We fabricated a 1.55-µm polarization insensitive Michelson interferometric wavelength converter (MI-WC). The MI-WC consists of a two-channel spot-size converter integrated semiconductor optical amplifier (SS-SOA) on a planar lightwave circuit (PLC) platform. Clear eye opening and no power penalty in the back-to-back condition were obtained at 10 Gb/s modulation. We also confirmed the polarization insensitive operation on the input signal. Moreover, for an application of the MI-WC to DWDM networks, we demonstrated the selective wavelength conversion of 2.5 G/s optical packets from Fabry-Perot laser diode (FP-LD) light to four ITU-T grid wavelengths. We confirmed the good feasibility of this technique for use in DWDM networks. The wavelength conversion we describe here is indispensable for future all-optical networks, in which optical signal sources without wavelength control will be used at user-end terminals.

For the purpose of equalisation of rapidly time variant multipath channels, we derive a novel adaptive algorithm, the amplitude banded LMS (ABLMS), which implements a non-linear adaptation based on a coefficient matrix. Then we develop the ABLMS algorithm as the adaptation procedure for a linear transversal equaliser (LTE) and a decision feedback equaliser (DFE) where a parallel adaptation scheme is deployed. Computer simulations demonstrate that with a small increase of computational complexity, the ABLMS based parallel equalisers provide a significant improvement related to the conventional LMS DFE and the LMS LTE in the case of a second order Markov communication channel model.

This paper proposes three MAC protocols over APON to provide residential and small business customers with multimedia services. The proposed protocols support the frame structure of ITU-T recommendation G.983.1 and also provide diverse ATM service classes such as CBR, rtVBR, nrtVBR, ABR, and UBR traffics. Each service is allocated on the basis of priority. Especially, for allocating CBR and rtVBR services, each protocol uses different cell arrival timing information which is achieved with specific coding and ranging procedure. Focusing the difference of cell arrival timing information, we will investigate the performance of proposed protocols. For the proposed MAC protocols, we present grant field format, minislot format, and bandwidth allocation algorithm. Computer simulation shows the performance of the proposed protocols in terms of CDV and delay, comparing with the normal FIFO protocol.

This letter points out some flaws in the previous works on UKS (unknown key-share) attacks. We show that Blake-Wilson and Menezes' revised STS-MAC (Station-to-Station Message Authentication Code) protocol, which was proposed to prevent UKS attack, is still vulnerable to a new UKS attack. Also, Hirose and Yoshida's key agreement protocol presented at PKC'98 is shown to be insecure against public key substitution UKS attacks. Finally, we discuss countermeasures for such UKS attacks.

In this letter we propose a filter for extracting a quasi-periodic signal from a noisy observation using wavelets. It is assumed that the instantaneous frequency of the signal is known. A particularly difficult task when the frequency and amplitude of the desired signal are varying with time is shown. The proposed algorithm is compared with three other methods.

We propose an adaptive complex-amplitude texture classifier that takes into consideration height as well as reflection statistics of interferometric synthetic aperture radar (SAR) images. The classifier utilizes the phase information to segment the images. The system consists of a two-stage preprocessor and a complex-valued SOFM. The preprocessor extracts a complex-valued feature vectors corresponding to height and reflectance statistics of blocks in the image. The following SOFM generates a set of templates (references) adaptively and classifies a block into one of the classes represented by the templates. Experiment demonstrates that the system segments an interferometric SAR image successfully into a lake, a mountain, and so on. The performance is better than that of a conventional system dealing only with the amplitude information.

A constant amplitude transmission scheme for multicode wideband CDMA systems is proposed. Multicode wideband CDMA systems result in large amplitude fluctuation because the multicode signal is the sum of constituent code channel signals. This large amplitude fluctuation brings out large non-linear distortion and then, if unaccounted, can significantly degrade the bit error rate (BER) performance. Constant amplitude transmission, achieved by using a Walsh code and parity generator, is proposed to combat the large amplitude fluctuation and reduce the peak-to-average power ratio (PAPR). Unlike other constant amplitude transmission scheme, the proposed scheme does not use a redundant code channel. Computer simulation results show that the proposed scheme improves BER performance significantly and that the proposed scheme is extremely effective to the non-linear distortion of high power amplifier (HPA).

In this letter, the constant amplitude transmission for orthogonal multicode systems is discussed. In order to obtain the high power efficiency, we require the high power amplifier which has non-linear characteristic. The nonlinear distortion, however, may occur because of the multicode signals having large amplitude fluctuations. If we can achieve the constant amplitude transmission, the nonlinear distortion can be neglected. In this letter, I investigate the property of the information bit streams that can achieve the constant amplitude transmission and show that the bent sequences can achieve the constant amplitude transmission.

This paper analyzes a generalized secret-key authentication system from a viewpoint of the information-spectrum methods. In the generalized secret-key authentication system, for each n 1 a legitimate sender transmits a cryptogram Wn to a legitimate receiver sharing a key En in the presence of an opponent who tries to cheat the legitimate receiver. A generalized version of the Simmons' bounds on the success probabilities of the impersonation attack and a certain kind of substitution attack are obtained.

Medium noise is the dominant noise in ultrahigh density disk recording systems. The peak, width and jitter noise are analyzed by micromagnetic simulations. Four different media, with a fixed grain size of 135 and a coercivity of 2900 Oe, are chosen for medium noise analysis. The linear recording density is increased from 340 KFCI (Kilo flux-changes per inch) to 750 KFCI, while the area density goes up from 14.3 Gb/in2 to 31.5 Gb/in2. The peak-amplitude noise is studied by the distribution of the peak magnetization Mp in each bit. The distribution of Mp develops from a delta-function around the remanence Mr at low densities to a flat distribution at extremely high densities. It is found that the transition a-parameter is no longer proportional to the square root of Mrδ, as given in the William-Comstock approximation. The peak-jitter noise in the read back voltage is analyzed by the percentage of the transition jitter in a bit length.

Magnetic layer thickness dependences of magnetic properties are investigated for Co-Cr-Pt polycrystalline thin films with different Cr-alloy underlayers (Cr-Ti, Cr-W, Cr-Mo, Cr-V, Cr-Mo-V). The specimens with Cr-Ti, Cr-V, and Cr-Mo-V underlayers show higher coercivities by about 30% and lower activation magnetic moments than those with Cr-Mo underlayer. The effective diameter of activation volume increases by 10-20% when the magnetic layer thickness is decreased from 12 to 8 nm. Temperature dependences of magnetic properties are also determined and discussed by referring to the data obtained using single crystal magnetic thin films with similar composition.

This paper provides the Shannon theoretic coding theorems on the success probabilities of the impersonation attack and the substitution attack against secret-key authentication systems. Though there are many studies that develop lower bounds on the success probabilities, their tight upper bounds are rarely discussed. This paper characterizes the tight upper bounds in an extended secret-key authentication system that includes blocklength K and permits the decoding error probability tending to zero as K . In the extended system an encoder encrypts K source outputs to K cryptograms under K keys and transmits K cryptograms to a decoder through a public channel in the presence of an opponent. The decoder judges whether K cryptograms received from the public channel are legitimate or not under K keys shared with the encoder. It is shown that 2-KI(W;E) is the minimal attainable upper bound of the success probability of the impersonation attack, where I(W;E) denotes the mutual information between a cryptogram W and a key E. In addition, 2-KH(E|W) is proved to be the tight upper bound of the probability that the opponent can correctly guess K keys from transmitted K cryptograms, where H(E|W) denotes the conditional entropy of E given W.

In this paper, we propose a projection based design of near perfect reconstruction QMF banks. An advantage of this method is that additional design specifications are easily implemented by defining new convex sets. To apply convex projection technique, the main difficulty is how to approximate the design specifications by some closed convex sets. In this paper, introducing a notion of Magnitude Product Space where a pair of magnitude responses of analysis filters is expressed as a point, we approximate design requirements of QMF banks by multiple closed convex sets in this space. The proposed method iteratively applies a convex projection technique, Hybrid Steepest Descent Method, to find a point corresponding to the optimal analysis filters at each stage, where the closed convex sets are dynamically improved. Design examples show that the proposed design method leads to significant improvement over conventional design methods.

In this paper, a modified neural network approach called the Guided Neural Network is proposed for the longitudinal dynamics identification of a vehicle using the well-known gradient descent algorithm. The main contribution of this paper is to take account of the known information about the system in identification and to enhance the convergence of the identification errors. In this approach, the identification is performed in two stages. First, the Guiding Network is utilized to obtain an approximate dynamic characteristics from the known information such as nonlinear models or expert's experiences. Then the errors between the plant and Guiding Network are compensated using the Compensating Network with the gradient descent algorithm. With this approach, the convergence speed of the identification error can be enhanced and more accurate dynamic model can be obtained. The proposed approach is applied to the longitudinal dynamics identification of a vehicle and the resultant performance enhancement is given.

An analytical error characteristics of GPS compass which determines heading and elevation of the vehicle using carrier phase measurements from 2 antennae is given. It is also shown that to obtain more precise heading, longer baseline along the vehicle is preferred and the accuracy of heading is always better than that of elevation since the vertical measurement uncertainty caused by geometry of satellites affects only on that of elevation. These results can be applied as basic directions for attitude determination: to what direction should the baseline be located to minimize the error, which satellites should be selected to minimize the error.

A low-cost technique using commercial UV grade silica fibers to construct microlens array that is suitable for mass-production of long-period gratings is reported. The growth rate of gratings fabricated using these arrays is much faster than the conventional amplitude masks. Our previous work had shown that this technique was 400% more efficient than the metal mask technique. Further improvement of this grating writing technique using plano-convex microlens array is reported in this paper. Under the same writing conditions, long-period gratings with absorption peaks of 1.5 dB and 17 dB were fabricated by using a microlens array and a plano-convex microlens array, respectively.

A novel technique has been developed for in situ sensing of thin film growth. In this method, a fiber optic probe is placed at an appropriate position in a deposition chamber, and the thin film builds up on the end of the fiber. This film is either the same as on the wafer where deposition occurs, or it bears a fixed relationship to the film on the wafer. By an analysis of the intensity of the light reflected from the film and guided by the fiber, information on the film may be obtained. With interference causing maxima, minima and a point of inflection as the film grows, it is possible to obtain near real time information on the following quantities: the real and imaginary parts of the refractive index of the film, a Gaussian parameter characterizing surface roughness, and the film thickness itself. To demonstrate this technique, we have studied the deposition of silicon nitride films in a CVD reactor and how reactor temperature and reactant flow rates influence film growth. This technique may be applied to measure in situ reflectivity of multi layer films, so that reflectance as a function of temperature and time may be obtained. Because the measurement is simple and direct and the information is optical, we believe that this technique has the potential to supplant quartz oscillators in the measurement of thin film growth.

In this paper, we review recent developments in interferometric fiber-optic gyroscopes for industrial applications. These gyroscopes use only elliptical-jacket or elliptical-core polarization-maintaining-fibers to make their optical systems immune to environmental effects, and they use open-loop or closed-loop signal processing circuitry. We have begun mass production of a gyroscope for automotive navigation and location systems. The more accurate gyroscopes have been applied to a number of consumer applications such as attitude control systems of unmanned agricultural helicopter, pipe-mapping and north-finding systems. For further enhancement in terms of size, cost, and accuracy, we have developed an application specific integrated circuit and an integrated optical circuit.

The statistical behavior of the amplitude probability distribution of intermodulation distortion interference in multichannel optical-cable TV systems was experimentally investigated. In multichannel transmission, the non-linearity of a laser diode (LD) or an electrical amplifier can cause intermodulation distortion (composite-second-order beat; CSO, composite-triple-beat; CTB, etc. ). Even though it has been discussed as laser-clipping distortion, intermodulation distortion is usually distortion from AM-VSB carriers. The statistical analysis and evaluation of the distortion in transmitted channel is in controversial. We evaluated the distortion in 20 frequency-division-multiplexed 16-QAM channels, with each carrier carrying 80 Mbps for an optical cable TV system. We first enumerated the distortion components causing interference in each transmission channel so as to identify the intermodulation products. Then, in selected channels, we precisely measured the power of each kind of distortion and the amplitude distributions of the intermodulation distortion from sinusoidal and digital-modulated carriers on cable TV as a function of optical modulation depth (OMD) of LD. And we clarified how the probability distribution function (PDF) changed as the OMD increased. Also, the BER performance of a 16-QAM signal was measured and compare to the intermodulation behavior of the different distortion sources. We found evidence that the amplitude distribution of intermodulation distortion from digital carriers differs from that of thermal noise. Experimental results showed that the PDF of the intermodulation distortion changed when the ratio of intermodulation distortion among all undesired signals varied with the OMD. The BER performance varied with intermodulation of both analogue and digital carriers even when the carrier to interference noise power ratio (CIR) is the same.

The statistical behavior of the amplitude probability distribution of intermodulation distortion interference in multichannel optical-cable TV systems was experimentally investigated. In multichannel transmission, the non-linearity of a laser diode (LD) or an electrical amplifier can cause intermodulation distortion (composite-second-order beat; CSO, composite-triple-beat; CTB, etc. ). Even though it has been discussed as laser-clipping distortion, intermodulation distortion is usually distortion from AM-VSB carriers. The statistical analysis and evaluation of the distortion in transmitted channel is in controversial. We evaluated the distortion in 20 frequency-division-multiplexed 16-QAM channels, with each carrier carrying 80 Mbps for an optical cable TV system. We first enumerated the distortion components causing interference in each transmission channel so as to identify the intermodulation products. Then, in selected channels, we precisely measured the power of each kind of distortion and the amplitude distributions of the intermodulation distortion from sinusoidal and digital-modulated carriers on cable TV as a function of optical modulation depth (OMD) of LD. And we clarified how the probability distribution function (PDF) changed as the OMD increased. Also, the BER performance of a 16-QAM signal was measured and compare to the intermodulation behavior of the different distortion sources. We found evidence that the amplitude distribution of intermodulation distortion from digital carriers differs from that of thermal noise. Experimental results showed that the PDF of the intermodulation distortion changed when the ratio of intermodulation distortion among all undesired signals varied with the OMD. The BER performance varied with intermodulation of both analogue and digital carriers even when the carrier to interference noise power ratio (CIR) is the same.