A method to estimae the coupling length of the fiber in which modes couple each other due to the random bending of fiber axis is given. The coupling length is estimated from the comparison of the measured transfer function to the theoretical one which is derived previously. The coupling length of a graded-index fiber is estimated to be about 0.8 km using this method. Further, the coupling length of recent graded-index fibers is presumed to be about several Km. For step-index fibers, it is estimated to be in the range between 0.5-5 Km.

We describe the use of integrated optical waveguides for the study of locally illuminated superconductors. The creation of optically controlled Josephson junctions is discussed.

A nonlinear modified Laplacian operator for ridgeline extraction in a picture is proposed. The operator shows better performance in enhancing the ridgeline and suppressing noise compared with the conventional Laplacian operator.

Detailed investigation has been made of a surface acoustic wave FM demodulator in which the phase difference between the input and output signals of a SAW delay device is detected. Total harmonic distortion of the audio output signal is measured to be 0.05%, a value comparable with best commercial practice with demodulators operating at a frequency deviation of 75 KHz with a center frequency of 10.7 MHz. Distortion mainly consists of evenorder harmonic components which are less objectionable to a listener than the odd-order harmonic components found in conventional high quality FM demodulators. Analysis shows that the distortion can be reduced reducing both the amplitude of the SAW spurious signals and the delay time difference between the spurious and main delay signals. The spurious SAW signals of concern included those from direct feed-through, triple-transit echoes, bulk waves, and edge reflections. Techniques for reducing or eliminating these are described. Calculated results are in fairly good agreement with experiment.

In this research, design concepts of a parallel processing oriented FFT processor are suggested. Problems of previous FFT harware and previous FFT algorithms are pointed out in the aspect of parallelism in the FFT. Solving such problems, an array hardware structure for parallel processing in butterfly operations is proposed, and a two-dimensional FFT algorithm for parallel processing in data permutations is also proposed. The new FFT algorithm derived from a two-dimensional Fourier transform permits a data permutation by the exchange of butterfly algorithms. The proposed array structure and the algorithm provide highly parallel processing suited for high speed FFT on a large number of data, and eliminate hardware for butterflying and data permutating.

In this paper, a mechanism of the frequency variation during a pulse in TRAPATT oscillators and some methods for suppressing the frequency variation are demonstrated theoretically and experimentally. A model for explaining the frequency variation during a pulse is proposed, in which the avalanche delay time varies with the temperature variation so that the frequency varies. It is shown that this model is reasonable to explain the frequency variation during a pulse by a comparison between the frequency variation estimated from the model and directly measured one. It is shown that the model can also well explain the suppression mechanism how the frequency variation can be suppressed by the use of distorted bias pulse. This suppression phenomena have been already confirmed experimentally and reported by the authors. Moreover, possibilities of suppressing the frequency variation by controlling diode parameters are discussed. It is shown that the frequency variation can be suppressed by emphasizing a temperature depenedence or a time dependence of diode parameters causing an avalanche, such as the reverse current.

Design theory of coupled-waveguide optical modulator/switch with pn junction is presented for a new structure with two parallel strip-loaded channel waveguides, and numerical analyses on GaAs and GaAs-AlxGa1-xAs devices at 1.06µm are carried out. It is analyzed that P/f (modulating power per bandwidth) is much smaller in this device than in its predecessor with multi-layered structure in planar waveguide configuration, and that promising devices with P/f for 100% modulation as low as 22 µW/MHz can be designed within the limits of present fabrication technology.

The mechanism of reflection of radio waves from the anisotropic lower ionosphere with exponential profile has been investigated over a wide frequency range from ELF (extremely low frequency) to LF (low frequency) by means of a full-wave method. The reflection levels deduced from the full-wave study have been compared with those which are analytically obtained from the concept of the modified refractive index for the isotropic ionosphere.

We propose a preorder tree which satisfies an order relation: Keys placed at nodes appear in lexicographic order, when the tree is traversed in preorder. Algorithms for search, insertion and deletion are given. The number of key comparisons in the search is investigated theoretically and by simulation studies and compared with the case of binary search trees. We also give an algorithm for constructing a preorder tree which minimizes the number of key comparisons. Simulation experiments confirm the effectiveness of optimization.

This paper describes the orbit utilization increase by virtue of side-lobe reduction in a homogeneous geostationary satellite link. The antenna side-lobe envelope may conveniently by expressed by next two cases: the slope of the side-lobe envelope is enlarged from α to α' (Case ), and the side-lobe level is reduced by a uniform factor of β (Case ). If the total interference noise temperature for the system with equal spacing θ is assumed to be equal to that for the system with shortened spacing owing to the side-lobe reduction, the relationship between orbit utilization increase U and antenna gain function can be obtained by a straight forward way. In this paper, U is given for the cases where side-lobes are reduced at, () earth stations, () satellites, and () earth stations and satellites. Numerical examples are given assuming the orbit spacing θ of 3, earth antenna beamwidth of 0.16, and satellite antenna beamwidth of 1.0. It is quantitatively concluded that the side-lobe reduction is very effective for increasing the orbit utilization.

Surface acoustic wave (SAW) propagations along V/V Waveguides at an angle 30 to Z crystal axis on Y-cut LiNbO3 were observed by the FTH method, and the results showed the efficient guiding effect of the waveguides. On the multi-moded waveguides, complicated SAW propagation patterns were observed, and were expected to be related to the higher-order-mode excitations. The mode excitations at the entrance of the waveguide were studied theoretically by the method of a modal analysis, and the theoretical propagation patterns on the waveguides were found to be fairly consistent with the observed patterns.

In This paper, the accuracy of the transverse interference method has been raised up by fully correcting a probing ray refraction due to the index gradient of the fiber. A simulation shows that the error is in principle within 0.3% of the index difference between the core center and the cladding. The index profiles of some fibers were practically measured and it was confirmed that this method can be used for a precise, nondestructive, and fast measurement.

Some power spectral reshapings of digital coded signals caused by changing the input statistics are treated in this paper. After presenting a power spectral calculation method directly applicable to a Mealy-type encoding automaton, we have shown that it is possible for some transmission codes to have spectral nulls at submultiples of pulse repetition frequency if the set of input sequences are restricted appropriately. The condition for a given transmission code to have such a property is also referred. Secondly, it is proven that discrete line spectra can be generated for some transmission codes if the set of input sequences are properly restricted. As an illustration, we have shown that bipolar coded parity check code sequences produce line spectra, although bipolar coded sequences with independent inputs do not.

Two new types of biquadratic active RC filters are presented. The Q sensitivities of the filters with respect to the passive elements can be made zero. The filter structures are canonic. The amplifier gains required are moderate values.

The backscattering of a spherical wave which is incident on a random medium with large-scale fluctuations is studied. The spatial correlation function of the backscattered field taking account of the effect of the multiple scattering is obtained theoretically in the closed form for an arbitrary fluctuation of the medium. The dependence of the spatial correlation function on the medium fluctuation is clearly shown. The multiple scattering effects on the backscattered field received by a point and finite apertures are also considered by using the spatial correlation functions, and it is shown that as the aperture size increases the results tend to those for the plane wave case.

Theoretical and experimental studies on power flow in a bent step index fiber are made. Theoretical study is made on a slab model under the condition that mode conversion occurs at joints between straight parts and bent parts of a fiber. It is assumed that the propagation angle deviation by mode conversion depends both on the propagation angle and the curvature radius of the bent part. The power flow equation in a partially bent fiber is derived and solved generally by series expansion. Theoretical mode power distributions at different propagation lengths are compared with the experimental results and they are in good agreement with each other. The mode power distribution expressed by the first term of the series, which is considered to be the theoretical steady state mode power distribution, is observed experimentally.

Dependence of the conduction properties of Al-Al2O3-Au sandwich structure on ambient gas pressure was investigated. It was found that the diode current decreases with time nearly exponentially in oxygen atmosphere and that the relaxation time is a function of oxygen pressure and applied voltage.

In ceramic samples of YIG, an anomalous behavior of photo-induced effect on permeability was observed at 77K: the peak at the beginning of xenon flash and then usual decrease in permeability were detected. This can be explained by the maximum of free electrons during flash time.

Experimental results of atmospheric light transmission tests for three years, from March 1970 to March 1973, are described. The experiments were performed in the downtown area of Tokyo. A He-Ne laser at the wavelength of 0.63 µm and a light emitting diode at the wavelength of 0.85 µm were used as light sources, which were modulated by PCM signals at a bit rate of 122 Mb/s and 6.3 Mb/s, respectively. It is confirmed that the cumulative probability distribution of lightwave attenuation can be estimated precisely by that of the visual range. Based on the estimation, it will be necessary to use a tandem optical transmission system through the atmosphere with repeaters at intervals shorter than 1 km, in order to attain a higher reliability of about 99.9 percent. In addition, this paper clarifies the dependency of optical pulse atmospheric transmission upon weather conditions under the condition of constant received light power.