A hybrid integrated optical module composed of a silica-based planar lightwave circuit (PLC), a laser diode with an integrated monitor-photodiode, and a pin-photodiode is fabricated for use in high-performance, compact and cost-effective fiber optic subscriber systems. Its applicability to a wavelength-division-multiplex (WDM) system with a 1.3-µm bi-directional signal and a 1.5-µm one-way signal is demonstrated. The PLC was fabricated by a combination of flame hydrolysis deposition (FHD) and reactive ion etching (RIE), and it simultaneously achieved 1.3-µm/1.5-µm multi/demultiplexing and 1.3-µm Y-branching functions. The optical module exhibited insertion losses of 4.1dB at 1.31µm (including a Y-branch circuit loss of 3dB) and 0.5dB at 1.53µm. An optical output power of more than -4dBm was obtained from the optical module and the crosstalk was sufficiently low at less than -20dB between wavelengths of 1.3µm and 1.5µm. Temperature cycle tests on the optical module showed reliable and stable operation with an optical power fluctuation of less than 0.3dB for 500 cycles.

This paper describes the integration of a qualitative method and a quantitative method by Bottleneck Diagnosis/Improvement Expert Systems for Synchronized queueing network (BDES-S and BIES-S). On the basis of qualitative reasoning, BDES-S can carry out parameter tuning in order to diagnose and improve bottlenecks of synchronized queueing networks. BDES-S can produce several alternative qualitative improvement plans for one bottleneck server. BIES-S can produce quantitative improvement equations for each qualitative improvement plan. Our method using BDES-S and BIES-S can integrate both quantitative and qualitative methods for parameter tuning on complicated queueing synchronized networks.

The mechanisms for executing concurrent applications proposed so far fall into one of three groups: processes, kernel-level threads, and user-level threads. Each of them is insufficient in terms of either parallelism, the flexibility to combine separately developed programs at run-time, or costs of operations such as creation, switching, and termination. A thread facility in the XERO operating system overcomes this problem and provides a uniform framework for executing concurrent applications. To achieve parallelism of threads, the flexibility to combine separately developed programs at run-time, and fast thread operations, the operating system kernel and a thread management module in a user address space manage threads cooperatively. We implemented the cooperative thread management mechanism and measured its performance to examine the effectiveness of our approach.

Thin Si films grown on anodized porous silicon have been characterized using a high-energy ion scattering technique with related simulations of MeV ions in solids. It turned out that the simulations are necessary and very usuful for quantitative and nondestractive analysis of thin films with thicknesses less than 100 nm. In the case of the epitaxial Si films examined, it is often insufficient for the characterization of crystalline quality to measure only the channeling minimum yield, and therefore, it is emphasized that angular scans over the critical angle in the vicinity of a channeling direction must be performed for the analysis of possible imperfections in thin films. The possible imperfections observed in the epitaxial specimen are treated quantitatively.

A novel harmonic retrieval algorithm is proposed in this paper based on Hopfield's neural network. Frequencies can be retrieved with high accuracy and high resolution under low signal to noise ratio (SNR). Amplitudes and phases in harmonic signals can also be estimated roughly by an energy constrained linear projection approach as proposed in the algorithm. Only no less than 2q neurons are necessary in order to detect harmonic siglnals with q different frequencies, where q denotes the number of different frequencies in harmonic signals. Experimental simulations show fast convergence and stable solution in spite of low signal to noise ratio can be obtained using the proposed algorithm.

This paper first discusses the software reusability-based development process in a lifecycle and reusable objects modification process called differentiation. Next, the supporting environment is described. Both the method and the environment allow developers to carry out requirement definitions, specification and implementation in a reusable way. Some quantitative evaluations are given about how productivity and quality have been improved by using this method and environment, based on a number of case studies made on development projects. Reusability has been largely improved by differential specification, and adjustment method and a direct transformation capability.

A new channel stop design for submicton local oxidation of silicon (LOCOS) isolation was presented. The n-channel stop was designed with boron implanation after forming LOCOS, while the p-channel stop was constructed with high energy phosphorus or arsenic implantation before or after forming LOCOS. These optimized channel stop designs can extend an isolation spacing to the submicron region without a decrease in junction breakdown voltage and an increase in junction leakage current. Narrow channel effects were found to be effectively suppressed by optimum channel stop design issues.

This paper describes a new metric for evaluating the cost effectiveness of software reviews. The proposed metric is based on the degree to which costs needed for detecting all faults from software are reduced by software reviews in a project. The metric can be interpreted as combining two conventional metrics proposed by Fagan (1976) and Collofello and Woodfield (1989). As the proposed metric is normalized by virtual testing cost, we can compare the values of it among any different kind of projects. Using an experimental evaluation of the conventional metrics and the proposed metric for data collected in an industrial environment, we show the validity and usefulness of the proposed metric. In addition, we present a method to estimate a value of the proposed metric by using only the values which can be computed during the software reviews.

A specification formalism for business application software is presented. Our approach is to investigate specification documents which are actually used in development projects of business applications in banking, insurance, and government systems. Since the specification documents are prepared mainly for users' review for the developing software, the representation of the documents is designed to be easy to understand for users, only in business terminology without losing a certain level of formality. Also, to avoid redundancy of the specification, there are some implicit assumptions in the specification. We have analyzed some commonality of these assumptions hidden in specification documents and are trying to construct a language by formalizing the underlying system model.

The mode partition noise of 1.3µm distributed feedback laser diodes (DFB LD's), which is induced by the externally reflected light, is studied experimentally and numerically. The mode partition noise is evaluated by the k-value. It is observed that the mode parition noise monotonically increases with the DC bias current when the reflected light affects DFB LD's and the DC bias current is above the threshold current. From the dependence of the k-value on the external power reflection coefficient, it is observed that the k-value dramatically increases when the external power reflection coefficient is above a value which differs from LD to LD. This is closely related to the fact that the tolerance to the externally reflected light depends on the threshold gain difference between the main mode and the dominant side mode.

In case of the system identification problem, such as an echo canceller, estimated impulse response obtained by the frequency-domain adaptive filter based on the circular convolution has estimation error because the unknown system is based on the linear convolution in the time domain. In this correspondence, we consider a sufficient condition to reduce the estimation error.

Recently most of the singularities of the equivalent edge currents for flat plates were eliminated by the authors using the paths of most rapid phase variation. A unique direction on the plate was determined for given incidence and observer. This paper extends this method for arbitrary angle wedges and presents the new expressions of the equivalent edge currents. The resultant expressions are valid for any incidence and observation aspects and have no false singularities. Diffraction patterns and radar cross sections of 3-D objects composed of wedges are calculated by using these currents. They show good agreements with experimental data or the results by the other methods.

An accurate numerical solution is presented for the electromagnetic scattering from infinite strip gratings attached to both sides of a dielectric slab. This structure is a model of polarization discriminating devices. The period of the strips is common to both planes, but the widths and the axes may be different. The direction of propagation and the polarization of an incident plane wave are arbitray. We derive a set of singular integral equations and solve it by the moment method, where the Chebyshev polynomials are successfully used as the basis and the testing functions. This method is accurate and effective owing to the incorporation of the edge condition and the decomposition of the kernel functions into the singular and the regular parts. Numerical calculations are carried out for the purpose of designing polarization discriminators, and it is shown that the band width is widened by decreasing the permittivity of the slab. The cross-polarization characteristics at skew incidence are also discussed.

Diffusion of phosphorus impurities from a polycrystalline silicon films into a silicon substrate was investigated as a function of the mean concentration of phosphorus in a polycrystalline silicon film at the first diffusion stage. We presented that good control of the redistribution of implanted phosphorus impurities was possible by optimizing the normalized dose, which is the value: [the total dose of phosphorus impurities]/[the polycrystalline silicon film thickness], in the case of samples both with and without an arsenic doped layers. In the range where the normalized dose was less than 1.52.51020 cm-3, deeper junctions were formed in samples with an arsenic doped layer. In the range where the normalized dose was more than 1.52.51020 cm-3, however, deeper junctions were formed in samples without any arsenic doped layer rather than in samples with an arsenic doped layer. These results mean that formation of the junction in the device structure where a high concentration phosphorus doped polysilicon layer is stacked on to the high concentration arsenic layer embeded at the surface of the substrate can be restricted by optimizing the normalized dose. Moreover, a trade-off relationship between suppressing phosphorus diffusion and maintaining low contact resistance against normalized doses was also observed.

In this letter, it is clarified that the quantum noise properties of the linear amplification and locking amplification in the injection locked laser process are different. The noise property of the locking amplification is newly given.

In this paper, we analyze a photodetection process of new kind theoretically, which transforms a coherent state of light so as to lead to nonstandard property, namely, sub-Poissonian distribution of its output photoelectron during its photodetection process. The properties of the photoelectron distribution are studied used as preamplifiers of both direct-detection and homodyne detection cases.

Subscriber network opticalization is the key issue for the next generation network. Fiber-optic systems have been limited to mainly big business applications, so far. Massive opticalization including home and small business customers remains the ultimate goal. Opticalization of the subscriber network needs an enormous investment and a long construction period. In order to achieve smooth evolution towards B-ISDN, the subscriber network must be effectively opticalized well in advance of full B-ISDN deployment. This paper presents the development concept of optical subscriber network. It also describes the design concept and configuration of fiber-optic subscriber systems. Deployment strategies and the developing technologies for the future subscriber network are also addressed.

It often occurs in the acoustic environment that a specific signal is contaminated by the additional noise of non-Gaussian distribution type. In order to extract exactly the various statistical information of only specific signal from the observed noisy data, a stochastic signal processing by use of digital computer is essential. In this study, a stochastic method for estimating the probability function of the specific signal embedded in the additional noise is first theoretically proposed in a suitable form for the quantized level observation. Then, the effectiveness of the proposed method is experimentally confirmed by applying it to the observed data in the acoustic environment.

In the maximum-likelihood decoding under a non-Gaussian noise, the decoding region is bounded by complex curves instead of a perpendicular bisector corresponding to the Gaussian noise. Therefore, the error rate is not evaluated by the Euclidean distance. The Bhattacharyya distance is adopted since it can evaluate the error performance for a noise with an arbitrary distribution. Upper bound formulae of a bit error rate and an event error rate are obtained based on the error-weight-profile method proposed by Zehavi and Wolf. The method is modified for a non-Gaussian channel by using the Bhattacharyya distance instead of the Euclidean distance. To determine the optimum code for an impulsive noise channel, the upper bound of the bit error rate is calculated for each code having an encoder with given shift-register lehgth. The best code is selected as that having the minimum upper bound of the bit error rate. This method needs much computation time especially for a code with a long shift-register. To lighten the computation burden, a suboptimum search is also attempted. For an impulsive noise, modeled from an observation in digital subscriber loops, an optimum or suboptimum code is searched for among codes having encoders with a shift-register of up to 4 bits. By using a code with a 4-bit encoder, a coding gain of 20 dB is obtained at the bit error rate 10-5. It is 11 dB more than that obtained by Ungerboeck's code.

A new image restoration filter based upon a physical model of an image degradation is constructed. By means of this filter, signal dependent noise and blur can be suppressed. In particular, image degradation noise can be modeled in generalized form. Noise suppression and deblurring are performed separately. This filter has additional applications when used in conjunction with the degradation model, such as real photographic images and photoelectronic images. Simulation results show that this filter gives a superior performance in restoring an image degraded by signal dependent noise and blur.