[Show abstract][Hide abstract] ABSTRACT: Thulium-doped tantalum-oxide (Ta2O5:Tm) thin films were prepared using a simple co-sputtering method. A remarkable photoluminescence peak having a wavelength of around 800 nm due to Tm3+ was observed from a film annealed at 900°C for 20 min. The δ-Ta2O5 (hexagonal) phase of the Ta2O5:Tm sputtered film is very important for obtaining strong PL.
[Show abstract][Hide abstract] ABSTRACT: Co-sputtered tantalum (V) oxide and yttrium (III) oxide (Ta2O5:Y2O3) thin films were fabricated using radio-frequency magnetron sputtering for the first time, and their photoluminescence (PL) and X-ray diffraction properties were evaluated. Broad PL spectra from 380 to 800 nm were observed only from films annealed at 700°C. The maximum PL intensities were found around a wavelength of 500 nm regardless of the Y concentrations of the films, and the films annealed at 700°C were primarily amorphous phases. It seems that the broad PL spectra from the Ta2O5:Y2O3 films originated from oxygen vacancies of Ta2O5 and Y2O3 particles that may be produced in Ta2O5 by co-sputtering.
[Show abstract][Hide abstract] ABSTRACT: The photoluminescence (PL) properties of P or B single-doped Si nanocrystals (Si-nc's) and P and B co-doped Si-nc's are studied. In the single-doped Si-nc samples, PL quenching occurs as a result of the Auger nonradiative recombination process between the photoexcited excitons and free carriers supplied by doped impurities. In the (P, B) co-doped sample, on the other hand, the donor-acceptor (D-A)-pair recombination emission is clearly observed on the long-wavelength side of the intrinsic Si-nc emission peak at ∼900 nm. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc. PL spectra are measured at 50 and 300 K and found to indicate that strong thermal quenching occurs in a (P, B) co-doped sample at 300 K. This quenching effect is probably because of carrier migration among the donor and acceptor states. The PL decay rate is determined as a function of the emitted-light wavelength for the pure and (P, B) co-doped Si-nc samples.
[Show abstract][Hide abstract] ABSTRACT: We investigated theoretically the interference of two counterpropagating polarized light beams in optically anisotropic media whose optical axis is in the film plane and is gradually rotated around the thickness direction. Results indicated that pure polarization modulation without intensity variation is obtained in the inhomogeneous media when the total angle of the rotation is much smaller than the total retardation. Reflective anisotropic gratings recorded by the polarization modulation were formulated as the perturbation of the dielectric tensor, and diffraction properties were studied using coupled-wave analysis (CWA) and a numerical method. By assuming that the period of the intrinsic distribution is substantially larger than that of the induced one, we demonstrated that CWA estimates the diffraction efficiency and the polarization state of the diffracted light with high accuracy.
[Show abstract][Hide abstract] ABSTRACT: The diffraction properties of reflective anisotropic gratings, which can be recorded in photoanisotropic media with uniaxial birefringence by three-dimensional vector holography, were characterized through the use of coupled-wave analysis (CWA). By investigating the perturbation of the dielectric tensor, we demonstrated that the gratings with sinusoidal distribution of the azimuthal angle of the optic axis diffract polarized light in which the ordinary and extraordinary components are converted for incident light. The polarization conversion was consistent with that calculated by a numerical method. In addition, it was shown that CWA enables highly accurate calculation of the diffraction efficiency with wavelength dispersion when the amplitude of the azimuthal angle is small.
[Show abstract][Hide abstract] ABSTRACT: Proton beam writing (PBW) has attracted much attention recently as a technology. We next generation micro-fabricatio n fabricated the first single-mode, straight-line waveguides and Y -junction waveguides for A=l.55 flm consisting of PMMA films using the PBW technique.
OptoeElectronics and Communications Conference (OECC), 2011 16th; 01/2011
[Show abstract][Hide abstract] ABSTRACT: The diffraction properties of thick vector holograms were analyzed with the use of a simple coupled-wave theory. Two eigenpolarizations in the holograms were determined based on the dielectric perturbation, and diffraction efficiencies for the polarizations were calculated by applying the Kogelnik method. The results were compared with those simulated by the finite-difference time-domain method. As a result, it was demonstrated that the diffraction efficiencies calculated by the two methods are in good agreement for any incident polarization when the modulation depth of the anisotropic phase retardation is substantially smaller than the mean retardation. In addition, we confirmed that coupled-wave analysis provides reasonable accuracy for relatively large modulation in the case of Bragg incidence with eigenpolarization.
[Show abstract][Hide abstract] ABSTRACT: A novel photonic crystal waveguide was fabricated utilizing Si-ion implantation and two-dimensional structures. The transmission and reflection properties of a straight line and two 60-degree bend waveguides were characterized numerically using finite-difference time-domain (FDTD) method.
[Show abstract][Hide abstract] ABSTRACT: In this paper, a modified and easy finite-difference time-domain (FDTD) method based on a regular cartesian Yee's lattice is developed for calculating the dispersion diagram of triangular lattice photonic crystals (PCs). Our method uses the standard central-difference equation, which is very easy to implement in any computing environment. The Bloch periodic boundary conditions are applied on the sides of the unit cell by translating the periodic boundary conditions to match with the directions of periodicity in the triangular lattice. Complete and accurate bandgap information is obtained by using this FDTD approach. Convergence, accuracy, and stability analysis were carried out, which ensures the reliability of this method. Numerical results for 2-D TE/TM modes in triangular lattice PC are in good agreement with results from 2-D plane wave expansion method. To ease the practical application of this method, clear explanations on the computer implementation are also provided.
Journal of Lightwave Technology 12/2009; · 2.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple finite-difference time-domain (FDTD) method based on regular Cartesian Yee's lattice is developed for calculating the dispersion diagram of triangular lattice photonic crystals (PCs). Numerical results from two-dimentional (2D) FDTD agrees well with plane wave expansion (PWE) method.
[Show abstract][Hide abstract] ABSTRACT: We obtained blue photoluminescence from tantalum oxide films deposited by radio-frequency magnetron sputtering after annealing. The maximum peak intensity of the photoluminescence was observed from a sample annealed at 600°C for 20 min, and the peak wavelength was approximately 430 nm. Tantalum oxide films that emit blue light may be useful materials for novel active optical devices utilizing Ta 2 O 5 /SiO 2 multilayered photonic crystals.
IEICE Transactions on Electronics 10/2008; · 0.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We fabricated Si/SiO2 multilayered films having nanometer-order thicknesses of Si and SiO2 layers by using radio-frequency magnetron sputtering and subsequently annealed the samples at high temperatures of 1150 to 1250 °C. We observed ultraviolet photoluminescence having a sharp peak at a wavelength of around 370 nm, generated by using a He–Cd laser (wavelength λ = 325 nm) at room temperature, from a sample annealed at 1200 °C. The peak energy was 3.4 eV (λ ~ 370 nm), and the full width at half maximum of the peak was 0.20 eV. Ultraviolet-light emission can be useful for light sources of higher-density optical-disk systems.
Thin Solid Films 09/2008; 516(21):7732-7734. · 1.87 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We obtained blue photoluminescence from tantalum oxide films deposited by radio-frequency sputtering after annealing. Intense photoluminescence having a peak wavelength of around 430 nm was observed from a sample annealed at 600degC for 20 min. Tantalum oxide films that emit blue light can be useful as materials for novel active optical devices utilizing Ta2O5/SiO2 multilayered photonic crystals.
[Show abstract][Hide abstract] ABSTRACT: Ge/SiO2 multilayer type two-dimensional photonic crystals (PhCs) for short wave infrared (lambda˜ 2000 nm) application are demonstrated. The PhCs are fabricated by the autocloning method, which stacks multilayer on a glass substrate with initial line and space pattern by bias-sputtering. We verified their multi-channel wavelength filtering operation. Long wave pass or short wave pass filtering function is observed. Typical PhC dimensions are: Ge and SiO2 thickness is 220 nm, total number of layers is 16, horizontal lattice constant is approximately 500 nm. Transmission losses are the order of 30%, which mainly originates from the absorption of Ge layer. Extinction coefficient (kappa) of the sputtered Ge was estimated to be less than 0.05 for the wavelength range between 1600 and 2400 nm.
Japanese Journal of Applied Physics 04/2007; 46:1511-1515. · 1.07 Impact Factor