We consider applications of optical solitons to signal processing. Soliton switching devices promise ultrafast operation and compatibility with communications systems using optical pulses. Quantum soliton effects include broadband squeezing and quantum nondemolition measurements, and can reduce noise and increase sensitivities of optical measurements. We report the demonstration of two-color soliton switching and describe progress towards implementation of quantum nondemolition measurement of photon number using soliton collisions.

In this paper we review the recent progress and basic technology of vertical cavity surface emitting lasers together with related parallel surface operating optical devices. First, the concept of surface emitting lasers is presented, and then currently developed device technologies will be reviewed. We will feature several technical issues, such as multi-layer structures, 2-dimensional arrays, photonic integration, etc. Lastly, future prospects for parallel lightwave systems will be discussed.

Several issues on semiconductor lasers with low dimensional quantum systems are discussed. First, described are fabrication techniques for quantum wire and box structures, particularly a selective growth MOCVD growth technique which have been recently developed. Using this technique, we obtained 20 nm 15 nm triangular-shaped quantum wire structures. Next, we investigate band structures of the quantum wires having strain effects, including lasing characteristics of quantum wire lasers with the strain effects. Finally we discuss importance to control both the electron wave mode and the optical wave mode for future high performance lasers, which leads to the concept of quantum micro-lasers. In order to demonstrate possibility to control the spontaneous mode in the laser cavity, an experimental result is shown on enhancement and inhibition effects of the spontaneous emission mode in a vertical cavity laser having two kinds of the quantum well.

We review the role of optics in interconnects, analog processing, neural networks, and digital computing. The properties of low interference, massively parallel interconnections, and very high data rates promise extremely high performance for optical information processing systems.

The nonlinear optical properties of organics with unsaturated bonds were compared with those of inorganics including semiconductors and dielectrics. Because of the mesomeric effect, namely quantum mechanical resonance effect among configurations, aromatic molecules and polymers have larger optical nonlinear parameters defined as δ⁽ⁿ⁾=X⁽ⁿ⁾/(X^(l))ⁿ both for the second (n=2) and third-order (n=3) nonlinearities. Experimental results of ultrafast nonlinear response of conjugated polymers, especially polydiacetylenes, were described and a model is proposed to explain the relaxation processes of photoexcitations in the conjugated polymers. Applying the model constructed on the basis of the extensive experimental study, we propose model polymers to obtain ultrafast resonant optical nonlinearity.

We propose parallel rate-variable punctured convolutional coded PPM in photon communication to achieve high energy information efficiency I_e for desired bit error rate (BER) and transmission bandwidth. We theoretically show the BER performance, bandwidth expansion factor β and necessary I_e to achieve BER=10^-6 of the proposed systems for some combinations of code rates. It is found that the proposed system can achieve high I_e for desired BER and β by selecting a suitable combination of code rates depending on the channel conditions. Moreover, it is shown that the proposed system has better BER performance than RS-coded PPM in the range of small β.

We propose Polarization-Shift-Keying (POLSK) homodyne system using phase-diversity receivers and theoretically analyze its bit-error-rate (BER) performance. Since the proposed system uses polarization modulation and homodyne detection, it can cancel the phase noise and is attractive at a high bit-rate transmission. It is found that the receiver sensitivity of the proposed POLSK homodyne system is the same as that of POLSK heterodyne system and is much better than that of DPSK phase-diversity homodyne systems at high signal-to-noise ratio (SNR). We also cosider theoretically the effect of the fluctuation of state of polarization (SOP) on the BER performance of POLSK homodyne system.

The heterointerfaces of Al_0.3Ga_0.7As/GaAs single quantum wells (SQWs) and the characteristics of SQW lasers grown on Si substrates with Al_0.5Ga_0.5As/Al_0.55Ga_0.45P intermediate layers (AlGaAs/AlGaP ILs) entirely by metalorganic chemical vapor deposition (MOCVD) are reported. The effects of thermal cycle annealing on the crystallinity and the lasing characteristics of GaAs/Si are also reported. By using the AlGaAs/AlGaP ILs, SQWs with a specular surface morphology and a smoother heterointerface can be grown on a Si substrate. Thermal cycle annealing is found to improve the crystallinity of GaAs/Si and to contribute to room-temperature continuous-wave operation of lasers on Si substrates. The combinations of the techniques of AlGaAs/AlGaP ILs and thermal cycle annealing improve the lasing characteristics: an average threshold current density of 1.83 kA/cm², an average differential quantum efficiency of 52%, an internal quantum efficiency of 83%, an intrinsic mode loss coefficient of 23cm^-1, a differential gain coefficient of 1.9cm/A, and a transparency current density of 266 A/cm², which are superior to those of the two-step-grown laser on a Si substrate. The improvements of the lasing characteristics result from the smooth heterointerfaces of the AlGaAs/AlGaP ILs.

The characteristics of a LiNbO₃ light modulator using the resonant YBa₂Cu₃O_y superconducting electrode were studied on the basis of the calculated results of surface resistances and transmission losses. The two-fluid model and the conventional transmission theory were used for the calculations. It was found that the modulation depth of this modulator using the YBCO electrode at 77 K was 7.5 times that using the Al electrode at room temperature. The drive voltage for the phase modulation of π radians was estimated to be a very low value of 2.3 V.

The VSTEP concept and its practical application in the form of an LED-type pnpn-VSTEP demonstrating low power consumption through electro-photonic operational modes are both shown. Further, with focus primarily on the new laser-mode VSTEP with high-intensity light output and narrow optical beam divergence, the design features such as threshold gain and optical absorptivity, device fabrication, and characteristics are explained. The possibility of ultimate performance based mainly on electrical to optical power conversion efficiency, important from the application viewpoint of optical interconnection, are also discussed. Also, as two examples of functional optical interconnection achieved by VSTEP, serial-to-parallel data conversion and optical self-routing switches are shown. Finally, future opto-electronic technologies to be developed for two-dimensionally integrable surface-type optical semiconductor devices, including the VSTEP, are discussed.

Suppose that there are terminals on two concentric circles C_in and C_out, with C_in inside of C_out. A set of two-terminal nets is given and the routing area is the annular region between the two circles. In this paper, we present an O(n²) time algorithm for testing whether the given net set is two-layer routable, where n is the number of nets. Applying this algorithm repeatedly, we can find, in O(n³) time, a maximal subset of nets which is two-layer routable.

This paper presents an approximation method for deriving the availability of a parallel redundant system with preventive maintenance (PM) and common-cause failures. The system discussed is composed of two identical units. A single service facility is available for PM and repair. The repair times, the PM times and the failure times except for common-cause failures are all assumed to be arbitrarily distributed. The presented method formulates the problem of the availability analysis of a parallel redundant system as a Markov renewal process which represents the state transitions of one specified unit in the system. This method derives the availability easily and accurately. Further, the availability obtained by this method is exact in a special case.

This paper investigates the performance of the line spectrum pair (LSP) frequency parameter representation for speech recognition. Transitional parameters of LSP frequencies are defined using first-order regression coefficients. The transitional and the instantaneous frequency parameters are linearly combined to generate a single feature vector used for recognition. The performance of the single vector is compared with that of the cepstral coefficients (CC) representation using a minimumdistance classifier in speaker-independent isolated word recognition experiments. In the speech recognition experiments, the transitional and the instantaneous coefficients are also combined in the distance domain. Also, inverse variance weighted Euclidean measures are defined using LSP frequencies to achieve Mel-scale-like warping and the new warped-frequencies are used in recognition experiments. The performance of the single feature vector defined with transitional and instantaneous LSP frequencies is found to be the best among the measures used in the experiments.