Akinori Furuya

Compact Electro-Optic Sensor Module for Intra-Body Communication Using Optical Pickup Technology

We developed a compact and low-cost electro-optic (EO) sensor module for intra-body communication using optical pickup technology. An EO crystal of zinc telluride (ZnTe) mainly contributes to use of the cost-effective optical pickup technology. ZnTe has the shortest wavelength for optical transmission, about 570 nm; therefore it can use a low-cost 790-nm wavelength laser diode widely used in compact disc players. The measured modulation depth of the new EO sensor module was about 1.56 times deeper than our old one. The measured value agreed with the calculated value; therefore, there is no performance deterioration by downsizing the sensor module. The sensor module was successfully applied to 10-Mbps half-duplex intra-body communication.

Magnetooptical and crystalline properties of sputtered garnet ferrite film using a stress relaxation buffer layer

The purpose of this study was to improve the optical characteristics of garnet ferrite films sputter-deposited on a glass substrate. The magnetooptical properties of the garnet ferrite film are strongly influenced by the thermal stress imposed on the substrate during crystallization. The condition of the interface between the garnet film and the substrate during the initial film deposition affects the magnetooptical characteristics of the entire film. In particular, we revealed the effect of stress generated at the interface on the crystallinity of the deposited garnet films with a stress relaxation buffer layer by observing the film cross section and the film surface. In addition, we qualitatively estimated of the effect of cracking in the garnet film on a glass substrate.

Method for systematically designing polarization optics to maximize sensitivity of electrooptic sensors

A systematic design method is considered for maximizing the sensitivity of electrooptic sensors used for electric-field detection. The design method can be reduced to a routine procedure that includes matrix manipulation and differentiation. By applying the design method, the maximum sensitivity is realized with fewer optical components than in conventional electrooptic sensing systems. Since the proposed method shows a wide generality, it can be applied to designing sensors including various optical crystals.

Magnetooptical and crystalline properties of sputtered garnet ferrite film on spinel ferrite buffer layer

The purpose of this study is to provide garnet films for volumetric magnetic holography. Volumetric magnetic holography usually employs an easily obtainable short-wavelength laser (visible light, not infrared light) with a large diffraction intensity. Bi-substituted garnet ferrite with a large Faraday rotation is promising for volumetric magnetic holography applications in the visible light region. However, a garnet film without a deteriorated layer must be obtained because a deteriorated layer (minute polycrystalline grains containing an amorphous phase) is formed during the initial deposition on a glass substrate. In particular, the required magnetooptical properties have not been obtained in a thin garnet film (100 nm or less) after annealing (1 h, 700 °C, oxygen atmosphere). Therefore, there is a need for excellent garnet films with the required magnetooptical (MO) properties even if the films are thin. By using a spinel ferrite buffer layer for garnet film deposition, we could obtain a thin garnet film with excellent MO properties. We determined the effect of the initial buffer layer on the crystallinity of the deposited garnet films by observing the film cross section. In addition, we undertook a qualitative estimation of the influence of the crystallinity and optical properties of the garnet film on a glass substrate with a spinel ferrite buffer layer.

Electro-Optical Sensor Fabricated Using a Bulk Cleavage Technique and Its Characteristics for Near-Field Intra-Body Communication

This paper describes how to obtain a low cost electro-optical (EO) sensor module for the mass production of near-field intra-body communication devices. In this study, we used a bulk cleavage technique to fabricate EO modulators without the need for any optical polishing or washing processes, and clarified the feasibility of assembling optical components using only a passive alignment technique with a compact housing.

Two-Dimensional Constant-Weight Block Code in Orthogonal Aperture-Multiplexing for Multilayered Waveguide Holographic Memory

For a two-dimensional constant-weight block code, we show that the recording density is proportional to code rate and the second power of the size of the bright point. Second, we show four constant-weight block codes (two 2:16 codes, a 4:24 code, and a 4:16 code) with different code rates. In simulation experiments, we measured the maximum size of bright points for each code, the bit error rate was practical (10-4 or less), and simulation results show that the maximum size increases as the code rate decreases. Then, we show that the highest recording density is achieved with the two 2:16 codes and the 4:24 code and that these codes are suitable for orthogonal aperture-multiplexing. We also show that there is a trade-off between multiplexity and the code rate.

Theoretical Method of Calculating Raw Bit-Error-Rate of 2:N Constant-Weight Block Code for Multilayered Waveguide Holographic Memory

We present an expression for the probability density functions of the ON and OFF pixels of a 2:N constant-weight block code to estimate the raw bit error rate (BER). We also show that they are similar to Gaussian ones through an analysis of an actual code image reconstructed from a multilayered waveguide holographic memory. From these results, we show that this expression for estimating the raw BER can be obtained using averages and standard deviations of the ON and OFF pixels. Finally, we demonstrate that the relationship between the signal-to-noise ratio and the raw BER derived from the expression for estimating the raw BER closely fits simulation results. This expression is useful for roughly estimating the value of the raw BER from the averages and standard deviations of the ON and OFF pixels.

Near-Field Signal Detection Using Sub-Wavelength Sized Planar Aperture Slider on Oxide Ferrite Media

Optical transmission and surface characteristics of oxide ferrite (Fe3O4) as a write-once medium for near-field optical surface recording were investigated. Narrow line patterns were recorded on the surface of as-sputtered Fe3O4 (100 nm thick) using cw laser (532 nm) under various laser powers. Optical transmission intensities under far-field and near-field illumination methods were compared. Near-field signals exhibited signal transition width close to the aperture width, indicating high near-field readout resolution. However normalized transmission intensities were nearly the same, suggesting that signal characteristics depends on the recorded pattern not on the illumination method. No surface deformation were observed using atomic force microscope for low write power range (2.6–3.4 mW). Therefore, laser illumination of the medium surface probably causes a local oxidization of Fe3O4 to defect spinel ferrite (γFe2O3) resulting in a purely optical change without any surface deformation. Surface hardness and roughness were comparable with conventional hard disk surfaces.