Haruya Kasa

Surface-relief gratings with high spatial frequency fabricated using direct glass imprinting process

Surface-relief gratings with high spatial frequencies were first fabricated using a direct imprinting process with a glassy carbon mold at the softening temperature of phosphate glass. A grating with maximum height of 730 nm and 500 nm period was formed on the glass surface by the pressing at the softening temperature of glass under constant pressure of 0.4 kN/cm(2). Phase retardation of 0.1 lambda was observed between TE-polarized and TM-polarized light at 600 nm wavelength.

Fabrication of Antireflective Subwavelength Structure on Spherical Glass Surface Using Imprinting Process

For the first time, an antireflective structure (ARS) on a convex spherical glass surface was fabricated using an imprinting process. The inverted pattern of the ARS with a 250-nm period was fabricated on a SiC mold with a concave surface using electron beam (EB) direct writing and reactive ion etching. The sample surface height was adjusted to the EB focal position along the mold curvature during the step-and-repeat EB lithography. The imprinted lens with the ARS exhibited surface reflectance of 0.2% at a wavelength of 530 nm and a spherical error magnitude of less than 500 nm.

Glass Imprinting Process for Fabrication of Sub-Wavelength Periodic Structures

Using direct glass imprinting with glassy carbon molds, one-dimensional surface-relief gratings with 500 nm pitch were fabricated on phosphate glasses. The maximum grating height attained in this study was 730 nm, which was formed by pressing at the softening temperature of the glass at a constant pressure of 0.4 kN/cm2. A large area pattern 6 ×6 mm2 with a 350-nm groove depth was also fabricated. Phase retardation of 0.1 λ was attained between transverse electric (TE)- and transverse magnetic (TM)-polarized light in the visible wavelength region. Calculated retardation using a rigorous coupled wave analysis agreed well with the experimental results.

Co thickness dependence of structural and magnetic properties in spin quantum cross devices utilizing stray magnetic fields

We investigate the Co thickness dependence of the structural and magnetic properties of Co thin-film electrodes sandwiched between borate glasses in spin quantum cross (SQC) devices that utilize stray magnetic fields. We also calculate the Co thickness dependence of the stray field between the two edges of Co thin-film electrodes in SQC devices using micromagnetic simulation. The surface roughness of Co thin films with a thickness of less than 20 nm on borate glasses is shown to be as small as 0.18 nm, at the same scanning scale as the Co film thickness, and the squareness of the hysteresis loop is shown to be as large as 0.96–1.0. As a result of the establishment of polishing techniques for Co thin-film electrodes sandwiched between borate glasses, we successfully demonstrate the formation of smooth Co edges and the generation of stray magnetic fields from Co edges. Theoretical calculation reveals that a strong stray field beyond 6 kOe is generated when the Co thickness is greater than 10 nm at a junction gap distance of 5 nm. From these experimental and calculation results, it can be concluded that SQC devices with a Co thickness of 10–20 nm can be expected to function as spin-filter devices.

Mold Design and Fabrication for Surface Relief Gratings by Glass Nanoimprint

Mold shape has been optimized to fabricate one-dimensional glass gratings with a high aspect ratio. Comparison of experimental and simulated results demonstrated that a periodic groove with a tilted sidewall, a parabolic top tooth, and a large width was preferable to imprint high-aspect-ratio gratings on a glass surface. In particular, a mold with a parabolic top tooth and a wide groove was effective to increase the aspect ratio. In the case of a mold with a 500 nm period, a grating of 540 nm height could be imprinted under the respectively optimized imprinting parameters of 430 °C, 5 MPa, and 5 min.

Fabrication of Sub-Wavelength Periodic Structures upon High- Refractive-Index Glasses by Precision Glass Molding

One-dimensional surface-relief gratings were fabricated using a direct imprinting process with a glassy carbon (GC) mold at the softening temperatures of oxide glasses. The maximum grating height attained in this study was 730 nm when the grating period was 500 nm, which could be formed by the pressing at the softening temperature of glass under constant pressure of 0.4 kN/cm2. A large area glass imprinting was attempted using a GC mold with a periodic patterned area of 6 mm x 6 mm, which has the period of 500 nm and groove depth of 350 nm, respectively. Phase retardation of 0.1 λ was recognized between TE-polarized and TM-polarized lights at 600 nm wavelength. The measured values were in excellent agreement with those calculated using a rigorous coupled wave analysis.

Using Laser Interference Lithography in the Fabrication of a Simplified Micro and Nanofluidic Device for Label-free Detection

Recently, we developed a label-free detection method based on optical diffraction, and implemented it in on our fabricated micro- and nanofluidic device. This detection method is simple and useful for detecting biomolecules, but the device fabrication consists of complicated processes. In this paper, we propose a simple method for fabricating the micro- and nanofluidic device; the fabrication combines laser interference lithography with conventional photolithography. The performance of a device fabricated by the proposed method is comparable to the performance of the device in our previous study.

Resonance Modes in Si Micro-Cubic Cavity Coupled with Ge:SiO2 Waveguide

Si micro-cubic cavities coupled with Ge:SiO2 waveguides were examined theoretically and experimentally. Resonance spectra and field distributions in the 3×3 µm2 cavity were numerically calculated by the finite-difference time domain method. The resonance wavelengths were 1.5381 and 1.5526 µm for transverse electric and transverse magnetic modes, respectively, in the wavelength range from 1.50 to 1.58 µm. A Si cubic cavity was fabricated on the Ge:SiO2 core of a single-mode waveguide by DC sputtering, photolithography, and reactive ion etching. The near-field pattern at the fabricated micro-cubic cavity was observed by exciting a guided mode in the waveguide. The observed pattern should be influenced by a resonance mode (whispering gallery mode), because the pattern at 1.55-µm wavelength was similar to the simulated mode-field distribution in resonance and the patterns at other wavelengths were deformed.