To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

We experimentally demonstrate the ultrafast and high-repetition capabilities of a polarization-discriminating symmetric Mach-Zehnder (PD-SMZ) all-optical switch. This switch, as well as an original symmetric Mach-Zehnder (SMZ) all-optical switch, is based on a highly efficient but slowly relaxing band-filling effect that is resonantly excited in a passive InGaAsP bulk waveguide. By using a mechanism that cancels out the effect of the slow relaxation, ultrafast switching is attained. We achieve a switching time of 200 fs and demultiplexing of 1.5 Tbps, showing the applicability of the SMZ or PD-SMZ all-optical switches to optical demultiplexing of well over 1 Tbps for the first time. High-repetition capability, which is another important issue apart from the switching speed, is also verified by using control pulses at a repetition rate of 10.5 GHz. We also discuss the use of nonlinearity in a semiconductor optical amplifier to further reduce the control-pulse energy.

Predicate Circumscription is a fundamental formalization of common sense reasoning. In this paper, we study a new approximation formula of it. In our previous works, we investigated Lifschitz's pointwise circumscription and its generalization, which functions as a finite approximation to predicate circumscription in the first-order framework. In this paper, at first, we study the ability of the generalized pointwise circumscription more closely, and give a simple example which shows that it cannot be complete even when a minimized predicate has only finite extension on the minimal models. Next, we introduce a new approximation formula, called finite constructive circumscription, in order to overcome that limitation. Finally, we compare expressive power of the two approximation methods with of predicate circumscription schema, and propose a open problem that should be solved to clarify that the completeness of predicate circumscription schema with respect to minimal model semantics.

The tera-bit order capacity of ultrahigh-speed and wide-band networks will become necessary to provide highly advanced multimedia services. In conventional networks, electronic circuits limit the speed capability of the networks. Consequently, all-optical networks are essential to realize ultrahigh-speed and wide-band communications. In this paper, we propose the configuration of an all-optical code division multiplexing (CDM) switching network based on self-routing principles and the structure of a nonlinear all-optical switching device as one of the key components for the network. We show that the required performances of the optical devices used in the CDM switching fabric are lower than those used in the TDM and illustrate the basic transmission characteristics of the switching device utilizing FD-BPM. To evaluate the multiplexing performance, we demonstrate the maximum number of channels under an error-free condition and the BER characteristics when the Gold sequence is applied as one of the CDM code sets, and show that the network of the sub-tera-bit order capacity is realizable by adopting TDM, WDM and CDM technologies. We also illustrate the packet assembly method suitable for self-routing transmissions and one of network architectures where the proposed switching fabric can be exploited.

The tera-bit order capacity of ultrahigh-speed and wide-band networks will become necessary to provide highly advanced multimedia services. In conventional networks, electronic circuits limit the speed capability of the networks. Consequently, all-optical networks are essential to realize ultrahigh-speed and wide-band communications. In this paper, we propose the configuration of an all-optical code division multiplexing (CDM) switching network based on self-routing principles and the structure of a nonlinear all-optical switching device as one of the key components for the network. We show that the required performances of the optical devices used in the CDM switching fabric are lower than those used in the TDM and illustrate the basic transmission characteristics of the switching device utilizing FD-BPM. To evaluate the multiplexing performance, we demonstrate the maximum number of channels under an error-free condition and the BER characteristics when the Gold sequence is applied as one of the CDM code sets, and show that the network of the sub-tera-bit order capacity is realizable by adopting TDM, WDM and CDM technologies. We also illustrate the packet assembly method suitable for self-routing transmissions and one of network architectures where the proposed switching fabric can be exploited.

Recent work in the area of ultrafast optical time-division multiplexed (OTDM) networking at MIT Lincoln Laboratory is presented. A scalable helical local area network or HLAN architecture, presented elsewhere as an architecture well-suited to ultrafast OTDM LANs and MANs, is considered in the context of wide area networking. Two issues arise in scaling HLAN to the wide area. The first is protocol extension, and the second is supporting the required bandwidth on the long-haul links. In this paper we discuss these challenges and describe progress made in both architecture and technologies required for scaling HLAN to the wide area.

A 116 arrayed waveguide grating multiplexer operating around 1550 nm has been realized using newly synthesized fluorinated poly(arylene ethers). The channel spacing is 0.8 nm (100 GHz). The insertion loss of the multiplexer is 17-20 dB and the cross talk is less than -15 dB. The propagation loss of a rib waveguide is less than 0.5 dB/cm at 1550 nm.

The hybrid electrical/optical multi-chip integration technique for optical modules for optical network system has been developed. Employing the technique, a 44 broadcast-and-select type optical matrix switch module has been realized. The module consists of four sets of silica waveguide 1 : 4 splitters/4 : 1 combiners, four 4-channel arrays of polarization insensitive semiconductor optical amplifiers with spot-size converters as optical gates, printed wiring chips for electrical wiring and single mode fibers for optical signal interface on planar waveguide platform fabricated by atmospheric pressure chemical vapor deposition. All the gates and the wiring chips were mounted precisely onto the platform at once in flip-chip manner by self-align technique using AuSn solder bumps. Coupling loss between the waveguide and the SOA gate was estimated to be 4.5 dB. Averaged fiber-to-fiber signal gain, on-off ratio and polarization dependent loss for each of the signal paths was 7 dB 2 dB, more than 40 dB and 0.5 dB, respectively. High speed 10 Gb/s photonic cell switching as short as 2 nsec has been successfully achieved.

Real-time services, including constant bit rate (CBR) and real-time variable bit rate traffic (rt-VBR), have become increasingly important owing to the rapid proliferation of multimedia applications. A cell multiplexing method capable of handling real-time traffic should satisfy related quality of service (QoS) requirements, including cell transfer delay (CTD), cell delay variation (CDV) and cell loss ratio (CLR). In this paper, we present an efficient cell multiplexing method, called longest delay beyond expectation (LDBE), to schedule real-time and non-real-time traffic in ATM networks. For the real-time traffic, LDBE scheme can minimize the CDV, and reduce the CLR and CTD, particularly when different CDV tolerance (CDVT) values are applied at each node along the path of a connection. Simulation results demonstrate that the proposed LDBE performs better than other multiplexing methods regarding these CLR, CDV and CTD criteria for real-time traffic. Furthermore, the proposed LDBE is also suitable for scheduling non-real-time traffic by providing a low CLR for non-real-time variable bit rate (nrt-VBR) and minimizing the CTD for unspecified bit rate (UBR) traffic.

Wavelength Division Multiplex (WDM) photonic networks are expected as key for global communication infrastructure. The accurate measurement methods for AWG-MUX/DMUX are desirable for WDM network design. We measured a transfer function matrix of an AWG-MUX to find that polarization mode dispersion (PMD) and polarization dependent loss (PDL) shows the bandpass characteristics, which may limit the maximum size and the bit rate of the system. These bandpass characteristics of PMD and PDL are reproduced by a simple AWG-MUX model: The phase constant difference of 0.5% between orthogonal modes in arrayed waveguides is sufficient to obtain the measured passband characteristics of PMD and PDL. We find phase distribution difference between two orthogonal modes in the arrayed waveguide grating gives arise to complex PMD.

A new low voltage high-speed CMOS composite transistor is presented. It lowers supply voltage down to |Vt|+2 Vds,sat and considerably extends input voltage operating range and achieves high speed operation. As an application example, it is used in the design of a high-speed four quadrant analog multiplier. Simulations results using MOSIS 2µm N-well process with a 3 V supply are given.

We have been working on a project called ParaBIT (for parallel inter-board optical interconnection technology) to achieve large-capacity switching systems. The ParaBIT module being developed as the first step in this project is a front-end module with 40 channels providing throughput of 28 Gb/s, cost-effectiveness and compactness. To realize the module, this project has developed five novel technologies: (1) 850-nm 10-ch Vertical-cavity Surface-emitting laser (VCSEL) arrays as very cost-effective light sources, (2) new high-density multiport bare fiber connectors that do not need a ferrule and spring, (3) passive optical alignment using polymeric optical waveguide film with a 45-degree mirror for coupling to the optical array chips and the waveguide, (4) transferred multichip bonding to mount optical array chips on a substrate with a positioning error of only a few micrometers, and (5) simple electronic circuits with a fixed-decision-level receiver and an APC-less transmitter, and low power consumption. Experimental results show that the design targets of throughput of 700 Mb/s per channel and a compact and cost-effectiveness structure were met. Thus, ParaBIT is a promising technology for large-capacity switching systems.

We introduce a new methodology for designing block ciphers with provable security against differential and linear cryptanalysis. It is based on three new principles: change of the location of round functions, round functions with recursive structure, and substitution boxes of different sizes. The first realizes parallel computation of the round functions without losing provable security, and the second reduces the size of substitution boxes; moreover, the last is expected to make algebraic attacks difficult. This structure gives us a simple and effective method for designing secure and fast block ciphers in hardware as well as in software implementation. Block encryption algorithm MISTY was designed on the basis of this methodology.

This letter examines outline measures of strength against the differential and linear cryptanalysis. These measures are useful to estimate the number of rounds giving an immune iterated cipher. This letter reports that the outline measures of strength are useful to relatively estimate the strength of generalized feistel ciphers.

Resonant coupling type microstrip line interconnects using a bonding ribbon and dielectric pad have been designed and fabricated. The basic concept of this interconnect is the LC serial resonance of the pad capacitor and ribbon inductor. Both numerical simulation and experiment reveal low return loss and high efficiency connection at the predicted resonant frequency region, which can be readily shifted to higher frequencies by tuning the structural parameters. Improvement in bandwidth of the interconnect is demonstrated by using a pad with higher dielectric constant. Furthermore, it is also shown that a slight modification allows DC connection in addition to efficient coupling at the resonant frequency.

This paper is concerned with radio resource allocation in multiple-chip-rate (MCR) DS/CDMA systems accommodating multimedia services with different information rates and quality requirements. Considering both power spectral density (PSD) over a radio frequency (RF) band and the effect of RF input filtering on the receiver in MCR-DS/CDMA systems, criteria for capacity estimation are presented and the characteristics of co-channel interference between subsystems are investigated. System performance in MCR-DS/CDMA systems is strongly affected by radio resource assignment. A minimum power-increment-based resource assignment scheme for an efficient resource assignment scheme is proposed herein. The performance of this scheme is compared with that of a random-based resource assignment scheme in terms of blocking probability and normalized throughput. The minimum power-increment-based resource assignment scheme yields a better performance than the random-based resource assignment scheme for multimedia services.

This study presents a method that can be used to manage individual pieces of information in large scale distributed geographic information systems (GIS). In a distributed GIS, ordinary users usually cannot alter any of the contents on the server. The method in this study can be used to alter the content or add individual datums onto these types of non-write-permitted data sets. The authors have called it a 'Geographic Differential Script File' (GDSF). A client creates a GDSF, which contains private information that is to be added onto the served data. The client keeps this file on a local disk. When the user employs the data, he applies the differential script sequence onto the downloaded data in order to retrieve the information. GDSF is a collection of graphic operation commands which insert and delete objects as well as modify operations. GDSF also contains modifications of the attribute information of geographic entities. This method can also be used to revise information that is published on ROM media, e. g. CD-ROM or DVD-ROM, as well as in a distributed environment. In this paper, the method and results of applying it are presented.

We analyze the security of iterated 2m-bit hash functions with rate 1 whose round functions use a block cipher with an m-bit input (output) and a 2m-bit key. We first show a preimage attack with O(2m) complexity on Yi and Lam's hash function of this type. This means that their claim is wrong and it is less secure than MDC-2. Next, it is shown that a very wide class of such functions is also less secure than MDC-2. More precisely, we prove that there exist a preimage attack and a 2nd preimage attack with O(2m) complexity and a collision attack with O(23m/4) complexity, respectively. Finally, we suggest a class of hash functions with a 2m-bit hashed value which seem to be as secure as MDC-2.

Recently the study and implementation of elliptic curve cryptosystems (ECC) have developed rapidly and its achievements have become a center of attraction. ECC has the advantage of high-speed processing in software even on restricted environments such as smart cards. In this paper, we concentrate on complete software implementation of ECC over a prime field on a 16-bit microcomputer M16C (10 MHz). We propose a new type of prime characteristic of base field suitable for small and fast implementation, and also improve basic elliptic arithmetic formulas. We report a small and fast software implementation of a cryptographic library which supports 160-bit elliptic curve DSA (ECDSA) signature generation, verification and SHA-1 on the processor. This library also includes general integer arithmetic routines for applicability to other cryptographic algorithms. We successfully implemented the library in 4 Kbyte code/data size including SHA-1, and confirmed a speed of 150 msec for generating an ECDSA signature and 630 msec for verifying an ECDSA signature on M16C.

A novel family of keystream generators is proposed employing a linear cellular automata over GF (q) with time-varying transition rule. The analysis indicates that the generator, which is the general member of the family, reaches standard minimal security conditions (large period and good statistical properties) and that it is secure against all known attacks. An important feature of the proposed generators is that they are compact and suitable for high speed applications.