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.

In the first stage of ATM switching system development, the specifications are sometimes changed in order to match revisions in ITU standards. Fatal problems due to specification changes and unexpected bugs force ASIC redesign and subsequent debugging is seriously restricted. These situations demand the introduction of new hardware design methodologies. This paper proposes a flexible hardware design methodology, based on a novel real-time emulation technique, suitable for large-scale high-speed communication switching systems. The emulation technique offers desirable system performance without Application Specific Integrated Circuit (ASIC) fabrication by using commercial Field Programmable Gate Arrays (FPGAs) along with many simply-structured high-speed interconnect switch devices for multiple FPGA connection. This technique suits line interface units (LUs) that have ASICs operating at about 20 MHz; each LU employs an LU board and emulation boards, both of which have hierarchical structures with sub-boards. The emulation boards are indispensable for realizing prototype systems rapidly and dealing with specification changes. Different types of LUs can be realized by mounting different sub-boards to the common LU board. Each emulation board is attached to the LU board by the same connector used for LU sub-board mounting. Therefore, the proposed structure has the advantage of utilizing a common LU board for system emulation as well as permitting the development of practical systems. To suppress undesirable multiple FPGA partitioning, we propose the emulation board architecture that has two types of sub-boards, each of which carries a different type of FPGA. We produced some portions of the proposed LU and tested the nearly 20 MHz real-time emulation of a complicated ASIC designed to realize ATM cell header conversion functions. The results of multiple FPGA partitioning on the emulation board suggest that the proposed design methodology will yield economic systems that can be freely modified to overcome hardware bugs and comply with future ITU standards.

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.

We demonstrate an electrooptic synthesis technique for generating arbitrarily shaped short optical pulses from a CW narrow linewidth laser. For the optical pulse shaping, a large-amplitude electrooptic phase modulator is specially fabricated by employing the quasi-velocity-matching. The phase modulated light having sidebands as wide as 1 THz is separated and phase-only-controlled spatially by a liquid crystal modulator array. After composing the light by using a grating, nearly 1. 2 ps of Fourier-transform-limited optical pulses is obtained.

It is shown from the Hilberts theory that if the real function Π(θ) has no zeros over the interval [0, 2π], it can be factorized into a product of the factor π+(θ) and its complex conjugate π-(θ)(=). This factorization is tested to decompose a real far-zone field pattern having zeros. To this end, the factorized factors are described in terms of bicomplex mathematics. In our bicomplex mathematics, the temporal imaginary unit "j" is newly defined to distinguish from the spatial imaginary unit i, both of which satisfy i2=-1 and j2=-1.

If the fiber dispersion of soliton transmission line is optimized, the amplifiers output power becomes almost constant for different amplifier spacing and pulse width. Numerical simulations indicate the optimal dispersion can be determined, as the ratio of amplifier spacing to dispersion length is about 0. 8 for uniform dispersion line.

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.

An ultra-broadband optical parametric amplification can be attained by a noncollinear phase-matching. The group-velocity matching of the signal and idler reduces the signal-pulse width to 14-fs in an optical parametric amplifier based on a β-BaB2O4 crystal pumped by a second harmonics of a Ti: sapphire regenerative amplifier. This simple novel method shows the potential light source of a tunable sub-10-fs pulse in a visible region.

The reduction of Soliton-soliton interaction to stabilize the soliton pulse propagation in the periodic dispersion-compensated standard fiber system using optical bandpass filter has been investigated by numerical simulation, and experimentally 10 Gbit/s soliton transmission was realized without fine tuning dispersion management over 5700 km, using appropriate optical bandpass filters and polarization scrambler.

We study nonlinear pulse propagation in an optical transmission system with dispersion compensation. This is particularly important for designing an ultra-fast long-haul communication system in the next generation. There exists a quasi-stationary pulse solution in such a system whose width and chirp are rapidly oscillating with the period of dispersion compensation. This pulse also has several new features such as enhanced power when compared with the soliton case with a uniform dispersion and a deformation from the sech-shape of soliton. We use the averaging method, and the averaged equation to describe the core of the pulse solution is shown to be the nonlinear Schrodinger equation having a nontrapping quadratic potential. Because of this potential, a pulse propagating in such a system eventually decays into dispersive waves in a way similar to the tunneling effect. However in a practical situation, the tunneling effect is estimated to be small, and the decay may be neglected.

This paper describes a low-skew clock distribution technique for multiple targets. An automatic skew compensation circuit, that detects the round-trip delay through a pair of matched interconnection lines and corrects the delay of the variable delay lines, maintains clock skew and delay from among multiple targets below the resolution time of the variable delay lines without any manual adjustment. Measured results show that the initial clock skew of 900 ps is automatically reduced to 30 ps at a clock frequency of up to 250 MHz with 60 ps of clock jitter. Moreover, they show that the initial clock delay of 1500 ps is cancelled and 60 ps of clock delay can be achieved. The power dissipation is 100 mW at 250 MHz.

The aim of this study is to offer additional experimental evaluation on learning algorithms for artificial neural networks by testing and comparing the normalized backpropagation algorithm (NBP), previously proposed by the authors, and six other alternatives based on a particular application to financial forecasting. The algorithms are the original backpropagation (OBP), the NBP, backpropagation with momentum (two versions), the delta-bar-delta, the superSAB, the rprop and the quickprop algorithm.

This paper summarizes our recent efforts in modelocking Ti:sapphire lasers with semiconductor saturable absorber mirrors (SESAMs). We present the shortest optical pulses ever generated directly from a laser. The modelocking build-up time (T BU) of 60 µs is, to our knowledge, the shortest reported for a passively modelocked KLM laser to date.

The dependence of the output characteristics of a regeneratively and harmonically FM mode-locked erbium-doped fiber laser on intracavity dispersion have been investigated by changing the group velocity dispersion (GVD) of the fiber. It is shown that a stable pulse train can be obtained only when the GVD of the cavity is anomalous in the presence of self-phase modulation (SPM). The shortest pulse obtained was 2. 0 ps at a repetition rate of 10 GHz.

Multicasting is an important feature for any switching network being intended to support broadband integrated services digital networks (B-ISDN). This paper proposes an improved multicast packet switch based on Lee's nonblocking copy network. The improved design retains the desirable features of Lee's network including its nonblocking property while adopting techniques to overcome the various limitations mentioned in various literature. The proposed network architecture utilizes d-dilated banyan networks to increase the amount of cells that can be replicated within the copy network. Cell splitting is used to optimize the utilization of the network's available bandwidth. Furthermore, the proposed architecture allows for the modular expansion in capacity to accomodate changing traffic patterns. The modular design of the proposed switch likewise offers easy handling and replacement of faulty modules.

This paper proposes a novel low power dissipation technique for a low voltage OTA. A conventional low power OTA with a class AB input stage is not suitable for a low voltage operation (1. 5 V supply voltages), because it uses composite transistors (referred to CMOS pair) which has a large threshold voltage. On the other hand, the tail-current type OTA needs a large tail-current value to obtain a sufficient input range at the expense of power dissipation. Therefore, the conventional tail-current type OTA has a trade-off between the input range and the power dissipation to the tail-current value. The trade-off can be eliminated by the proposed technique. The technique exploits negative feedback control including a current amplifier and a minimum current selecting circuit. The proposed technique was used on Wang's OTA to create another OTA, named Low Power Wang's OTA. Also, SPICE simulations are used to verify the efficiency of Low Power Wang's OTA. Although the static power of Low Power Wang's OTA is 122 µW, it has a sufficient input range, whereas conventional Wang's OTA needs 703 µW to obtain a sufficient input range. However, we can say that as the input signal gets larger, the power of Low Power Wang's OTA becomes larger.

In this paper, we propose a new multicast address scheme based on bit map address (BA) and vertex isolation address (VIA) schemes. The proposed scheme can be utilized by the self-routing switch in a speed manner, while preserving the multicast capability. We analyze the processing delay of the proposed scheme and show the efficiency.

The symbol basis side information generated by Viterbi's ratio threshold test technique is proposed to improve the performance of the asynchronous slow-frequency-hopped multiple access system with BFSK signaling in the frequency non-selective fading channel. By properly setting the ratio threshold to produce erasure decisions for the received symbols, the system performances are optimized. The relationship among the hit symbols in a hop duration is exploited by this symbol basis side information to greatly reduce the packet error probability. This packet error rate improvement can be as large as two order of magnitude, compared with perfect hop basis side information systems.

In an iterative decoding algorithm, such as Chase Type-II decoding algorithm and its improvements, candidate codewords for a received vector are generated for test based on a bounded-distance decoder and a set of test error patterns. It is desirable to remove useless test error patterns in these decoding algorithms. This paper presents a sufficient condition for ruling out some useless test error patterns. If this condition holds for a test error patterns e, then e can not produce a candidate codeword with a correlation metric larger than those of the candidate codewords generated already and hence e is useless. This significantly reduces the decoding operations in Chase type-II decoding algorithm or decoding iterations in its improvements.

To construct the future multimedia network, ATM network technology and services should support cost-effective, high-speed interconnectivity and a variety of service-providing functions. Furthermore, as the infrastructure of future multimedia service, the ATM architecture should be adaptable to changes without needing replacement of its core functions and platform capabilities. This paper presents an overview of the current state of development, standardization and deployment of the ATM network service technologies and architecture concept. It also discusses the trend toward the integration of ATM technology and Internet technology. Also reported is the state of development and standardization for the individual ATM technologies and related issues, including access networks, bearer services, signalling, network middleware, and future ATM switching system technology.