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).

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.

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.

A technique for realization of low-voltage OTAs is presented in this letter. A very low-voltage differential-output OTA is realized by employing a new common-mode amplifier in the common-mode feedback circuit. The results of PSpice simulations are shown. The proposed OTA can operate at a 0. 9 V supply voltage.

This paper describes the design and evaluation of a high-performance multicast ATM switch and its feasibility study, including its 40 Gbit/s LSI packaging. The multicast switch is constructed using a serial combination of rerouting networks and employs an adapted Boolean interval-splitting scheme for a generalized self-routing algorithm. Analysis and computer simulation results show that the cell loss probability is easily controlled by increasing the number of switching stages. It is shown that the switch configuration can be transformed into other patterns to be built from banyan-based subnetworks of arbitrary size for LSI packaging. It is also shown that an LSI chip integrating an 88 banyan-based subnetwork using 0. 25-µm CMOS/SIMOX technology can attain a 40-Gbit/s switching capability.

Widely tunable coherent terahertz (THz)-wave generation was successfully demonstrated based on the laser light scattering from the lowest A1-symmetry polariton mode by using a Q-switched Nd:YAG laser pumping. This method exhibits multiple advantages like wide tunability (frequency: 0. 9-2. 2 THz), coherency and compactness of its system. In this paper, the general performances of this THz-wave generator, as well as the recent development of the system and its application are reported. Measurements of tunability, coherency, power, polarization, radiation angle, and divergence are shown. The cryogenic cooling of the crystal was performed in addition, and a more than one hundred times higher THz-wave output was observed. A spectroscopic application of our wave source is demonstrated by measuring the water vapor absorption.

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 consider statistical multiplexing for various types of input data with different statistics in an integrated multimedia system such as ATM networks. The system is assumed to have a constant service rate and a finite buffer. The bit-rate of each data input is variable and is modeled by a fractional Brownian motion process. Under a criterion of quality of service, we obtain an acceptable region of statistical multiplexing. We introduce a new method of investigating the acceptable region of a statistical multiplexer. The results show that transmitting multitype input processes will increase the multiplexing gain.

In this paper, two universal building blocks for complex filter using CCIIs, CFCCIIs, grounded resistors and grounded capacitors are presented. These can be used to realize various complex bandpass filters with arbitrary order. The paper shows that the response error of the proposed circuit caused by nonideality of active components is more easily compensated than that of the conventional one employing op-amps, and that the sensitivities for all components are relatively small. Experimental results are used for verifying the validity of the proposed circuits.

A 2-GHz monolithic Si-bipolar logarithmic/ limiting amplifier is described. It features a waveform-dependent current phase shifter that compensates for the intrinsic dependence of unit-amplifier phase shifts on input signal amplitudes and layout techniques that minimize crosstalk in Si substrate. The amplifier dissipates 250 mW at a 3-V supply, which is less than 1/4 of that of previously reported ICs. The dynamic range of a received signal strength indicator (RSSI) is 60 dB and the limited-output phase deviation is less than 7 deg. at 2 GHz. Therefore, this amplifier is quite suitable for single-conversion transceivers for broadband wireless access systems.

A large-scale modular multicast ATM switch based on a three-stage Clos network architecture is proposed and its performance is studied in this paper. The complexity of our proposed switch is NN if the switch size is NN. The first stage of the proposed multicast switch consists of n sorting modules, where n=N. Each sorting module has n inputs and n outputs and is responsible for traffic distribution. The second and third stages consist of modified Knockout switches which are responsible for packet replication and switching. Although it is a multipath network, cell sequence is preserved because only output buffers are used in this architecture. The proposed multicast switch has the following advantages: 1) it is modular and suitable for large scale deployment; 2) no dedicated copy network is required since copying and switching are performed simultaneously; 3) two-stage packet replication is used which gives a maximum fan-out of n2; 4) translation tables are distributed which gives manageable table sizes; 5) high throughput performance for both uniform and nonuniform input traffic; 6) self-routing scheme is used. The performance of the switch under uniform and non-uniform input traffic is studied and numerical examples demonstrate that the cell loss probability is significantly improved when the distribution network is used. In a particular example, it is shown that for the largest cell loss probability in the second stage to be less then 10-11, the knockout expander, with the use of the distribution network, needs only be larger than 6. On the other hand, without the distribution network, the knockout expander must be larger than 13.

Optimization of InGaAs/InAlAs multiple quantum well structures for high-speed and low-driving modulation, as well as polarization insensitivity and low chirp, was investigated as a function of well thickness and strain magnitude. As a result, very short optical pulses with 4-6 ps was obtained using a low driving-voltage (<2. 0 Vpp) electroabsorption modulator module operating at a 40-GHz large signal modulation. Small chirp operation for low insertion loss (<8 dB from fiber-to-fiber) with prebias was also demonstrated and the product of the pulse width and the spectral width was estimated to be 0. 39 for a 5 ps pulse width that is nearly transform-limited.

This paper proposes a secure electronic sealed-bid auction protocol (SEAP) that provides an auction service on the Internet by combining three providers: an auction service provider, a key service provider, and a time service provider. The SEAP uses public key cryptography and the concept of a time-key certificate. The most important property of this protocol is that time-dependent security requirements can be strictly satisfied. The SEAP satisfies the following nine security requirements: (a) no one can deny having made a bid; (b) the protocol should be secure against malicious acts; (c) no bidder can act for another bidder; (d) no one can know who else is bidding until the time comes for the bids to be opened; (e) no one can discover the contents of any of the bids until the time comes for the bids to be opened; (f) the successful bid must have been submitted before the bidding deadline; (g) all bidders can verify that the auction policy has been correctly implemented; (h) the successful bidder can be identified without being required to make himself or herself known; and (i) the bidding contents cannot be altered. The protocol consists of three subprotocols: the Registration Subprotocol, the Bidding Subprotocol, and the Auction Subprotocol. The protocol parameters and algorithm are described in detail.

A group-oriented cipher communication method is developed and implemented on a WWW-based (World Wide Web) network system. In this method, a group key common to all entities of the group is generated based on the group name or the identities of entities belonging to the group. The group key, in turn, is used for encrypting the data being shared among the group via the WWW server. The data theft at the WWW cache sites on the intermediate communication line is prevented, establishing a unified feature of the good WWW cache performance and security. A prototype of our method proved the feasibility and the efficiency.

In this paper, a new traffic shaping mechanism for ATM networks, the RC Shaper, is proposed and studied. The objective of a shaping mechanism is, to smoothen the traffic by reducing the burstiness. Using the analogies between the RC low pass filter and the proposed shaper, performance measures such as burstiness reduction factor and cell mean waiting time of the shaper can be obtained. In this current exploratory stage of study, the shaper is used to shape the well-known Markov Modulated Poisson Process. Behaviour of the shaper is established through examining the burstiness reduction achieved by the device. Another performance measure obtained for the shaper is the cell mean waiting time. Difference in shaping each connection individually and a group of connections collectively is also observed. From our results, it seems better to shape VCs within a virtual path `aggregately' instead of shaping each of these VCs individually. Comparison with fixed-rate shaper is reported and difference in multiplexing shaped and unshaped cell streams is also observed.

This paper proposes to apply random mapping methods of a pseudo random function to find collisions of a hash function. We test a hash function including a block cipher (see ISO/IEC 10118-2) with computers, where users can select its initial vector. In particular, the paper shows that a hash function with multiple stages generates a lot of collision hash values, so our probabilistic consideration of a small model for the hash function well explains the computational results. We show that it's feasible to find collisions between the selected messages in advance for 64-bit-size hash functions with WSs linked via an ordinary LAN (Local Area Network). Thus, it is dangerous to use the hash function -- single block mode -- defined in [6] and [7].