A new configuration is proposed for an optoelectronic network (OEN) using microwave frequency mixing and multiplexing. The mn OEN consists of m optical sources, m-parallel n-stage cascaded optical intensity modulators, and m-photodetectors. The mn OEN matrix is theoretically discussed, and 12, 22 and 33 OENs are analyzed in detail. The 22 OEN, which mixes and multiplexes microwaves, is further investigated and the theoretical prediction derived from OEN equations is experimentally confirmed.

GDL is the language whose membership problerm is polynomial-time Turing equivalent to the discrete logarithm problem for a general finite group G. This paper gives a characterization of GDL from the viewpoint of computational complexity theory. It is shown that GDL NP co-AM, assuming that G is in NP co-NP, and that the group law operation of G can be executed in polynomial time of the element size. Furthermore, as a natural probabilistic extension, the complexity of GDL is investigated under the assumption that the group law operation is executed in an expected polynomial time of the element size. In this case, it is shown that GDL MA co-AM if G MA co-MA. As a consequence, we show that GDL is not NP-complete unless the polynomial time hierarchy collapses to the second level.

RDES cryptosystem is an n-round DES in which an probabilistic swapping is added onto the right half of the input in each round. It is more effective than a simple increase of DES rounds for a countermeasure against differential attack. In this paper, we show that the RDES is also effective against linear cryptanalysis. We applied Matsui's search algorithm to find the best expression for RDES-1 and RDES-2. The results are as follows: (a) The 16-round RDES-1 is approximately as strong as a 22-round DES, and the 16-round RDES-2 is approximately as strong as a 29-round DES. (b) Linear cryptanalysis for a 16-round RDES-1 and a 16-round RDES-2 requires more than 264 known-plaintexts.

As an optically controlled array antenna, a "two-laser type" using two laser diodes whose frequency difference is set to the desired microwave frequency has been proposed. In this paper, we confirm experimentally that the beamforming network of the two-laser type array antenna has very broadband characteristics by measuring the amplitude and phase of microwave signals at 1.5 GHz, 10 GHz and 20 GHz. Using the optically controlled beam forming network, the radiation pattern of a 4-element linear array antenna was measured at 1.5 GHz.

This paper proposes a new RSA-type scheme over non-singular parts of singular cubic curves En(α,β):(y-αx)(y-βx)x3(mod n). In usual one-to-one communication, we prove that breaking the proposed scheme is not easier than breaking the RSA scheme for the whole ciphertexts. If encryption key e is larger than 19 for 512 bits modulus n, then the proposed scheme is secure against the Hastad attack in broadcast applications. A plaintext of two blocks, i.e., x and y coordinates in En(α,β), is encrypted to a ciphertext of three blocks, where the size of one block is log2n bits. The decryption speed ofthe proposed scheme is as fast as that of the RSA scheme for the even block plaintext.

This paper describes a finite element method to obtain an accurate solution of the scalar Helmholtz equation with field singularities. It is known that the spatial derivatives of the eigenfunction of the scalar Helmholtz equation become infinite under certain conditions. These field singularities under mine the accuracy of the numerical solutions obtained by conventional finite element methods based on piecewise polynomials. In this paper, a regularized eigenfunction is introduced by subtracting the field singularities from the original eigenfunction. The finite element method formulated in terms of the regularized eigenfunction is expected to improve the accuracy and convergence of the numerical solutions. The finite element matrices for the present method can be easily evaluated since they do not involve any singular integrands. Moreover, the Dirichlet-type boundary conditions are explicitly imposed on the variables using a transform matrix while the Neumann-type boundary conditions are implicitly imposed in the functional. The numerical results for three test problems show that the present method clearly improves the accuracy of the numerical solutions.

This paper describes a novel shared file system, whose main features are enhanced security and its concurrency control mechanism. The system is especially suitable for access from mobile hosts. Users can edit their shared files concurrently. Shared files are encrypted and decrypted only by clients, and the file server cannot know the contents. The server asynchronously receives the edited parts, which are already encrypted, and merges them into the current version, deciphering neither the stored file nor the encrypted editing data. We call the mechanism 'privacy enhanced merging'. The mechanism and the underlying encryption algorithm, shared file data structure and procedures followed by clients and the server are shown.

Exploitation of air interfaces for mobile communications is rapidly increasing because of diversified service demands, technology trends and radio propagation conditions. This paper summarizes the radio and optic interaction devices and systems that can solve the future problems resulting from spreading demands in mobile multimedia communications. The concept of the Virtual Free Space Network (Radio Highway Network) is proposed for universal mobile access networks that can support any mobile service or radio air-interface. As one example of the proposed network, the optical TDMA network for radio is analyzed and results of some theoretical calculations are shown.

This paper proposes a novel optical modulator for a millimeter wave (MMW) subcarrier optic link. The modulator enables the bi-phase modulation of MMW subcarriers. It simplifies the optic link by unifying such functions as IF modulation, up-convertion to MMW, and optical modulation, which are separately equipped in a conventional system. A simple model of a Mach-Zehnder external optical modulator (EOM) is used to illustrate how bi-phase modulation of millimeter wave (MMW) subcarriers can be accomplished by switching the EOM bias with a binary data signal. Experimental results are presented to confirm predictions. A wideband communications test system employing the EOM as a bi-phase modulator and utilizing spread spectrum modulation (1.3 µm optical wavelength, 40 GHz subcarrier, 100 MHz chip rate, 10MHz data rate) was developed. Bit error rate (BER) characteristics of an optical link that includes the proposed modulator are presented and compared with ideal performance and simulated predictions. Degradation of the BER characteristics from the simulation was less than 1 dB at a BER of 10-6. A frequency doubling subcarrier bi-phase modulator is also described.

Performances of photodetectors for ultrawide-band systems are outlined. Among several kinds of long-wavelength photodetectors, the waveguide p-i-n photodetector has achieved the largest bandwidth-efficiency product by using two designs: a multimode waveguide and a mushroom structures. The ultrawide-band high-efficiency operation of this photodiode has enabled the construction of a wide-band receiver opto-electronic integrated circuit and has made possible such novel system applications as 20-Gbit/s optical digital transmission using an Er-doped fiber amplifier and a 72-Gbit/s optoelectronic pulse-pattern generator.

This paper reviews some of the recent effort in the area of microwave-optical interaction as applied to enhance the utility of the active integrated antennas and arrays. The paper consists of two parts. In the first part, the optical bias is used as a hidden port to control the characteristics of the active integrated antennas. Two examples will be presented. In the second part, an optical carrier is used for remoting of active integrated antenna for beam control.

External modulators, which have smaller chirping characteristics than laser diode direct modulation, are desired for high-speed and long-distance optical fiber communication systems. This paper reviews semiconductor and Ti:LiNbO3 guided-wave high-speed optical modulators. Since several effects exist for semiconductor materials, various kinds of semiconductor optical modulators have been investigated. Among these, absorption type intensity modulators based on Franz-Keldysh effect in bulk materials and quantum confined stark effect in multiple quantum well materials, are promising because of compactness, low drive voltage nature and integration ease with DFB lasers. Recent progress on semiconductor absorption modulators and DFB-LD integrated semiconductor modulators is discussed with emphasis on a novel fabrication method using selective area growth by MOVPE (Metal Organic Vapor Phase Epitaxy). The Ti:LiNbO3 optical modulators are also important, due to the advantage of superior chirping characteristics and wide bandwidth. Since the Ti:LiNbO3 optical modulator has low propagation loss and low conductor loss natures for optical waves and microwaves, respectively, the traveling-wave electrode configuration is suitable for high-speed operation. Here, broadband Ti:LiNbO3 optical modulators are discussed with emphasis on traveling-wave electrode design.

In this paper, we propose a new method of dialogue data collection which can be used to evaluate modules of a spoken dialogue system. To evaluate the module, it is necessary to use suitable data. Human-human dialogue data have not been appropriate to module evaluation, because spontaneous data usually include too much specific phenomena such as fillers, restarts, pauses, and hesitations. Human-machine dialogue data have not been appropriate to module evaluation, because the dialogue was unnatural and the available vocabularies were limited. Here, we propose 'Hybrid method' for the collection of spoken dialogue data. The merit is that, the collected data can be used as test data for the evaluation of a spoken dialogue system without any modification. In our method a human takes the role of some modules of the system and the system, also, works as the other part of the system together. For example, humans works as the speech recognition module and the dialogue management and a machine does the other part, response generation module. The collected data are good for the evaluation of the speech recognition and the dialogue management modules. The reasons are as follows. (1) Lexicon: The lexicon was composed of limited words and dependent on the task. (2) Grammar: The intention expressed by the subjects were concise and clear. (3) Topics: There were few utterances outside the task domain. The collected data can be used test data for the evaluation of a spoken dialogue system without any modification.

Semi-Orthogonally Associative Memory neural network model (SAM) uses the orthogonal vectors in Un = {-1, 1}n as its characteristic patterns. It is necessary to select the optimum characteristic parameter n so as to increase the efficiency of this model used. This paper investigates the dynamic behavior and error correcting capability of SAM by statistical neurodynamics, and demonstrates that there exists a convergence criterion in tis recalling processes. And then, making use of these results, its optimum characteristic parameter is deduced. It is proved that, in the statistical sense, its recalling outputs converge to the desired pattern when the initial similar probability is larger than the convergence criterion and not true otherwise. For a SAM with N neurons, when its characteristic parameter is optimum, its memory capacity is N/2 ln ln N, the information storage capacity per connection weight is larger than 9/23 (bits/weight) and the radius of attractive basin of non-spurious stable state is about 0.25N. Computer simulations are done on this model and the simulation results are consistent with the results of theoretical analyses.

An optoelectronic beam forming network (BFN) is presented for a single beam, 3-element phased array antenna that utilizes electrically controllable birefringence mode nematic liquid-crystal cells (ECB mode NLC cells) for phase shifting and amplitude control. In the circuit, a microwave signal is carried by a pair of orthogonal linearly polarized lightwaves (signal and reference lightwaves) using the optical heterodyning technique. Birefringence of liquid-crystals is utilized to selectively control the phase of the signal and reference lightwaves. Because an interferometer is formed on a single signal path, the complexity of the optical circuit is much reduced, compared to the BFNs based on arrays of Mach-Zender interferometers. A prototype circuit is built using laser sources of 1.3 µm, and its performance experimentally examined. With small deviations among the three cells, phase shifts of up to 240 degrees are achived for MW signals from 0.9 GHz to 20 GHz with good stability; attenuation of more than 18dB is achieved. An optoelectronic technique for parallel control of amplitude and phase of MW signals was developed.

This paper proposes a photonic integrated beam forming and steering network (BFN) that uses switched true-time-delay (TTD) silica-based waveguide circuits for phased array antennas. The TTD-BFN has thermooptic switches and variable time delay lines. This TTD-BFN controls four array elements, and can form and steer a beam. An RF test was carried out in the 2.5 GHz microwave frequency range. The experimental results show a peak-to-peak phase error of 6.0 degrees and peak-to-peak amplitude error of 2.0 dB. Array factors obtained from the measured results agree well with the designed ones. This silica-based beam former will be a key element in phased array antennas.

This paper describes the performance of a predistorter implementation to a superluminescent diode (SLD) in fiber-optic wireless systems under the optical reflection. SLD intensity noise and 3rd-order intermodulation distortion (IM3) are experimentally compared with those of DFB-and FP-LD. It is observed that the IM3 of SLD has ideal 3rd characteristics and output noise remains unchanged against the number of optical connectors. It is also found that the predistorter reduces IM3 by 8 dB. Receiver sensitivity of the system is discussed from the view point of overall design. the BER performance of an SLD with predistorter using a π/4-QPSK signal as a subcarrier is also described theoretically and experimentally.

This article considers a hybrid data backup model for a file system, which combines both conventional magnetic disk (MD) and write-once, read-many optical disk (OD). Since OD recently is a lower cost medium as well as a longer life medium than the ordinary MD, this kind of backup configuration is just recognized to be important. We mathematically formulate the hybrid data backup model and obtain the closed-form average cost rate when the system failure time and the recovery time follow exponential distributions. Numerical calculations are carried out to obtain the optimal backup policy, which is composed of two kinds of backup sizes from the main memory to MD and from MD to OD and minimizes the average cost rate. In numerical examples, the dependence of the optimal backup policy on the failure and the recovery mechanism is examined.

The authors propose a waveguide π-junction with an inductive wall. Galerkin's method of moments is applied to analyze it and small reflection and desired power division ratio is realized. Good agreement between the calculated result and the measured one verifies the design of a unit π-junction. The characteristics of aπ-junction with a wall are almost the same as those of a conventional π-junction with a post. Important advantage of the new π-junction with a wall is that it can be manufactured in the die-cast process of the waveguide while a post in the conventional one must be attached in an additional process. A 16-way power divider consisting of 8 π-junctions is designed at 11.85 GHz and the characteristics are predicted.

This paper presents a 15-GHz MMIC direct optical injection-locked oscillator (MMIC OILO) with very-wide locking range that uses photosensitive HBTs. The MMIC OILO consists of an HBT and a positive feedback circuit including a Q-damping variable resistor. By utilizing the high-fT/fmax photosensitive HBT, we realize both high-frequency oscillation of 15 GHz and increased equivalent electrical injection power. In addition to increasing the RF injection power, the Q-damping variable resistor effectively reduces the quality-factor of the oscillator, thus realizing the very wide locking range (f) of 567 MHz (f/fosc3.8%). The locking bandwidth of 3.8% is over 10 times wider than that of any yet reported microwave direct OILO. Furthermore, it is shown that the MMIC OILO can also work as a high-gain Q-variable filter photoreceiver by increasing a Q-damping variable resistance over the self-oscillation suppression range.