bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical fiber loss reduction
Authors: Ohashi Masaharu , Tateda Mitsuhiro , Shiraki Kazuyuki , Tajima Katsusuke , Tsujikawa Kyozo
Published: July 2007

With the introduction of optical fiber amplifiers, numerous experiments on long‐haul and large‐capacity transmissions at 1.55‐μm band have been done. To realize high‐grade transmission systems, further reduction of optical fiber losses is necessary.

In reduction of optical fiber losses, Rayleigh scattering loss, infrared absorption loss, and losses due to imperfections should be further reduced. Among these, Rayleigh scattering and infrared absorption losses are fixed by the used dopants. On the other hand, losses due to imperfections depend not only on the fabrication process but also on the viscosity properties of the core and cladding materials. To reduce loss due to imperfections, the viscosity matching of core and cladding materials is quite effective. This type of viscosity‐matching technique, unexplored until now, will be clarified by the authors.

The method of viscosity matching over the fiber cross section is first presented; then the viscosity characteristics of silica glasses doped with GeO2, F, or codoped with GeO2 and F together with their Rayleigh scattering behavior are experimentally clarified. Finally, the loss behavior of fabricated viscosity‐matched fibers is described and the effectiveness of the matching technique is demonstrated.
Stress‐applied polarization‐maintaining optical fibers. Design and fabrication
Authors: Hosaka Toshihito , Sasaki Yutaka , Okamoto Katsunari , Noda Juichi
Published: July 2007

To realize low‐loss low‐crosstalk long‐length polarization‐maintaining fibers, this paper examines the “PANDA fibers” having a circular stress‐applying part which has a high design accuracy and ease of fabrication. Stress‐applied type polarization‐maintaining optical fibers generally have two orthogonal polarized modes, and their coupling causes crosstalk which makes the transmission of polarized mode through a long‐length of fibers difficult. To suppress this mode‐coupling, it is important (a) to make the modal birefringence larger, and (b) to reduce the deterioration of the symmetry of the stress applied. This paper examines the circular stress‐applying type PANDA fiber and compares it with two other types of PANDA fiber having the typical shapes of the stress‐applying part. As a result, (1) the structure parameters of the stress‐applying part which gives the maximum modal birefringence and a low loss, and (2) the mode‐coupling parameter, with the stress‐applying part deviated, which can evaluate the crosstalk characteristics, have been obtained. Based on the results of these theoretical analyses, the symmetry in the stress‐applying part is improved by using a large preform, and the increase of the modal birefringence by increasing the outer diameter of the fiber is carried out. The circular stress‐applying type PANDA fiber having a crosstalk as low as ‐42 dB in 1 km has been realized.
Remanent polarization of vacuum‐deposited BaTiO3 films
Authors: Iijima Yoshio
Published: July 2007

Hysteresis curves exhibited by vacuum‐deposited BaTiO3 films are studied. Platinum substrates and temperatures from 600 to 900°C were employed. The hysteresis curves did not vary greatly in height despite frequency variations. This was due to the generation of terminal voltages on the integrating capacitor as a result of remanent polarization of the samples. The measured value of the remanent polarization exceeded 10 μC/cm2 (E = 5.3 kV/cm).
Bipolar transistor CAD model including quasi‐saturation phenomena
Authors: Shinmi T. , Inohira S. , Nagata M. , Iida K. , Nakagome Y.
Published: July 2007

In the Ebers‐Moll type model excluding quasi‐saturation phenomena and the Van der Ziel model neglecting the base electrical conductivity modulation effect, simulation of integrated circuits was insufficient due to the degrading accuracy of hFE and the fT fall‐off at high currents and collector voltage dependency. This paper proposes a new model introducing the conductivity modulation of the base region (Kirk effect) and the critical current ICRI with a simple formulation. To put the new model into a circuit analysis program of the nodal analysis, a linearization method using an equivalent linear current source is demonstrated. Circuit simulation of a linear IC for a Hi‐Fi stereo preamplifier is performed using the circuit analysis program into which the new model is programmed and a very good agreement is obtained with the experimental results. Hence, it is confirmed that the accuracy of fFE and fT at high currents is improved. Also, simulation accuracy even in an operating region in which quasi‐saturation for the IC level occurs, is improved.
Measurement of electrical field distribution around a biological body by an optical technique
Authors: Endo Hideto , Shimizu Koichi , Matsumoto Goro
Published: July 2007

When a biological body enters a uniform unperturbed field, the field is distorted by the body and the field concentration occurs on various parts of the body. To elucidate the biological effects of strong electric field, the coupling of the electric field to a biological body has to be well understood and the field exposure dose to a biological body has to be evaluated qualitatively. Using an optical field sensor with a minimum field perturbation, we have developed a system which can visualize the spatial distribution of the field around an object with a complex shape such as a biological body. First, the accuracy of the measurement was confirmed through comparison between the measurement and theoretical calculation using the model with a simple geometry. Second, the field distributions were measured with experimental animals and it was shown that a conductor model can be used instead of a living body in this frequency range. Based on these results, the field distributions were measured with a human model in various conditions found in common everyday life. These results will provide useful information on the behavior of the field around a human body.
Formation and properties of vacuum‐evaporated high conductivity n‐type CdTe film
Authors: Kawai Yoshiji , Ema Yoshinori , Hayashi Toshiya
Published: July 2007

High dark conductivity CdTe films have been prepared by a co‐evaporated process of CdTe and Cd. The structural, electrical and optical properties were investigated. Dark conductivity of the film increased monotonically with an increase of the co‐evaporated Cd. The highest dark conductivity of the film obtained in this experiment was 0.54 ohm‐1 cm‐1. The film structure was of the zinc‐blend type with a preferential orientation of the (111) planes parallel to the substrate and fibers. The crystallinity of the dark films was similar to films without Cd doping. This high dark conductivity film will be useful for thin film CdTe solar cells.
Magneto‐optic readout of magnetically recorded signals using magnetic garnet film
Authors: Nomura Tatsuo , Tokumaru Haruki
Published: July 2007

Experiments have been carried out to obtain a method different from the conventional method, to optically read out the signal recorded on a magnetic recording medium by transferring it to a magnetic garnet film. This method forms straight parallel stripe magnetic domains in the garnet film, and the read‐out is done by varying the domain width using the stray field from the recording medium.

Static transfer and dynamic readout experiments have been done using a garnet film with straight stripe magnetic domains with the domain width of 2.25 μm and the domain period of 4.5 μm. Statically, the transfer of the signal with a wide range of recording wavelength 5 μm‐200 μm was done without any domain disturbances. Also, there were no unnecessary domains between the transferred tracks. On the other hand, when the magnetic sheet disk was rotated with a relative speed of 50 m/s, a stable readout of the signal with 0.25 MHz to 10 MHz was possible using a laser beam with a spot radius of 5 μm.

These experimental results indicate that the new transfer method is suitable for a signal read‐out of narrow track recording, and that it is superior in high‐speed response. Further, from the analysis of the readout model, a further improvement of the readout characteristics is shown possible by reducing the spot radius.
Finite‐element analysis of planar anisotropic inhomogeneous optical waveguides
Authors: Kumagami Hiroshi , Koshiba Masanori , Suzuki Michio
Published: July 2007

Diffused optical waveguides are of considerable interest for the construction of optical integrated circuits. Generally, it is difficult to analyze inhomogeneous waveguides, such as diffused waveguides, because their refractive indices change continuously. Further, it is complicated and difficult to analyze anisotropic inhomogeneous lossy optical waveguides. This paper describes the finite‐element method for the analysis of planar anisotropic inhomogeneous lossy optical waveguides. The validity of the method is confirmed by comparing numerical results of planar isotropic inhomogeneous optical waveguides with exact results. The numerical results of metal‐clad planar anisotropic inhomogeneous optical waveguides are also presented and the effects of metal claddings on the propagation characteristics for the surface waves and the leaky surface waves are examined.
Effects of smoothing condenser on the stability of the push‐pull current‐fed dc‐dc converter
Authors: Harada Koosuke , Kim Heejun
Published: July 2007

The push‐pull current‐fed dc‐dc converter has been considered as one of the circuit configurations for the dc‐dc converter. According to past studies, this converter is useful from the viewpoint of the voltage stability compared to traditional circuits. This paper considers the fact that the capacitance of the smoothing condenser can be reduced by raising the switching frequency. The relation is determined between the voltage stability and the capacitance of the smoothing condenser by analysis, considering the phase‐delay element in the feedback circuit and the equivalent series resistance of the smoothing condenser. Hence, the push‐pull current‐fed dc‐dc converter is shown to have better voltage stability than the traditional buck‐type converter, even if the capacitance of the smoothing condenser is reduced, while the output voltage ripple increases with the increase of the output current, thereby limiting practical applications.
A simplified model for the diffusion and collection of alpha‐particle‐induced carriers
Authors: Kawakami Akira
Published: July 2007

As LSI technology advances, the evaluation of noise charge due to α‐particle or the like has become more important in the total design. In the case of RAMs, in particular, the amount of charge collected by circuit nodes can easily be approximated by the solution to the heat conduction differential equation for the diffusion charge component, and assuming that all of the charge in the depletion region is collected. Using the diffusion equation point source solution with the method of images to satisfy the boundary conditions, a simplified analytic expression can be obtained. However, since a more realistic noise source is usually a finite line, a Fourier expansion approximation extending the initial source along the coordinates directions is useful. In an infinite medium, introducing an absorbing boundary sufficiently removed from the collecting region still remains a Dirichlet problem. The analytic expressions developed as a result of these considerations are applicable to arbitrary incidence and are suitable for computer treatment. They allow estimates to be made easily for such things as the effect of buried protection layers or the influence of device isolation structures, etc.
GaAs broadband monolithic switches
Authors: Yamao Yasushi , Sugeta Takayuki
Published: July 2007

A high‐frequency switch utilizing a GaAs FET as an analog switch is expected to operate in a broad band and can be integrated in a monolithic IC form. Since only a single power supply is needed for the gate bias and the power consumption of the switch can be made zero, it is useful in the area where a small size and low power consumption are required. To investigate the feasibility of a broadband GaAs monolithic switch, this paper first derives an equivalent circuit of the switch from the structural model of the FET and the relation between the switch characteristics and the device parameters of the FET. The design method of the switch is then developed. Next, the monolithic switches of SPDT and DPDT structures are fabricated by ion‐implantation technology and their characteristics are evaluated so that the validity of the equivalent circuit model is confirmed. The GaAs monolithic SPDT switch realized has the passband of dc to 3.3 GHz, insertion loss less than 0.7 dB (dc to 2 GHz), isolation more than 20 dB, switching time 2 ns and the maximum distortionless signal input power 20 dBm. Similarly, good performance has been obtained for the DPDT switch.
Measuring system for ionic channel noise of the biological membrane current—application to the exocrine gland acinar cells
Authors: Izumi Takashi , Hoshimiya Nozomu , Kazami Kunio , Matsuo Tadayuki , Nishiyama Akinori
Published: July 2007

Ionic channels in biological membranes are one of the elementary transport elements passing specific ions across the membranes. The objective of this investigation is to design a two‐microelectrode‐voltage clamp system which is able to detect ionic channel noise of the membrane current in the mammalian exocrine gland acinus, an electrical unit, consisting of about 100 acinar cells. Since two high‐resistance intracellular microelectrodes are used, the coupling capacitance between two electrodes makes the operation of the measurement system unstable and places a severe restriction on the experiment. In our measurement system a simple low‐pass filter is inserted in the feedback system of the membrane voltage. As a result, the system operation is stabilized via the compensation of the frequency characteristic of the feedback system. If the noise inherent to the measurement system is large enough to mask the ionic channel noise of the membrane current, the channel noise below the noise level of the system cannot be detected. Since the noise of the measurement system is found to be due mainly to microelectrodes, properties of the electrode noise are analyzed in the present work. From the results, the system noise is evaluated quantitatively and the detection limit of the ionic channel noise is determined. Furthermore, the voltage is clamped for the electrically equivalent circuit to the acinar surface membrane and the operation of the voltage clamp system and the system noise level are investigated experimentally.
Short‐term frequency stability of crystal oscillator circuits with the current noise in transistor
Authors: Sakuta Yukinori , Sekine Yoshifumi , Suyamas Masatoshi
Published: July 2007

With the widespread and detailed applications of the frequency bands, it is desired especially to improve the short‐term frequency stability of the highly stable crystal oscillator. It is necessary to investigate not only the crystal element, but also the oscillator circuit. In the past, the amplifier has primarily been investigated theoretically from the viewpoint of frequency stability, and studies on the oscillator have been insufficient. This paper investigates the effect of the current noise of the transistor in the crystal oscillator on the short‐term frequency stability. By converting the current noise of the transistor equivalently to the change of the dc operating point, the change in the load capacitance of the oscillator circuit is evaluated. Then the short‐term frequency stability is valued, revealing that it is determined largely in the crystal oscillator by the current noise of the transistor. By the analysis based on Ebers‐Moll's model, it is verified that the analysis describes clearly the operational characteristics of the oscillator, taking into account the nonlinear property of the transistor. It is also shown that the change of the oscillation frequency by the change of the dc biasing point of the transistor is due to the change of the load capacitance.
Accuracy of optical path lengths computed with an asymptotic solution for a meridional ray equation in GRIN‐rod lenses
Authors: Sakamoto Toyokazu
Published: July 2007

The accuracy is studied of the optical path lengths computed with an asymptotic solution of a meridional ray equation in GRIN‐rod lenses derived by Streifer and Paxton [4]. Assuming the sech index profile, it is shown that the accuracies of normalized optical path lengths computed with second‐, third‐ and higher‐order asymptotic solutions are, respectively, O(10−5) and over (10−6) within N.A./n0 = 0.3, where N.A. and n0 denote the numerical aperture and the refractive index on the center axis, respectively. It is shown also that within N.A./n0 = 0.2, an accuracy of O(10−6) can be obtained using the second‐order asymptotic solution.
High‐performance optical switch using thermo‐optic effect
Authors: Hashimoto Ken‐Ya , Nakamura Yutaka , Yamaguchi Masatsune , Kogo Hiroshi
Published: July 2007

The TO switch, in which the temperature dependence of the refractive index is used, is considered to have a potential for replacing a purely mechanical version as a switching device for optical channel selection. This paper studies theoretically and experimentally TO switches for improving their performance. First, for a simple model of a TO switch, the switching speed and deflection angle are obtained theoretically. Fundamental experiments have been performed for these characteristics so that the validity of the theory is confirmed. It is found that the switching speed and deflection angle depend not only on the fundamental material constants, but also on the shape of the heating parallel electrodes has been proposed in which the optical beam is extracted by reflection inside the switch substrate. A switch based on this principle has been fabricated. With switching speed less than 0.4 ms and a driving power of 1 W, the deflection angle is more than 1.7 deg. The results confirm the effectiveness of the proposed structure.
Effect of humidity on electrical properties of thin‐film Li‐Te junction
Authors: Kitagawa Hiraku
Published: July 2007

Relative humidity (H) ‐ current (I) characteristics were investigated on test samples of thin‐film Li‐Te junction humidity sensing devices. (Fabricated by vacuum deposition and then thermally treated for 60 min at 100°C.) The devices had 15‐V ac applied, and the H ‐ I characteristics were measured for relative humidities between 30 and 90 percent

The H ‐ I characteristic curves had minima at 80 percent R.H., and were linear from 30 to 70 percent. The devices differ from conventional humistor resistive humidity sensors in that the H ‐ I characteristics has decreasing current at high R.H., decreases. This unique characteristic can be exploited for a sensor well suited to low R.H. measurements. The response time is 4 to 20 s depending on the initial R.H. and the humidity change. The H ‐ I characteristic also shows good reproducibility for relative humidities between 30 and 70 percent. Auger depth profile analysis revealed that the Li‐Te junction device is formed of an Li2O + Te surface layer, and an inner layer Li2O layer, with a boundary junction between them.
1/f noise in ion‐implanted GaAs
Authors: Hashiguchi Sumihisa , Sugiyama Hisashi
Published: July 2007

The 1/f noise is believed to be caused by the lattice scattering in the bulk, and also that the noise is proportional to (μ/μL)2, the square of the ratio of the total mobility μ to the lattice scattering mobility μL. In this paper, the mobility has been changed by varying temperature, and the relation between the noise and the mobility has been studied

In the measurements with a GaAs Hall device, we have observed that the 1/f noise is proportional to (μ/μL)2 at low temperature, but that an effect of the temperature change on the magnitude of the 1/f noise appears strongly around the room temperature. In the present measurements we used GaAs MeS samples in order to control the effect of the surface current on the noise performance. In the samples with a low gate‐leakage current, the 1/f noise was proportional to (μ/μL)2 at 77 K ˜ 300 K. In the sample with a high gate‐leakage current, a strong temperature dependence, which coincides with that of the gate‐leakage current, was observed in the 1/f noise. Thus, it is concluded that there is a strong effect of the surface current on 1/f noise.
Computer analysis of crystal oscillator
Authors: Adachi Takehiko , Tsuzuki Yasuo , Hirose Motoyoshi
Published: July 2007

It has been considered almost impossible to analyze the characteristics of a crystal oscillator circuit on the operating signal level. Such oscillator usually consists of a capacitive active circuit with a negative resistance connected to a crystal resonator. If the crystal oscillator circuit is divided into the resonator and the active circuit at the terminal of the crystal resonator and the characteristic of the active circuit is independently obtained, the oscillation characteristics can be found for connection of an arbitrary resonator. Based on this concept, a method for analysis of the characteristics of the crystal oscillator is introduced in this paper by means of a general purpose circuit analysis program. The analysis is conducted for an adjustment‐free Colpitts crystal oscillator used in practice in the frequency range of 10∼30 MHz. The results are compared with the measured data. The negative resistance, equivalent capacitance and the resonator current of the circuit are analyzed and the results are seen to be in good agreement with the measured data. The source voltage dependence of the oscillation frequency, which is important in design, is investigated. The frequency variation of the ppm order is analyzed and agreement with the measured data is excellent. The method in this paper is believed useful for improvement of oscillator design.
Prototype of micro ISFET for biomedical research
Authors: Shoji Shuichi , Esashi Masayoshi , Matsuo Tadayuki
Published: July 2007

With a view to developing an ion sensor capable of simple measurement of ion concentration at the cell level, a micro ionsensitive FET (micro ISFET) has been studied. For this purpose, it is necessary that the micro ISFET be a probe structure whose tip size is smaller than the cell and that the ion‐sensitive gate be placed at the tip of the probe. Special micro fabrication techniques are required for such a micro ISFET. This paper describes a three‐dimensional processing technique to fabricate a microprobe from an Si wafer and a method for forming an ISFET on a Si probe. Based on these fabrication techniques, a fundamental design of the micro ISFET is performed. An Si3N4 gate micro ISFET for pH is fabricated that has a tip size of 10 μm and a gate area of 5 × 5 μm2. Its characteristics are evaluated.
A quantitative evaluation method for the biological effects |of ion‐current
Authors: Yamashita Masaji , Shimizu Koichi , Shimizu Hideo , Matsumoto Goro
Published: July 2007

An experimental apparatus called an ion‐current shuttlebox, was developed to evaluate quantitatively the biological effects of ion‐current in air. It consists of an ion‐generating long narrow cage for a rat and an automatic data acquisition system. The cage is divided into two parts, i.e., an ion‐exposing area and a control area. Ion‐current is generated by corona discharge of thin wires located above the cage. Two pairs of grids control the amount of ion‐current in the exposing area and eliminate ion‐current in the control area. In a computer simulation, the loci of ion‐particles were obtained which provide the appropriate conditions of potentials for the two grids. In basic experiments it was confirmed that ion‐current distribution is uniform in each area and is symmetrical between the two areas. The apparatus can expose ion‐current of between 0 to 1 μA/m2 (continuously controllable) to a rat. A technique was devised which depresses the ozone generation by heating the corona wires. The behavior of a rat is recorded and analyzed in an automatic position sensing system controlled by a microcomputer. In sham exposing experiments, it was confirmed that this apparatus does not affect the circadian rhythm of the rat and there is no preference by the rat for either of the two areas.
A quasi‐millimeter wave gaas high‐power fet
Authors: Mitsui Yasuo
Published: July 2007

A monolithic quasi‐millimeter wave power combiner type GaAs high‐power FET is proposed which combines source island viahole PHS structure FET cell and power combiner and divider circuits on the same substrate. Since the individual island source electrode is connected directly to the heat sink electrode via holes through an extremely thin GaAs substrate, the parasitic source inductance per unit gate width has been reduced to 1.0 pH/mm, and the thermal resistance of the device has been reduced by 40 percent compared to conventional structures. Also, the power added efficiency of more than 80 percent has been achieved by the four‐cell combiner of FET cells with gate width 800μm. This shows that this monolithic structure is effective in suppressing the gain reduction due to the phase differences between the parallel gate figures at high frequency. At 28 GHz, the fabricated FET achieves 1 dB compression point power of 1.1 W, linear power gain of 4.0 dB, the power · (frequency)2product of 860 W · GHz2. Also, such reliability tests as temperature cycling, operation test, and high‐temperature ambient have been carried out, and it has been confirmed that the test device has the basic reliability level suitable for practical quasi‐millimeter wave communication systems.
Analysis of polarization‐maintaining optical fibers with circular pits outside a circular core
Authors: Hinata Takashi , Yoshikawa Hiroshi , Kuroiwa Hitoshi , Hosono Toshio
Published: July 2007

This paper investigates the polarization‐maintaining optical fibers with one circular hollow pit (SCF) and two circular hollow pits (DCF) outside a circular core. The modal birefringence of the following fibers are investigated:

with homogeneous core,

with radially inhomogeneous core.

The relation between the modal birefringence (ΔB) and the polarization dispersion (Δτ) is also investigated. The homogeneous core fibers are analyzed by the improved point‐matching method. To analyze the inhomogeneous core fibers, the core is divided into several homogeneous layers and the improved point‐matching method is then applied. The main conclusions drawn in this paper are as follows: (1) the maximum modal birefringence for DCF can be attained 3.5 times larger than that for SCF; (2) the modal birefringence for inhomogeneous core fiber cannot be greater than that for homogeneous core fiber, even if the core index is chosen equal to the maximum index value of inhomogeneous core; (3) zero polarization mode dispersion can be attained near the wavelength where the modal birefringence takes the maximum value; however, it is not zero at that very wavelength. The relative error of propagation constant computed by our method is less than 10−9 so that the relative errors of the modal birefringence and polarization mode dispersion are less than 10−4.
Considerations of distributed capacitance of high‐voltage transformers
Authors: Ohtsu Satoshi , Ogata Tsutomu
Published: July 2007

An effective means to achieve a small and light‐weight high‐voltage power supply is to raise the conversion frequency of the supply. At present, however, the conversion frequency is largely limited by the distributed capacitance of high‐voltage transformers and the switching time of semiconductor devices. Reduction of the distributed capacitance of a high‐voltage transformer and a new method of analysis which can quantitatively describe the relation between transformer structure and distributed capacitance were achieved. Using the proposed method of analysis, the distributed capacitance is calculated using the winding scheme, core dimension, number of bobbin splits, class and material for winding insulation, core size and impregnation material as the parameters. The calculated values are compared with the measured values and the effects of the parameters on the distributed capacitance are discussed. By using a four‐split bobbin, the distributed capacitance is reduced by 10 percent less than the nonsplit bobbin. The capacitance using the core with a circular center pole is reduced by approximately 10 percent compared with the square center pole. Using class 1 insulation winding, the capacitance is reduced by 10 percent compared with class 2 winding insulation material.
High‐speed switching of the power transistor in a DC‐DC converter with current feedback and core saturation
Authors: Harada Koosuke , Sakamoto Hiroshi , Shoyama Masahito
Published: July 2007

To reduce the size and weight of a switching dc‐dc converter, it is effective to increase its switching frequency. This requires the reduction of the switching time and switching loss. This paper introduces a dc‐dc converter with a short turn‐off time and a high efficiency at a switching frequency up to the order of megahertz. This is achieved by using a bipolar transistor with current feedback and core saturation. The turn‐off mechanism was analyzed by using an equivalent circuit. The turn‐off time was found to be considerably shortened by the quick discharge of the excess carrier in the base region. This is due to the formation of an LC circuit consisting of the saturated inductance of the current feedback transformer which magnetically saturates during the turn‐off period, and the base‐emitter capacitance of the switching transistor. This phenomenon can be used widely for high‐speed and high current switchings.
Os‐doped γ‐Fe2O3 thin‐film media for perpendicular recording
Authors: Ohtani Yoshimitsu , Ohta Satoshi , Terada Akira
Published: July 2007

Since Os‐doped γ‐Fe2O3 sputtered thin film can be added in perpendicular anisotropy by annealing in the magnetic field perpendicular to the film surface, it has potential as a perpendicular magnetic recording media. Herein we examine both a method to dope Os by reactive sputtering and the causes contributing to the induced magnetic anisotropy. Its performance as a perpendicular magnetic disk has yielded the following results. When Os is solidified during the formation of Fe3O4 film by reactive sputtering, reproducible doping is possible. When γ‐Fe2O3 is formed in atmospheric oxidation, the coercive force increases in proportion to the Os doping (Hc ∝ 500x, x = Os at. %). Magnetic anneal is effective for the γ‐Fe2O3 state, and a large anisotropy can be added when the oxygen partial pressure in the atmosphere is increased. Furthermore, the activation energy for the induced anisotropy was approximately 1.0 eV. The induced anisotropy seems to be related to the vacancies. In the recording reproduction using a thin‐film ring head, the reproduced isolated waveform is dipulse, thereby confirming the recording with a large perpendicular component (dipulse ratio 0.7).
Theoretical investigation for coupling between a laser diode and an optical waveguide via a gap
Authors: Fujii Yukio , Matsuhara Masanori , Kumagai Nobuaki
Published: July 2007

To develop a high‐grade optical communication system, numerous studies have been performed on the single longitudinal mode operation of a laser diode (LD). The optical feedback generated at the coupling junction of the LD and the optical waveguide is a serious problem since it is a cause of the deterioration of the stability of the operation of the single mode laser. This paper describes a theoretical study of the reflected and transmitted light at the open end of the LD and at the junction between the LD and the optical waveguide via a gap by means of the boundary element method and the eigenmode expansion method. It is confirmed from the viewpoint of electromagnetic theory that among various configurations for elimination of the feedback, the one with a double‐layered antireflection coating is the most effective. The analysis method used in this paper, unlike many other methods, has no restriction on the difference in the refractive index between the core and cladding. It can be extended easily to the case where the gap region consists of multimedia.
A mode‐filter type light intensity modulator using zincblende crystals
Authors: Ohke Shigeaki , Cho Yoshio
Published: July 2007

This paper investigates optical‐wave propagation characteristics in a light intensity modulator using zincblende crystals. Special attention is given to the transformation of the quadratic surface equations (the refractive‐index ellipsoid equations) and the quadratic curve equations (the polarization plane equations) into their standard forms. Assuming that the light wave enters from a cleavage plane {110}, the behavior of the main refractive index axis in the direction of an electric field which is perpendicular to an arbitrary plane {aac} was investigated. The results show that there are two main refractive‐index axes in the incidental light‐wave plane in the new coordinate system. The results were applied to the examination of the characteristic of the crystal‐axis direction dependence of the retardation modulator, a device using the electrooptical effect. Highest efficiency can be obtained by using the crystal plane {110} for the TE polarized light‐wve incident. The modulating factor can be controlled by the length of the device alone, except for {100} and {111} in which the direction of the polarized light agrees with the direction of the principal refractive‐index axis.
Characteristics of compressed magnetic field (CMF) magnetron sputtering technique using magnetic target
Authors: Hata Tomonobu , Ohtsubo Katsuaki , Hada Toshio , Takahashi Takakazu
Published: July 2007

This paper reports on the experiment of the high‐rate sputtering of Co‐Cr film by the compressed magnetic field magnetron sputtering technique. When a magnetic target is used in the magnetron sputtering technique, utilization efficiency of the target is as low as 20 percent and the deposition rate is low. To cope with this problem, Co‐Cr film is fabricated by the method which has been proposed and successfully used for the dielectric target. The characteristics of the fabrication system and the constructed film were evaluated. It is seen that the area utilization of the target is as high as 90 percent. The film deposition rate is 0.15 μm/min for the target‐substrate distance of 30 mm, gas pressure 0.3 Pa, and input power 4.6 W/cm2. The deposition rate is 0.08 μm/ min for the target‐substrate distance of 50 mm, for which a uniform deposition is obtained. These figures are sufficiently high. It is also seen that when the third component (Fe) is to be included in the film, the content can be adjusted over the wide range of 3 to 12 percent by varying the magnetic field of the solenoid coil.
Vectorial wave analysis of stress‐applied polarization‐maintaining optical fibers
Authors: Hayata Kazuya , Koshiba Masanori , Suzuki Michio
Published: July 2007

The modal analysis of stress‐applied polarization‐maintaining optical fibers is very difficult due to their complex refractive‐index distribution and their large anisotropy caused by a thermal stress. Therefore, only a few approximate analyses have been tried so far. In this paper, to estimate accurately the transmission characteristics of these stress‐applied polarization‐maintaining optical fibers, we present a vectorial wave analysis using a vector H‐field finite‐element method. First, to verify the accuracy of solutions, numerical results for a step‐index circular‐core fiber are presented and the relation between the number of elements and the accuracy of calculation is also clarified. Next, the stress analysis and the vectorial wave analysis of stress‐applied polarization‐maintaining optical fibers with an inner cladding are carried out and the difference of transmission characteristics between the fibers having a different parameter is discussed. Further, we propose an approximate method for calculating the splice loss between two optical fibers and show the normalized radiated power caused by transverse offset, longitudinal separation, and angular misalignment between two stress‐applied polarization‐maintaining optical fibers.
Fabrication of NbN josephson junction integrated circuits using Si insulation layer
Authors: Hirano Mikio , Mori Hiroyuki , Tarutani Yoshinobu , Yano Shinichiroo
Published: July 2007

In the fabrication of Josephson junction integrated circuit, it is most important to align the superconducting critical current ImO of the junction. This paper reports a fabrication of interlayer insulating film with a view to reducing the fluctuation of ImO of NbN‐Oxide‐PbInAu junction of 1.5 μm. The main cause of the fluctuation of ImO is the variation of the junction area due to remnant of interlayer SiO insulating film generated in the aperture of the junction. To solve this problem, several interlayer insulators other than SiO have been investigated. It is found that Si is appropriate for forming the junction aperture without remnant. The Si film fabricated by evaporation has been a film close to amorphous. The pinhole defect density is 10/cm2 (film thickness 300 nm), which is smaller by two orders of magnitude than the one in SiO films. When Si films are used for interlayer insulation of NbN Josephson junction devices, the maximum distribution width of ImO is ±12% (σ ± 8%), which is about 1/2 for the case of SiO films. Usefulness of the film has been confirmed in application to the interlayer insulation film of the logic array with 750 gates. The measured delay time of a chain circuit made for trial is 14 ps/gate in a 2 input OR gate.
Preparation and properties of grain‐orientation Bi4Ti3O12 ceramics by cold‐uniaxial pressing method
Authors: Shoji Kazuo , Uehara Yasuo
Published: July 2007

When Bi4Ti3O12 is viewed as a piezoelectric material, since the direction of the spontaneous polarization is limited in two dimensions, it is necessary to perform grain orientation. In this paper, as a method for the grain orientation at room temperature, a cold‐uniaxial pressing method is considered, and the fabrication method of Bi4Ti3O12 grain‐orientation ceramic is examined. Furthermore, the electrical characteristics of the obtained grain‐orientation sample are also examined. This method performs grain orientation by utilizing the shape anisotropy of the ceramic powder. Therefore, first, the relation between the firing process and the grain growth is examined for normal firing sample. Next, the orientation sample is obtained by applying a uniaxial pressing and a main firing to the obtained plate‐like primary particles. As a result, it has been found that the orientation by this cold‐uniaxial pressing method is due both to the orientation of primary particles during the deformation by uniaxial pressing, and also to the grain growth during the main firing. It has also been found that oriented samples comparable to the hot‐working method can be obtained by this method in terms of grain orientation and electrical characteristics.
Solid thin‐film energy‐transfer dye lasers
Authors: Muto Shinzo , Shiba Fumikazu , Iijima Yoshitsugu , Hattori Kiminori , Ito Chiaki
Published: July 2007

Solid thin‐film energy‐transfer dye lasers (thin‐film ETDL) were developed by doping donor‐acceptance dye pairs in the polymer waveguide. Many types of thin‐film ETDL having a slight degradation of the pumping light were obtained. As a result, the wavelength range of the ETDLs became very wide covering almost the entire region from near UV to near IR. The thin‐film cascade ETDL operation was materialized on the first attempt. The spectral narrowing and the tuning of the solid‐film ETDLs are easily obtained by using the DFB operation. The results show the possibility of making a practical compact laser source with a variable wavelength.
Preparation and characteristics of Co‐Cr films with perpendicular magnetization by CMF‐magnetron sputtering
Authors: Hata Tomonobu , Ohtsubo Katsuaki , Kita Yutaka , Hada Toshio , Takahashi Takakazu
Published: July 2007

It is known that the high‐rate deposition of magnetic thin‐films by using the magnetron sputtering method is very difficult since the target shields the magnetic field. We carried out the high‐rate deposition of Co‐Cr films by using the compressed magnetic‐field (CMF) magnetron sputtering method in which the magnetic pole does not touch the target. This paper describes the features of the apparatus, and the investigation of the orientation of the c axis and the difference in the magnetic characteristics, from the changes of the gas pressure of Ar, the temperature of the substrate, and the deposition rate of the film. The results show: (1) the deposition rate of the film was 0.26 μm/min maximum showing the possibility of a high‐rate deposition of the films; (2) the lower the gas pressure, and the higher the film deposition rate, the better the film characteristics; (3) the temperature of the substrate has a slight effect on the orientation, so that the films can be prepared at a temperature as low as 100°C; and (4) the smaller the half width of the rocking curve, the greater the coercive force. Finally, the CMF‐magnetron sputtering method is very effective in preparing perpendicular‐magnetization Co‐Cr films at a low temperature and a high preparation speed.
ESCA compositional profiles and electrical properties of diamond‐like carbon film/Si MIS structure
Authors: Mizokawa Yusuke , Komoda Osamu , Miyasato Tatsuro , Hasegawa Shigehiko , Tokumura Masao , Nakamura Shogo
Published: July 2007

Diamond‐like carbon (DLC) films were deposited on silicon wafers by hydrogen gas reactive dc‐sputtering of graphite and fabricated MIS diodes. ESCA chemical depth profiles showed that almost no impurities such as oxygen and nitrogen were present in the bulk of DLC films. In the interfacial region between DLC and Si substrate, a small amount of Si‐C bonding as well as natural oxide of silicon were detected. It is found that the 1st‐derivative spectrum of C‐KLL Auger line in ESCA from the DLC film surface was very similar to the C‐KLL AES spectrum from natural diamond. This suggests that DLC film has a fairly diamond‐like tetrahedral sp3 C‐C bonding configuration. The C‐V curves of the Hg/DLC/Si MIS diodes showed accumulation, depletion and inversion characteristics. The charge trapped in DLC film and the interface state density distribution as a function of the surface potential were obtained first. Both the amount of trapped charge and the C‐V hysteresis were considerably smaller compared to an Si3N4/Si diode.

The interface state density curve exhibits a “U” shape and the minimum density was less than 3 × 1010/cm2/eV in the vicinity of the mid‐band gap.
High‐precision coaxial cable attenuation measurement using resonant method
Authors: Aida Kazuo
Published: July 2007

This paper discusses a highly precise method of measurement for the attenuation of a coaxial cable using a short test‐piece. The proposed method is used to compose an open‐ended resonator by the coaxial cable and to determine the attenuation from the resonant characteristics. To realize a highly accurate measurement using a very short test‐piece, the end effect of the cable must be corrected. A correction formula is presented, which by experiment, is verified as useful. The end effect in the proposed measurement is one order of magnitude less than that in the short‐circuit resonant method, which has been used in the past as the method measurement for the attenuation of the short test‐piece cable. It is shown that if the test‐piece is longer than a certain value, the measurement can be performed without considering the end effect. The measurement accuracy of 0.2 percent and the repeatability of 0.1 percent are realized by the proposed method. The upper limit of the cable attenuation that can be measured by the proposed method is discussed. When the resonant characteristics are measured by the half‐amplitude width, the upper limit is 7.6 dB, indicating that a wide range of attenuations can be measured. The proposed method is then applied to the measurement of the attenuation‐pressure characteristics of the submarine coaxial cable verifying the usefulness of the method.
Ferroresonant DC‐DC converter with high‐frequency drive
Authors: Karada Koosuke , Murata Katsuaki
Published: July 2007

Since the switching loss in inverter circuits and the iron loss in ferroresonant circuits increase with frequency, the conversion efficiency decreases and the heat loss in the switching element and magnetic core increase at high frequencies. The requirement of radiating the heat has restricted the size reduction of power supplies. In view of the relation between the loss in the output transistor of an inverter and the switching frequency, it is found that the loss consists of the one independent of the switching frequency and the switching loss increasing in proportion to frequency. As the switching frequency increases, the latter becomes predominant. Hence, for a small and efficient converter at high switching frequencies, the switching loss has to be reduced. To this end, a relatively large capacitor is connected in parallel with the output transistor in this paper. As a result, sudden increase of the collector voltage at the shutdown of collector current is suppressed and the instantaneous collector loss is reduced. In the ferroresonant circuit for stabilization of output voltage, two saturable cores operating on a minor loop on the BH curve are used. Hence, the loss is small even at high frequencies and a superior constant voltage characteristic is realized by a feedback. The conversion efficiency is about 80% at the switching frequency of 500 kHz.
Design and characteristics of an optical wave meter
Authors: Okada Kenji
Published: July 2007

A new optical wavemeter using a quartz azimuth rotator for direct reading of wavelength is described. When linearly polarized light having a certain wavelength enters the quartz rotator the plane of polarization rotates, the angle of rotation depending on the thickness of the quartz and the wavelength. Since the thickness of the quartz in the wavemeter is kept constant, the wavelength can be read from the angle of rotation of the polarized input light. This angle is obtained from the ratio of two polarized light beams which are divided from the input light by using an optical analyzer. The quartz thickness at which the error in measurement of wavelength is minimum is found. The relationship between the dividing ratio of the beams and the wavelength is also found. An azimuth quartz rotator with optimum thickness is fabricated. It is confirmed that the calculated and measured characteristics of the dividing ratio versus wavelength are in good agreement. The wavemeter has a wavelength range of 0.6‐1.6 μm and measurement accuracy better than 1 nm at input power of ‐35 dBm. To increase the utility of the wavemeter, a device to measure its input power with high sensitivity is added to the apparatus, the resulting accuracy being better than 0.1 dB at an input level of ‐35 dBm.