Showing papers by "Din Ping Tsai published in 2007"

High birefringence photonic crystal fiber with a complex unit cell of asymmetric elliptical air hole cladding

Abstract: High birefringence induced by elliptical air hole photonic crystal fibers (EHPCFs) is analyzed numerically using the finite-element method. Statistical correlations between the birefringence and the various parameters are obtained. We found that the complex elliptical air hole is better than that of a circular one to obtain high birefringence in photonic crystal fibers. Our suggested structures can considerably enhance the birefringence in EHPCFs and show that the birefringence can be as high as 1.1294×10−2, which is higher than the birefringence obtained from conventional step-index fiber (5 × 10−4), circular air holes PCF (3.7×10−3), and elliptical hollow PCF (2.35 × 10−3).

Plasmonic optical properties of a single gold nano-rod

Abstract: Polarization-contrast microscopy coupled with an atomic force microscope is utilized to attain far-field optical images of the multipolar surface plasmon resonance (SPR) modes of single gold nano-rod. Modulated standing modes resulted from the interference of longitudinal SPR modes and incident light are observed and studied. By counting the average distance of adjacent beats on this single gold nano-rod, the wave vector of longitudinal SPR modes can be obtained. We found a linear relationship between the wave vectors of the incident light and the induced SPR modes. Experimental results demonstrate a feasible way on acquiring plasmonic optical properties from an individual single gold nano-rod.

Reflection and emission properties of an infrared emitter.

Abstract: The reflection and emission properties of an infrared emitter, which is a plasmonic multilayer structure consisting of a relief metallic grating, a waveguide layer, and a metallic substrate are investigated both experimentally and theoretically. A localized surface plasmon polariton (SPP) mode which is angular-independent in almost the full range of incident angles is observed. The thermal emission of this structure is also measured. It is found that the emission peak coincides with the angular-independent localized SPP mode. In addition, the emission spectrum of the plasmonic emitter can be predicted by investigating the reflectance spectrum.

Imaging of soft matter with tapping-mode atomic force microscopy and non-contact-mode atomic force microscopy

Abstract: In this work, we take topographic images of DNA molecules and nanometre-sized polystyrene spheres in air as well as in water using an atomic force microscope (AFM). We would like to compare the applied forces and the resolution for images taken with the amplitude-modulation (AM) detection, or the tapping mode, and the frequency-modulation (FM) detection, or the non-contact (NC) mode. Experiments for these two modes are carried out on the same area of the samples, with the same tip, under the same environment, and with the same oscillation amplitude. Our experiments indicate that, in the FM mode, the tip exerts a very gentle force on soft materials and provides a height measurement close to the true value. In the AM mode, the tip exerts a stronger force on soft materials and causes their deformation, especially in the liquid environment. The resolution of the FM mode is about the same as that of the AM mode for operation in air, but the former is significantly superior to the latter in water. We thus conclude that the FM mode can obtain images with a higher resolution and provides a sufficient sensitivity to image the true and fine structure of soft matter on surfaces.

Significantly Enhanced Birefringence of Photonic Crystal Fiber Using Rotational Binary Unit Cell in Fiber Cladding

Abstract: We propose a novel high-birefringence index-guiding photonic crystal fiber (PCF). This PCF is composed of a solid silica core and a cladding with rotational squeezed-triangular-lattice elliptical air holes, which consist of binary unit cells. The birefringence of a fundamental mode in such a PCF is analyzed numerically using the finite element method. A binary unit cell in a PCF cladding that combines its rotational effects can enhance the birefringence as high as a magnitude of the order of 10-2. This study provides a new viewpoint for the characterization and design of a high-birefringence PCF.

Study of Nanoscale Recorded Marks on Phase-Change Recording Layers and the Interactions With Surroundings

Abstract: Conductive-atomic force microscopy (C-AFM) has been used for studying nanoscale recorded marks with different length on the phase-change recording layer of optical disks. Through C-AFM images, a comparison of nanoscale recorded marks on phase-change recording layer under different writing strategies and writing power has been taken. The comparison can help analyze the combination of writing strategy, writing power and laser pulse width. The various lengths of recorded marks for high density data storage have also been found out. The interactions between phase-change recording layers and their surroundings have also been studied. This study opens up a possibility to improve the capacity of data storage in today's commercial optical disks

Readout contrast beyond diffraction limit by a slab of random nanostructures

Abstract: A simplified Fourier optics approach is applied to study how near-field optical disks retrieve evanescent signals through random nanostructure. The statistical properties of the random nanostructures are used to realize the general behavior of near-field optical disks. The mechanism of its super-resolution capability and an analytical expression of the readout contrast of near-field optical disks with random apertures are derived. The resolution of near-field optical disk is determined by the size of the random nanostructure.

Optical Fiber Photocatalytic Reactor And Process For The Decomposition Of Nitrogen Oxide Using Said Reactor

Abstract: An optical fiber photocatalytic reactor is provided. The reactor comprises a reaction zone and multiple fibers located in the reaction zone. The fiber comprises a photocatalyst that is coated onto its surface via a thermal hydrolysis method. The adhesion between the fiber and the photocatalyst thereon is strong, and thus, the delamination of the photocatalyst film on the fiber can be prevented. Moreover, the optical fiber photocatalytic reactor is useful for the decomposition of nitrogen oxide which is one of air's most harmful contaminants. The present invention exhibits a high conversion of nitrogen oxide.

Subwavelength optical imaging through a silver nanorod

Abstract: We numerically investigated subwavelength imaging in a silver nanorod of 50-nm height and 20-nm diam buried in dielectric background (SiO2) with a finite-difference time-domain (FDTD) method in the three dimensions. The near-field components of the Gaussian incident beam were plasmonically transferred through the input end of a silver nanorod to reproduce the light distributions of the incident wave at the output end. The field distributions were calculated at the different sectional planes of the rods, and it was found that the spatial resolution was less than 40 nm given by the rod size, which is much beyond the diffraction limit of the conventional imaging system. The field intensity in the image plane was well resolved due to the collection of surface plasmon polaritons. The behaviors of the three components of field distribution at entrance and exit from the nanorod and the influences of the optical field distribution generated by some factors are also discussed in detail. The proposed structure possesses a deep transfer of super-resolution image and can be used with image transfer.

The optical properties between an incident wave and the active layer of a bubble-pit AgOx-type super-resolution near-field structure

Abstract: The deformation and plasmon effects of collective localized surface plasmons between incident light and bubble-pit AgOx-type super-RENS structure have been studied using finite-difference time-domain (FDTD) method. We find that the polarization, wavelength of incident light, and particle sizes of Ag nanoparticles are sensitive to the plasma resonance. The Ag nanoparticles inside the bubble-pit AgOx-type super-RENS structure give the additional outer boundaries to the motion of the Ag nanoparticles, and excite more evanescent field which located in the far edge of the bubble from the optical axis of the incident beam. The optical properties between active layer and incident light with polarization direction, different wavelengths, and varied particle sizes of Ag nanoparticles exhibits nonlinear optical behavior in the near field. The far-field signals of different wavelength of incident light confirm the relation between highly localized near-field distributions and enhanced resolution of far-field signals. The subwavelength recording marks smaller than the diffraction limit were distinguishable since the Ag nanoparticles with high localized fields transferred evanescent waves to detectable signals in the far field.

Near-Field Optics Imaging in Silica Waveguide Using Near-Field Scanning Optical Microscope

Abstract: We investigated the near-field optics imaging by a numerical method using special spherical chains created in a silica waveguide (SWG) and explored the possibility of how this can be used for near-field scanning optical microscopy (NSOM) applications. There are two types of spherical nanochain; type A includes nano-dielectric spheres connected closely, and type B includes silver nanoparticles 4 nm in diameter randomly distributed inside the nanospheres of type A. A spherical nanochain with the 80-nm-diameter spheres was embedded in the SWG. The interactions between light emerging from SWG and the electric field near the sample surface that affects the properties of the images produced by NSOM are analyzed using a three dimensional finite-difference time-domain method. The effects of the optical field distribution generated by some factors are also discussed. A method of controlling the light field localized in the SWG is proposed that uses the external protrusion (dielectric sphere). The proposed structure will yield some useful information and give an idea of applications in NSOM.

Photocatalytic reactor with movable conformal light guiding plate

Abstract: A photocatalytic reactor is disclosed herein, which includes a rotatable light guide plate and a light source. The light guide plate is coated with a photocatalyst film on a surface thereof. A light beam emitted from the light source can be coupled into and propagate inside the light guide plate to activate the photocatalysis of the photocatalyst film. Additionally, the rotation of the light guide plate further expedites the photocatalysis so as to enhance the reaction efficiency of the photocatalytic reactor.

Readout contrast enhancement of near-field optical disk with random nanostructures

Abstract: Optical effect of the near-field optical disks with random nanostructure is studied by Fourier optics approach. The general behavior of near-field optical disk with random nanostructure is realized by the statistical property of random nanostructure.

Optical Waves Transmission Raised by Localized Surface Plasmons

Abstract: A corrugated metal thin film can enhance the emission of light-emitting devices by the assistance of radiative surface plasmons. But, away from the resonant frequency, the metal thin film has a shielding effect on transmission. We replace the corrugated thin film by a discontinuous metal nanostructure, the isolated metal nanohemispheres can induce localized surface plasmons. The angular dependence and two different wavelengths are studied. The reflection on dielectric layers may be reduced and the transmission could be raised by the localized surface plasmons even the resonance condition is not fulfilled. The scattered Ey component is sensitive to the tilt angle, it might be useful to some novel applications.