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Experimental results on the frequency dispersions of the transconductance (Gm) and the drain conductance (Gd) in ion-implanted gallium arsenide (GaAs) metal-semiconductor field-effect transistors (MESFETs) are analyzed by two-dimensional device simulations. In the experiment, Gm exhibits negative frequency dispersion and Gd shows positive frequency dispersion in the drain current saturation region, and the activation energy is close to 0.7 eV for both. Gm exhibits positive dispersion with an activation energy of 0.42 eV in the linear current region, and no frequency dispersion is observed in Gd. Based on the drain voltage conditions of the experiment and the effect of a p-type buffer layer, a simulation assuming traps at 0.42 eV at the surface and 0.71 eV in the substrate has shown that features of the experimental results for Gm and Gd can be reproduced. These results show that the positive dispersion of Gm in the linear region is caused by the surface traps, and the negative dispersion of Gm and the positive dispersion of Gd in the saturation region by the substrate traps. Through the simulated potential and carrier distribution during the gate or drain transient, we conclude that the positive dispersion of Gd is due to the capture delay of electrons by the traps, and the negative dispersion of Gm in the saturation region is due to the emission delay of electrons from the substrate traps, which are accumulated by the drain current penetration into the substrate. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(4): 20–28, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20205 [ABSTRACT FROM AUTHOR]

Scattering of a TM plane wave from a finite periodic surface is studied by the spectral formalism. First, the diffraction beam, the optical theorem, the total scattering cross section and the relative power of diffraction beam are defined. By use of the principle of reflection, it is shown that the spectrum of the scattered wave can be written by the boundary value only on the corrugated part of the surface. Expanding such boundary value into a Fourier series, the integral equation determining the boundary value is transformed into a matrix equation of the Fourier coefficients, which is solved numerically. Then the total power of scattering and the relative power of diffraction beam are calculated against the angle of incidence. Wood's anomaly, the beam width of a diffraction beam, and the singularity of the spectrum of the scattered wave are discussed. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(3): 10–19, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20217 [ABSTRACT FROM AUTHOR]

We demonstrate a remarkable improvement in the waveguiding characteristics of silicon wire waveguides, and show their application to functional optical devices. Applying a novel spot-size converter consisting of an ultrathin silicon taper and a SiON waveguide, coupling losses between silicon wire waveguide and optical fiber were greatly reduced to just 0.5 dB/coupling. Propagation losses were also reduced to less than 3 dB/cm, by smoothing the surface of the waveguide core. Some functional devices, such as photonic crystals, ring resonators, and lattice filters, were tested and showed superior optical characteristics. Enhancement of nonlinear phenomena due to a high power density effect was also observed. © 2006 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 89(3): 42–55, 2006; Published online in Wiley InterScience (www.interscience. wiley.com). DOI 10.1002/ecjb.20210 [ABSTRACT FROM AUTHOR]

Increases in the speed and capacity of ultrahigh-speed optical communication systems have made dispersion compensator technology an essential tool. In view of this fact, we have proposed a virtually imaged phased array (VIPA)-type variable dispersion compensator (VIPA-VDC) capable of trailing a dispersion that changes as a function of time in an optical transmission path, and we have pursued its development. Because the dispersion compensator is comprised of multiple components, an optimal design for the dispersion compensator as a whole is essential to obtaining favorable performance characteristics. Therefore, we have created a simulation algorithm based on Fresnel/Kirchhoff's diffraction integral, calculated the dispersion characteristics of an actual VIPA dispersion compensator, and verified the validity of the simulation algorithm. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(12): 34–42, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10109 [ABSTRACT FROM AUTHOR]

The responsivity characteristics of an efficient tilted-beam total-reflection photodiode (TBR-PD) are analyzed by a wave-optical approach. Since the incident wave is totally reflected at the interface between the absorption layer and the p-InP cladding layer, the optical absorption by the p+-InGaAs contact layer can be substantially reduced in the TBR-PD. The responsivity is derived from the measured received photocurrent in the fabricated TBR-PD by taking account of the effect of formation of an AR coating on the incidence plane. The results show that the maximum value reaches about 1 A/W and is substantially improved over the conventional photodiode without total reflection. The responsivity obtained in the analysis exhibits excellent agreement with the measured results for the device, and the validity of the present analysis method is confirmed. Further, the polarization dependence of the responsivity is found to be extremely small over a wide range of angles of incidence. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(10): 1–9, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20184 [ABSTRACT FROM AUTHOR]

We developed a technique to directly observe at nanoscale resolution the degradation of gate SiO2 films observed in metal-oxide-semiconductor (MOS) capacitors by using conductive atomic force microscopy (C-AFM). As a result of observing gate SiO2 films subjected to a constant current stress, local leakage current spots related to the stress-induced leakage current (SILC) were detected. Distribution of defects induced by the electrical stress and the conduction mechanism of local leakage current caused by them are discussed. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(6): 18–26, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20123 [ABSTRACT FROM AUTHOR]

There is now great interest in optical memory using a three-level atom embedded in photonic crystals, which can be used for quantum computing; however, quantum-information detection from the optical memory has not been demonstrated. In this paper, first, considering the relative position of the photonic band gap (PBG) and two atomic levels split from the upper level of the atom used for the optical memory, we demonstrate that one of the split levels must be outside the PBG for quantum-information detection. In this case, the quantum state of the atom can be changed by moving the other split level, where the quantum information is maintained or emitted for the cases in which the split level is inside or outside the PBG, respectively. The emitted quantum information can be measured as spontaneous emissions by a photon detector. Next, we propose two methods of moving the split level: one is realized by applying a direct current (DC) field to the atom and the other is realized by changing the intensity of the control laser field. Furthermore, by evaluating the intensities of the DC and the control laser fields, we find that the quantum information can be measured using the fields on the millielectronvolt order. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(8): 10–19, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10205 [ABSTRACT FROM AUTHOR]

A new technology has been developed for optically visualizing the intensity distribution of the acoustic wave within a surface acoustic wave (SAW) device. In this technique, the strain generated by the SH (Shear Horizontal) wave in a LiTaO3 crystal is detected via the photoelastic effect as a change of polarization state of the light passing through the device. By detecting the SH component, which is the main component of the SAW on a 42°YX LiTaO3, the method provides for more direct observation of the behavior of the acoustic wave in a device than in the conventional technique that detects the SV (Shear Vertical) component, a secondary component. Based on the present technique, an acoustic wave observation setup is developed and a simple resonator is evaluated. It is found that the acoustic-wave distributions within an IDT depend on the driving frequencies and that acoustic wave energy is leaked outside the resonator at specific frequencies. Further, a more accurate visualization of the acoustic wave component is made possible by correcting for the influence of the electro-optical effect on the observation results. Another setup has been developed in which a probe light beam is incident from the back side of the substrate and the light reflected from the device surface is used in order to determine the distribution under an electrode. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(6): 10–17, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20066 [ABSTRACT FROM AUTHOR]

A waveguide-type collinear acoustooptic device can work as a wavelength-selective switch for wavelength division multiplexed (WDM) light. Therefore, its applications to WDM routing switching are expected. In this paper, in order to evaluate the wavelength-selective switching characteristics of the device consisting of a directional coupled waveguide and a Y-branch, simulation is carried out by the FDTD method. The results of the simulation are compared with those of the coupled mode theory, and agreement between them is confirmed. A method of propagating an optical pulse is studied in the segment-divided region in order to analyze the acoustooptical coupling characteristics in a long scale interaction region. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(6): 18–27, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20064 [ABSTRACT FROM AUTHOR]

Deformation of an organic photosensitive azopolymer by near-field light generated by an optical fiber probe with a very small aperture diameter of about 50 nm is studied. The azopolymer is deformed in response to the polarization state of the light incident on the probe. If the probe aperture diameter is made smaller, the mark shape can be made smaller but the probe must be moved closer to the material. However, the mark width is about 6 times the probe aperture diameter. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(3): 55–61, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10129 [ABSTRACT FROM AUTHOR]

If the phase match condition is satisfied in a 1.55-µm dispersion-shifted fiber (DSF), four-wave mixing (FWM) between the signals is generated at a lower optical power level than other nonlinear phenomena. In this paper, the polarization dependence of the FWM generating efficiency is discussed. From the maximum mixing efficiency, the nonlinear refractive index and the zero-dispersion wavelength are simultaneously measured. Both DSFs of 20 and 4 km are used for studies of the polarization dependence of FWM light with respect to linear polarization from the wavelength variable DFB-LD. For a 20-km DSF, a nonlinear refractive index of n2 = 2.50 × 10-20 m2/W and a zero-dispersion wavelength of λ0 = 1553.0 nm are obtained. For a 4-km DSF, n2 = 2.42 × 10-20 m2/W and λ0 = 1557.9 nm. For the 4-km DSF, it is confirmed by the CW-SPM method that n2 = 2.40 × 10-20 m2/W. The measured results for the two methods are found to be in good agreement. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(3): 45–54, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10146 [ABSTRACT FROM AUTHOR]

In the formation of β-FeSi2 by means of FeSi2 alloy evaporation, there are problems that the vapor pressure of Fe and Si is low and that there is a vapor pressure difference of close to one order of magnitude between Fe and Si. In this paper, by using electron beam (EB) evaporation equipment, these problems are resolved and the success of β-FeSi2 formation is reported. First, the Fe and Si composition ratio of the EB evaporated film of FeSi2 alloy is analyzed by XPS. It is confirmed that the ratio is almost 1 to 2. Next, a sample with FeSi2 alloy EB evaporated on a Si substrate is annealed within a nitrogen environment by using an infrared heating furnace (at 700 to 900 °C) so that β-FeSi2 is synthesized. Also, it is found that the β-FeSi2 layer is made thicker and the optical absorption characteristic is improved by vapor-depositing an Fe layer between the FeSi2 alloy layer and a Si substrate. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(1): 9–15, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10118 [ABSTRACT FROM AUTHOR]

We have constructed a terahertz-wave parametric oscillator (TPO) with pulse-to-pulse access to random wavelengths, using an optical beam scanner and a confocal optics system (1:1 telescope) to vary the pump light angle of incidence. In addition, we used the TPO in a spectroscopic study of HCl gas in order to test its tunability, and confirmed that the TPO was continuously tunable from 1 to 2 THz and could rapidly access random frequencies in that range. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(4): 18–26, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10060 [ABSTRACT FROM AUTHOR]

The four-wave mixing (FWM) used in optical fibers is expected to be a simple wavelength conversion technique for ultrafast optical signals. Highly efficient generation of stable FWM light is desired. FWM efficiency depends on the zero-dispersion wavelength of the fiber, the wavelength of the pump light, and the wavelength of the signal light, and reaches its maximum efficiency when the pump wavelength and zero-dispersion wavelength match in degenerate FWM. However, the zero-dispersion wavelength fluctuates in the longitudinal direction in actual optical fibers, and these changes affect the FWM generation characteristics. In this paper, we analyze FWM generation that accounts for the zero-dispersion wavelength fluctuations in the longitudinal direction of the optical fibers and explain the theory of the dependence of the FWM efficiency on the pump wavelength. In addition, by conducting FWM generation experiments, we demonstrate the differences in the characteristics of the optical fibers and clearly show the relationship between the FWM generation characteristics and zero-dispersion wavelength distribution. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(8): 16–24, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10032 [ABSTRACT FROM AUTHOR]

In this paper, a structure using the optical leakage phenomenon is proposed as a relatively simple TM mode selective filter for optical circuits. The filter characteristics are discussed. In the TM mode selective filter discussed herein, a layer with refractive index higher than that of the waveguide layer (guided layer) is used as a cladding together with a thin buffer layer with a lower refractive index (ultralow-refractive-index layer). The cladding material used to realize a TM mode selective filter need not be a lossy material such as a metal with a so-called complex index of refraction. A layer with a refractive index equal to or higher than that of the guiding layer suffices. In this paper, it is shown with specific configuration examples (partly numerical examples) that an optical leakage structure with an ultralow-refractive-index buffer layer can exhibit excellent TM mode selective filter characteristics. © 2002 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 85(8): 9–15, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10037 [ABSTRACT FROM AUTHOR]

In a broad-area laser diode (LD) having a wide stripe width, a Gaussian pattern is not obtained in the near field (NFP) and the far field pattern (FFP) has multiple peaks, which is known as filamentation. Thus, when used in communications, the losses in the side lobes are large, and antenna directivity problems develop. In this paper, we solve the wave motion equation and the dispersion equation to explain the radiation characteristics during filamentation. In particular, we explain the relationship between the phase distribution at the LD facets and the NFP and FFP. We also investigate the improvements in the radiation characteristics by examining the phase distribution at the facets and the injected current distribution in the direction perpendicular to the wave propagation direction. The results showed that the FFP can be a single peak with a side lobe suppression ratio of -13.4 dB when phase correction having two peaks was performed at the facets. The results also showed effective narrowing of the current distribution. ©2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(3): 40–49, 2002 [ABSTRACT FROM AUTHOR]

Our research examines the generation of an optical near field by a vertical cavity surface emitting laser (VCSEL), which can readily be formed into a two-dimensional array, and the possible application to optical recording capable of high-speed data transfers due to the higher density and parallel processing achieved when the optical near field is used as the optical head. We propose a VCSEL with metal micro-aperture for generating the optical near field. Then we demonstrate the ability to create a micro spot size of 100 nm or smaller based on this structure from analysis of the intensity distribution of the micro-aperture by the two-dimensional finite element method. We also form a micro-aperture by using a focused ion beam in a GaAs/AlGaAs VCSEL with an 850-nm wavelength and perform initial evaluations. In these evaluations, we obtained an emitted power density of 0.12 mW/µm2 from a 400-nm square micro-aperture. Furthermore, we observed the light from a 100-nm square aperture in near field observations and verified the generation of an optical near field by this structure. © 2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(2): 43–53, 2002 [ABSTRACT FROM AUTHOR]

Symmetric Mach-Zehnder (SMZ) type all-optical switches, namely, the SMZ, polarization-discriminating SMZ (PD-SMZ), and delayed interference signal wavelength converter (DISC), are described in detail. All of these all-optical switches are characterized by push–pull operation and allow ultrafast switching not limited by the relaxation time of high-efficiency nonlinear optical materials that are suitable for low-power operations. They make possible a low-chirp switching window of a quasi-square type that is important in practice. Ultrafast all-optical signal processing with an SMZ, namely, 168 → 10.5 Gbit/s error-free DEMUX (using a hybrid-integrated SMZ, HI-SMZ), zero-penalty optical signal pulse regeneration at 84 and 168 Gbit/s, and error-free all-optical wavelength conversion are reported. In experiments with pulse regeneration and wavelength conversion, the error rate is evaluated after DEMUX to 10.5 Gbit/s by HI-SMZ because the signal light after signal processing has ultrahigh speed. © 2002 Scripta Technica, Electron Comm Jpn Pt 2, 85(2): 1–17, 2002 [ABSTRACT FROM AUTHOR]

In order to reduce the phase error in the FDTD analysis, Cole proposed the NS-FDTD method. However, in the paper by Cole, numerical dispersion characteristics and accurate stability condition were not presented. Also, definition was given only for cubic lattices. In this paper, the NS-FDTD method is extended to the rectangular lattices and the numerical dispersion characteristic and the stability condition are derived. From the analysis for the stability condition, it is found that the stability condition in the present method is larger than those for the FDTD method and the FDTD(2, 4) method. From the analysis of the dispersion characteristic, it is shown that the present method has much higher accuracy than the FDTD method whether the lattices are cubic or rectangular. An analysis of a waveguide model is carried out in which the NS-FDTD method and the FDTD method are mixed. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 85(1): 22–30, 2002 [ABSTRACT FROM AUTHOR]

In FDTD analysis, one of the problems is numerical dispersion caused by the discretization of time and space. In a previous publication, the present authors generalized a speed-of-light correction method previously applied only to isotropic meshes so that it could be applied to an anisotropic mesh. However, in the previously reported correction method the speed of light was corrected isotropically. Therefore, the error compression was small in the aniso-tropic mesh. In this paper, a correction method is proposed in which more compression of the phase error than in the previous method is possible in an anisotropic lattice. By applying the new method to a two-dimensional nonuniform mesh, the effectiveness of the method is demonstrated. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 85(1): 50–58, 2002 [ABSTRACT FROM AUTHOR]

A method for fabrication of binary holograms with a laser punch is proposed. In the present method, the hologram pattern is first computed in a computer so that a given reconstruction image can be obtained. This hologram pattern is binarized by a newly proposed algorithm. Based on the binary hologram pattern, laser illumination and motion of the stage with a film attached are computer controlled. In this way, holes with a fixed diameter are punched into the film to form binary holograms. Further, in order to verify the method's effectiveness, it is confirmed that excellent reconstruction images can be obtained from the holograms fabricated by the proposed method. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(10): 17–23, 2001 [ABSTRACT FROM AUTHOR]

Nonlinear interactions between neighboring pulses in an optical time division multiplexed (OTDM) system may cause timing jitter of the signal pulse, which degrades transmission quality. A dispersion-managed (DM) soliton is a stable pulse in a DM line and is less influenced by various nonlinear effects than conventional solitons. On the other hand, interactions between DM solitons depend on the strength of the DM line, which is defined as the length of DM period times the variation of the fiber dispersion, and the transmission quality is degraded mainly due to the interactions in a strongly DM line. In this paper, the interactions between DM solitons are studied theoretically and numerically, and we then show that alternating the phases or amplitudes of pulses in the time sequence is effective for reducing the interactions. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(6): 24–29, 2001 [ABSTRACT FROM AUTHOR]

A novel approach for asymptotic reduction of physical optics (PO) integration is proposed for two-dimensional line source diffraction from a half-sheet. The field equivalence principle provides alternative integration surfaces not on the original half-sheet but on the geometrical shadow (SB) and reflection (RB) boundaries, where analytical integration leads to the well-known Fresnel-type uniform PO diffraction coefficient of UTD type. The superiority of the uniform diffraction coefficient to those of other types is explained in terms of the location of the integration surfaces and is demonstrated numerically. © 2001 Scripta Technica, Electron Comm Jpn Pt 2, 84(2): 54–62, 2001 [ABSTRACT FROM AUTHOR]

A physical optics approximation is discussed for the analysis of the scattered electromagnetic field when a cylindrical wave radiated from a line source is incident near the edge of a concave conducting surface with its radius of curvature slowly varying as a function of position. By analyzing approximately the integral of the scattered electromagnetic field expressed in terms of the physical optics current, a uniform asymptotic solution is derived by superposition of the geometrical optics wave and the edge diffraction wave. The diffraction coefficient for the edge diffraction wave is expressed in terms of the Fresnel function, while the expressions on the reflection boundary (RB) side and the shadow boundary (SB) side have symmetry. The argument of the Fresnel function uses a new representation containing information on the radius of curvature of the wave front of the diffracted wave and the location of the caustic, or the radius of curvature of the wave front of the incident wave, so that a scattered field continuous on the RB and SB is formed. The effectiveness of the uniform asymptotic solution is numerically clarified by comparison with the rigorous solution obtained by the Wiener–Hopf method and the reference solution obtained by direct numerical integration of the integral on the scattered field. The results are compared with analytical results based on the physical optics approximation published elsewhere. The causes of the difference from the present results are discussed. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(6): 32–42, 2000 [ABSTRACT FROM AUTHOR]

A large signal model of an optically illuminated MESFET and a method for design and analysis of an optically controlled HMIC oscillator based on the proposed model are reported in this paper. Measured values of the S parameters and dc characteristics of the optically illuminated MESFET are described. A modeling of the optically illuminated MESFET is described in detail, and an optically illuminated MESFET model containing an optical intensity parameter is proposed. The Ids-Vds characteristics and the S parameters computed with this optically illuminated MESFET model are found to agree well with the measured values. A simulation analysis is presented for the optical control of oscillation frequencies and the optical pulse modulation experiment. The computed output spectra of the optically pulse modulated oscillator agree well with the measured results. It is confirmed that the microwave is modulated by light. Further, the envelope distortion is studied, and we investigate how illumination of the high-speed optical pulse affects the envelope of the MESFET oscillator output and what the applicable maximum bit rate is. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(5): 1–12, 2000 [ABSTRACT FROM AUTHOR]

This paper considers the electromagnetic propulsion of a body radiating directed electromagnetic waves. As the source of electromagnetic waves, a system consisting of two electric dipoles is chosen. The electromagnetic propulsion this system receives from the surrounding space is theoretically analyzed and discussed. This propulsion is related to the near field formed by the dipoles and exhibits the maximum propulsion at a characteristic dipole spacing. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(4): 31–39, 2000 [ABSTRACT FROM AUTHOR]

Homoepitaxial and heteroepitaxial growths of InGaN/GaN have been reviewed with an emphasis on the growth method, InGaN phase separation, and the optical properties. The nitride semiconductor material used to be surrounded with many mysteries and so-called “common sense” did not hold. The reasons for these mysteries are described. © 2000 Scripta Technica, Electron Comm Jpn Pt 2, 83(2): 17–25, 2000 [ABSTRACT FROM AUTHOR]

A formulation of the time domain beam propagation method based on the finite element method (FETD-BPM) is presented for the first time, so far as the authors are aware. The performance of the FETD-BPM is enhanced by introducing the Padé equation, allowing broadband characterization, and by using perfectly matched layer boundary conditions so as to eliminate spurious reflection from the edges of the analysis region. Specifically, the characteristics are analyzed for optical filters using a refractive index-modulated optical grating and a photonic bandgap, and the validity and usefulness of the present method are demonstrated. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(11): 52–58, 1999 [ABSTRACT FROM AUTHOR]

3D photonic crystals can produce a number of fascinating optical devices utilizing the band gap, the dispersive passband, and unisotropic band structure. We previously proposed a process for fabricating a 3D periodic nanostructure which can behave as photonic crystals. The key technique in the process is the deposition of a multilayer by bias sputtering replicating periodically a corrugated layer pattern, which is named the autocloning effect. This paper reviews our recent works on 3D photonic crystals: the mechanism of the autocloning effect, propagation analysis in the 3D photonic crystal by an FDTD method, and applications such as plane-normal waveguides or wavelength-selective filters. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(9): 43–52, 1999 [ABSTRACT FROM AUTHOR]

Although there has been active research on the optical quadratic nonlinearity that appears in poled glass, its origin has not been clarified. There have been many reports on bulk glass but little research on poled glass thin film waveguides. Waveguide structures are important for future applications to optical IC devices, and clarifying the origin of the nonlinearity is very important. In this work we report experiments on phase-matched blue second-harmonic generation in a corona-poled Corning 7059 glass film waveguide with a titanium sapphire laser as a fundamental wave and investigate the origin of its nonlinearity. After relaxation of the nonlinearity optical constant once the poling has been measured, the analysis is performed using a biexponential function, and the origin is elucidated by separating the fast and the slow relaxation components. In particular, an etching experiment has been carried out noting the latter component, and it has been shown that the charge distribution generated in the waveguide by the poling and the interface between the glass film and glass substrate play important roles in generating quadratic nonlinearity. It has also been confirmed by X-ray photoelectron spectroscopy that sodium diffuses in Pyrex glass substrate as a result of poling. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(8): 53–61, 1999 [ABSTRACT FROM AUTHOR]

Diffraction of plane waves from a strip grating deposited on a magnetized ferrite substrate is studied analytically, with the incident electric field and biasing magnetic field assumed to be parallel to the edges of the strips, since the incident wave in these circumstances excites magnetostatic surface waves most strongly. Analytical complexity is concisely reduced to a nonreciprocal Riemann–Hilbert problem that is solved in a rigorous manner for an arbitrary incident angle. The numerical results show that a large number of scattering resonances occur in the short-wavelength range owing to magnetostatic surface waves excited in the ferrite. The characteristics obtained here are asymmetric in the sense that the distribution of the scattering resonances is dependent on the sign of the incidence angle. For normal incidence, the asymmetry shows that the intensity of the reflected beam depends on the sign of its angle. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(7): 41–49, 1999 [ABSTRACT FROM AUTHOR]

In this article, we discuss the preparation of indium tin oxide (ITO) by ion beam sputtering and irradiation of the film surface with He and O2 gas with an assist ion gun during deposition. The physical properties of the thin film were examined using the van der Pauw, SEM, and X-ray diffraction techniques. The influence of the assist ion gun on the ITO film was studied and adjusted to improve the reflectivity of the film. Details on the optical and electrical properties of the ITO film and structural changes that occurred are presented. ©1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(5): 30–35, 1999 [ABSTRACT FROM AUTHOR]

Terahertz wave generation by the optical parametric oscillation using LiNbO3 is expected to provide a terahertz source with excellent coherence and wavelength variability in a wide range of applications. In this paper, in order to achieve high performance of the source, the basic characteristics of generation are studied. First, the basic properties of the gain coefficient and the absorption coefficient, including temperature, are studied theoretically, and it is made clear that the cooling of crystals is effective for improvement of generation efficiency. Next, an experimental investigation of the temperature characteristics of the parametric generation is carried out by measurement of the temperature dependence of the idler output. At 17.5 K, generation efficiency is increased by more than one order of magnitude in comparison with room-temperature operation. [ABSTRACT FROM AUTHOR]

This paper describes angled-physical-contact (APC) optical connectors for SM optical fibers, each with a stepped ferrule that consists of a short cylindrical portion at its end portion forming an angled convex surface on the endface at a slanted angle of 8 or 12°. Since the insertion loss increases when one stepped ferrule rotates relative to the other in a connection, the parameters affecting the increase in insertion loss were analyzed based on studies of the angled convex surfaces of stepped ferrules in connections. From the above analysis, the theoretical expression of rotation allowing the elimination of an air gap on the mating optical fiber endfaces was obtained. The insertion loss was given in terms of the rotation between the mating stepped ferrules of the APC connectors, comparing the results of the theoretical analysis with experimental data. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(4): 9–16, 1999 [ABSTRACT FROM AUTHOR]

A new beam propagation method based on the finite element method (FE-BPM) has been developed for the analysis of nonlinear optical waveguides. A formulation for the FE-BPM that is applicable not only to the TE mode but also to the TM mode is presented. Various techniques for enhancing the performance of the FE-BPM are introduced, including the Padé equation of wide-angle beam propagation, the transparent boundary condition, the perfect matched layer condition for prevention of spurious reflection from the edge of the analysis region, and an algorithm for adaptive updating of the reference index of refraction and the finite-element grids. Beam propagation analysis of spatial soliton emission in a nonlinear optical waveguide is performed in order to investigate the performance of the new FE-BPM. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(4): 47–53, 1999 [ABSTRACT FROM AUTHOR]

The vertical-cavity surface-emitting laser (VCSEL) operating with low threshold current is a promising way to realize future parallel optical interconnects. In this study, we propose a novel structure of p-type delta-doped InGaAs/GaAs quantum wells for low-threshold, high-speed VCSELs. Edge-emitting lasers having p-type delta-doped quantum wells were grown by metal-organic chemical-vapor deposition and a low-threshold current density of 152 A/cm2 (51 A/cm2/well) was realized. We also fabricated p-type delta-doped quantum well InGaAs/GaAs VCSELs with a low-resistance GaAs/AlAs distributed Bragg reflector, and achieved a low threshold current of 0.37. Further threshold reduction by controlling the doping concentration in the p-type delta doped layers is expected. ©1999 Scripta Technica, Electron Comm Jpn Pt. 2, 82(4): 54–60, 1999 [ABSTRACT FROM AUTHOR]

Taking into consideration the phase match condition, which is dependent on the intensity of the pumping light, the wavelength of the signal light is set on the longer wavelength side than the zero dispersion wavelength of the fiber and the small-diameter fiber with which the dispersion slope can be made small is used. It is seen that by means of these provisions high-efficiency wavelength conversion becomes possible with a converted-light gain of more than 5 dB in the wide pumping wavelength region of more than 8 nm. Since the power density can be made large with a small pumping energy in this small-diameter fiber, high-efficiency wavelength conversion becomes possible. Also, when this fiber is used and the pumping light is set at a longer wavelength than the zero dispersion wavelength, the four-wave mixing efficiency quickly increases with the increase of the pumping light intensity. Because of this characteristic, pulse compression with a gain for the signal optical pulse can be carried out. In experiments, a light signal with a pulse width of 93 ps is compressed to 20 ps and a 29-dB gain is observed. It is also shown that in this case a similar compression is possible for the converted light. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 82(3): 41–50, 1999 [ABSTRACT FROM AUTHOR]

Hollow retroreflectors installed on satellites are used as targets for satellite laser ranging and earth-satellite laser long-path absorption measurements. The optical characteristics of a space retroreflector are determined by several parameters, including mirror curvatures, dihedral angles, and the direction of the retroreflector on the satellite. In this paper, we propose using a genetic algorithm to design space retroreflectors. We applied this method for design of a retroreflector 50 cm in diameter. We found that the optimum design of space retroreflectors having high optical efficiency is obtained in a short time by using the genetic algorithm. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 81(12): 10–16, 1998 [ABSTRACT FROM AUTHOR]

We studied the epoxy and silicone resins used for the plastic packaging of laser-diode (LD) modules with regard to their temperature dependence of the refractive index, stability at high temperature in a very humid atmosphere, contraction strain during the thermal curing process, temperature dependence of the thermal strain, and water sorption. We found that these resins have refractive index temperature coefficients on the order of 10–4/deg, and that there is no variation in the refractive index in an 85 °C, 85% RH atmosphere. Moreover, the epoxy resins exhibited a thermal contraction strain of about 0.1% and a thermal strain temperature coefficient of about 10–6/deg. With silicone resins, there is negligible strain resulting from thermal curing or temperature variation. Furthermore, we have determined that the moisture diffusion and permeability coefficients are, respectively, three orders and one order of magnitude smaller in the epoxy resin than in the silicone resin. © 1999 Scripta Technica, Electron Comm Jpn Pt 2, 81(12): 17–26, 1998 [ABSTRACT FROM AUTHOR]

We have proposed and demonstrated a method of linearizing the optical frequency sweep of a laser diode by superimposing a rectangular signal on the modulating triangular signal for high-resolution FMCW reflectometry. First, we describe the principle of the proposed method. The waveform of the optical frequency sweep is simulated by using a simplified model, in which only the frequency modulation response is taken into account. The optimum amplitude of the rectangular signal and the linearity of the optical frequency sweep are discussed. Next, the proposed method is applied to FMCW reflectometry to confirm the usefulness of the method. The spatial resolution is minimized when the amplitude of the rectangular signal normalized to the amplitude of the triangular signal is between 0.5 and 0.7. It is difficult to linearize the optical frequency sweep perfectly by using the proposed method. However, the method is very effective because the linearity of the optical frequency sweep can be significantly improved despite the simple configuration. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(10): 30–36, 1998 [ABSTRACT FROM AUTHOR]

Programmable optical frequency filters with a lattice configuration composed of circuit units can provide a wide variety of filter characteristics. A circuit unit is composed of a tunable coupler and a thermo-optic phase shifter. We have already fabricated programmable optical frequency filters using planar lightwave circuits and have realized a variable group-delay equalizer. The filter frequency range of these programmable optical frequency filters, however, is limited to less than 1000 GHz because of the wavelength dependence of the tunable couplers and optical phase shifters. In this paper, we report the design of a novel tunable coupler with wavelength-independent amplitude and phase characteristics, and use it to propose a novel algorithm for synthesizing programmable optical frequency filters in order to broaden the filter frequency range. We show numerically that this novel filter can realize a broad filter frequency range of about 10,000 GHz, which is ten times that of our conventional programmable filters. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(10): 1–11, 1998 [ABSTRACT FROM AUTHOR]

The format of the diffusion coefficient in the optical diffusion equation is determined experimentally. For the diffusion coefficient D in the optical diffusion equation used for description of optical propagation in a turbid medium, two representations have been proposed, one containing the absorption coefficient μa and another without it. In the present research the scattered light is measured with steady light in a medium with large absorption in order to determine which of the diffusion coefficient expressions describes optical propagation in a turbid medium more accurately. The diffusion coefficient is found not to be affected by absorption even if the absorption varies from almost 0 to a value close to the reduced scattering coefficient μ′s, and its value agrees well with (3μ′s)-1. Hence, it is confirmed that the absorption coefficient used is not included in the diffusion coefficient used in the optical diffusion equation, and that the coefficient is given by D = (3μ′s)-1 © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(11): 34–41, 1998 [ABSTRACT FROM AUTHOR]

This paper explains the principle of near field optics and lists the problem of high density optical memory for which a storage density of 1 Tbit/inch2 is expected as an application. Furthermore, the possibility of tracking avoidance is introduced in storage and read out, especially the latter, by using a planar probe array. The present status of probe array fabrication discussed. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(8): 41–48, 1998 [ABSTRACT FROM AUTHOR]

By using room-temperature parametric oscillation of LiNbO3 pumped by a Q-switched Nd:YAG laser, a tunable terahertz-wave source in the range between 1 and 2 THz has been realized with a simple configuration. Since the terahertz wave is strongly absorbed inside the crystal and is affected by total internal reflection at the crystal edge, terahertz radiation outside the crystal has been difficult. A grating coupler and a prism coupler have resulted in wide tunability, high efficiency, and high spatial coherency. In this paper, the basic configuration of the optical source, various radiation characteristics, and the terahertz spectroscopic system using the present source are described. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(7): 10–18, 1998 [ABSTRACT FROM AUTHOR]

Transmission electron microscopy (TEM) is a very useful method for clarifying crystalline or amorphous structures of carbon materials. In order to discuss the contrast of TEM images, we studied the change of TEM images versus the underfocus value Δf. An amorphous carbon film with no orientation and random structure was used as a sample and was observed by TEM at different values of Δf. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(7): 64–70, 1998 [ABSTRACT FROM AUTHOR]

This paper proposes a transmission type filter that combines a high-quality fiber Bragg grating, fabricated by a scanning ultraviolet irradiation method, with an optical circulator. Improvements in wavelength selectivity and wide-banding are discussed. Spectral filtering is actually applied to the gain switched pulse from the semiconductor laser and the very short pulse from the mode-locked fiber laser. A short pulse close to the transform limit is generated. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(9): 1–9, 1998 [ABSTRACT FROM AUTHOR]

Four-wave mixing using the photorefractive crystal is one of the methods used to generate the phase-conjugate optical beam. This paper considers the case where the pulse beam is used for the backward pump and calculates the diffraction efficiency. The coupled wave equation that describes the four-wave mixing process using the photorefractive crystal is analyzed numerically by Euler's method, and the transient characteristics of the diffraction efficiency are calculated. The following situation is considered. A crystal reaches the steady state, being radiated by two beams, i.e., the forward pump beam and the probe beam, and only the transmission diffraction grating is produced. Then, the continuous beam or the pulse beam is incident to the crystal as the backward pump. The transient characteristics of the diffraction efficiency are compared and it is shown that the diffraction efficiency is greatly improved by using the pulse beam. In order to verify the results of this study, a BaTiO3 crystal is used as the photorefractive crystal, and the phase conjugate beam generation experiment is tried. The measured waveform for the case where the continuous beam and the pulse beam are incident as the backward pump is shown and improvement of the diffraction efficiency is demonstrated by pulsed beam. © 1998 Scripta Technica. Electron Comm Jpn, Pt 2, 80(9): 10–18, 1997 [ABSTRACT FROM AUTHOR]

An accurate and efficient characterization method of mitered H-plane waveguide bends is developed by combining the mode-matching method and the port reflection coefficient method. In the analysis, the two-port waveguide bend is converted to a one-port structure composed of cascaded waveguide step-junctions only. The analysis and computation procedures are greatly simplified thereby. Convergence properties and reliabilities of the obtained numerical results are verified. Variations of the return loss of the mitered bend are investigated with various dimensions of the mitered part. Wide band and low return loss characteristics of the mitered bend are found with the obtained optimal compensation dimension. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(5): 1–7, 1997 [ABSTRACT FROM AUTHOR]

Various new technologies have been proposed for optical soliton communications as a consequence of progress in the development of erbium-doped optical fiber amplifiers, and excellent experimental results with optical soliton communications have been reported. Since transform-limited pulses are very important in soliton transmission, optical soliton generation technologies using mode-locked semiconductor lasers, fiber lasers, gain-switched semiconductor lasers, and electroabsorption modulators are described first in this paper. The realization of soliton transmissions is then discussed along with advances in technology. Soliton transmission using dispersion allocation is shown to be more feasible because of the large power margin and large dispersion tolerance. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(4): 53–66, 1997 [ABSTRACT FROM AUTHOR]

With progress in phase conjugate optics, studies on forward four-wave mixing have been actively carried out. From the practical optical system design point of view, it is important to understand the angular dependence of phase conjugate intensity when pumping beams with limited spot size are used, especially with beam separation taken into consideration. In this paper, the angular dependence of phase conjugate intensity distribution is theoretically analyzed for the first time, in forward four-wave mixing when an optical Kerr medium is used. First, the phase conjugate intensity is calculated for a nonlinear medium thinner than the overlapping region of two pumping beams, where the intensity is relatively low. The results are used to calculate the output angle of the phase conjugate beam against the z-axis and the azimuth angle in the x-y plane. Then, a similar analysis is conducted for a medium sufficiently thick to cover the interaction region of two pumping beams. The differences between the above two cases are described and comparison with plane-wave pumping is made. Finally, the effects of spot size and curvature variation with Gaussian beam pumping on conjugate beam intensity are discussed for the case of a thick medium. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 2, 80(4): 67–75, 1997 [ABSTRACT FROM AUTHOR]