Kentaro Setsune

PLZT thin-film waveguides

PLZT thin-film channel waveguides have been successfully formed in ridges by an ion-beam etching process. The electrooptic Kerr coefficients of the waveguides have been newly obtained. We have determined that the electrooptic coefficients R11′ and R12′ were 0.1–0.2 × 10−16 (m/V)2 and 0.01 × 10−16 (m/V)2, respectively, by Mach-Zehnder interferometric measurement. It was confirmed that PLZT channel waveguides were much more efficient than conventional Ti-diffused LiNbO3 waveguides.

Electro‐optic effects of (Pb, La)(Zr, Ti)O3 thin films prepared by rf planar magnetron sputtering

Epitaxial (Pb, La)(Zr, Ti)O3 thin films were grown successfully on (0001) sapphire substrates at below 600 °C. High quadratic electro‐optic coefficient of 0.8×10−16 (m/V)2 was also obtained at 6328 A. The rf planar magnetron sputtering process improved the quality of the film, which will be suitable for thin‐film integrated optic devices.

Low‐temperature process for the preparation of high Tc superconducting thin films

We have established the low‐temperature process for the preparation of high Tc superconducting films by rf magnetron sputtering. The films were deposited at a temperature (650 °C) lower than the tetragonal‐orthorhombic transition point with sufficient crystallizing and oxidizing conditions. The as‐deposited Er‐Ba‐Cu‐O film on MgO exhibited a sharp superconductive transition with zero resistance at 86 K. This process prevented diffusion at the film and substrate interface and reduced the porous structure in the films.

Fabrication of thin‐film‐type Josephson junctions using a Bi‐Sr‐Ca‐Cu‐O /Bi‐Sr‐Cu‐O/Bi‐Sr‐Ca‐Cu‐O structure

Thin‐film Josephson junctions with normal metal barriers using a Bi‐based high Tc oxide superconductor were successfully fabricated. Bi2Sr2Ca1Cu2Ox films were used for both superconducting electrodes and Bi2Sr2Cu1Oy for the barrier layer. The junction area of 20×40 μm2 was defined by photolithography and Ar ion milling. These S/N/S‐type junctions clearly exhibited the ac Josephson effect under the irradiation of radio frequency waves of 12 GHz and more than 20 Shapiro steps were observed.

Rectangular-apertured micro-Fresnel lens arrays fabricated by electron-beam lithography.

Rectangular-apertured micro-Fresnel lens arrays are proposed. These lens arrays have been fabricated by an electron-beam writing system specially developed for the fabrication of microoptical devices. It is experimentally demonstrated that the lens arrays showed uniform focusing characteristics, and that each lens exhibited a diffraction-limited focusing characteristic with efficiency of 74%.

Formation of Superconducting Bi-Sr-Ca-Cu-O Thin Films with Controlled c-Axis Lattice Spacings by Multitarget Sputtering

Thin films of the Bi-Sr-Ca-Cu-O system were prepared by sequential deposition of Bi, SrCu, CaCu and SrCu oxides using multitarget sputtering. It was confirmed that the c-axis spacing of lattice planes could be controlled by the variation of the CaCu oxide layer. Also, thin films of the Bi system with the insertion of four Cu-O2 planes were synthesized. The Tcs of the films were found to be 80 K, 110 K and 90 K for the Bi system with two, three and four Cu-O2 planes, respectively.

A new tupe of crystal structure in the Pb-Pr-Sr-Cu-O system

Abstract A classification of p-type superconductors is proposed. According to this classification, PbPr 2.4 Sr 1.6 Cu 2.6 O y ceramic was designed and synthesized as a ceramic having a new crystal structure. This ceramic has a tetragonal symmetry ( a =0.388 nm, c =2.914 nm) and consists of three blocks which are a (Pb/Cu)-O single layer, a Cu-O 5 pyramid and a fluorite-type Pr 2 -O 2 layer. It is expected to be a mother material of superconductors.

Reflection micro-Fresnel lenses and their use in an integrated focus sensor.

Blazed reflection micro-Fresnel lenses and their use in an integrated focus sensor are proposed. Theoretical analysis indicates that the optical characteristics of reflection Fresnel lenses can be improved compared with a conventional transmission micro-Fresnel lens. These reflection Fresnel lenses were fabricated using electron-beam lithography and exhibited the diffraction-limited focusing characteristics with 71% high efficiency. The focus sensor has a folded optical path and includes a beam splitter integrated with thin film components, such as a reflection elliptical Fresnel lens and a quadrant photodetector. The reflection elliptical Fresnel lens in the focus sensor exhibiting excellent astigmatic characteristics agreed with the theoretical results, and the focus error signal was detected. This sensor can be developed as the optical head of an optical disk system.

Highly oriented superconducting Tl‐Ca‐Ba‐Cu oxide thin films with 2‐1‐2‐2 phase

Thin films of the Tl‐Ca‐Ba‐Cu‐O system with 2‐1‐2‐2 phase have been prepared stably on MgO substrates by rf magnetron sputtering and post‐annealing. The post‐annealing of the films was carefully carried out in order to reduce the effect of evaporation of Tl. The annealed films showed a c‐axis‐oriented structure perpendicular to the substrates. The highest zero‐resistance temperature of the films was 102 K. The highest critical current density obtained so far was 1.2×105 A/cm2 at 77 K.

Superconducting (Sr, Nd) CuOy thin films with infinite-layer structure

Abstract Thin films with infinite-layer structure have been prepared using a magnetron sputtering system and the substitution of neodymium for strontium in SrCuO 2 has been successfully carried out, which is similar to the case of the high-pressure synthesis. (Sr, Nd)CuO y films were grown in a reducing atmosphere on SrTiO 3 single crystals and epitaxial growth with [001] orientation normal to the substrate was realized at the substrate temperature of 550–600°C. Superconducting transition was observed for some as-grown films, and the Sr 0.88 Nd 0.12 CuO y film showed the highest T c of 16 K.