FM laser operation of a Ti:sapphire laser is studied experimentally for the first time with an internal phase modulator. We obtained extremely wide FM sidebands of 8 THz width whose phase modulation index was 25,000 rad at a modulation frequency of 160 MHz.

Feasibility of 20 Gbit/s single channel transoceanic soliton transmission systems with a simple EDFA repeaters configuration has been studied. Both a simple and versatile soliton pulse generator and a polarization insensitive optical demultiplexer, which can provide a almost square shape optical gate with duration of full bit time period, have been proposed and demonstrated by using sinusoidally modulated electroabsorption modulators. The optical time-division multiplexing/demultiplexing scheme using the optical demultiplexer results in drastic improvement of bit error rate characteristics. We have experimentally confirmed that the use of alternating-amplitude solitons is an efficient way to mitigate not only soliton-soliton interaction but also Gordon-Haus timing jitter constraints in multi-ten Gbit/s soliton transmission. Timing jitter reduction using relatively wide band optical filter bas been investigated in 20 Gbit/s loop experiments and single-carrier, single-polarization 20 Gbit/s soliton data transmission over 11500 km with bit error rate of below 10-9 has been experimentally demonstrated, using the modulator-based soliton source, the optical demultiplexer, the alternation-amplitude solitons, and wide-band optical filters. Obtained 230 Tbit/skm transmission capacity shows the feasibility of 20 Gbit/s single channel soliton transoceanic systems using fully practical technologies.

The polarization dependence of femtosecond soliton-soliton interactions is investigated in detail. When the polarization direction of two solitons is orthogonal, the soliton interaction can be reduced in comparison to that for parallel polarization. The soliton self-frequency shift (SSFS) is still observed even in the orthogonal condition, but the quantity of the SSFS is much smaller than in the parallel condition. A stronger soliton interaction is observed between two solitons in an in-phase condition, than in an out-of-phase condition. The largest SSFS occurs in-phase with parallel polarization. The polarization dependence of femtosecond soliton interaction in a distributed erbium-doped fiber amplifier (DEDFA) is also investigated. It is shown that when the optical gain of the DEDFA is given adiabatically, the input pulse separation at which the first soliton occurs is less with orthogonal polarization. This is because the soliton pulse width is reduced due to the adiabatic soliton narrowing caused by the optical amplification.

A new device consisting of an optical pulse generation section and pulse coding section monolithically integrated on a single-chip has been developed. The pulse generation section consists of a multiple quantum well (MQW) electroabsorption modulator integrated with an MQW DFB laser. The modulator operates at large-signal modulation and low voltage (from 2 to 3-V DC bias with a 3.2-V peak-to-peak RF signal). The second modulator is operated independently as a pulse encoder. An approximately transform-limited optical pulse train, whose full width at half maximum (FWHM) in the time domain is less than 17-ps and spectral FWHM is 28-GHz, is obtained with a repetition frequency of 10-GHz. Compressive strain is introduced in both InGaAsP quantum wells in order to obtain efficient device characteristics. These include a low threshold current (18-mA) for the laser, and low driving voltage (30-dB for 3-V swing) and high-speed operation (over 12-GHz for a 3-dB bandwidth) for the modulators. Demonstrations show that this new device generates short optical pulses encoded by a pseudo-random signal at a rate of 10 Gbit/s. This is the first time 10 Gbit/s modulation has been achieved with a multi-section electroabsorption modulator/DFB laser integrated light source. This monolithic device is expected to be applied to optical soliton transmitters.

This paper discusses pulse responses of multi-conductor transmission lines terminated by linear and nonlinear subnetworks. At first step, the circuit is partitioned into a linear transmission lines and nonlinear subnetworks by the substitution voltage sources. Then, the linear subnetworks are solved by a well-known phasor technique, and the nonlinear subnetworks by a numerical integration technique. The variational value at each iteration is calculated by a frequency domain relaxation method to the associated linearized time-invariant sensitivity circuit. Although the algorithm can be efficiently applied to weakly nonlinear circuits, the convergence ratio for stiff nonlinear circuits becomes very small. Hence, we recommend to introduce a compensation element which plays very important role to weaken the nonlinearity. Thus, our algorithm is very simple and can be efficiently applied to wide classes of nonlinear circuits.

A 3.2 GHz, 50 mW, 1 V, GaAs clock pulse generator (CG) based on a phase-locked loop (PLL) circuit has been designed for use as an on-chip clock generator in future high speed processor LSIs. 0.5 µm GaAs MESFET and DCFL circuit technologies have been used for the CG, which consists of 224 MESFETs. An "enhanced charge-up current" inverter has been specially designed for a low power and high speed voltage controlled oscillator (VCO). In this new inverter, a voltage controlled dMESFET is combined in parallel with the load dMESFET of a conventional DCFL inverter. This voltage controlled dMESFET produces an additional charge-up current resulting in the new VCO obtaining a much higher oscillation frequency than that of a ring oscillator produced with a conventional inverter. With a single 1 V power supply (Vdd), SPICE calculation results showed that the VCO tuning range was 2.25 GHz to 3.65 GHz and that the average VCO gain was approximately 1.4 GHz/V in the range of a control voltage (Vc) from 0 to 1 V. Simulation also indicated that at a Vdd of 1 V the CG locked on a 50 MHz external clock and generated a 3.2 GHz internal clock (=50 MHz64). The jitter and power dissipation of the CG at 3.2 GHz oscillation and a Vdd of 1 V were less than 8.75 psec and 50 mW, respectively. The typical lock range was 2.90 GHz to 3.59 GHz which corresponded to a pull-in range of 45.3 MHz to 56.2 MHz.

Numerical simulations for the (3+1)-dimensional optical-field dynamics of nonstationary pulsed beams that propagate down Kerr-like nonlinear channel waveguides are carried out for what is to our knowledge the first time. Time-resolved intrapulse switching due to spontaneous symmetry breaking of optical fields from a quasilinear symmetric field to a nonlinear asymmetric field is analyzed. A novel instability phenomenon triggered by the symmetry breakdown is found.

We studied the selective epitaxy of GaAs grown by a technique called pulsed-jet epitaxy. Pulsed-jet epitaxy is a kind of atomic layer epitaxy (ALE) based on low-pressure metalorganic vapor-phase epitaxy (MOVPE). We compared growth behavior and layers grown by ALE and MOVPE. During ALE we supplied trimethylgallium (TMGa) and arsine (AsH3) alternately; however, during MOVPE we supplied TMGa and AsH3 simultaneously. At a growth temperature of 500, we obtained a better growth selectivity using ALE than using MOVPE. The lateral thickness profile of the ALE-grown GaAs layer at the edge of SiO2 mask was uniform. In contrast, the MOVPE growth rate was enhanced near the mask edge. Using ALE, we selectively grew GaAs epilayers even at mask openings with submicron widths. Scanning electron microscopy revealed that the ALE selectively grown structures had an uniform thickness profile, though the facets surrounding the structures depended on the orientation of mask stripes. After MOVPE, however, the (001) surface of the deposited layer was not flat because of the additional lateral diffusion of the growth species from the gas phase and/or the mask surface and some crystal facets. The experimental results show that, using ALE, we can control the shape of selectively grown structures. Selective epitaxy by ALE is a promising technique for fabricating low-dimensional quantum effect devices.

The performance of multi-pulse pulse position modulation (MPPM) consisting of m slots and 2 pulses, denoted as (m, 2) MPPM, with imperfect slot synchronization is analyzed. The word error probability of (m, 2) MPPM in the presence of timing offset is analyzed, and the optimum symbol sets of (m, 2) MPPM minimizing the symbol error probability are assigned. When an unassigned symbol is detected, the receiver decodes the unassigned symbol as one of the assigned symbols having the highest probability of transition from the assigned symbol to the unassigned symbol. The bit error probability of (m, 2) MPPM in the presence of the timing offset is analyzed, and the bit error probability of (m, 2) MPPM is compared with that of PPM for the same transmission bandwidth and the same transmission rate. Moreover, the bit error probability of (m, 2) MPPM synchronized by a phase-locked loop (PLL) is also analyzed. It is shown that a word with two continuous pulses has better performance than a word with two separate pulses. It is also shown that when the timing offset occurs, and when the slot clock is synchronized by a PLL, (m, 2) MPPM performs better than PPM because (m, 2) MPPM has the optimum assigned symbols, and can decode detected words more correctly than PPM.

We developed an automatic data processing algorithm for a ground-probing radar which is essential in analyzing a large amount of data by a non-expert. Its aim is to obtain an optimum result that the conventional technique can give, without the assistance of an experienced operator. The algorithm is general except that it postulates the existence of at least one isolated target in the radar image. The raw images of underground objects are compressed in the vertical and the horizontal directions by using a pulse-compression filter and the aperture synthesis technique, respectively. The test function needed to configure the compression filter is automatically selected from the given image. The sensitivity of the compression filter is adjusted to minimize the magnitude of spurious responses. The propagation velocity needed to perform the aperture synthesis is determined by fitting a hyperbola to the selected echo trace. We verified the algorithm by applying it to the data obtained at two test sites with different magnitude of clutter echoes.

This paper discusses a new image resolution conversion method which converts not only spatial resolution but also amplitude resolution. This method involves considering impulse responses of image devices and human visual characteristics, and can preserve high image quality. This paper considers a system that digitizes the multilevel input image with high spatial resolution and low amplitude resolution using an image scanner, and outputs the image with low spatial resolution and high amplitude resolution on a CRT display. The algorithm thus reduces the number of pixels while increasing the number of brightness levels. Since a CRT display is chosen as the output device, the distribution of each spot in the display, which is modeled as a Gaussian function, is taken as the impulse response. The output image is then expressed as the summation of various amplitudes of the impulse response. Furthermore, human visual perception, which bears a nonlinear relationship to the spatial frequency component, is simplified and modeled with a cascade combination of low-pass and high-pass filters. The output amplitude is determined so that the error between the output image and the input image, after passing through the visual perception filter, is minimized. According to the results of a simulation, it is shown that image quality can be largely preserved by the proposed method, while significant image information is lost by conventional methods.

A design of an Ada IPC (Inter-Program Communication) interface is proposed, through which a designer of distributed systems can (a) specify arbitrary data types needed for inter-program communication and (b) use parallel programming features to build highly parallel systems; a test simulator was built for execution of the IPC interface and a multi-window system was realized as an application of the interface on the simulator; the interface was found to be useful, making description of inter-program communication simpler and easier.

A novel pulse neural network model for sound localization has been proposed. Our model is based on the physiological auditory nervous system. Human beings can perceive the sound direction using inter-aural time difference (ILD) and inter-aural level difference (ILD) of two sounds. The model extracts these features using only pulse train information. The model is divided roughly into three sections: preprocessing for input signals; transforming continuous signals to pulse trains; and extracting features. The last section consists of two parts: ITD extractor and ILD extractor. Both extractors are implemented using a pulse neuron model. They have the same network structure, differing only in terms of parameters and arrangements of the pulse neuron model. The pulse neuron model receives pulse trains and outputs a pulse train. Because the pulses have only simple informations, their data structures are very simple and clear. Thus, a strict design is not required for the implementation of the model. These advantages are profitable for realizing this model by hardware. A computer simulation has demonstrated that time and level differences between two signals have been successfully extracted by the model.

The modular and growable photonic ATM switch architecture described in this paper uses both time-division and wavelength-division multiplexing technologies, so the switch capacity can be expanded in both the time and frequency domains. It uses a new implementation of output buffering scheme that overcomes the bottleneck in receiving and storing concurrent ultra fast optical cells. The capacity in one stage of a switch with this architecture can be increased from 32 gigabits per second to several terabits per second in a modular fashion. The proposed switch structure with output channel grouping can greatly reduce the amount of hardware and still guarantee the cell sequence.

A multi-beam airborne pulsed-Doppler radar (MBR) system is presented and its clutter rejection performance compared with conventional phased array radar (PAR)'s by PRF tuning is discussed. The pulsed-Doppler radar equations taking account of the multi-beam operation are introduced and some kinds of computer simulations for seeking the conditions to get maximum signal to clutter ratio are carried out. As a results of this, it is cleared that same order of signal to clutter ratio improvement gotten in high PRF operation by conventional PAR can be realized at lower PRF operation by MBR on clutter free area, and higher clutter rejection effect, which is proportional to beam numbers, is obtained under affection of both of mainlobe and sidelobe clutters with order of beam numbers. This also means observable numbers of range bin are increased in MBR operation.

The size and weight of marine pulse radar systems must be limited in order to mount them on board boats. However, the azimuthal resolution of a marine radar with a small antenna is degraded by the antenna beam width. It is desirable to use signal processing techniques to increase both the azimuthal resolution and the range resolution of such systems without changing their external configuration. This paper introduces a resolution enhancement method based on deconvolution, which is a kind of inversion. The frequency domain deconvolution method is described first. The effectiveness of the proposed method is shown by simulation. Then, an example of resolution enhancement processing is applied to a pulse radar. The results of practical experiments show that this method is a promising way of upgrading radars by simply processing the received signals.

Monopulse technique is widely used for tracking radars. For tracking at a low elevation angle, a narrow beam is required in the elevation plane to reduce multipath signals such as gound reflections. In this case, an elliptical aperture is desired. We have developed an antenna with a high tracking accuracy and a high aperture efficiency which is composed of a monopulse feed and an elliptical aperture. In this paper we discuss a design of the feed through lens array with an elliptical aperture and a new monopulse feed. Evaluation test results of a production model proved validity of our design and showed good performance.

In this letter, we study on the sensitivity to the electrical stimulus pulse for biomedical electronics for the purpose to make a tactile vision substitution system for binds. We derive the equivalent circuit of finger by measuring sensitive voltages with various touch condition and various DC voltage. And we consider to the sensitivity of finger against electrical stimulus pulse. In order to convert the sense of sight to tactile sense, we consider four types of touch condition and various types of pulse. It is shown that the sensitivity of finger to electrical stimulus pulse is determined by duty-ratio, frequency, hight of pulse and the type of touch condition. In the case that duty-ratio is about 20%, frequency is within about 60-300Hz and touch condition is A-4 type, the sensitive voltage becomes the lowest. With this result, a tactile vision substitution system can be developed and the system will be used to transfer various infomations to blinds without paper.

An optical On-Off Keyed (OOK) pulse is often stretched in dispersive channels, thus producing intersymbol interference (ISI) and degrading the performance. In this paper, error probability is presented for a convolutionally encoded optical OOK channels with ISI. Both ISI-matched and ISI-mismatched decoders are taken into account in the error probability analysis. The encoded optical OOK signal is received by Avalanche Photo Diode (APD) and the number of APD output photo-electrons is counted for soft decision Viterbi decoding. Error probability is derived for a 3-bit and an ideal soft decision schemes in ISI-mismatched decoder and for an ideal soft decision scheme in ISI-matched decoder. Numerical results demonstrate the effects of mismatching or 3-bit soft decision scheme. Some computer simulations are carried out to confirm the validity of the analysis.

Recent progress in high-speed semiconductor devices and integrated circuits (ICs) has outpaced the conventional measuring and testing instruments. With advent of ultrashort-pulse laser technology, the electro-optic sampling (EOS) technique based on the Pockels effect has become the most promising solution way of overcoming the frequency limit, whose bandwidth is approaching a terahertz. This paper reviews recent progress on the research of the EOS technniques for measuring ultrahigh-speed electronic devices and ICs. It describes both the principle of the EOS and the key technologies used for noncontact probing of ICs. Internal-node measurements of state-of-the-art high-speed ICs are also presented.