We will discuss performance optimization of strain and temperature sensors based on long period fiber gratings (LPFGs) through control of the temperature sensitivity of the resonant peak shifts. Distinction between the effects of strain and temperature is a major concern for applications to communication and sensing. This was achieved in this work by suppressing or enhancing the temperature sensitivity by adjusting the doping concentrations of GeO2 and B2O3 in the core or cladding. The LPFGs were fabricated with a CO2 laser by the mechanical stress relaxation and microbending methods. The optimized temperature sensitivities were 0.002 nm/ for the suppressed case and 0.28 nm/ for the enhanced case, respectively. These LPFGs were used for simultaneous measurement of strain and temperature. The result indicates the rms errors of 23 µstrain for the strain and 1.3 for the temperature.

In digital signal processing, bit width of intermediate variables should be longer than that of input and output variables in order to execute intermediate operations with high precision. Then a processor core for digital signal processing is required to have two types of register files, one of which is used by input and output variables and the other one is used by intermediate variables. This paper proposes a hardware/software cosynthesis system for digital signal processor cores with two types of register files. Given an application program and its data, the system synthesizes a hardware description of a processor core, an object code running on the processor core, and software environments. A synthesized processor core can be composed of a processor kernel, multiple data memory buses, hardware loop units, addressing units, and multiple functional units. Furthermore it can have two types of register files RF1 and RF2. The bit width and number of registers in RF1 or RF2 will be determined based on a given application program. Thus a synthesized processor core will have small area with keeping high precision of intermediate operations compared with a processor core with only one register file. The experimental results demonstrate the effectiveness of the proposed system.

We describe FMCW reflectometry for characterization of long optical fibers by using an external-cavity laser diode as a light source. Since the optical path difference between the reference beam and the reflected beam from the optical fiber under test is much longer than the coherence length of the light source, the reference and the reflected beams are phase-decorrelated. As a result, the beat spectrum between the reference and the reflected beams is measured. In the phase-decorrelated FMCW reflectomety, the spatial resolution is enhanced by narrowing the spectral linewidth of the light source and increasing the repetition frequency of the optical frequency sweep as well as increasing the chirping range of the optical frequency sweep. In the experiments, an external-cavity DFB laser is used as a narrow linewidth light source, and the optical frequency is swept by minute modulation of the external cavity length. Long single mode optical fibers are characterized, and the maximum measurement range of 80 km is achieved, and the spatial resolutions of 46 m, 100 m and 2 km are achieved at 5 km, 11 km and 80 km distant, respectively. The Rayleigh backscattering is clearly measured and the propagation loss of optical fiber is also measured. The optical gain of an erbium-doped optical fiber amplifier (EDFA) is also estimated from the change in the Rayleigh backscattering level in the optical fiber followed after the EDFA.

This paper surveys how geometric information can be effectively used for efficient algorithms with focus on clustering problems. Given a complete weighted graph G of n vertices, is there a partition of the vertex set into k disjoint subsets so that the maximum weight of an innercluster edge (whose two endpoints both belong to the same subset) is minimized? This problem is known to be NP-complete even for k = 3. The case of k=2, that is, bipartition problem is solvable in polynomial time. On the other hand, in geometric setting where vertices are points in the plane and weights of edges equal the distances between corresponding points, the same problem is solvable in polynomial time even for k 3 as far as k is a fixed constant. For the case k=2, effective use of geometric property of an optimal solution leads to considerable improvement on the computational complexity. Other related topics are also discussed.

In the paper, a theoretical and experimental investigation of a new type of the in-line optical fiber ellipsometer is described. The discussed device, based on the Sagnac interferometer, has the possibility to detect the changes of full polarisation state. The detection of the polarisation state in real time by a system containing standard single-mode fiber and an appropriate applied modulation technique is a new system property. The device uses interferometric measurement technique based on the fourth Fresnel-Arago's condition, which secures very good system accuracy and stability, also presented in the paper.

An epoxy-modified urethane rubber mixed with carbon particles is now chosen as the millimeter-wave absorber material in our study. The absorption characteristics of the absorber is measured under temperature changes. The weatherability of our absorber is also clarified based on absorption characteristics, thickness and hardness of the sample. As a result of the temperature characteristics of the absorber, the difference of the maximum absorption frequency under temperature changes is about 1 GHz, however the absorption of 20 dB or more is obtained between 54 and 58 GHz. The result of accelerated artificial exposure test is that 2.8% of the thickness of our sample is shrunk after 1000 hour exposure, and the hardness of rubber is hardened with increasing test time. It is also confirmed that the deterioration of the absorption ranges from 1 to 3 dB, although the absorption of about 20 dB is kept at the frequency range. As a consequence, it is confirmed that the wave absorber using the epoxy-modified urethane rubber mixed with carbon particles has good weatherability including our desired temperature characteristics, and it is suitable for outdoor use.

A general analytical expression for describing the growth of the resonant peak wavelengths of long period gratings is derived. The theoretical calculations explain the shift of peak loss wavelengths in the direction of either shorter or longer wavelengths as the induced index change of grating increases. We have calculated and experimentally verified the sensitivity of the resonant peak wavelengths with respect to an overlay index for various grating periods. It is shown that the center wavelength shift of the claddding modes depends strongly on the grating period and the claddding mode order.

It is well known that the electromagnetic interference (EMI) radiated from industrial, scientific and medical (ISM) apparatus seriously degrades the performance of wireless communication systems. In this paper, an ISM-band wireless local area network (WLAN) which employs a direct sequence-spread spectrum (DS-SS) system is designed to be sufficiently robust and reliable to operate in the presence of this EMI. To satisfy this goal, a technique to suppress EMI in the DS-SS system using a multicode transmission and an EMI observation channel is proposed. In the study, the EMI radiated from switching-type microwave ovens (MWO interference) which are ISM apparatus is concerned, and for a tractable investigation, a statistical model to represent MWO interference based on experimental measurement results is employed. As well known that MWO interference exhibits a bursty impulsive characteristic in time, a technique to transmit multiple long spreading codes (multicode transmission) is introduced for the DS-SS system to overcome the burstness of the interference. Moreover, inspired by the broadband in frequency of MWO interference, a technique to estimate the channel MWO interference by means of observing its levels in an adjacent channel is proposed, and this technique is applied to construct a multicode DS-SS receiver which can suppress the channel MWO interference. An evaluation of the bit error rate performance of the proposed multicode DS-SS system is conducted by computer simulation, and the numerical results demonstrate that the proposed DS-SS system can operate effectively even in the presence of MWO interference.

A performance comparison between TCP and UDP in PHS Internet access is made by experiment from a media synchronization point of view. We consider a situation where PHS mobile terminals access H. 263 video and G. 726 audio stored at a media server by a streaming method. PIAFS is adopted as the data link protocol for the PHS wireless channels. We examined how white noise and Rayleigh fading on the PHS channel as well as the Internet traffic affect the performance. For the comparison, we evaluated several performance measures such as the coefficient of variation of output interval, and found that UDP outperforms TCP in almost all cases.

This paper describes a load carrying test for a concrete pipe designed to study the effectiveness of distributed strain measurement using an optical fiber sensor. We performed a load carrying test on a concrete pipe and attempted to detect the distributed strain inside it using an optical fiber sensor mounted inside the pipe. We confirmed that it was possible to detect the strain in a concrete structure by using an optical fiber sensor after a crack had occurred on the concrete surface. This paper shows that measurement using the optical fiber sensor was effective despite great changes in the strain conditions of the measured object over a short distance.

This paper proposes an efficient architecture for fractal image coding processors. The proposed architecture achieves high-speed image coding comparable to conventional JPEG processing. This architecture achieves less than 33.3 msec fractal image compression coding against a 512 512 pixel image and enables full-motion fractal image coding. The circuit size of the proposed architecture design is comparable to those of JPEG processors and much smaller than those of previously proposed fractal processors.

When a micromachine works inside a narrow space inside tubes and equipment such as a microfactory, a microdevice that has a visual function is indispensable. To monitor the minute shapes of microfabrication and microassembly process that are impossible to observe, fiber-optic sensors and actuators for environmental recognition devices have been developed. The devices are designed to allow stereoscopic and microscopic observation and to measure the dimensions of microparts. To achieve these goals and to realize minute structures and functions, we developed environmental recognition devices for microfabrication process with functions of far and near field observation, tactile sensing and tip articulation, for microassembly process with functions of stereoscopic observation and tip articulation. The results show that easy and safe environmental recognition is possible in the narrow spaces of a microfactory.

As a new idea for analyzing the wave scattering and diffraction from a finite periodic surface, this paper proposes the periodic Fourier transform. By the periodic Fourier transform, the scattered wave is transformed into a periodic function which is further expanded into Fourier series. In terms of the inverse transformation, the scattered wave is shown to have an extended Floquet form, which is a 'Fourier series' with 'Fourier coefficients' given by band-limited Fourier integrals of amplitude functions. In case of the TE plane wave incident, an integral equation for the amplitude functions is obtained from the the boundary condition on the finite periodic surface. When the surface corrugation is small, in amplitude, compared with the wavelength, the integral equation is approximately solved by iteration to obtain the scattering cross section. Several properties and examples of the periodic Fourier transform are summarized in Appendix.

This paper shows quantitative evaluation of coupling between a monopole antenna outside a shield case and a strip line inside that for a portable telephone. The amount of the coupling is calculated using FDTD method together width EMF method. This combination of methods can raise the calculation efficiency. Dependence of the coupling on the length of gaps, the height of the strip line and the length of the antenna is clarified. The correspondence between calculated and measured results shows the validity of the calculation.

Nonlinear dynamics of xn+1=λ {4xn (1-xn)}q is studied in this paper. Different from the logistic map (q=1), in the case of q

This paper describes the mechanisms of power-distribution-plane resonance in multilayer printed circuit boards and the techniques to control the resonance. The power-distribution-plane resonance is responsible for high-level emissions and circuit malfunctions. Controlling the resonance is an effective technique, so adequate characterization of the resonance is necessary to achieve control. The resonance characteristics of four-layer printed circuit boards are investigated experimentally and theoretically by treating the power-distribution planes as a parallel-plate transmission line with decoupling circuits. Analysis of the forward traveling wave shows that the resonance frequency is determined by the phase delay due to wave propagation and by the phase progress of interconnect inductance in the decoupling circuit. Techniques to control the resonance characteristics are investigated. The resonance can be shifted to a higher frequency by adding several decoupling circuits adjacent to the existing decoupling capacitor or by increasing the number of via holes connecting the capacitor mounting pads to the power-distribution planes.

The wavelength demultiplexer, using cascaded optical fiber gratings and circulators, was proposed and developed for application to optically amplified wavelength-division multiplexing (WDM) submarine cable systems with 100 GHz channel spacing. Our proposed demultiplexer cannot only achieve high wavelength selectivity, small excess loss and effective allocation of dispersion compensation fibers for each channel, but also be upgraded without affecting other existing channels. By using this demultiplexer, it has been successfully confirmed that 8 WDM channels were demultiplexed even after 6,000 km transmission including separate compensation of accumulated chromatic dispersion in each channel.

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.

A new sensing method for measuring directly flow velocity by using low coherence interference techniques is proposed and demonstrated. In this method, a temporally fluctuating signal, not the Doppler frequency shift, is detected. Theoretical analysis shows that a spectrum of light backscattered from a particle takes a Gaussian form whose width is simply proportional to the flow velocity. The measured velocity is in good agreement with the actual flow velocity derived from the flow rate. The dynamic range of this sensing method is governed by the frequency range of the FFT processor used and is estimated to be 1.4 10-4 14 m/s. The depth position can be adjusted with an accuracy of approximately 30 µm which is determined by the coherence length of the light source. The velocity distribution along the depth is easily measured by changing mechanically the length of the reference arm in the low coherence interferometer.

We review public-key cryptosystems from lattice problems, which are inspired by Ajtai's remarkable result, and consider their security from the point of view of both theory and practice. We also survey recent results on the power of the lattice reduction algorithm in cryptanalysis.