We propose ATM switching nodes with a feedback rate control scheme, AREX, which does not require a large buffer space and does not deteriorate throughput even in large-scale and high-speed ATM-WANs. The goal of our study is to establish the ATM multi-protocol emulation network ALPEN, which is an ATM-WAN architecture for establishing a backbone for multimedia networks. ALPEN achieves an ATM-WAN which is robust against long propagation delays. It also provides high performance without a large buffer space in an ATM-WAN environment. In ALPEN, each transit node informs the edge nodes only its residual bandwidth ratio. The edge nodes support multiple ATM-layer services by emulating them based on the information notified by transit nodes. Our research has been directed towards achieving high performance ABR (Available Bit Rate) service in an ATM-WAN by using ALPEN. The conventional ABR service requires transit nodes to have relatively high calculation power and large buffer space to overcome the effect of the long propagation delays common in WANs. ALPEN node systems have been developed for trials with actual network traffic. ALPEN with AREX reduces the calculation load of transit nodes for ABR service. That is confirmed by the size of the DSP program created for a test system. ALPEN with AREX is, therefore, able to emulate ABR service with higher performance in ATM-WANs, because ALPEN edge nodes are able to indicate the users allowed by ER (Explicit Rate) feedback. The network throughput, maximum queue length at congestion point, and burst transmission rate are determined by simulation. ALPEN with AREX achieves better performances than the conventional ABR network.

Predicting the performance of high speed wide area ATM networks (WANs) is a difficult task. Evaluating the performance of these systems by means of mathematical models is not yet feasible. As a result, the creation of simulation models is usually the only means of predicting and evaluating the performance of such systems. In this paper, we use measurements to validate simulation models of TCP/IP over high speed ATM wide area networks. Validation of simulations with measurements is not common; however, it is needed so that simulation models can be used with confidence to accurately characterize the performance of ATM WANs. In addition, the appropriate level of complexity of the simulation models needs to be determined. The results show that under appropriate conditions simulation models can accurately predict the performance of complex high speed ATM wide area networks. This work also shows that the user perceived performance is dependent on host processing demands.

We present a collection of new network control protocols for high-speed networks that are geared to overcome some of the important drawbacks of existing protocols, namely (a) the inefficiencies of existing wait-for-reservation type of protocols for multigigabit wide area networks, (b) the implementation difficulties of credit-based flow control schemes, and (c) the packet resequencing problem of deflection-based schemes. Two of the protocols that will be outlined here were designed in the context of the DARPA sponsored Thunder and Lightning project, at the University of California, Santa Barbara, which is a continuing research effort to design and build a virtual-circuit switched, ATM-based, fiber optic network operating at link speeds of up to 40 Gb/s (see, for instance). The third protocol was designed in the context of MOST project, which is a project on (almost) all-optical switching supported by DARPA. All protocols achieve lossless transmission, efficient utilization of the capacity, and minimum pre-transmission delay for delay-sensitive traffic.

Multicast ATM switches are essential to support various types of services in the Broadband ISDN. In this paper we present an efficient architecture to support multicasting in shared buffer ATM switches. A lookahead technique is employed to resolve the head-of-line blocking problem in the multicast-queue approach, thus improving the throughput of the multicast traffic. The arbitration between multicast and unicast services is investigated to prevent the lookahead technique from increasing the multicast dominance. We show through performance and complexity comparisons that with a small hardware overhead over the multicast-queue approach, our architecture provides a throughput performance comparable to address-duplication or searchable-queue-based approaches.

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.

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 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.

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.

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 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.

This correspondence reports novel computationally efficient algorithms for multiplication of bicomplex numbers, which belong to hypercomplex numbers. The proposed algorithms require less number of real multiplications than existing methods. Furthermore, they give more effective implementation when applied to constant coefficient digital filters.

We implement a graphical interface that automatically transforms a figure input by a mouse into a regular figure which the system infers is the closest to the input. The difficulty lies in the fact that the classes into which the input is to be classified have inclusion relations, which prohibit us from using a simple distance criterion. In this letter, we show that this problem can be resolved by introducing the geometric AIC.

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.

Recently fiber optic links have been applied to radio signal distribution networks and also to signal feeder networks for phased array antennas, because they are able to offer wide bandwidth for achieving the high bit-rates and large capacity needed in the multimedia age. In these networks, a great many modules are needed to convert optical signals to radio signals. In order to reduce the complexity and cost of these modules, direct optical control techniques, which inject optical signals directly into microwave circuits, are very attractive. Thus, this paper proposes a novel optical control technique using tunable inductance circuits. This technique employs direct illumination as a means of optically tuning the inductance. Since the inductance value is inversely proportional to the square of the transconductance, it varies widely when the FET is directly illuminated. With direct illumination, the measured inductance variation in an experimental inductance circuit built with Pseudomorphic AlGaAs/InGaAs/GaAs HEMTs is more than 20 % from 0.5 to 2 GHz. As an application, a direct optically controlled oscillator was fabricated. The measured optical tuning range of the oscillation frequency is more than 19 % with an output power of -51 dBm. This is a promising technique for a variety of devices, including optically controlled oscillators, filters, phase shifters, and active antennas.

This paper describes a method for analyzing active impedance, i. e. equivalent resistance and equivalent reactance, of a narrow-band transistor Colpitts crystal oscillator. This oscillator, employing an AT-cut resonator filter, has a very narrow-band width and an achievement of extremely low phase-noise characteristics is expected. The analysis proposed is based on an algebraic formula, which employs a nonlinear approximation for transistor gm, and a simplified circuit model. Calculated results are compared with the experimental results in the frequency characteristics of the oscillator active impedance with changing the driving signal current. Good agreement between the calculation and experimental results shows that the proposed technique is suitable for designing Colpitts crystal oscillators with resonator filters. In addition we apply this technique to the analysis of dual-mode crystal oscillators.

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.

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.

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.