This paper describes a simple polarization-independent wavelength conversion method using degenerated four-wave mixing (FWM) in single-mode fibers pumped with cross-polarized high frequency, saw-tooth pulses from a single pump source. Successful polarization-independent wavelength conversion is experimentally confirmed with less than 12% and 5.6% variation using a gain-switched LD pumping and a mode-locked fiber laser pumping, respectively. We clarify that the interference effect between two orthogonal pump pulses must be taken into account to achieve a good polarization-insensitive operation, since even the small pulse edges bring about the large polarization fluctuations when they are interfered. Furthermore, it is reveal that the shorter pump pulse broadens its own spectrum due to the self-phase modulation in fibers, resulting in poor FWM efficiency. Finally, possibility of high-speed operation is discussed taking into account the pump pulse conditions.

This paper describes a simple polarization-independent wavelength conversion method using degenerated four-wave mixing (FWM) in single-mode fibers pumped with cross-polarized high frequency, saw-tooth pulses from a single pump source. Successful polarization-independent wavelength conversion is experimentally confirmed with less than 12% and 5.6% variation using a gain-switched LD pumping and a mode-locked fiber laser pumping, respectively. We clarify that the interference effect between two orthogonal pump pulses must be taken into account to achieve a good polarization-insensitive operation, since even the small pulse edges bring about the large polarization fluctuations when they are interfered. Furthermore, it is reveal that the shorter pump pulse broadens its own spectrum due to the self-phase modulation in fibers, resulting in poor FWM efficiency. Finally, possibility of high-speed operation is discussed taking into account the pump pulse conditions.

A K-band MMIC subharmonically pumped mixer integrating local oscillator (LO) amplifier has been developed. For up-converter application, it is necessary to reduce the leakage of second harmonic component of LO frequency to RF port, which is generated by nonlinear operation of LO amplifier. A quasi-lumped short-circuited stub using microstrip structure has been successfully applied to the MMIC mixer to enhance 2fLO-suppression. We propose a new configuration of a quasi-lumped short-circuited stub, which reduces the influence of parasitic elements of via-holes. The developed MMIC has a one-stage LO amplifier and it has shown about 10 dB-improvement of 2fLO-suppression compared to conventional configuration using a quarter-wavelength short-circuited stub.

This paper presents a Mix-net that has the following properties; (1) it efficiently handles long plaintexts that exceed the modulus size of the underlying public-key encryption scheme as well as very short ones (length-flexibility), (2) input ciphertext length is not impacted by the number of mix-servers (length-invariance), and (3) its security in terms of anonymity can be proven in a formal way (probable security). If desired, one can add robustness so that it outputs correct results in the presence of corrupt users and servers. The security is proven in such a sense that breaking the anonymity of our Mix-net is equivalent to breaking the indistinguishability assumption of the underlying symmetric encryption scheme or the Decision Diffie-Hellman assumption.

In this paper, we examine an optimal reliability assignment/redundant allocation problem formulated as a nonlinear mixed integer programming (nMIP) model which should simultaneously determine continuous and discrete decision variables. This problem is more difficult than the redundant allocation problem represented by a nonlinear integer problem (nIP). Recently, several researchers have obtained acceptable and satisfactory results by using genetic algorithms (GAs) to solve optimal reliability assignment/redundant allocation problems. For large-scale problems, however, the GA has to enumerate a vast number of feasible solutions due to the broad continuous search space. To overcome this difficulty, we propose a hybridized GA combined with a neural-network technique (NN-hGA) which is suitable for approximating optimal continuous solutions. Combining a GA with the NN technique makes it easier for the GA to solve an optimal reliability assignment/redundant allocation problem by bounding the broad continuous search space by the NN technique. In addition, the NN-hGA leads to optimal robustness and steadiness and does not affect the various initial conditions of the problems. Numerical experiments and comparisons with previous results demonstrate the efficiency of our proposed method.

A direct conversion receiver IC including an on-chip balun, an I/Q mixer, a variable gain amplifier and a 90 phase-shifter is fabricated in a Bi-CMOS technology with 15 GHz transition frequency (fT). This paper demonstrates that cascaded connection of an on-chip balun and a double balanced mixer as the I/Q mixer is effective to achieve a low DC offset and a low second-order distortion, on the basis of both careful examination of the mixer behavior and measurement. Input-referred DC offset voltage of less than 300 µV and spurious free dynamic range (SFDR) of over 67 dB are obtained by measurement. The IC consumes 52 mA from 2.7 V power supply voltage. The die size is 3 mm 3 mm.

This paper presents a new implementation of fuzzy filters for edge-preserving smoothing of an image corrupted by impulsive and white Gaussian noise. This filter structure is expressed as an adaptive weighted mean filter that uses fuzzy control. The parameters of this filter can be adjusted by learning. Finally, simulation results demonstrate the effectiveness of the proposed technique.

A merged analog-digital circuit architecture is proposed for implementing intelligence in SoC systems. Pulse modulation signals are introduced for time-domain massively parallel analog signal processing, and also for interfacing analog and digital worlds naturally within the SoC VLSI chip. Principles and applications of pulse-domain linear arithmetic processing are explored, and the results are expanded to the nonlinear signal processing, including an arbitrary chaos generation and continuous-time dynamical systems with nonlinear oscillation. Silicon implementations of the circuits employing the proposed architecture are fully described.

C-axis junction-arrays, with a-b plane sizes of sub-microns to 10 microns, were patterned on Bi2Sr2CaCu2O8+x single crystals with either a mesa or an overlap structure. We measured the current-voltage (I-V) characteristics with microwave irradiation at a few to 100 gigahertz. At a few gigahertz, often observed were chaotic properties. Under irradiation at 100 GHz, we successfully performed harmonic mixings between the 100 GHz signal and up to the 100th harmonic of a local oscillator at about 1 GHz. Given in this paper are discussions on the observation of individual Shapiro steps, and descriptions of the relevant results. Our experimental results show that intrinsic Josephson junctions in layered superconductors can be good candidates for high frequency applications.

The maximum likelihood estimate of a mixture model is usually found by using the EM algorithm. However, the EM algorithm suffers from a local optima problem and therefore we cannot obtain the potential performance of mixture models in practice. In the case of mixture models, local maxima often have too many components of a mixture model in one part of the space and too few in another, widely separated part of the space. To escape from such configurations we proposed a new variant of the EM algorithm in which simultaneous split and merge operations are repeatedly performed by using a new criterion for efficiently selecting the split and merge candidates. We apply the proposed algorithm to the training of Gaussian mixtures and the dimensionality reduction based on a mixture of factor analyzers using synthetic and real data and show that the proposed algorithm can markedly improve the ML estimates.

The delta-sigma modulator (DSM) is an excellent choice for high-resolution analog-to-digital converters. Recently, a band-pass DSM has been a desirable choice for direct conversion of an IF signal into a digital bit stream. This paper proposes a quadrature band-pass DSM for digitizing a narrow-band IF signal. This modulator can achieve a lower total order, higher signal-to-noise ratio (SNR), and higher bandwidth when compared with conventional band-pass modulators. An experimental prototype employing the quadrature topology has been integrated in 0.6 µm, double-poly, double-metal CMOS technology with capacitors synthesized from a stacked poly structure. This system clocked at 13 MHz and digitized a 200 kHz bandwidth signal centered at 4.875 MHz with 100 dB of dynamic range. Power consumption is 190 mW at 5 V.

To estimate moving object velocity in an image sequence is useful for a variety of applications, such as velocity measurement, computer vision and monitoring systems. An effective way is to approach it in the transform/spatiotemporal mixed domain (MixeD), which transforms the 3-D signal processing problem into 1-D complex signal processing. But it remains a problem how to select several spatial frequency points in the MixeD which may influence the accuracy of velocity estimation and object detection. In this paper, a spatial frequency selection method has been proposed, which can choose the appropriate spatial frequency points out of a number of points in MixeD automatically. So the velocity estimation problem can be addressed by solving the coupled equations established over two selected appropriate points in 2-D spatial frequency domain other than searching for the spectral energy plane over a number of points selected by experience. In this method, evaluation functions corresponding to image sequence with one moving object and two moving objects are established firstly, and the selection is then achieved by using the established evaluation functions together with a threshold. The simulation results show that the proposed method is effective on the appropriate spatial frequency selection.

This paper shows how a divisive state clustering algorithm that generates acoustic Hidden Markov models (HMM) can benefit from a tied-mixture representation of the probability density function (pdf) of a state and increase the recognition performance. Popular decision tree based clustering algorithms, like for example the Successive State Splitting algorithm (SSS) make use of a simplification when clustering data. They represent a state using a single Gaussian pdf. We show that this approximation of the true pdf by a single Gaussian is too coarse, for example a single Gaussian cannot represent the differences in the symmetric parts of the pdf's of the new hypothetical states generated when evaluating the state split gain (which will determine the state split). The use of more sophisticated representations would lead to intractable computational problems that we solve by using a tied-mixture pdf representation. Additionally, we constrain the codebook to be immutable during the split. Between state splits, this constraint is relaxed and the codebook is updated. In this paper, we thus propose an extension to the SSS algorithm, the so-called Tied-mixture Successive State Splitting algorithm (TM-SSS). TM-SSS shows up to about 31% error reduction in comparison with Maximum-Likelihood Successive State Split algorithm (ML-SSS) for a word recognition experiment.

An AC coupling configuration for the active guard band filters is introduced for suppressing substrate coupling noise in analog and digital mixed-signal integrated circuits. With this method, a substrate-coupling-noise cancellation signal can be supplied to a ground-level substrate by using a single 3-V supply on-chip circuits. Noise was suppressed to a maximum of less than 0.05 from 100 Hz to 2 MHz in a 0.35-µm CMOS test chip. Both experiments and a simulation based on the substrate extraction model showed the similar dependence of the noise-suppression effect on the arrangement of the guard-bands and analog circuits. The simulation is thus effective for optimizing the arrangement to suppress noise effects when designing a chip.

This paper describes a DLL (Delay Locked Loop) circuit with the mixed-mode phase tuning method. The circuit accomplishes unlimited phase shift and accurate phase alignment through the coarse and fine phase tuning technique. It is based on a dual delay locked loop structure. The main loop is for generating coarsely spaced clocks and the second loop is for fast and accurate phase tuning with digital and analog phase detection. Simulations show that this circuit has 360 degree phase shift capability and can resolve 10 ps phase error using 0.6 µm CMOS technology.

This paper presents a universally verifiable Mix-net where the amount of work done by a verifier is independent of the number of mix-servers. Furthermore, the computational task of each mix-server is constant with regard to the number of mix-servers except for some negligible tasks like computing hash function when no disruption occurs. The scheme also provides robustness.

In conventional methods for detecting vanishing points and vanishing lines, the observed feature points are clustered into collections that represent different lines. The multiple lines are then detected and the vanishing points are detected as points of intersection of the lines. The vanishing line is then detected based on the points of intersection. However, for the purpose of optimization, these processes should be integrated and be achieved simultaneously. In the present paper, we assume that the observed noise model for the feature points is a two-dimensional Gaussian mixture and define the likelihood function, including obvious vanishing points and a vanishing line parameters. As a result, the above described simultaneous detection can be formulated as a maximum likelihood estimation problem. In addition, an iterative computation method for achieving this estimation is proposed based on the EM (Expectation Maximization) algorithm. The proposed method involves new techniques by which stable convergence is achieved and computational cost is reduced. The effectiveness of the proposed method that includes these techniques can be confirmed by computer simulations and real images.

Simultaneous wavelength conversion of multi-WDM channels is expected to be a key technique in near-future networks. In this paper, 4-channel wavelength conversion using four-wave mixing (FWM) in a hybrid wavelength selector is successfully demonstrated. The wavelength selector consists of two four-channel spot-size-converter-integrated semiconductor optical amplifier (SS-SOA) gate arrays on a planar-lightwave-circuit (PLC) platform and two PLC-arrayed-waveguide-gratings (AWGs). As the wavelength selector has an individual SS-SOA for the wavelength conversion of each channel, there is negligible interference between channels. Four WDM channels with an 2.5 Gb/s modulation were converted from 1555 to 1575 nm. Clear eye openings and only a small power penalty of less than 0.5 dB were observed. The receiver sensitivity was -31 dBm at a bit error rate (BER) of 10-9.

We present three-wave mixing devices useful for signal processing functions in WDM and TDM systems, including wavelength conversion, spectral inversion, and gated mixing. These mixers exhibit extremely wide bandwidth, low noise, high efficiency, and format transparency.

We demonstrate a large nonlinear optical response of GaAs thin films using degenerate four-wave mixing (DFWM) with picosecond pulses. The obtained DFWM signal is thickness-dependent and peaks at around 110 nm. The nonlocal theory fully explains these results.