摘要:

AbstractA method for analysis of natural single‐phase unidirectional transducer (NSPUDT), which is one of unidirectional surface acoustic wave interdigital electrodes, is proposed in which the mode coupling theory and the finite‐element method are used. the finite‐element method is used for calculations of the upper and lower limit frequencies of the stop band, the potential standing wave distribution at these frequencies, and the static capacitance per electrode pair for the short and open gratings corresponding to the electric terminals either shorted or open. In the substrate used for NSPUDT, the locations of the maximum and minimum of the standing wave in general vary in the depth direction of the substrate. Hence, it is not possible to use the standing wave pattern in the substrate as is used for a substrate surface where electrodes are present. the variation of the potential in the depth directional of the substrate is incorporated into the mode coupling theory in this research, so that the depth dependence of the standing wave profile is qualitatively evaluated. Hence, it is made possible to confirm the locations of the maximum and minimum of the standing wave at the substrate surface from the standing wave profile in the substrate.Specifically, the present method is applied to NSPUDT on an ST‐cut 25deg; X‐propagation quartz substrate so that its validity and usefulness are

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractA new reflectometry method is proposed which enables measurements of light‐reflection‐distributions with spatial resolutions below tens of micrometers. the method can be applied to the detection of the damaged point of optical fibers, optical integrated circuits (ICs), reproduction of optical waveguide three‐dimensional memories, etc. By consideration of the coherency of a multimode laser, it becomes possible to construct the reflectometer without the need for frequency scanning of the optical source and movable parts.The interference light from the Michelson interferometer or from the interfaces of the multilayer object are analyzed (by the spectrometer) and square detected to obtain the interferospectrum of the interference light. Using the property that the interferospectrum is the duplicate of the reflection distribution, the Fourier inverse transform of the reflection distribution is carried out and the “spatialgram” is reproduced. the spatial resolution is determined by the inverse of the spectrumwidth of all modes. Therefore, even if a common multimode laser diode, available on the market with all‐mode spectrum‐width of 10 nm is used, the high resolution of about 34 μm can easily be achieved. Numerical results of the theoretical analysis of reflections, in the frequency domain, also

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractResearch and development of optical circuit elements become important as the degree of integration of the optical circuit is advanced. Since the optical devices are integrated and become more complex and as optical circuit elements with high index difference begin to appear, the conditions of the weakly guided wave and of the reflectionless wave no longer hold rigorously. Hence, rigorous numerical analysis is needed.One of the analysis methods for the optical circuit elements is the finite‐difference time‐domain (FD‐TD) method. Recently, as a generalization of the FD‐TD method, the nonorthogonal FD‐TD method has been proposed. In this paper, the optical circuit elements are analyzed by means of the nonorthogonal FD‐TD method which is capable of analyzing optical circuit devices with various shapes. First, tapered waveguides are analyzed. the results are compared with those by the beam propagation method (BPM) and the characteristics with respect to the tapered angle are derived. Next, a directional coupler with a high refractive index difference is analyzed. the effectiveness of the present method for the coupling characteristics i

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe longitudinal type optical voltage sensor made of Bi12GeO20(BGO) crystal is often used in practical applications because it has a large electrooptical coefficient γ41, temperature stability, and no natural birefringence. Since this electrooptic crystal has large optical rotary power, sensitivity degrades when the crystal is thick. However, if optical rotary power is utilized, it is possible to control arbitrarily the temperature coefficient × of the sensor sensitivity. It was proved theoretically that the temperature coefficient of sensor sensitivity was dependent on the temperature coefficient β of the half wavelength voltage Vπ, the temperature coefficient β of the optical rotary angle θ0 the crystal thickness d (optical rotary angle θ0), and the cut angle θ. In addition, in order to verify the theory, × was determined by evaluating a sensor at temperatures ranging from ‐20 to 80°C. As a result, it was found that the value of × varied arbitrarily from ‐7.6 × 10−4to +

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe optimum operating condition of a Peltier cooling system was accurately derived by using a thermoelectric differential equation developed by the author. Using the obtained result, the influences of the Peltier device current and length on the cooling characteristic were analyzed. One of the most serious drawbacks of the Peltier cooling system is the low value of COP; an increase of COP is the most important issue in designing a cooling system. the optimum operating condition described herein is that operation limit which provides maximum COP. When a large temperature difference is required, multiple stages of Peltier devices connected in cascade are used. Therefore, theoretical analysis for cascade structure used arbitrary N stages.

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIt is found that liquid crystal microdroplets become uniform and their sizes are reduced if the substrates are coated with some undercoating film before forming polymer‐dispersed liquid crystal using the photopolymerization‐induced phase separation method.In this study, polyvinylalcohol was used for the undercoating film because it has good wetting property to the liquid‐crystal material, resulting in suppression of nonuniform nucleation and growth of the microdroplets. In the polymer‐dispersed liquid crystal formed under ultraviolet (UV) irradiation with 10 mW/om2, the diameter of the liquid‐crystal droplets varied in a range up to approximately 6 μm without using an undercoating film while the variation of the droplet diameters became less than 2 μm when the undercoating film was used. As a result, the threshold characteristic in the electrooptic property, response time, spatial resolution, and film uniformity were improved drastically by using the undercoating film. By using the polymer‐dispersed liquid crystal formed in this new method, a high limiting resolution (as high as 128 1p/mm) was achieved. the polymer‐dispersed liquid crystal formed in this way is expected to be used for projection displays with high resolution and

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractIt is known that the anodic oxidation of Hf proceeds by the diffusion of anions into Hf thin film and is affected by the other overlayered films existing on Hf in multilayered anodized thin‐film capacitors. to characterize multilayered thin oxide film structures necessary for the fabrication of high‐quality capacitors, a correlation between dissipation factor and oxidation process has been investigated as a function of anodization voltage and thinfilm thicknesses of Al/Ta/Hf and Ta/Al/Hf multilayers.The results indicate that thin‐film capacitors with low dissipation factor can be obtained by anodizing Al/Ta/Hf thin films so long as their original multilayered structures are maintained during anodization and the Ta intermediate layer acts as a transport medium of oxygen ions for the bottom Hf layer. With increasing anodization voltage, Ta ions migrate toward the surface of the multilayer, which alters the original multilayered structure and contributes to higher dissipation factor.When the intermediate layer is Al such as in the case of Ta/Al/Hf multilayer capacitors, the flow of oxygen ions to the bottom Hf layer is restricted during anodization by the formation of an oxidized Al layer and this makes the dissipation factor higher. It has been concluded that in order to fabricate thin‐film capacitors with low dissipation factor, it is vital to have the presence of an intermediate layer such as Ta which has a lower heat of formation for oxidation

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractOptical communication systems underwent rapid development during the 1980s, and 10‐Gb/s systems are now being developed. Furthermore, asynchronous transfer mode (ATM) technology is being applied to the development of transport nodes with throughputs of 20 to 100 Gb/s for communications networks. However, such speeds are close to the limits of what can be achieved with systems based on electronic processing and, in the near future, it will become necessary to change over to photonic networks in which processing is done optically. Photonic networks are not just characterized by high speed and wide bandwidth; it is also possible to build them with a simple yet flexible configuration. This paper gives an overview of how photonic technology can be introduced in different parts of a network, including the core network, the access network, and private networks, and describes the areas requiring further research. Research into fundamental devices is also progressing, and research into photonic networks is also being actively pursued in the West. Photonic networks will form the foundation of wideband networks in the next century, and their research is extremely importan

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771208

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThis paper investigates the effect of channel‐to‐channel interference in optical frequency division multiplexing (FDM)‐homodyne detection systems that use optical filters for densely‐spaced optical FDM systems. Power penalties at BER = 10−9for double‐sideband (DSB), single‐sideband (SSB), and vestigial‐sideband (VSB) signals were evaluated by approximating the channel‐to‐channel interference as Gaussian noise. the authors investigated four cases: where no optical filter was used; where an optical channel selection filter was used at the receiver, where an optical filter suppressing spectrum broadening was used for each channel before multiplexing at the transmitter; and where both of these filters were used. It has been shown that using an optical filter before multiplexing is effective for reducing channel spacing. the optical filterings are effective especially for SSB and VSB signals. Extremely densely‐spaced multiplexing with a channel spacing of less than twice the bit rate can be achieved with a power penalt

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771209

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY

摘要:

AbstractThe purpose of this paper is to examine the occurrence mechanism of the current runaway phenomenon in the overcurrent limited mode of the dc‐dc converter with current injected control. Taking into account the time delay in the turn‐off instant of the switch, which is due to the dead time and the time constant of the control circuit and the dead time of the switch, this phenomenon is analyzed.As a result, it is clarified that there exist two operation modes in the overcurrent limited mode of the dc‐dc converter with current‐injected control; in one mode, the current limiting characteristics are affected by only the dead time of the control circuit and the switch and, in the other one, both the dead time and the time constant of the control circuit and the dead time of the switch have an effect. the current runaway phenomenon occurs in the latter mode. the boundary condition of these two modes is defined. Consequently, the design criterion is presented to prevent the current runaway phe

ISSN:8756-663X    

DOI:10.1002/ecjb.4420771210

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1994

数据来源: WILEY