We have achieved the room temperature cw lasing operation of GaInAsP/InP surface emitting lasers for the first time. By employing a buried heterostructure with 1.3 µm range active region and a MgO/Si heat sink mirror, cw operation was obtained up to 14 with the threshold current of 22 mA.

In this paper we consider multiuser detection using a neural network in a synchronous code-division multiple-access channel. In a code-division multiple-access channel, a matched filter is widely used as a receiver. However, when the relative powers of the interfering signals are large, i.e. the near-far problem, the performances of the matched filter receiver degrade. Although the optimum receiver for multiuser detection is superior to the matched filter receiver in such situations, the optimum receiver is too complex to be implemented. A simple technique to implement the optimum multiuser detection is required. Recurrent neural networks which consist of a number of simple processing units can rapidly provide a collectively-computed solution. Moreover, the network can seek out a minimum in the energy function. On the other hand, the optimum multiuser detection in a synchronous channel is carried out by the maximization of a likelihood function. In this paper, it is shown that the energy function of the neural network is identical to the likelihood function of the optimum multiuser detection and the neural network can be used to implement the optimum multiuser detection. Performance comparisons among the optimum receiver, the matched filter one and the neural network one are carried out by computer simulations. It is shown that the neural network receiver has a capability to achieve near-optimum performance in several situations and local minimum problems are few serious.

A novel external clocking magnetic disk recording channel is proposed and examined. Timing not only for data recovery but for recording is given by a bit clock which is synchronized with dedicated clock marks on patterned discrete track media. Jitter of the bit clock is 2.5 ns (rms), which is good enough for data rates up to about 20 Mbit/s. Using an MR/Inductive head and PRML (Partial Response Maximum Likelihood) signal processing, an error rate of 110-6 is obtained at linear density 3146 bit/mm.

Embossed disks with discrete magnetic tracks and servo marks are proposed and evaluated. The tracks and the servo marks are made by etching the glass substrate. The guard band depth was decided to be 0.2 µm. Using the disks, the head positioning accuracy of 0.09µm (rms) and the recording density of 192 tracks per millimeter were demonstrated.

In this paper, the characteristics of microstrip lines near the edge of dielectric substrate are analyzed by improving the rectangular boundary division method. The numerical results indicate the changes of the characteristics of a microstrip line when the strip conductor is closely located to the edge. When the distance the dielectric substrate edge to the strip conductor is less than the thickness of dielectric substrate, the effects of the edge on the line characteristics are no longer negligible. The numerical results in this paper show high computation accuracy without increasing computation time. Our improvement is effective for the analysis of the microstrip lines both for the narrow strip conductor and the strip conductor close to the edge. The relative errors between the numerical results and the measured values are less than 1.2%.

Recessed-gate DMTs (doped-channel hetero-MISFETs) with i-AlGaAs/n-GaAs structure and pseudomorphic i-AlGaAs/n-InGaAs/i-GaAs structure have been developed. Broad plateaus in gm and fT provide evidence that the DMTs make the devices suitable for high-speed large-signal operation. GaAs DMTs with 0.35 µm-length have gate turn on voltage of 0.7 V, maximum transconductance of 320 mS/mm and fT of 41 GHz. Pseudomorphic DMTs have gate turn on voltage of 0.9 V, maximum transconductance of 320 mS/mm, fT of 42 GHz and have the enhanced advantages of high current drivability and large gate swing. Further more, with the use of the recessed-gate DMTs, a high-speed laser driver IC for multi-Gb/s optical communication systems are demonstrated. This laser driver IC operates at 10 Gb/s with rise and fall times as fast as 40 psec, and it can drive up to 60 mA into a 25 Ω load.

The transient spectral spread of directly modulated DFB LD's, which appears in the time-resolved chirping measurement, is studied experimentally and numerically. Such a phenomenon has been already reported as a side mode oscillation called "subpeak", but there has been little argument as to the physical origin. We make it clear that the subpeak is a spurious mode due to the influence of the photodetector bandwidth. The minimum photodetector bandwidth which is necessary in the time-resolved chirping measurement is examined. Furthermore the distortion of the long-distance transmitted waveform is also explained by one mode oscillation.

This paper describes a 0.8-µm CMOS LSI developed for a 156-Mb/s serial interface in ATM switching systems. Recently, there have been increasing problems of connector pin neck and higher power consumption when enhancing switching system capacity. To overcome these problems, we have developed an LSI with a high-speed interface by using CMOS technology to achieve low power consumption. A low-swing differential signal level is used to achieve 156-Mb/s data transmission. We named this new circuit technique ALTS (Advanced Low-level Transmission circuit System). Using the LSI, transmission can be achieved between boards or racks through a 10-meter twisted pair cable. The LSI has a 156-Mb/s transmitter-receiver, a serial-to-parallel converter and a parallel-to-serial converter. It performs 19.5-Mb/s parallel data/156-Mb/s serial data conversion and 156-Mb/s serial data transmission. In addition, it has a bit phase synchronizer and cell synchronizer, which enables it to transmit and synchronize serial data without a paralleled clock or a paralleled cell top signal, by distributing a common 156-MHz clock and a common cell top signal to the whole system. We evaluated the bit error rate and timing margin on data transmission under several conditions. The results show that we can apply this LSI to commercially available ATM switching systems. This paper also describes methods of expanding switch capacity and transmitting 624-Mb/s data using this LSI.

In a cellular system for mobile communications, every service area is divided into a number of cells for utilizing the frequency spectrum efficiently. Service areas for such systems are two dimensional, however, the analysis of the characteristics of the communication traffic for the areas are quite complicated, since the motion of the vehicles in the area can not be predicted precisely. For making the analysis easily, the areas are assumed to be band-shaped like a highway. Furthermore, in the analysis, the traffic offered to a cell is assumed to be stationary. In actual systems, the density of vehicles and the offered communication traffic is not stationary, so that many differences exist between the analysis and the actual systems. This paper presents an analysis method using state equations. The equations represent the transient characteristics of mobile communication traffic when a band-shaped service area is assumed. The transition is made by accidents or congestion, and causes the rapid offered traffic change in a communication system. In the method, numerical analysis is made under the consideration of "handoff" operation. The operation consists of surrendering the channel used in the previous cell and reassigning a new channel when the vehicle crosses the cell boundary. The analytical results are compared with the simulations, and the two results show good agreement. The method presented in this paper can be used for designing the switching system when the offered traffic changes rapidly due to accidents or congestion.

A circuit emulation technique in the ATM network becomes necessary to guarantee user requirements similar to QOS grade offered by STM network where small bit error rates and constant delay times are offered. The Head-Of-Line method or other priority control schemes may be considered to provide such service in the ATM network, while it is known to give too inferior quality to non-circuit emulation service traffic. In this paper, we propose a new method called a periodical bandwidth allocation method for the circuit emulation technique. The cells of circuit emulation service traffic are transmitted periodically in our proposal. A periodical interval is determined from both the length of limit delay time of circuit emulation traffic in each switching node and the number of cell arrivals during the limit delay time. To evaluate our method, we consider three kinds of arrival patterns (the best case, the moderate case, and the worst case) for the circuit emulation traffic and a two-state MMPP for modeling the non-circuit emulation traffic. We show performance results in terms of the cell loss probability and the mean delay time in our proposal through analytic and simulation approaches.

The generation mechanism for excess intensity noise due to optical feedback is analyzed theoretically and experimentally. Modal rate equations under the weakly coupled condition with external feedback are derived to include the mode competition phenomena in DFB and Fabry-Perot lasers. We found that the sensitivity of the external feedback strongly depends on design parameters of structure, such as the coupling constant of the corrugation, the facet reflection and the phase relation between the corrugation and the facet. A DFB laser whose oscillating wavelength is well adjusted to Bragg wavelength through insertion of a phase adjustment region becomes less sensitive to external optical feedback than a Fabry-Perot laser, but other types of DFB lasers revealing a stop band are more sensitive than the Fabry-Perot laser.

In this paper, a new time series analysis method is proposed. The proposed method uses the exponential (EXP) model. The residual signal is assumed to be identically and independently distributed (IID). To achieve accurate and efficient estimates, the parameter of the system model is calculated by maximizing the logarithm of the likelihood of the residual signal which is assumed to be IID t-distribution. The EXP model theoretically assures the stability of the system. This model is appropriate for analyzing signals which have not only poles, but also poles and zeroes. The asymptotic efficiency of the EXP model is addressed. The optimal solution is calculated by the Newton-Raphson iteration method. Simulation results show that only a small number of iterations are necessary to reach stationary points which are always local minimum points. When the method is used to estimate the spectrum of synthetic signals, by using small α we can achieve a more accurate and efficient estimate than that with large α. To reduce the calculation burden an alternative algorithm is also proposed. In this algorithm, the estimated parameter is updated in every sampling instant using an imperfect, short-term, gradient method which is similar to the LMS algorithm.

Asynchronous machines are a topic of great interest in the research area of actuators. Due to the complexity of these systems and to the required performance, the modelling and control of asynchronous machines are complex questions. Problems arise when the control goals require accurate descriptions of the electric machine or when we need to identify some electrical parameters; in the models employed it becomes very hard to take into account all the phenomena involved and therefore to make the error amplitude adequately small. Moreover, it is well known that, though an efficient control strategy requires knowledge of the flux vector, direct measurement of this quantity, using ad hoc transducers, does not represent a suitable approach, because it results in expensive machines. It is therefore necessary to perform an estimation of this vector, based on adequate dynamic non-linear models. Several different strategies have been proposed in literature to solve the items in a suitable manner. In this paper the authors propose a neural approach both to derive NARMAX models for asynchronous machines and to design non-linear observers: the need to use complex models that may be inefficient for control aims is therefore avoided. The results obtained with the strategy proposed were compared with simulations obtained by considering a classical fifth-order non-linear model.

This paper describes the potential of KrF excimer laser lithography for the development and production of 64 M and 256 Mbit DRAMs on the basis of our recent developed results. Quarter micron KrF excimer laser lithography has been developed. A new chemically amplified positive resist realizes high stability and process compatibility for 0.25 micron line and space patterns and 0.35 micron contact hole patterns. This developed resist is characterized as the increase of dissolution characteristics in exposed areas, and hence means the high resolution is obtained. A multiple interference effect was greatly reduced by using our over coat film or anti-reflective coating. This over coat film has no intermixing to the resist and it is simultaneously removed when the resist is developed. This anti-reflective coating has low etch selectivity to the resist, and hence the over coat film is etched away when etching the substrate. The two major results indicate that the KrF excimer laser lithography is promising for the development of 256 MDRAMs.

Improvement of fatigue behavior of a fusion spliced portion on a carbon-coated fiber is achieved by recoating carbon using a thermal-CVD process with a CO2 laser as a local heat source. The fatigue parameters, so-called n-values, of 121 and 94 are obtained on the non-spliced portion and the spliced portion, respectively. Assuming a life time prediction model, these high values have been proved to have an advantage in a long-term reliability and to be sufficient in a practical submarine cable use.

A new redundancy technique especially suitable for ultra-high-speed static RAMs (SRAMs) has been developed. This technique is based on a decoding-method that uses two kinds of fuses without introducing any additional delay time. One fuse is initially ON and can be turned OFF afterwards, if necessary, by a cutting process using a focused ion beam (FIB). The other is initially OFF and can be turned ON afterwards by a connecting process using laser chemical vapor deposition (L-CVD). This technique is applied to a 64 kbit SRAM having a 1.5-ns access time. The experimental results obtained through an SRAM chip repaired using this redundancy technique show that this technique does not introduce any increase in the access time and does not reduce the operational margin of the SRAM.

Broadband ISDN based on ATM technologies is expected to offer enhanced and sophisticated services to customers. Since ATM will first be introduced in the business communication world, it will be worth to discuss the future image of desirable ATM customer premises network (CPN). In this paper, we first consider the possible migration scenario of Broadband CPN and some important requirements for the realization of the scenario. Then, we discuss the key issues to be solved for future ATM-CPN, which include network topology, traffic control and connectionless communication services.

Broadband multimedia information environments are part of the next big advance in communications and computer technology. The use of multimedia infrastructures in offices is becoming very important. This paper deals with a service concept and human interfaces based on a paper metaphor. The proposed service offers the advantages of paper and eliminates the disadvantages. The power of multimedia's expressiveness, user interaction, and hypermedia technology are key points of our solution. We propose a system configuration for implementing the service/human interface.

This paper proposes the laser diode receiving mixer which utilizes the laser diode nonlinearity. The laser diode receiving mixer can make the bidirectional fiber optic link simple and cost-effective. These laser diodes are applied to configure the LD-LD MIX link which consists of two laser diodes, two local oscillators, two microwave switches and one fiber cable. The LD-LD MIX link configuration is extended to introduce novel two fiber optic links, i.e. the local suppression link and the image cancellation link. These links utilize the combination of microwave circuits and optical devices. These configurations are experimentally investigated at microwave frequencies and the QPSK signal transmission is successfully demonstrated.

This paper theoretically evaluates the external electro-optic (EO) sampling of high-speed electrical signals using poled polymers as materials for a proximity electric-field sensor. Based on the derivation of the half-wave voltage and the analysis of a static electric field coupled to the polymeric media placed over IC interconnections, invasiveness, voltage sensitivity, and spatial resolution have been discussed. The polymeric sensors have shown to be used in contact with the IC interconnections with negligibly small invasiveness, thus making polymeric sensors provide higher sensitivity and spatial resolution than inorganic crystals such as GaAs and KD*P.