The use of a chirp signal is one of the methods to expand the detection range in subsurface radar. However, the presence of time-sidelobes after a conventional pulse-compression makes the detection range degraded because weak signals from underground objects are covered with a large time-sidelobe due to a ground surface reflection. In this paper, we propose a new pulse compression subsurface radar using a short chirp signal in which the echoes from the ground surface and the object are not overlapped. We show that the short chirp signal can improve the detection ability compared with a conventional chirp signal and examine the influence that the decreases of the signal duration and the compression ratio exert on the detection range. By the new pulse compression subsurface radar, the steel pipes buried down to 5 m in depth can be detected.

The origins of baseline shift were discussed considering the measured off-track properties using a wide write head with track widths of 97 µm and a narrow read head with track widths of 2.7 µm. The baseline shift increased when the read head was moved close to the track edge. Beyond the track edge, baseline shift decreased to negative values. The impulse response curve of the MR head to the perpendicular magnetization was estimated from the readback waves of the MIG head and the MR head. The response curve depended on the recorded track width. When the recorded track was narrow, the undershoot of the response curve was smaller than that of the head field based on the 2D double-gap ring head model with infinite track width. This small undershoot induces sensitivity of the DC-component of the recorded magnetization and causes the baseline shift. To calculate the readback waves of the MR head for single-layer perpendicular recording media with narrow-track recording, the effect from stray field at the recorded track edge must be included in the impulse response curve of read head.

Meteor storms and showers are now considered as potential hazard in the space environment. Radar observations of meteors has an advantage of a much higher sensitivity over optical observations. The MU radar of Kyoto University, Japan has a unique capability of very fast beam steerability as well as a high sensitivity to the echoes from ionization around the meteors. We developed a special observation scheme which enables us to determine the orbit of individual meteors. The direction of the target is determined by comparing the echo intensity at three adjacent beams. The Doppler pulse compression technique is applied to improve the signal-to-noise ratio of the echoes from the very fast target, and also to determine the range accurately. The developed scheme was applied to the observation made during the Leonid meteor storm on November 18, 1998 (JST). Estimated orbital distribution seems to suggest that the very weak meteors detected by the MU radar are dominated by sporadic meteors rather than the stream meteors associated with the Leonids storm.

The application of subsurface radar using electromagnetic waves in the VHF band is wide and includes surveying voids under the ground and archaeological prospecting. To achieve a wider application range, the survey depth must be deeper. In this paper, a method of pulse compression using a chirp signal as one of the methods to fulfill this requirement is described, and its advantages and problems are discussed. First, a delay correlation method is proposed as a processing method of pulse compression. It converts RF band chirp signal directly into a pulse. Moreover, the method improves the S/N ratio by over 40 dB compared with conventional pulse radar. Therefore, it has the same detection ability as conventional pulse radar even though it uses less transmitting power. Next, the influences of RF amplifier saturation and underground propagation characteristics on the chirp signal are discussed; both are shown to have little influence on the detection ability of the method.

As a flexible way to accommodate a variety of services, a number of spreading bands are now considered in International Mobile Telecommunications-2000 (IMT-2000) systems and more than two (overlaid) bands can be operated simultaneously in CDMA systems. Capacity estimation in CDMA systems is an important issue in performance analysis and call admission control (CAC), which is closely related to power control. This study derives the reverse link capacity of signal-to-interference ratio (SIR)-based power-controlled overlaid multiband CDMA systems in single and multiple cell environments. The weighted-aggregated data rate is introduced as the link capacity, which can reflect different spreading bandwidths and different QoS requirements. Various combinations of 5, 10, and 20 MHz subsystems are compared to one another in view of the maximum weighted-aggregated data rate. The impact of pulse shaping on CAC and the effect of multiple traffic accommodation on link capacity are also investigated.

Topographical changes induced by optical near-field around photo-irradiated nanoparticles were attained using a pulsed laser with a large peak power as a light source. The arrayed structure of nanoparticles was transcribed on urethane-urea azo copolymer film as dent structure. The experiments by the pulsed laser of different wavelength showed that the topographical change was caused by the light absorption. The dent diameter and the dent depth changed depending on the diameter of nanoparticles.

We have developed spectral separation devices for processing femtosecond pulses. These devices are based on an optical coupler structure with fiber gratings. In a computer simulation, we confirmed that these devices could extract <1 nm bandwidth light with 80% efficiency. We fabricated the spectral separation devices using single mode fibers and highly Ge-doped fibers. These devices successfully extracted narrow spectral light of 0.3 nm bandwidth with 37% efficiency from femtosecond pulses of 40 nm bandwidth. We also fabricated 2-channel spectral separation devices, which could extract the light from each grating channel.

The propagation and the gate operation of femtosecond pulses in nonlinear optical waveguides utilizing the saturation of the intersubband absorption at 1.55 µm in nitride multiple quantum wells are simulated for the first time. The calculation was carried out by a one-dimensional finite-difference time-domain (FD-TD) method combined with three-level rate equations describing the intersubband carrier dynamics. The absorption recovers within 1 ps when the pulse width is less than 200 fs, which will allow 1-Tb/s operation. However, the pulse shape may be deformed with the propagation due to the coherent effect and the interference between the signal and the control pulses, and thus, optimization of the pulse widths and the incident timing is required. Since the transparent window (width of the control pulse) becomes shorter according to the propagation, the width of the control pulse should be set broader than that of the signal pulse. As an example, we assume the case where a 1.6-µm, 100-fs signal pulse is gated by a 300-fs control pulse at a wavelength of 1.5 µm in a 500-µm length waveguide. A 140-fs gated signal pulse with a smooth envelope is expected to appear after the band-pass filter. The extinction ratio is expected to be greater than 15 dB.

In this paper, a method for finding the direction of arrival (DOA) of a single short pulse is proposed. The method is based on a waveform reconstruction technique using complex antenna factors (CAF). Since the frequency characteristics of CAF has angle dependency, the DOA of an electromagnetic pulse can be determined by the waveforms reconstructed with CAF. The results of a simulation and an experiment show the possibility to apply the two-dimensional DOA finding.

Attempts have been made to evaluate and investigate the radiated emissions from fiber optical modules that are currently available in the market. Far electric field strength measurements show that the radiated emission has a peak at a high-order harmonic wave of the fundamental pulse frequency and reaches a level exceeding the limiting values of the CISPR noise specifications. Near magnetic field distribution measurements show that the source of the interference noise lies between a light emitting diode (LED) module and an LED driver. These measurements are compared with those of electromagnetic field calculations based on a high-frequency equivalent circuit. As a result, it was established that both the peaking effects of deformed pulse waves transmitted between an LED module and an LED driver and the radiation characteristics of the optical transmitter circuit act as factors for increasing the radiation level of the peak frequencies in the radiated emission from fiber optical modules.

This paper proposes a nonlinear oscillator network model for gray-level image segmentation suitable for massively parallel VLSI implementation. The model performs image segmentation in parallel using nonlinear analog dynamics. Because of the limited calculation precision in VLSI implementation, it is important to estimate the calculation precision required for proper operation. By numerical simulation, the necessary precision is estimated to be 5 bits. We propose a nonlinear oscillator network circuit using the pulse modulation approach suitable for an analog-digital merged circuit architecture. The basic operations of the nonlinear oscillator circuit and the connection weight circuit are confirmed by SPICE circuit simulation. The circuit simulation results also demonstrate that image segmentation can be performed within the order of 100 µs.

Linear signal analysis (LSA) is the conventional method of estimating the playback voltage and pulse width in linearly operating shielded GMR heads. To improve the accuracy of LSA, a new, highly precise LSA which includes the effect of the magnetization distribution in the medium and inhomogeneous biasing by domain control magnets, was developed. Utilizing this new LSA to calculate the playback waveforms, the calculated peak voltage and pulse width were compared with the experimental values and agreement within 10% was obtained. As the result of estimation using the new LSA, it is considered that the use of a vertical-type spin-valve head will make it possible to achieve a recording areal density of 40 Gb/in2.

Optical Code Division Multiple Access (OCD- MA) has been emerging as an attractive scheme in fiber optic communication systems as well as in space communication systems in past few years. In OCDMA systems, M-ary Pulse Position Modulation (PPM), has been regarded as an efficient signalling format which has the capability to reduce the channel interference caused by the other users and also to increase the number of simultaneous users. We apply error control coding to improve the system performance of pulse position modulated OCDMA (PPM/OCDMA) systems and this paper investigates the performance of M-ary PPM/OCDMA systems with M-ary convolutional coding. Dual-k code is used as the M-ary convolutional code and Optical Orthogonal Codes with the maximum cross correlation value of 1 and 2 are employed as the signature sequences. We derive an expression for the bit error probability of the new system and show that combining M-ary convolutional coding and M-ary PPM results in an improved error performance. Also it is shown that the number of simultaneous users can be significantly increased with the proposed system compared to the uncoded PPM/OCDMA system with the same bit error probability and with the same information bit rate. We also analyze the system with binary convolutional coding and a comparison with the proposed system is given.

One of the limitation factors on the achievable distance for long-haul nonlinear Return-to-Zero (RZ)-Gaussian pulse transmission on optical fiber links is timing jitter. Although it is well known that the dispersion management technique is very effective to reduce the timing jitter, comparisons among some dispersion management methods based on the timing jitter reduction have not been reported yet. In this paper, timing jitter reduction by some dispersion management methods in nonlinear RZ-Gaussian pulse transmission systems are discussed. Moreover, we will report that the amount of timing jitter at the receiver side drastically changes depending on the configuration of dispersion managed optical fiber transmission line.

This paper proposes non-volatile analog memory circuits using pulse-width modulation (PWM) methods. The conventional analog memory using floating gate device has a trade-off between programming speed and precision because of the constant width of write pulses. The proposed circuits attain high programming speed with high precision by using PWM write pulses. Three circuits are proposed and their performance is evaluated using SPICE simulation. The simulation results show that fast programming time less than 20 µs, high updating resolution of 11 bits, and high precision more than 7 bits are achieved.

This paper reports on time-space conversion-based differential processing of optical signals using a high-resolution arrayed-waveguide grating (AWG) and a spatial filter at a wavelength of 1.55 µm. We clarify the advantages of the AWG device and show where it is applicable. In order to reduce loss at the spatial filter, we propose a new phase-only filter that functions as a differential filter. The difference between the exact differential filter and the proposed phase-only filter is calculated theoretically. We confirm experimentally that the optical pulse can be differentiated by the proposed filter. For application of differential processing, we also proposed a phase modulation to amplitude modulation (PM-AM) conversion and demonstrated the PM-AM conversion at 10 Gbit/s signals using a PSK-non-return-to-zero (NRZ) format.

In some applications, such as the echo cancellation problem of satellite-linked communication channels, there occurs a problem of estimation of a long impulse response, which consists of a long flat delay and a short dispersive response region. In this paper, it is shown that the use of the adaptive algorithm based on the frequency domain sampling theorem enables efficient identification of the long impulse response. The use of the proposed technique can lead to the reduction of both the number of adaptive weights and the complexity of flat delay estimation.

This paper reports on time-space conversion-based differential processing of optical signals using a high-resolution arrayed-waveguide grating (AWG) and a spatial filter at a wavelength of 1.55 µm. We clarify the advantages of the AWG device and show where it is applicable. In order to reduce loss at the spatial filter, we propose a new phase-only filter that functions as a differential filter. The difference between the exact differential filter and the proposed phase-only filter is calculated theoretically. We confirm experimentally that the optical pulse can be differentiated by the proposed filter. For application of differential processing, we also proposed a phase modulation to amplitude modulation (PM-AM) conversion and demonstrated the PM-AM conversion at 10 Gbit/s signals using a PSK-non-return-to-zero (NRZ) format.

This paper investigates a new class of pulse compression codes in which the phase rotates clockwise, and afterward, rotates anticlockwise (or rotates anticlockwise, and afterward, rotates clockwise). The spectrum energy then concentrates to the narrower band compared to the conventional code such as the Barker code and the pulse is compressed not to the width of a single subpulses, but to the width made by a collection of several subpulses. It is revealed that, using the new code, PSL (Peak Sidelobe Level) can be reduced to -25.6 dB (1/19) -25.1 dB (1/18), which is much smaller than using the Barker code and Frank code, when the compression ratio is about 10 or larger. Furthermore, the signal-to-noise ratio after compression, the appropriate IF bandwidth and Doppler tolerance for the new code are estimated by simulation.

A device simulator that simulates device performance in the cyclic bias steady state was developed, and it was applied to GaAs hetero-junction FET (HJFET) pulse pattern effect. Although there is a large time-constant difference between the pulse signals and deep trap reactions, the simulator searches the cyclic bias steady states at about 30 iterations. A non-linear shift in the drain current level with the mark ratio was confirmed, which has been estimated from the rate equation of electron capture and emission based on Shockley-Read-Hall statistics for deep traps.