We have constructed Bi based layer structured ferroelectric films and their superlattices by a pulsed laser deposition technique. The dielectric constants along c-axis increase with increasing of the number of pseudo-perovskite layers between double Bi2O2 layers. Ferroelectricity appears along the c-axis direction only for the odd number of the perovskite layers owing to the mirror symmetry in a crystal structure. Especially, the Bi2VO5. 5 film shows an atomically flat surface, low dielectric constant of 30 and ferroelectricity of Pr=3 µC/cm2 and Ec=16 kV/cm, respectively. This material is expected to the application for FRAMs.

Co-channel interference is a major deteriorating factor limiting the capacity of mobile communication systems. To mitigate the effect of the interference, a kind of nonlinear interference canceller named trellis-coded co-channel interference canceller (TCC) has been proposed. In TCC the trellis-coded modulation (TCM) is introduced to both the desired signal and the interference signal in order to enhance the cancelling performance. In this paper, the bit error rate (BER) performance of TCC in static channel is theoretically evaluated for the first time. An equivalent TCM (E-TCM) model is firstly established, and a BER asymptotic estimate (AE) and a BER upper bound (UB) of TCC are then evaluated respectively by analyzing E-TCM. In the evaluation of AE, the BER performance is calculated as a function of phase difference between the desired signal and the interference signal (φ), subsequently the average BER performance over φ can be evaluated. The UB of BER is calculated using a transfer function based on the matrix representation. This paper also demonstrates that AE gives higher accuracy and less calculation complexity than UB. Performance comparisons reveal the consistency of these theoretical results with that of computer simulations.

Method schemas were proposed as a formal model of object-oriented languages. A method schema S is called consistent if, for each method invocation during the execution of S, a method definition to be bound to the invoked method name is uniquely determined. However, the consistency testing problem is known to be undecidable in general. This paper presents an algorithm which analyzes the consistency of a given method schema. The algorithm decides the consistency problem in polynomial time for monadic method schemas. We also provide an incremental algorithm for testing consistency after updates of a method schema.

Time series prediction is very important technology in a wide variety of fields. The actual time series contains both linear and nonlinear properties. The amplitude of the time series to be predicted is usually continuous value. For these reasons, we combine nonlinear and linear predictors in a cascade form. The nonlinear prediction problem is reduced to a pattern classification. A set of the past samples x(n-1),. . . ,x(n-N) is transformed into the output, which is the prediction of the next coming sample x(n). So, we employ a multi-layer neural network with a sigmoidal hidden layer and a single linear output neuron for the nonlinear prediction. It is called a Nonlinear Sub-Predictor (NSP). The NSP is trained by the supervised learning algorithm using the sample x(n) as a target. However, it is rather difficult to generate the continuous amplitude and to predict linear property. So, we employ a linear predictor after the NSP. An FIR filter is used for this purpose, which is called a Linear Sub-Predictor (LSP). The LSP is trained by the supervised learning algorithm using also x(n) as a target. In order to estimate the minimum size of the proposed predictor, we analyze the nonlinearity of the time series of interest. The prediction is equal to mapping a set of past samples to the next coming sample. The multi-layer neural network is good for this kind of pattern mapping. Still, difficult mappings may exist when several sets of very similar patterns are mapped onto very different samples. The degree of difficulty of the mapping is closely related to the nonlinearity. The necessary number of the past samples used for prediction is determined by this nonlinearity. The difficult mapping requires a large number of the past samples. Computer simulations using the sunspot data and the artificially generated discrete amplitude data have demonstrated the efficiency of the proposed predictor and the nonlinearity analysis.

The proposed GCRA (Generic Cell Rate Algorithm) traffic shaper consists of a regulator and a scheduler. It can shape multiple incoming VBR (Variable Bit Rate) cell streams simultaneously to be strictly conforming according to the GCRA algorithm when the cells depart for the ATM output link. The impact of cell emission conflicts is considered and resolved by using an EDD (Earliest-Due-Date) scheduler and a feedback signal from the scheduler to the regulator. The call admission control condition and the cell delay bound are derived. Simulation results demonstrate that the output cell streams of the proposed GCRA traffic shaper do not contain any non-conforming cells and the scheduler queue size is significantly reduced. Meanwhile, the delay performance is almost not affected by the use of the feedback mechanism.

The effects of forced phase modulation (FPM) and self phase modulation (SPM) in dispersion tuned fiber lasers (DTFL) are examined. We show that FPM, such as chirp in the modulator, plays an important role in the pulse shaping because of the important role of dispersion in the cavity. In particular, compared to the case of zero FPM, significant pulse shortening can be obtained by using up-chirp modulation. The results suggest that modulators with large chirp parameters are desirable for DTFLs. When SPM is introduced, the pulse shapes differ greatly depending on the direction of the FPM. Significant deviations from Gaussian profiles are observed.

We extend the use of a saturable Bragg reflector to modelock a NaCl:OH- color center laser, producing pulses adjustable from 200 fs to 2 ps, and tunable from 1. 499 µm to 1. 535 µm, with the minimum pulsewidth near 1. 51 µm. The laser is self-starting, requires no dedicated dispersion compensating optics, and maintains a highly stable, nearly transform limited output pulse train with up to 150 mW average output power.

We propose a mechanically tunable passively mode-locked semiconductor laser with a high repetition rate using a simple configuration with a moving mirror located very close to a laser facet. This scheme is demonstrated for the first time by a novel micromechanical laser consisting of an InGaAsP/InP multisegment laser with a monolithic moving micro-mirror driven by an electrostatic comb structure. The main advantage of this laser is the capability of generating high-quality mode-locked pulses stabilized by a phase-locked loop (PLL) with low residual phase noise in a wide repetition-rate tuning range. This paper describes the basic concept and tuning performances utilizing the micromechanical passively mode-locked laser in 22-GHz fundamental mode-locking and in its second-harmonic mode-locking.

We propose a novel InGaAsP semiconductor laser which theoretically exhibits a high differential gain. The proposed semiconductor laser contains an asymmetric double quantum well structure as the active region. The differential gain enhancement invokes resonant tunneling of heavy holes in the asymmetric double quantum well structure, which takes place on the way of carrier injection process. The proposed laser is expected to be far more efficient in reducing pulse width and spectral broadening (chirping) than conventional multiquantum well lasers when driven by the gain switching method.

The effect of sampling-pulse pedestals, generated by pulse compression, on the temporal resolution in electro-optic (EO) sampling is studied both theoretically and experimentally. Analysis is made on how the pedestals degrade a measurement bandwidth and a temporal waveform. Based on the analysis, a practical guideline on the suppression of pedestals is also given. Gain-switched laser diode (LD) pulses adiabatically soliton-compressed using a dispersion decreasing fiber are used to confirm the theoretical results, and are successfully applied to high-temporal-resolution (>100 GHz) EO sampling measurements.

The semiconductor lasers operating with self-sustained pulsation are under developing to be lasers which are less disturbed by the optical feedback from a surface of optical disk. Structures setting saturable absorbing regions utilizing the multi-layer configuration become popularly used for giving stronger pulsation. However, the quantum (intensity) noise in these lasers tends to be enhanced. The ridge stripe structure, of which almost self-sustained pulsation lasers consist, seems to give a leak current flowing along plane of the cladding region. Such leak current also increases the quantum noise. In this paper, theoretical calculations of operating characteristics, such as the self-sustained pulsation, the optical output, the quantum noise as well as the transverse filed profile, are theoretically analyzed by including the above mentioned several phenomena.

Asynchronous Transfer Mode (ATM) networks are expected to support a diverse mix of traffic sources requiring different Quality Of Service (QOS) guarantees. This paper initially examines several existing scheduling disciplines which offer delay guarantees in ATM switches. Among them, the Earliest-Due-Date (EDD) discipline has been regarded as one of the most promising scheduling disciplines. The EDD discipline schedules the departure of a cell belonging to a call based on the delay priority assigned for that call during the call set-up. Supporting n delay-based service classes through the use of n respective urgency numbers D0 to Dn-1 (D0D1 Dn-1), EDD allows a class-i cell to precede any class-j (j>i) cell arriving not prior to (Dj-Di)-slot time. The main goal of the paper is to determine the urgency numbers (Dis), based on an in-depth queueing analysis, in an attempt to offer ninety-nine percentile delay guarantees for higher priority calls under various traffic loads. In the analysis, we derive system-time distributions for both high- and low-priority cells based on a discrete-time, single-server queueing model assuming renewal and non-renewal arrival processes. The validity of the analysis is justified via simulation. With the urgency numbers (Dis) determined, we further propose a feasible efficient VLSI implementation architecture for the EDD scheduling discipline, furnishing the realization of QOS guarantees in ATM switches.

The characteristics of several femtosecond solid-state laser systems are described illustrating the diversity of the operational parameters of these lasers. The systems include Pr:YLF, Cr:LiSAF, Cr:Forsterite and Cr:YAG, with wavelength of operation from the visible to the near infra-red. Particular emphasis is placed upon compact, efficient pumping schemes, all-solid-state diode-pumped femtosecond oscillator configurations and newly configured, highly-efficient, tunable, femtosecond lasers pumped by high power fibre lasers.

Recent advances in solid-state laser technology and ultrafast optics led to the generation of optical pulses as short as 5 femtoseconds with peak powers up to the subterawatt level from a compact kHz-repetition-rate all-solid-state laser. This source significantly pushes the frontiers of nonlinear optics. Exciting new possibilities include the investigation and exploitation of reversible nonlinear optical processes in solids at unprecedented intensity levels, the development of a compact laser-driven coherent soft-X ray source at photon energies near 1 keV, and the generation of attosecond xuv pulses. First, a brief review of recent milestones in the evolution of ultrafast laser technology is given, followed by a description of the high-power 5-fs source. The rest of the paper is devoted to applications in previously inaccessible regimes of nonlinear optics. We demonstrate that wide-gap dielectrics resist intensities in excess of 1014 W/cm2 in the sub-10 fs regime and the extension of high-harmonic generation in helium to wavelengths shorter than 2. 4 nm (Eph > 0. 5 keV).

The novel application potential of mode-locked laser diodes (MLLDs) in ultrafast optical signal processing in addition to coherent optical pulse generation is described. As the most fundamental function of MLLDs, we show that the generation of ultrashort (2 ps) coherent optical pulses with low timing jitter (<0. 5 ps) at precisely controlled wavelength and repetition frequency can be achieved by employing a rigid module configuration for an external-cavity MLLD. We then discuss new aspects of MLLDs which are functions of ultrafast all-optical signal processing such as optical clock extraction and optical gating. All-optical clock extraction is based on the timing synchronization of MLLD output to the injected optical data pulse. When the passive mode-locking frequency of an MLLD is very close to the fundamental clock pulse frequency of optical data, the former frequency is pulled into the latter frequency by optical data injection. We show that same-frequency and subharmonic-frequency optical clock pulses can successfully be extracted from optical data pulses at bit rates of up to 80 Gbit/s with very simple configurations and very low excess timing jitter (<0. 1 ps). On the other hand, optical gating is due to absorption saturation and the following picosecond absorption recovery in a saturable absorber (SA) in an MLLD structure incorporating optical gate-pulse amplification. Here, MLLDs are anti-reflection coated and used as traveling wave devices instead of laser oscillators, and small saturation energy (<1 pJ) and ultrafast recovery time (<8 ps) are demonstrated. By combining all these MLLD functions, we successfully demonstrated an experiment with 40- to 10-Gbit/s all-optical demultiplexing processing.

In this paper, we describe the properties of an external cavity modelocked semiconductor laser with a tunability of wavelength, pulse width and repetition rate. This modelocked laser generates optical pulses with pulse widths down to 180 fs and with repetition rates up to 14 GHz in a 120 nm wavelength range near 1. 55 µm or 1. 3 µm. The generated pulses are close to the transform limit and are therefore suitable for very high speed communication systems. In addition to the tunability, this pulse source is a compact and mechanically stable device. We report on two applications of this pulse source in optical time division multiplexing experiments. In the first example the modelocked laser is used as an all-optical clock recovery. In the second example the modelocked laser was used to characterize an interferometric switch by pump-probe experiments.

We investigate the relaxation oscillation characteristics of an actively mode-locked fiber laser and a novel stabilizing method of the laser theoretically and experimentally. The stabilizing method controls cavity length to suppress the rf power of the relaxation oscillation frequency of the laser output, and can directly monitor the stability of the laser to ensure the most stable operation. With this method, the rf power ratio between mode-locking frequency and the background noise can be kept to more than 70 dB, and highly stable transform-limited pulse generation is achieved. Bit-error-free operation at 6. 3 GHz over 10 hours is successfully demonstrated. The stability of the center wavelength of the laser output and the required accuracy of cavity control for high-speed laser operation are also discussed.

While active researches have been continuously made on the ATM switch architectures and the QoS service guarantees, most of them have been treated independently in the past. In this paper, we first explain the architectural requirement on the ATM switches to implement the mechanism of QoS guarantees in the context of ATM congestion control. Then we discuss how a vital link between two should be built, and remaining problems are pointed out.

In this paper we review the stretched-pulse principle and discuss its inherent advantages for ultrashort pulse generation and transmission. An analytic theory of the stretched-pulse fiber laser is presented and shown to be in good agreement with experimental results. An extension of the stretched-pulse theory is applied to both fiber lasers and dispersion-allocated soliton transmission and then compared to numerical results. We also discuss the design and operation of an environmentally stable stretched-pulse fiber laser.

The timing jitter of the optical pulse from a gain-switched laser diode is reduced by CW light injection. The reduction ratio of the timing jitter is 5. 5. The pulse width was compressed by a nonlinear optical loop mirror to a pedestal-free optical pulse with a pulse width of 420 fs.