For wavelength conversion based on cross-gain modulation (XGM) and cross-phase modulation (XPM) in semiconductor optical amplifiers (SOAs), a CW assist light is quite effective for acceleration of carrier recovery and reduction of pattern effects. We theoretically study assist light conditions both for XGM- and XPM-based wavelength conversion by numerically simulating eye-diagrams. Taking into account the spatial and temporal variations of carrier density along the SOA length, we successfully clarify the dependences of wavelength, power, and propagation direction of the assist light, and reveal the principal difference of response characteristics between XGM and XPM depending on carrier modulation.

We have developed a traveling-wave optical modulator using an n-i-n heterostructure fabricated on an InP substrate. The modulation characteristics are studied theoretically and experimentally. We obtained an extremely small π voltage (Vπ) of 2.2 V, even for a short signal-electrode length of 3 mm. We confirmed a wide frequency bandwidth and clearly open eye diagrams at 40 Gbit/s.

We propose a method of controlling the view divergence of data freshness when copies of sites in a replicated database are updated asynchronously. The view divergence of the replicated data freshness is the difference in the recentness of the updates reflected in the data acquired by clients. Our method accesses multiple sites and provides a client with data that reflects all the updates received by the sites. First, we define the probabilistic recentness of updates reflected in acquired data as read data freshness (RDF). The degree of RDF of data acquired by clients is the range of view divergence. Second, we propose a way to select sites in a replicated database by using the probability distribution of the update delays so that the data acquired by a client satisfies its required RDF. This way calculates the minimum number of sites in order to reduce the overhead of read transactions. Our method continues to adaptively and reliably provide data that meets the client's requirements in an environment where the delay of update propagation varies and applications' requirements change depending on the situation. Finally, we evaluate by simulation the view divergence we can control using our method. The simulation showed that our method can control the view divergence to about 1/4 that of a normal read transaction for 100 replicas. In addition, the increase in the overhead of a read transaction imposed by our method is not as much as the increase in the total number of replicas.

Based on traffic prediction, a new reservation method is proposed to reduce delay and void filling ratio at edge node of optical burst switching networks. Simulation studies show that our method achieves an important improvement and has a dynamic optimum weight value in a certain offset time.

The development of information/communication technology has made it possible to access substantial amounts of data and retrieve information. However, it is often difficult to locate the desired information, and it becomes necessary to spend considerable time determining how to access specific available data. This paper describes a method to quantitatively evaluate the usability of large-scale information-oriented websites and the effects of improvements made to the site design. This is achieved by utilizing the Cognitive Walkthrough for the Web and website modeling using Markov chains. We further demonstrate that we can greatly improve usability through simple modification of the link structure by applying our approach to an actual informational database website with over 40,000 records.

Under the assumption that clock can be inputted to each register at an arbitrary timing, the minimum feasible clock period can be determined if delays between registers are given. This minimum feasible clock period might be reduced if delays between some registers are increased by delay insertion. In this paper, we propose a delay insertion algorithm to reduce the minimum clock period. First, the proposed algorithm determines a clock schedule ignoring some constraints. Second, the algorithm inserts delays to recover ignored constraints according to the delay-slack and delay-demand of the obtained clock schedule. We show that the proposed algorithm achieves the minimum clock period by delay insertion if the delay of each element in the circuit is unique. Experiments show that the amount of inserting delay and computational time are smaller than the conventional algorithm.

Large-capacity photonic packet switch using the wavelength division multiplexing (WDM) technology is proposed. In this switch, the optical buffers, consisting of the fiber delay lines, are shared in many input ports by using the WDM. Furthermore, to reduce the number of optical buffers, the speed-up effect in the optical switch part is investigated. A high-speed tunable optical filter incorporating a semiconductor ring resonator is a key device in the proposed packet switch because many optical filters are used. Optical ring resonators should be possible to fabricate them at a low cost because of their simple structure. To achieve a wide tuning range we designed a double-ring structure, in which two ring resonators are connected in series, and fabricated it using the InGaAsP-InP material system. This device exhibits a total free spectral range (FSR) of 1.7 THz and contrast ratio of 9.5 dB. The ring radii are 25.2 and 17.8 µm, which correspond to FSRs of 340 and 425 GHz, respectively. The switching time of the device is 2.5 ns.

In this letter, a novel wavelet-based semi-fragile watermarking scheme is presented which exploiting the time-frequency feature of discrete wavelet transform (DWT) and high sensitivity on initial value of chaotic map. We also analyze the robustness to mild modification and fragility to malicious attack of our scheme. Its application includes tamper detection, image verification and copyright protection of multimedia content. Simulation results show the scheme can detect and localize malicious attacks with high peak signal-to-noise ratio (PSNR), while tolerating certain degree of JPEG compression and channel additive white Gaussian noise (AWGN).

The comparative analysis of the well known Double Drift Region (DDR) IMPATT diode structure and the n+pvnp+ structure for the avalanche diode has been realized on the basis of the drift-diffusion nonlinear model. The last type of the diode was named as Double Avalanche Region (DAR) IMPATT diode. This structure includes two avalanche regions inside the diode. The phase delay which was produced by means of the two avalanche zones and the drift zone v is sufficient for the negative resistance obtained for the wide frequency region. The numerical model that is used for the analysis of the various diode structures includes all principal features of the physical phenomena inside the semiconductor structure. The admittance characteristics of both types of the diodes were analyzed in very wide frequency region.

This paper presents 160-Gbit/s full channel time-division demultiplexing using a semiconductor optical amplifier hybrid integrated demultiplexer on a planer lightwave circuit. Error-free demultiplexing from a 160-Gbit/s signal to 8 channel 20 Gbit/s signals is successfully demonstrated. Results of a 160-Gbit/s optical time-division-multiplexed full channel OTDM signal transmission experiment using the circuit and successful 80-km transmission are presented.

Tamper proofing is a crucial problem in the watermarking application. Aiming at the credibility of multimedia, we present a semi-fragile watermark based on the image permutation. Watermarking detection is performed without resorting to the host image and it is only controlled by secrete keys, thus the whole scheme does not have certain security gaps. The simulation experiments show that it can survive the JPEG compression and effectively specify the region of the image that has been modified maliciously.

In this paper, we consider a data mining problem for semi-structured data. Modeling semi-structured data as labeled ordered trees, we present an efficient algorithm for discovering frequent substructures from a large collection of semi-structured data. By extending the enumeration technique developed by Bayardo (SIGMOD'98) for discovering long itemsets, our algorithm scales almost linearly in the total size of maximal tree patterns contained in an input collection depending mildly on the size of the longest pattern. We also developed several pruning techniques that significantly speed-up the search. Experiments on Web data show that our algorithm runs efficiently on real-life datasets combined with proposed pruning techniques in the wide range of parameters.

Ultrafast all-optical switching was experimentally demonstrated using four-wave mixing in an SOA. Two pump pulses with different wavelengths and timings were used for 12 switching. The cross-correlation measurements of FWM signals using a short reference pulse show the high-speed switching capability for wavelength routing in OTDM networks.

Next generation advanced power devices show remarkable progress in wide band-gap power devices such as silicon carbide and gallium nitride devices, as well as novel silicon devices called as super junction FETs and so on. The future direction of power electronics applications is surveyed in terms of output power density as an index of future power electronics development, instead of the power conversion efficiency, taking the device progress in sight. Over the last 30 years, the output power density of power electronics apparatuses has increased by a factor of two figures. New markets, such as a power supply for future generation CPU, a compact unit inverter and a electric vehicle-driving inverter unit, are expected to grow rapidly from 2010 to 2015 with the advance in the out power density of power converter. The possibility of power electronics innovation with progress in the output power density will be discussed in conjunction with development of next generation advanced power devices and related technologies.

A huge amount of information is being accumulated on the Internet as the Internet usage spreads and numbers of Web pages increase. However, it is also becoming very difficult to find required information, even when the information exists. The actual value of the Web is thus much lower than its potential value. In order to solve this problem, technologies which allow machines to handle Web content in an efficient, accurate, and flexible way by using machine-readable metadata are being developed. This paper is a survey of knowledge representation on the Web, and the utilization of metadata and ontology for data integration and information sharing, with a focus on the Semantic Web concept.

We have proposed and theoretically verified a 2R (reshaping and regeneration) limiter circuit using continuous wave (CW) holding beam for cross-gain modulation (XGM) wavelength converter, through simulation. The gain clamping effect of semiconductor optical amplifier (SOA), which is caused by CW holding beam injected into SOA, was used to obtain the accurate optical gain and phase conditions for SOA's in 2R limiter circuit. XGM wavelength converter with the proposed 2R limiter circuit provides higher extinction ratio (ER) as well as more enhanced operation speed than any other wavelength converter. Our numerical results show that after the wavelength-converted signal from XGM wavelength converter passed the 2R limiter circuit, it was re-inverted with the improved ER of 30 dB at 5 Gb/s. In case of high-speed operation, great enhancement to decrease power penalty of about 12 dB was shown at 10 Gb/s.

In this paper, we provide explicit representations of average weight and stopping set distributions and asymptotic expressions of their exponent for detailedly represented irregular LDPC code ensembles. Further we present numerical examples which compare a detailedly represented irregular LDPC code ensemble with a conventional one with respect to both of weight and stopping set distributions.

Intensity-noise characteristics of stable multi-mode Fabry-Perot semiconductor lasers are analyzed experimentally and theoretically. Mode-partition noise caused by optical filtering and propagation through optical fibers is investigated by evaluating the relative intensity noise and signal-to-noise ratio. The experimental results indicate that the simplified two-mode analysis provides a good approximation. Suppression of the mode-partition noise by nonlinear gain is experimentally confirmed.

Orthogonal Frequency Division Multiplexing (OFDM) is a promising technique for achieving high bit-rate transmission in radio environments. Various techniques to estimate channel attenuation have been proposed for OFDM transmission. In these techniques, the added pilot semi-blind (APSB) channel estimation has been proposed, which does not require any additional bandwidth. For an OFDM packet transmission that includes preambles, it is difficult to track the channel variation of the latter of packet due to time-varying channels in fast fading environments. We expect that the channel estimation is improved by applying the APSB channel estimation technique to the last symbols of packets without any additional bandwidth or degradation of bit rate. In this paper, we propose an OFDM packet transmission system with APSB channel estimation technique where this technique is applied to the last symbols of packets. We expect that the proposed system can track the fast time-variant channels without decrease of the data-rate, and the packet error rate (PER) is improved. We show that our proposed system is effective for improving the accuracy of the channel estimate in fast fading channels.

Various effective and draft legislations and rules in Europe (WEEE--Waste Electrical and Electronic Equipment ROHS--Restrictions on the use of certain substances and ELV--End of life of vehicles) and Japan (Recycling Law for Home Electric Appliances) have either targeted restrictions or fully banned on the use of lead, to be enforced from 2001, 2003 and 2006 onwards. Up to now, mainly tin-lead alloys have been used in electronics. The process temperatures usually applied have been in the range of 230. All currently discussed lead-free alternatives for professional electronics need process temperatures which are at least 20 higher. In addition, the process duration is significantly longer. The combination of higher process temperatures and longer duration results in significant thermal stress on electromechanical devices. In particular the precision mechanics of electromechanical relays must withstand the solder process with maximum process temperatures of 255 without dimensional changes. During the transition from tin-lead to lead-free solder processes all combinations of component surfaces and solder must be possible. The selection of pure Sn100 or SnCu0.7 as terminal surface allows mixed assemblies with tin-lead as well as lead-free solders. All tested combinations of terminal surface, PCB surface and solder showed good results. From these results it can be concluded that mixed assemblies are possible during the transition time without any negative impact on the reliability of the electronic devices.