Yoshinori Maeno

Bidirectional optical subassembly with prealigned silicon microlens and laser diode

We have succeeded in developing a low-cost bidirectional optical subassembly chip using a silicon microlens for fiber-to-the-home application. The main optical elements of the bidirectional function were automatically aligned and integrated on a silicon optical bench. The cost of subassembly was markedly lowered both by reducing the part number and simplifying the assembly process. The prototype bidirectional optical component was successfully fabricated on the basis of the proposed chip. A receiver minimum sensitivity of -28.5 dBm was experimentally demonstrated even at 75 degC

Annealing effects on multilayered Co/Pt and Co/Pd sputtering films

Effects of air annealing on magnetic properties and structures of multilayered Co/Pt and Co/Pd sputtering films were studied. The dual‐source rf magnetron sputtering method was employed in fabricating the films. The thicknesses of the Co layer and Pt layer of the Co/Pt films were 4.3 and 10.0 A, respectively: the total thickness was 4300 A. The thicknesses of Co layer and Pd layer of the Co/Pd films were 3.6 and 11.8 A, respectively: the total thickness was 5600 A. Residual magnetizations and coercivities of the Co/Pt and Co/Pd films increased with air‐annealing at 250–350 °C for 30 min to 2.5–3 kG and 2–3 kOe, respectively. The increases were observed only during air annealing, but not in vacuum annealing. Saturated magnetizations and intensities of the superlattice x‐ray peak decreased uniformly relative to annealing temperature.

I-V measurement of NiO nanoregion during observation by transmission electron microscopy

Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the “forming process” required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30–40 nm. This finding supports the “breakdown” type forming in the so-called “filament model” of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated.

Changes in film structure and increase in coercivity for Co/Pd multilayered films with atmospheric annealing

Co/Pd multilayered films exhibit large perpendicular magnetic anisotropy and have attracted attention as new materials for recording media and for other applications. The coercivity (Hc), however, is small in as‐sputtered films. We have found that Hc increased markedly with the atmospheric annealing at 300 °C to 2 kOe, and studied the change in film structure and reason of the increase in Hc with the annealing. The rf magnetron sputtering method was employed in fabricating the films. Film structure changes were observed by x‐ray diffraction, Auger electron spectroscopy, transmission electron microscopy, energy dispersive x‐ray spectrography, and atomic force microscopy. The increase in Hc was observed only in the atmospheric annealing, and not in the vacuum‐annealing. The internal structure of films after the atmospheric annealing at 300 °C consisted of columnar parts that had the multilayered structure that undertook vertical magnetization and column boundaries being surrounded by Co oxides. As a consequ...

Design of Polarization-Independent Si-Wire-Waveguide Wavelength Demultiplexer for Optical Network Unit

We report the design of a compact wavelength demultiplexer using a Si wire waveguide as an optical network unit. We use a Mach–Zehnder lattice interferometeric filter structure to attain a flat-top response. The large wavelength dispersion of the Si wire waveguide requires special design considerations for widely separated wavelength channels. Preliminary experimental results obtained by the device fabricated in a silicon-on-insulator wafer showed a flat-top filter response.

Surface-mountable silicon microlens for low-cost laser modules

A surface-mountable silicon microlens that can be passively aligned in a silicon V-groove is proposed. The microlens has a diffractive optical element on the end facet of a semicylindrical structure whose diameter is identical to that of a single-mode fiber (SMF). The experimental result of coupling efficiency between a distributed feedback laser diode and SMF shows low loss (-3.0 dB) as determined using the microlens. Monte Carlo simulations indicate that the microlens is suitable for low-cost and high-performance optical modules for metro networks.

Magnetic properties of multiple‐structure multilayered Co/Pd films

Co/Pt and Co/Pd multilayered films exhibit large perpendicular magnetic anisotropy and have attracted attention as new materials for magneto‐optical recording media and for applications in other areas. The coercivity and the squareness ratio of these films are small at thick films of 1000 A or more. We studied Co/Pd multiple‐structure multilayered films, consisting of periodic piles of Co/Pd multilayered film layers and Pd thin‐film layers in order to improve the magnetic characteristics. By adopting such multiple structures, a squareness ratio of unity, coercivity of 2.5 kOe, and residual magnetization of 1.5 kG were obtained at a thick film of 2000 A.

A low-cost micro-BOSA using Si microlens integrated on Si optical bench for PON application

We propose single TO-CAN type bi-directional optical subassembly in which. LD, PD chips, filter and Si microlenses are passively integrated on Si optical bench. High performance such as minimum sensitivity of -28 dBm was experimentally demonstrated.

A low cost PON transceiver using single TO-CAN type micro-BOSA

A novel low-cost small-form-factor (SFF) optical transceiver using a micro-compact bi-directional optical sub-assembly (micro-BOSA) for passive optical network (PON) application is proposed. In this micro-BOSA, optical transmitting and receiving functions are incorporated in a single TO-CAN package. The BOSA is compact and its pin assignment provides fine connection to printed circuit board and fit in transceiver housing. Bi-directional optical transmission at 1.25Gbit/s with the receiver minimum sensitivity of -28.2dBm is demonstrated for the fabricated transceiver with the proposed micro-BOSA

High‐corrosion‐resistant magneto‐optical recording media using TbFeCoTi films

The effects of adding Ti to TbFe and TbFeCo films with and without protective layers were studied. The addition of Ti improved the corrosion resistance of the films. The transmittance of TbFeCo films was reduced by a factor of 10 by the substitution of 5% Ti for Fe, and by a factor of 100 by the substitution of 10% Ti for Fe. Pit formations in TbFeCo during aging in a corrosive condition and immersion in a NaCl solution were almost completely eliminated by the substitution of 5% Ti for Fe. The Kerr rotation angle (θk) decreased slightly in TbFeCo by the substitution of 10% Ti for Fe, while improving the corrosion resistance.