2層構造のNi膜の光学定数と構造をATR法，SEM，X線回折法を用いて明らかにした．Al(AlOx·Al)，CuOxCuの上のNi膜は島状構造で，Cu上では層状構造となることが判明した．Ag上では，SEMはNi膜が島状構造となっていることを示し，ATR法は成長の初期段階で連続膜の光学定数となることを示した．


Determination of the Anisotropic Optical Constant of Evaporated Polydiacetylene-C4UC4Films at 632.8nm

膜の光学定数と膜厚を測定するための簡単な反射法を提案した．BK-7プリズム上の無配向の青相PDA-C4UC4膜の波長632.8nmでの光学定数と膜厚を提案した反射法で測定し，膜は無配向であるが光学的に異方性であることが判明した．このことにより膜の分子配列の状況が明らかになり，膜面に沿った方向に大きな3次非線形光学定数を持つことがわかった．さらに，膜の重合状態の情報も提案した反射法から得られることがわかった．

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


Optical Bistability in Periodic Channel Waveguides

周期構造を持ったチャネル導波路に適応できる正確な非線形結合方程式を導出した．従来の方程式には含まれていない項の導出に成功し，それを非線形結合方程式に組み込んだ所，その項が光双安定現象のスイッチ強度を小さくすることが判明した．種々の導波路パラメータへのスイッチ強度の依存性を計算し，周期構造を持ったチャネル導波路の最適設計のための指針を明確にした．


Prolagation length of long-range surface optic waves in islandized silver films

波長632.8nmで，島状Ag膜の表面モードの伝搬距離Lを測定した．Lの測定にはATR法と反射光強度の空間分布法を用いて行い，同じ結果を得た．このように島状の膜でも長距離伝搬できる表面モードの存在を確認できた．


Experimental instrument for observing angle- and frequency-scanned attenuated total reflection spectra

周波数·角度同時スキャンのATR信号を0.7秒で測定できるATR装置を開発した．信号の検出にはCCDカメラを用いた．画像処理にはデジタル画像処理システムを採用し，500∼800nmの波長域での信号観測用のものを製作した．Ag膜の誘電率の波長依存性を測定し，従来の測定値と一致することを確認した．


Temperature Dependence of Raman Spectra in Si-doped GaAs/AlAs Multiple Quantum Wells

SiドープのGaAs/AlAsMQWの二つの縦光学フォノン·サブバンド間遷移結合モードによるラマン信号の温度依存性を測定した．結合モードの周波数はサブバンドの電子密度の変化に伴い変化した．高周波数結合モードによるラマン散乱強度は温度上昇と共に減少した．ある条件下で基底サブバンドの電子密度は温度変化と共にフェルミエネルギーを通して変化することを確認した．このような結果から結合モードの種々のパラメータを決定できた．


Propagation length of guided waves inlossy Si film sandwiched by identical dielectrics

波長632.8nmで，Si膜を伝搬するTM0およびTE0導波光の伝搬距離Lを測定した．Si膜を薄くしていくと，Lは非常に大きくなる．そのようなLを直接測定する方法を提案し，厚さ6.1nmのSiに対してTM0モードの場合，L=1.6mmという損失のあるSiに対して極めて大きな値を得た．この値は理論値と一致し，提案した方法の有効性も確認できた．

Journal of the Optical Society of America


Temperature dependence of photothermal divergence signal of GaAs

光熱分光法を用いてドープしてないGaAsとドープしたGaAsの光熱分光信号の温度依存性を測定した．信号強度と信号のカットオフ周波数の温度依存性は理論予測と一致した．試料の熱伝導度の温度依存性を決定できた．


Experimental Observation of Intersubband Excitations in Si-Doped GaAs/AlAs Multiple Quantum Wells

ATR法とラマン散乱法を用いてドープしたGaAs/AlAsMQWのサブバンド間遷移と結合した光学フォノンの観測をした．サブバンド間遷移によるステップをATR信号の中に観測できた．荷電密度サブバンド間遷移による二つのピークをラマン信号で観測した．これらの結果からサブバンド遷移のパラメータと井戸層のシートキャリア密度を決定できた．


Surface plasmon polariton radiation from silver films on fluoride films and surface roughness parameters of those silver films

CaF2, MgF2およびLiF蒸着膜上のAg膜の表面凹凸を実験的に評価した．CaF2およびLiFの場合，膜厚を大きくすると凹凸は大きくなるが，MgF2の場合，膜厚を変えても凹凸に変化はなかった．表面プラズモンエネルギーの凹凸による光放射特性を測定し，それをK-K理論によって説明することを試みた．K-K理論がどのような凹凸領域で通用可能か明確にした．


Propagation Length of Surface Plasmon Polaritons Propagating along Air-Metal Interface

波長10.6μmでCu-空気界面およびCaF2膜上のCu-空気界面の表面プラズモンの伝搬距離Lを測定した．CaF2 膜はLを減少させることがわかった．またLはCuの蒸着速度の違いによって異なることがわかった．さらに0.6328μmでAg-空気界面の表面プラズモンのLと表面凹凸の関係を明らかにした．

Journal of the Physical Society of Japan


Surface Plasmon Polaritons in Attenuated Total Reflection Geometry

オットATRおよびクレッチマンATR配置での表面ポラリトン(SP)特性を理論的に検討した．ある条件の時，SPの電磁界は伝搬と共に増加するなどの非現実的なことが生じる．この原因はプリズムの存在によって引き起こされ，それぞれの層の電磁界状態を検討することにより，非現実的なことを解釈できることを示した．さらに物理的に意味のある解はどのようなものかを明確に示した．


Surface Optic Waves in Ultrathin Films Bounded by Identical Slightly Lossy Materials

小さな損失を有する媒質で挟まれた超薄膜中の表面ポラリトンや導波光などの表面光モードの性質を理論的に検討した．そのようなわずかの損失でも表面光モードの特性に大きな影響を与え，例えば，伝搬距離やATR共鳴形は劇的に変わることが明らかになった．


Two modulation mechanisms for photoreflectance from GaAs/AlAs multiple quantum well

GaAs/AlAs MQWのフォトリフレクタンス信号のチョッピング周波数依存性を測定した．バッファーとMQWの界面状態やバッファー層の深い準位がバッファー層の変調場の周波数依存性を決めていることがわかった．さらに，フォトリフレクタンス法はMQWや超格子の深い準位の評価に有効な手段であることを示した．


Degradation Mechanism of Au/AlOx/Al Tunnel Junction

Al/AlOx/Alトンネル接合を空気中室温で発光状態にすると，接合の劣化が急激に進む．この劣化の原因をXPS分光法などを用いて詳細に検討した．結論として，Alの酸化および接合の破壊によって劣化が生じていることが明白になった．


Optical Bistability in Prism / Ag Film / Nonlinear Film / Air Geometry by Utilizing Surface Plasmon and Guided Wave Characteristics

表面プラズモンと導波光を励起することによって発生する光双安定性現象を理論検討した．非線形媒質としてはカー効果を示す4BCMU膜を用いた．TEおよびTM偏光に対する解析および数値計算を行った．導波光の方が光双安定現象を生じさせる臨界入力光強度Pcが小さい．条件を選べば，Pcを1W/cm2以下にすることが可能であることがわかった．


Surface Polaritons Due to the Folded Optical Phonons in GaAs/AlAs Superlattices

GaAs/AlAs超格子のATRスペクトルを250cm-1から600cm-1の範囲で測定した．超格子特有の折り返し光学フォノンによる表面ポラリトン信号を観測できた．さらに，GaAsとAlAsの光学定数を評価し，TOフォノンの衝突周波数が以前のバルク試料に対する測定値より低いことがわかり，その理由を明らかにした．


Studies on Surface Polaritons in Ultrathin Films Sandwiched by Identical Dielectrics

10nm以下の厚さのAg膜を同一媒体ではさんだ構造での表面ポラリトンの電磁界分布と伝搬特性を理論的に検討した．伝搬距離は，Ag膜の厚さを小さくすると単調に増加した．さらに，p偏光およびs偏光の両偏光に対して鋭いATR共鳴が生じることを明らかにした．


Optical Bistability Associated with Surface Plasmon Polariton Excitation

表面プラズモン(SP)の電界集中特性を用いたATR形光双安定性の理論検討を行った．非線形媒質としてカー効果を有するものを考えた．通常のSPおよび長距離伝搬SPの両方に対して，光双安定性現象の発生がありうることを示した．さらに，SP伝搬方向の非線形性は光双安定性に寄与しないことも示した．

Journal of the Physical Society of Japan


New type of photothermal spectroscopic technique

新しいタイプの光熱分光法を提案し実験に成功した．この方法は簡便で種々の環境下で実験が可能であることがわかった．さらに高いS/N比を示し，振動や揺れにも強く，今後広い範囲で使われうる分光法であることを明確に示した．


Photoreflectance Spectra from GaAs Buffer Layer of GaAs/AlAs Multiple Quantum Well/GaAs Buffer/GaAs Substrate

GaAs/AlAs系MQWのフォトリフレクタンス信号を測定した．結果を説明するためにエレクトロリフレクタンス用のAspnes理論を変形した理論を構築した．その結果，MQW層とGaAsバッファ層の間にできるビルトインフィールドが35kV/cmであることがわかった．さらにMQW層の厚さの均一性についての情報も得られた．

Japanese Journal of Applied Physics, Part 1 (Regular Papers & Short Notes)


In situ and real-time observation of optical constants of metal films during growth

I-ATR装置を用いて0∼50nmの膜厚を持った銀，銅，アルミニウム，金の光学定数を測定した．測定は,蒸着法により成長中の膜に対しその場観測によって行われた．従来，測定が難しくて，ほとんど情報のなかった極端に薄い膜，すなわち，不連続膜の光学定数の測定が正確に行える方法を提案し，実際に実験で示した．


Experimental observation of attenuated-total-reflection spectra of GaAs/AlAs superlattice

半導体超格子として広く研究されているGaAs/AlAs超格子のATRスペクトルを実験的に観測し，解析した結果を示した．ATRスペクトルは，超格子の表面フォノンポラリトン(SP)の励起がなされていることを示し，初めて超格子のSPの観測に成功した．またATRスペクトルの解析により，GaAsとAlAsの超薄膜(50Å)の光学定数が正確に決まること，超格子特有のフォノンモードの折り返し効果がスペクトルに現れることなどを指摘した．

Physical Review B, Condensed Matter and Materials Physics


Optical Response of Semi-Infinite and Finite GaAs/Al0.3Ga0.7As Superlattices

ATR法によって半導体超格子の表面ポラリトンを観測することが可能か否かの理論検討を行った．半無限と有限のGaAs/Al0.3Ga0.7As超格子のATR信号(クレッチマンとオットー配置)はSPによる共鳴をはっきりと示した．これらの信号は，市販の装置で容易に観測可能である．なお，ある周波数域では，大きな損失のため，ATR法がSP特性観測に必ずしも有効であるとは限らないことも示した．


Photoluminescence measurement in GaAs with high spatial resolution

20Kの低温下試料に対して空間分解能1μmのフォトルミネッセンス測定を行う装置を開発し，GaAs試料のバンド端発光の場所依存性測定を行い，その有効性を示した．その結果，半絶縁性GaAs基板には，強度比10倍を越える発光強度不均一性があることを明らかにした．


Surface Plasmon Polariton excitation by a Phase Shift Grating

World Academy of Science Engineering and Technology