Extremely compact multi-mode interference (MMI) devices using central wide-angle coupling of input and output waveguides are proposed. It is shown that MMI can be used to change the propagation direction of light without the need for corner mirrors or bent waveguides. The concept can also be used for very compact power splitters which are even smaller than conventional MMI power splitters. Coupling between waveguides at wide angles is discussed and a number of regularities are found. The results can be useful for the design of more compact integrated circuits by a reduction of the number of bent waveguides which usually take up the largest part of the area of a photonic integrated circuit.

Digital-switching noise coupled into sensitive analog circuits is a critical problem in large-scale integration of mixed analog and digital circuits. This paper describes noise coupling of this kind, especially, through the substrate in CMOS integrated circuits, and reviews recent technical solutions to this noise problem. Simplified models have been developed to simulate the substrate coupling rapidly and accurately. A method using a CMOS comparator was proposed for measuring the effects of substrate noise, and equivalent waveforms of actual substrate noise were obtained. A circuit tecnique, called active guard band filtering, that controls the noise source is a new approach to substrate noise decoupling. CAD methods for handling substrate-coupled switching noise are making design verification possible for practical mixed-signal LSIs.

This paper presents the performance of a proposed GaAs MESFET photodetector with wide drain-to-gate distances for improving the optical coupling efficiency in subcarrier optical transmission. Principle and design parameters of the proposed MESFET are described. Link gain, CNR, and BER, are experimentally investigated as functions of the drain-to-gate distance. It is experimentally found that the proposed MESFET improves the link gain by 8.5 dB compared to the conventional structure at the subcarrier frequency of 140 MHz. Discussions are also included compared to PIN-PD.

Laser module fabricated with silicon platform technology is very attractive for low-cost modules. The technology enables passive optical alignment of an LD to an optical fiber. Our marker design for passive alignment allows positioning accuracy within 1 µm of LD. However, coupling efficiency is a key issue because that by conventional butt coupling scheme is low with about 10 dB coupling loss. We investigated optical coupling characteristics in various types of coupling scheme: conventional flat end fibers, cone fibers, integrated GRIN rod lenses on the platform and the coupling with new-type LDs integrated with spot size transformer. Improvement of coupling efficiency with 3 dB and 7.5 dB compared to flat-end fiber is achieved by using the cone fiber and the GRIN rod lens, respectively, although 1-dB coupling tolerances for alignment deteriorated with these schemes. We obtained high efficient coupling with 3.5 dB coupling loss and wide alignment tolerance of 2.3 µm simultaneously with a new-type LD integrated with spot size transformer owing to its expanded spot size characteristics.

The local wiring structure which is known as a technique for reducing junction capacitance due to the area reduction of the Source/Drain junction by the "on-field" contact scheme was constructed. Its effect on speed/power improvement was evaluated with a ring oscillator. A speed improvement of 15% and a 17% reduction in power dissipation was obtained as compared with conventional non-local wiring structures. This technique was applied to a practical device application, that is, a 0.35 µm embedded dual port SRAM used as a buffer memory in an asynchronous transfer mode switch (ATM-SW) LSI. In order to suppress the coupling noise between the write and read bitlines with the small cell realized by the local wiring scheme, a new divided layer 'bitline architecture was developed. As a result, reduction of SRAM macro size of 31% was attained by also applying the local wiring scheme to peripheral circuits, such as decoder, sense amplifier, and driver. A detailed analysis on this embedded dual port SRAM revealed a 15.2% reduction of write port power at 3.3 V. It is also shown that the local wiring technique is more effective with low power supply voltages to allow for further power reduction.

In this paper, scattering problem of the grating coupler is analyzed by the mode-matching method in the sense of least squares for the gaussian light beam incidence. This coupler has a periodic groove structure of finite extent, which is formed on the surface of the core layer of the symmetric thin-film waveguide. In the present method, the approximate scattered fields of each region of the grating coupler are described by the superpositions of the plane waves with band-limited spectra, respectively. These approximate wave functions are determined by the minimization of the mean-square boundary residual. This method results in the simultaneous Fredholm type integral equations of the second kind for these spectra. The first and second order approximate solutions of the integral equations are derived analytically and the coupling efficiency and scattered fields are analyzed on the basis of those solutions. A qualitative and physical consideration for the scattering problem of the grating coupler is presented with the fundamental data derived from approximate solutions in this paper.

We consider a ring of n Rayleigh oscillators coupled hybridly. Using the symmetrical property of the system we demonstrate the degeneracy of the Hopf bifurcation of the equilibrium at the origin. The degeneracy implies the exstence and stability of the n-phase oscillation. We discuss some consequences of the perturbation of the symmetry. Then we study the case n = 3. We show the bifurcation diagram of the equilibria and of hte periodic solutions. Especially, we analyze the mechanism for the symmetry breaking bifurcation of the fully symmetric solution. We report and explain the occurrence of both chaotic attractors and repellors and show two types of symmetry recovering crisis they undergo.

In the design of a large slotted waveguide array, evaluation of mutual couplings between the slots is time consuming. This paper proposes an effective approximation analysis of the external mutual couplings using periodic boundary condition. Simple design procedure is verified for two-dimensional slot array.

We proposed a new marker design for passive alignment of a laser to a fiber on a silicon waferboard. Our fiducial marker is simple form and easy to fabricate. With a unique marker design, high accurate positioning of the laser chip is easily achieved using a conventional flip-chip bonder. We have successfully fabricated laser modules with uniform coupling, within 1 dB for a flat end single-mode fiber and within 2 dB for a hemispherical end fiber. This assembly method offers the potential for low-cost optical module packaging.

This paper describes a newly developed sensing scheme with a bit-by-bit program verify technique for NAND flash disk systems. This sensing scheme achieves good noise immunity for large capacitive coupling between bitlines, and makes NAND flash memories operable for flexible power supply voltages including both 3.3V and 5V. A highly reliable read operation is performed for power supply voltages above 3V and a bitline-bitline coupling ratio below 50%. The sensing scheme also achieves an intelligent page copy function with 20% reduction in time and without external buffers and CPU resources.

The coupling response of an external transient electromagnetic field to a transmission line is considered. An experiment has been conducted to verify the line equations for a transmission line excited externally by a transient near field. The model field is generated by a monopole antenna installed in the vicinity of the transmission line and driven by a step waveform. The waveform is analyzed into discrete spectrum components using a Fourier transform. The frequency-domain field components affecting the transmission line are estimated by the moment method, and then the induced frequency-domain voltage at the terminal load is converted into a time-domain voltage using an inverse Fourier transform. Comparison between the measured and the computed values provides verification of the line equations. The coupling mechanism is discussed from the experimental results. It seems equivalently that the transmission line picks up the field, generated at the feed point and the top point of the monopole antenna, at both terminal ends.

One of coupling coefficients appearing in the coupled power equations describing the crosstalk in an image fiber is derived based on the coupled mode theory. Cores arranged in the cross-section of the fiber differ randomly to the degree of several percent in size and consequently modes propagating along the cores differ randomly. Random fluctuations of the propagation constants of modes cause the random transfer process of power between the cores, whereas contributions of the random fluctuations of the mode coupling coefficients to the statistical process can be neglected. The coupling coefficient is described as the ratio of the power transfer ratio to the coupling length for two cores with slightly different radii characterizing the random cores. The theoretical results are in good agreement with measurement results except near cutoff.

The ultraclean sputtering process (UC-process) was newly introduced in the fabrication of Co62.5Ni30Cr7.5 and Co85.5Cr10.5Ta4 thin film media to establish a new concept in controlling microstructure. UC-process enables the realization of high coercive force Hc up to 2.7-3 kOe in both CoNiCr and CoCrTa media (15/50 nm magnetic/Cr thicknesses) without the decrement of saturation magnetization. The purification of the atmosphere during sputtering and the removal of the adsorbed oxygen impurity on the substrate surface play important roles in obtaining high Hc by applying the UC-process. This high Hc is mainly due to the realization of large magnetocrystalline anisotropy field of grains Hkgrain and low intergranular exchange coupling. UC-process realizes the adequate separation of grains by segregated grain boundaries even in media with thin Cr thickness of 2.5 nm, and enables grain size reduction without the remarkable increment in intergranular exchange coupling. In these media, the reduction of the grain size is most effective for the improvement of readback signal to media noise ratio S/Nm. In the media with grains sufficiently separated by segregated grain boundaries fabricated by the UC-process, control of grain size reduction and further increase in Hc/Hkgrain value through the decrement in intergranular magnetostatic coupling are required to obtain higher S/Nm value.

The authors have studied the demagnetization phenomenon which is observed in a conventional CoCrTa/CoZrNb double-layered (DL) perpendicular recording medium. The authors have also investigated the effects of an in-plane hard magnetic layer in a triple-layered (TL) perpendicular recording medium. The in-plane hard magnetic underlayer is made of CoSm or CoCrTa/Cr and is laid under the CoZrNb soft magnetic layer. In the DL medium, a demagnetization phenomenon i.e. decrease of the readback signal, is observed when the CoCrTa layer has a strong perpendicular orientation and the CoZrNb underlayer has a low coercivity. The amount of the signal decrease depends strongly on the accumulated disk revolutions. This demagnetization is considered to be caused by fact that the recorded magnetization in the CoCrTa layer is reduced by the magnetic field generated from the domain walls in the CoZrNb layer, since the CoZrNb layer is very sensitive to a magnetic environment such as geo-magnetism and domain walls move as the disk rotates. On the other hand in the TL medium, the hard magnetic layer has an effect of pinning the magnetic domain in the CoZrNb layer, by which the demagnetization problem is successfully prevented. The hard magnetic layer remarkably reduces the domain walls in the CoZrNb layer and contributes to medium noise reduction. Thus the TL medium presents a higher SN ratio than DL medium.

We propose an axially symmetrical Fabry-Perot multiple-device oscillator operating at an axially symmetrical TEM01n-mode, which has an excellent feature of uniform device-field coupling required for high efficiency power combining. By carrying out the boundary element analysis, it is shown that a plane-mirror output structure is remarkably advantageous compared with a concave-mirror output structure to obtain an adequate output coupling and to enable stable operation characteristic with respect to the axial mode number n. Experiments in X-band confirmed this excellent performance and achieved almost perfect power combining of efficiency as high as 106% and 99% for six- and eight-device case, respectively.

In this paper, a waveguide-fed slot-coupled microstrip antenna is proposed as enhanced feeding structure of microstrip antenna and an analysis is pesented. The presence of dielectric substrate between a strip and a slot is explicitly taken into account in this analysis. The evaluation of the antenna characteristics is carried out using the method of moments and the spectral domain approach in terms of the electric current distribution on the strip and the magnetic current distribution on the slot.

In this paper, mutual coupling S21 between RMSA (ring-shaped microstrip antenna) elements was estimated by the EMF method based on the cavity model. Then, the validity of the proposed method was tested by experiments. The experiments confirmed satisfactory agreement between the computed and experimental data for S21 in both E- and H-plane arrangements. In addition, a circularly polarized planar array composed of R-MSA elements was designed on the basis of the data of S21. The experimental results of such a planar array demonstrated high performance in radiation pattern as well as axial ratio property. Furthermore, the active reflection coefficient Γ in the R-MSA array was also investigated in both equilateral and square arrangements. The computed results of active reflection coefficient in the array demonstrated high performance in both arrangements.

We analyze all-optical switching property of a nonlinear directional coupler (NLDC) having an MQW coupling layer with both nonlinear and linear losses, and examine the effect of nonlinear losses. We use the Galerkin finite element method accompanied by a prodictor-corrector algorithm. The propagation loss along the strongly-coupled NLDC decreases with increasing nonlinear absorption coefficient due to saturation in absorption. A propagation loss of 8.18 dB or 2.38 dB in the bar state of the cross state is much smaller than the bulk loss of MQW structure which exceeds 50 dB. The nonlinear losses lengthen the coupling length and bring it close to that of a lossfree NLDC, while the linear losses shorten. It is found that the property of the cross state is greatly improved by counting the nonlinear losses: The cross-state output power and the output power ratio of two waveguides increase, and the cross state input power, that is, the switching power decreases.

On mutually coupling lines, the transmission signal is dispersively propagated by crosstalk coupling between lines and shows complex propagation characteristics caused by reciprocal reflections. Usually, the differential equation and the integral equation have been applied to analyze the solutions of transmission lines. In this paper, we propose a different analytical method of the propagation characteristics of signal and crosstalk noise. By setting up crosstalk coupling line as a sectionally divided digital transmission network and by using the signal flow graph and the difference equation, the propagation characteristics in the frequency domain, the space domain and the time domain on mutually coupling lines can be obtained. To verify the validity of this method and analyze the complex propagation problems, we first study the crosstalk characteristics of a twisted pair cable via the third circuit by unidirectional coupling. Subsequently we will analyze the coupling theory of bidirectional coupling lines.

There have been many investigations of mutual synchronization of oscillators. In this article, N oscillators with the same natural frequencies mutually coupled by one resistor are analyzed. In this system, various synchronization phenomena can be observed because the system tends to minimize the current through the coupling resistor. When the nonlinear characteristics are third-power, we can observe N-phase oscillation, and this system can take (N 1)! phase states. When the nonlinear characteristics are fifth-power, we can observe (N 1),(N 2)3 and 2-phase oscillations as well as N-phase oscillations and we can get much more phase states from this system than that of the system with third-power nonlinear characteristics. Because of their coupling structure and huge number of steady states of the system, our system would be a structural element of cellular neural networks. In this study, it is confirmed that our systems can stably take huge number of phase states by theoretical analysis, computer calculations and circuit experiments.