The application of an active noise control system in a finite-length duct is studied. Previously proposed single-input-single-output systems are inappropriate in this case, because reflection at the terminals degrades the performance, and/or infinite-impulse-response filters are required for perfect noise cancellation. In this paper, we propose a single-input-single-output system applicable to finite-length ducts, which theoretically achieves perfect noise cancellation while using finite-impulse-response filters only. The tap lengths of the filters are as short as the delays between the reference sensor and the secondary source. A useful implementation of the proposed system is also discussed.

When a single-mode LD is subjected to distant reflection, relative intensity noise and the width of the optical spectrum are drastically increased. This phenomenon is known as 'coherence collapse. ' This letter demonstrates that penalty-free operation is possible at 2.5 Gbit/s even when a DFB-LD is in a state of coherence collapse. In addition, an LD in a state of coherence collapse is applied to a situation where signal light suffers from interferometric crosstalk. The results show that the LD reduces the influence of interferometric noise because of its wide spectral width.

Nonlinear characteristics of a DBR (Distributed Bragg Reflector) Cherenkov laser are investigated with the aid of particle simulation, allowing for the nonlinear properties of the electron beam. Numerical results show that the EM power extracted from the cavity is considerably suppressed by the nonlinear effect of the electron beam. Additionally, the extracted EM power is found to be critically dependent on the reflection coefficient of the DBR at the output end. Thus the DBRs at both ends of the cavity should be carefully designed in order to extract the EM power from the cavity efficiently.

Short-circuit photocurrents (ISC) utilizing surface plasmon polariton (SPP) excitation were investigated for the merocyanine (MC) LB film photoelectric device. The device has a prism/MgF2/Al/MC LB film/Ag structure. In the attenuated total reflection (ATR) configuration, SPPs were resonantly excited at the interfaces between MgF2 and Al (MgF2/Al) and between Ag and air (Ag/air). The thickness and the dielectric constants of the layers were evaluated from the ATR measurements. Short-circuit photocurrents, ISCs, as a function of the incident angle of the laser beam were observed simultaneously during the ATR measurements. In the ISC curves, large and small peaks were observed, and the peak angles of the ISC almost corresponded to the dip angles of the ATR curves due to the SPP excitations. Electric fields and optical absorptions in the cell were calculated using the dielectric constants and the film thickness obtained from the ATR measurements. The calculated absorption in the MC layer as a function of the incident angle corresponded to the ISC curve. It was thought that the optical absorption in the MC layer affected directly to the profile of the ISC. Furthermore, the calculated absorption in the cell with the prism and the MgF2 layer exhibited much larger than that of the cell without them. It was estimated that the photocurrents were enhanced by the excitation of SPPs in the ATR configuration.

A new method for measuring the scattering coefficient using a metal-plate reflector was developed in order to provide a non-destructive way for the assessment of microwave materials in free space. By displacing the position of the metal-plate reflector on the specimen to be tested, the incident wave and the scattered wave from the measured area were determined without the influence of extraneous waves such as the direct coupling between transmitting and receiving antennas and scattered waves from background objects. Because the behavior of a metal-plate reflector is similar to that of an optical shutter in optics, our new scattering measurement system enables us to measure both backward- and forward-scattering coefficients of small regions of the specimen for various types of materials in a non-destructive manner. Our study examined the metal-plate size dependence of the complex reflection and transmission coefficients of some dielectric sheet samples. The measured data indicated that the reflection and transmission coefficients of a Bakelite flat plate and Styrofoam sheet were constant for various sizes of metal plates at the X-band.

This paper proposes a new method for reconstruction a shape of skin surface replica from shaded image sequence taken with different light source directions. Since the shaded images include shadows caused by surface height fluctuation, and specular and inter reflections, the conventional photometric stereo method is not suitable for reconstructing its surface accurately. In the proposed method, we choose measured intensity which does not include specular and inter reflections and self-shadows so that we can calculate accurate normal vector from the selected measured intensity using SVD (Singular Value Decomposition) method. The experimental results from real images demonstrate that the proposed method is effective for shape reconstruction from shaded images, which include specular and inter reflections and self-shadows.

We report a new type of electrooptic deflector using lens effect which is able to scan a space in two dimensions. The proposed device was developed from a quasi-velocity-matched electrooptic phase modulator with periodic domain inversion, therefore, it can operate efficiently at a microwave frequency. In the experiments, the demonstration of its operation and applications to ultrafast light control was done at 16.25 GHz.

Investigations were carried out on metalorganic-chemical-vapor-deposition (MOCVD)-grown strained AlGaN/ GaN/sapphire structures using X-ray diffratometry. While AlGaN with lower AlN molar fraction (< 0.1) is under the in-plane compressive stress, it is under the in-plane tensile stress with high AlN molar fraction (> 0.1). Though tensile stress caused the cracks in AlGaN layer with high AlN molar fraction, we found that the cracks dramatically reduced when the GaN layer quality was not good. Using this technique, we fabricated a GaInN multi-quantum-well (MQW) surface emitting diodes were fabricated on 15 pairs of AlGaN/GaN distributed Bragg reflector (DBR) structures. The reflectivity of 15 pairs of AlGaN/GaN DBR structure has been shown as 75% at 435 nm. Considerably higher output power (1.5 times) has been observed for DBR based GaInN MQW LED when compared with non-DBR based MQW structures.

This paper reports the performance of an AC-voltage sensor with a LiNbO3 integrated retroreflective structure based on the Y-junction Mach-Zehnder interferometer. This structure is capable of realizing a low-cost sensor chip because of the small chip size and single optical-fiber connection. In the sensitivity and frequency response evaluation, detection sensitivities of 6.3 µ V / Hz have been measured with a frequency response from 6 Hz to 2 GHz. These measurement limitations were also analyzed theoretically and compared with the experimental results. This unique sensor enables precise voltage measurement in an EMI environment, even inside a computer.

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.

A novel optical technique for the measurement of temperature is proposed. This is accomplished by depositing alternating 1/4 wave layers of silicon nitride and silicon-rich silicon nitride at the end of an optical fiber. These layers of alternating refractive index form the equivalent of a Bragg grating of a high temperature material. When the fiber and the Bragg grating are heated, the Bragg stack expands, and there is a change in the reflective peak wavelength of this wave stack. Thus, the wavelength of peak reflectivity is a function of temperature. Currently, the 15 nm spectral width of the Bragg stacks is achieved in our laboratory, which is conveniently monitored with a CCD solid state spectrometer and the temperature sensor probes can be also multiplexed at separated specific reflection wavelength. In the experiment, the temperatures in excess of 1,100 centigrade have been measured with a resolution of less than 3 centigrade degree.

We investigated the reflection of light caused by sharp bends in optical fiber experimentally. The position distribution of reflection power was measured using an OTDR and an OLCR. We found that the reflection power increased linearly as the logarithm of the bending loss increased, which agrees with expectation from a simple theoretical model. We believe that the light we observed was part of the leaked light, which was reflected between the primary and secondary coatings.

Active frequency-tuning beam-scanning leaky-mode antenna arrays have been demonstrated in this paper. These antennas integrated one or several microstrip leaky-wave antenna elements with a single varactor-tuned HEMT VCO as an active source. Noted that the measured scan angles of the 11 and 14 antennas were approximately 24 and the scanning range of the 12 antenna was 20. Furthermore, reflected wave due to the open end of each leaky-wave antenna element has been suppressed by the symmetric configuration of this antenna array and the antenna efficiency increases. When comparing with the measured radiation pattern of the single element antenna, we found that the 12 and 14 antenna arrays can effectively suppress the reflected power by more than 5.5 dB and 10.5 dB, respectively, at 10.2 GHz. The power gain are more than 2 dB and 3.16 dB higher than the single element antenna with a measured EIRP of 18.67 dBm.

A software system has dynamic adaptability if it can adapt itself to dynamically changing runtime environments. As open-ended distributed systems and mobile computing systems have spread widely, the need for software systems with dynamic adaptability increases. We propose a software model with dynamic adaptability called DAS and its description language LEAD++. The basic mechanism for dynamic adaptability is called adaptable procedure. An adaptable procedure is a special kind of generic procedures (functions) whose methods are selected based upon the state of its runtime environment. Furthermore, control mechanisms of adaptable procedures -- including method selection strategies -- are realized using generic procedures. This sort of reflective architecture enables us to write a dynamically adaptable software system in highly flexible, extensible, readable and maintainable way. LEAD++ is an object-oriented reflective language that provides adaptable procedures and their control mechanisms as its basic language functionalities. We are currently implementing a prototype of LEAD++ as a pre-processor of Java. Using LEAD++, we can systematically describe dynamically adaptable applets, mobile objects, etc.

In this paper we present a rigorous vector 3D lithography simulator METROPOLE-3D which is designed to run moderately fast on conventional engineering workstations. METROPOLE-3D solves Maxwell's equations rigorously in three dimensions to model how the non-vertically incident light is scattered and transmitted in non-planar structures. METROPOLE-3D consists of several simulation modules: photomask simulator, exposure simulator, post-exposure baking module and 3D development module. This simulator has been applied to a wide range of pressing engineering problems encountered in state-of-the-art VLSI fabrication processes, such as layout printability/manufacturability analysis including reflective notching problems and optimization of an anti-reflective coating (ARC) layer. Finally, a 3D contamination to defect transformation study was successfully performed using our rigorous simulator.

This paper describes a new method for permittivity measurement using microwave free-space technique. The general consideration is to measure the amplitudes of transmission and reflection coefficients and calculate the permittivity from the measurement values. Theoretical analysis shows that the permittivity of the sample can be calculated solely from the measurement values of the amplitudes of transmission and reflection coefficients when the sample is prepared with so large attenuation that the multiple reflections between the two surfaces of the sample can be neglected. Using this method, the permittivity measurement can be performed without reflection influence, and on-line measurement of the permittivity becomes possible because the permittivity can be measured instantaneously and without contact with the material.

A method to improve the reflection efficiency of holographic polymer dispersed liquid crystal (HPDLC) is proposed and its effectiveness is confirmed. Controlling the alignment of liquid crystal (LC) in tiny droplets of HPDLC can increase the refractive-index difference between the LC droplet layer and the polymer layer, causing the peak reflectance and reflective spectral width to expand. We observed experimentally that 96% of the light components excluding the scattering loss can be diffracted in a transmission HPDLC device by ordering the LC. In a reflection HPDLC, we found that reflection could be improved by ordering through an applied shear force. Our findings should lead to an improvement in the quality of reflective display devices.

An electroabsorption (EA) modulator array using a double optical-pass (DP) configuration has been developed to obtain high-speed modulation in parallel. Feeding electrical signals from the highly reflective side of the modulator eliminated component assembly problems with lenses and microwave feeder lines. Passive waveguide integration enabled wafers to be cleaved with very short absorbers. The degradation in frequency response was theoretically calculated to be <0. 2 dB compared to that of EA modulators without a passive waveguide. A common upper doping layer in the absorber and passive waveguide regions was introduced to attain high product throughput due to good epitaxial flatness and processing. The integrated 4-channels multiquantum well DP EA modulator array demonstrated high overall performance for a wavelength range from 1545 to 1558 nm. It features a drive voltage of 2 V for 10 dB attenuation, an insertion loss of 12 dB, and 4 channels17 GHz bandwidths for each channel, with low -20 dB crosstalk between adjacent waveguides.

As open-ended distributed systems and mobile computing systems have spread widely, the need for software which can adapt itself to the dynamic change of runtime environments increases. We call the ability of the software dynamic adaptability. We designed and implemented a language LEAD that provides an architecture for dynamic adaptability. The basic idea is to introduce the mechanism which changes procedure invocation dynamically according to the states of runtime environments. Using LEAD, we can easily realize 1) the highly extensible dynamically adaptable applications, and 2) the introduction of the dynamic adaptability into existing applications.

In this paper, a new simulation approach to the analysis of the reflection characteristics on nonuniform transmission lines (NTLs) is presented. The input and output responses in the time domain and the reflection coefficients in the frequency domain are effectively obtained by using the modified central difference (MCD) simulation and the fast Fourier transform (FFT) technique for Gaussian pulse responses. The simulated results for the reflection characteristics of the NTL transformers are in excellent agreements with the theoretical values. By representing both the reflected voltage and the reflection coefficient, it is shown that this approach is useful to analyze for various types of tapered and stepped NTLs.