A GaAs/AlGaAs directional-coupler-type device that use polariton propagation was fabricated and its switching operation was demonstrated. The length of the switching region is as small as 300 µm. The output signal modulation under an electric field shows typical characteristics of directional-coupler type switching. The measured operation voltage is 2 V for an operation wavelength of 805 nm at 10 K. The corresponding signal extinction ratio is 8 dB. These experimental results confirm the efficient operation of the polariton devices, which can be applied to especially small optical -switching devices with low-voltage operation.

An optical add-drop multiplexer with a grating-loaded directional coupler in silica waveguides is demonstrated. The device for this configuration has a large fabrication tolerance and is small in size. A new scheme, in which the coupling length of the directional coupler is twice the complete coupling length, enables low cross-talk for both add and drop operations. This device is polarization-independent due to its relatively low-temperature process.

Precise plastic V-grooved alignment parts for connecting single-mode optical fiber arrays to multi-port optical devices were successfully molded with a thermosetting resin by using a highly productive injection molding technique. The molded parts are two types of V-grooved blocks that are compatible with the size of optical devices having eight or twelve optical ports. Their dimensional accuracy must be better than 1 µm over the whole length of the V-grooves for efficient optical coupling. This strict requirement was satisfied using precisely processed molding tools with a specially chosen resin under optimum molding conditions. The feasibility of the optical alignment parts was assured by an evaluation of their loss characteristics and reliability in coupling single-mode fibers to 18 power splitters, where the average optical loss was 0.2 dB and the change in loss was less than 0.2 dB under a temperature cycling test and also under a damp heat test. These results show that plastic molded parts can be used for precise coupling of single-mode optical devices, and will lead to a breakthrough in innovation in the field of optical packaging.

Coaxial-core erbium-doped fiber amplifiers (EDFA's) having a property of self-regulated gain spectrum are developed. The operation of a coaxial-core EDFA is based on the partial separation of the light paths for different wavelength channels in the directionally-coupled waveguides of a coaxial-core geometry. The degree of channel equalization depends on the geometrical and optical parameters of the coaxial-core EDFA and on relative channel power levels. A numerical analysis based on the coupled-mode theory and on the rate equation shows that, under fully optimized conditions, a coaxial-core EDFA provides equalization rates in excess of -0.4 dB per dB of input-power imbalance in the case with two WDM channels. A cascade experiment demonstrates the effect of coaxial-core EDFA's toward channel-power equalization in fiber links with a small number of WDM channels.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.

In many applications of digital video database systems such as digital library, video data is often compressed with MPEG video algorithms. It will be an important technique to insert the additional information data like indexes and contents effectively into video database which is compressed with MPEG, because we can always deal with the additional information with video data itself easily. We propose a method for inserting optional binary data such as index information of digital library into MPEG-1 and -2 bitstreams. The binary data inserted MPEG video bitstreams using our proposed scheme are also according to the specification of the MPEG video frame structure. The proposed method allows us to extract the inserted binary data perfectly though MPEG-1 and -2 video are lossy algorithms. And the quality of decoded images after extracting added information is almost the same as that of ordinary MPEG bitstreams. Furthermore, traditional standard MPEG-1 and -2 video decoder which can not extract inserted binary data can also decode images from the binary data inserted MPEG video bitstreams without obvious image degradation. There are some different points between the proposed insertion technique of the binary data and the watermarking technique. The technique of watermarking prepares to deal with alter watermarking by others. And the technique of watermarking is required for the identification of the signature and the perfect extraction of the inserted image signature is not required in the lossy MPEG video environment. On the other hand, we have to extract all of the inserted binary information data correctly with the insertion technique of the binary information. Simulations using MPEG video sequences with inserted binary data are presented to quantify some performance factors concerned. We have not heard about inserting data method which purpose is such as index and content information insertion.

We propose a query processing method for amalgamated knowledge bases. Our query processing method is an extension of the magic sets technique for query processing in amalgamated knowledge bases, augmented with the capabilities of handling amalgamated atoms. Through rewriting rules in a given amalgamated knowledge base, our method offers the advantages associated with top-down as well as bottom-up evaluation. We discuss how to handle amalgamated atoms, consider how to check whether an amalgamated atom is satisfiable in a fact set and how to extend a fact set by inserting an amalgamated atom. We also give the transformation procedures for amalgamated knowledge databases and show the correctness of our method.

Wavelet filters used in usual applications are not time-varying filters. In this paper, we present a novel method to design biorthogonal wavelet filters which are orthogonal to the input signals. We call newly designed filters time-varying lifting wavelet filters (TVLWF). Their feature is to vary the wavelet filters adapting to the input signal by tuning free parameters contained in the lifting scheme developed by Sweldens. These filters are almost compact support and perfect reconstruction. By using TVLWF, we demonstrate an application to data compression of electrocardiogram (ECG) which is one of the semi-periodic time-series signals and show that the time-varying system can be constructed easily and the proposed method is very useful for data compression.

In this paper, a new scheme for designing multilevel BTC coding is proposed. Optimal quantization can be obtained by selecting the quantization threshold with an exhaustive search. However, this requires an enormous amount of computation and is, thus impractical when we consider an exhaustive search for the multilevel BTC. In order to find a better threshold so that the average mean square error between the original and reconstructed images is a minimum, the genetic algorithm is applied. Comparison of the results of the proposed method with the exhaustive search reveal that the former method can almost achieve optimal quantization with much less computation than that required in the latter case.

This paper describes a spatial spectral subtraction method by using the complementary beamforming microphone array to enhance noisy speech signals for speech recognition. The complementary beamforming is based on two types of beamformers designed to obtain complementary directivity patterns with respect to each other. In this paper, it is shown that the nonlinear subtraction processing with complementary beamforming can result in a kind of the spectral subtraction without the need for speech pause detection. In addition, the optimization algorithm for the directivity pattern is also described. To evaluate the effectiveness, speech enhancement experiments and speech recognition experiments are performed based on computer simulations under both stationary and nonstationary noise conditions. In comparison with the optimized conventional delay-and-sum (DS) array, it is shown that: (1) the proposed array improves the signal-to-noise ratio (SNR) of degraded speech by about 2 dB and performs more than 20% better in word recognition rates under the conditions that the white Gaussian noise with the input SNR of -5 or -10 dB is used, (2) the proposed array performs more than 5% better in word recognition rates under the nonstationary noise conditions. Also, it is shown that these improvements of the proposed array are same as or superior to those of the conventional spectral subtraction method cascaded with the DS array.

This paper proposes an adaptive noise canceller with low signal-distortion in the presence of crosstalk. The proposed noise canceller has two pairs of cross-coupled adaptive filters, each of which consists of the main filter and a sub filter. The signal-to-noise ratios (SNRs) of the primary and the reference signals are estimated by the sub filters. To reduce signal distortion at the output of the adaptive noise canceller, the step sizes for coefficient adaptation in the main filters are controlled according to the estimated SNRs. Computer simulation results show that the proposed noise canceller reduces signal distortion in the output signal by up to 15 dB compared to the conventional noise canceller.

We analyze the dispersion-managed optical transmission system for the non-return-to-zero (NRZ) pulse format. First, we investigate the physical image of dispersion management by computing small-signal-based transfer functions, and summarize the dependence of transmission performance on system parameters. Next, the Q-map is computed numerically to design long-distance large-capacity dispersion-managed transmission systems for a single channel in a more detailed manner. It is shown that the third-order dispersion of fibers negatively influences transmission performance, and third-order dispersion compensation is proved to be an effective method for extending the transmission distance of high bit-rate systems. Utilizing these results, guidelines can be derived for the optimal design of long-distance large-capacity NRZ transmission systems.

Fractal immittance, expressed by an admittance sa (0<|a|<1), is simulated by the analog circuits composed of finite numbers of conventional elements, resistance R, capacitance C and inductance L, based on the distributed-relaxation-time models. The correlation between the number of R-C or R-L pairs and the optimum pole interval to give the widest bandwidth is estimated for each a-value by the numerical calculation for each circuit against a given criterion with respect to the phase angle. It is found that the bandwidth of 5 decades with a phase-angle error of 1 can be composed for |a|=0.1-0.9 using eighteen pairs or less of the elements.

In this paper, a new feature which is characterized by the extrema density of 2-D wavelet frames estimated at the output of the corresponding filter bank is proposed for texture segmentation. With and without feature selection, the discrimination ability of features based on pyramidal and tree-structured decompositions are comparatively studied using the extrema density, energy, and entropy as features, respectively. These comparisons are demonstrated with separable and non-separable wavelets. With the three-, four-, and five-category textured images from Brodatz album, it is observed that most performances with feature selection improve significantly than those without feature selection. In addition, the experimental results show that the extrema density-based measure performs best among the three types of features investigated. A Min-Min method based on genetic algorithms, which is a novel approach with the spatial separation criterion (SPC) as the evaluation function is presented to evaluate the segmentation performance of each subset of selected features. In this work, the SPC is defined as the Euclidean distance within class divided by the Euclidean distance between classes in the spatial domain. It is shown that with feature selection the tree-structured wavelet decomposition based on non-separable wavelet frames has better performances than the tree-structured wavelet decomposition based on separable wavelet frames and pyramidal decomposition based on separable and non-separable wavelet frames in the experiments. Finally, we compare to the segmentation results evaluated with the templates of the textured images and verify the effectiveness of the proposed criterion. Moreover, it is proved that the discriminatory characteristics of features do spread over all subbands from the feature selection vector.

This paper proposes and investigates the adaptive single-user receiver with co-channel interference (CCI) canceller based on orthogonalizing matched filter (OMF) using the multi-dimensional (multi-D) lattice filters for DS/CDMA in a multipath environment. A conventional single-user receiver using OMF cannot correctly cancel CCI in the presence of multipath in a channel, because the desired user's signal component and other users' intersymbol interference (ISI), due to multipath, still remain at the output of OMF, and then a correct replica of CCI cannot be generated. The proposed receiver can solve this problem because a multi-D IIR lattice filter can distinguish the desired user's signal component from the other users' ones and remove the ISI of all users' signals by Gram-Schmidt orthogonalization. And a multi-D FIR lattice filter can selectively regenerate undesired users' signal components which contain neither the desired user's signal component nor ISI. The proposed receiver based on multi-D lattice filters can apply orthogonality property of the OMF to not only a direct wave but also to delayed waves in a multipath channel. Since the proposed receiver does not have to know spreading codes of multiusers except the desired user, it will be applicable at a mobile terminal in the forward link in a multipath environment. Computer simulations show the proposed receiver have capability to cancel the CCI and converges fast in a multipath channel.

We proposed a new model for non-stationary time series analysis based on the IAR (inhomogeneous autoregressive) model, and a method for model parameter estimation when the set of basis is given. In this paper, we further propose a method for parameter estimation including that of basis set: we set a new condition that power of the input sequence is concentrated in low-frequency domain, and developed an iterative estimation method. We firstly select an initial set of basis, from which new sets are created in order to minimize the difference between the model and data. Among new sets of basis, we select a good one that gives minimum standard deviation of estimated frequencies.

In this paper, a new gradient-based adaptive algorithm for the estimation of discrete Fourier coefficients (DFC) of a noisy sinusoidal signal is proposed based on a summed least mean squared error criterion. This algorithm requires exactly the same number of multiplications as the conventional LMS algorithm, and presents much improved performance in both white and colored noise environments at the expense of some additional memories and additions only. We first analyze the performance of the conventional LMS algorithm in colored additive noise, and point out when its performance deteriorates. Then, a summed least mean squared error criterion is proposed, which leads to the above-mentioned new gradient-based adaptive algorithm. The performance of the proposed algorithm is also analyzed for a single frequency case. Simulation results are provided to support the analytical findings and the superiority of the new algorithm.

Classification of the new and used bills using the spectral patterns of raw time-series acoustic data (observation data) poses some difficulty. This is the fact that the observation data include not only a bill sound, but also some motor sound and noise by a transaction machine. We have already reported the method using adaptive digital filters (ADFs) to eliminate the motor sound and noise. In this paper, we propose an advanced technique to eliminate it by the neural networks (NNs). Only a bill sound is extracted from observation data using prediction ability of the NNs. Classification processing of the new and used bills is performed by using the spectral data obtained from the result of the ADFs and the NNs. Effectiveness of the proposed method using the NNs is illustrated in comparison with former results using ADFs.

Waveguide photodiodes (WGPDs) are key devices for high-speed optical receivers in trunk lines because of their potential ability to provide both high efficiency and a high-speed response. We have designed a waveguide photodiode for 40-Gb/s-range optical receivers. The optical coupling characteristics were simulated in detail to optimize the waveguide structure, and the electrodes of the photodiode were designed to form a coplanar transmission line to match the system impedance, which minimized frequency-response degradation. A highly beryllium-doped, low-temperature-grown InGaAs contact layer grown by gas source molecular beam epitaxy was used to reduce the series resistance, and approximately 40% reduction of series resistance was achieved. The fabricated device exhibited both a very high external quantum efficiency of 81% for 1.55-µm light and a sufficient bandwidth of more than 40 GHz. Though we used a simple conventional fabrication process, excellent characteristics were achieved due to the optimized optical design and well suppressed parasitic parameters.

We developed an optical transceiver diode (TRAD) module for bi-directional time-compression-multiplexing (TCM) transmission systems. A wavelength-insensitive structure as a receiver and a low-capacitance configuration in the module provide a high sensitivity. Stable switching of 156 Mbit/s NRZ burst signals between the transmitter and receiver modes is achieved. In addition, it is shown that optical module cost can be further reduced by using passive alignment on a Si bench.