We describe the fabrication method and characteristics of hybrid external cavity lasers composed of a spot-size converter integrated LD (SS-LD) and a UV written Bragg grating in a planar lightwave circuit (PLC) on a Si substrate. The SS-LD is passively aligned on a Si platform formed in the PLC, and the UV grating is created in the PLC with ArF laser irradiation through a phase mask. This structure enables us to fabricate a stable single-mode laser with a precisely controllable oscillation wavelength. By using the above techniques, we obtained a threshold current of 7-8 mA and a side mode suppression of 37 dB for an external cavity laser operating at 1.3 µm. Moreover, we successfully demonstrated a four-channel external cavity laser with a wavelength interval of 2 nm 0.1 nm by integrating 4 SS-LDs on a PLC and controlling the Bragg wavelengths with ArF laser irradiation without a phase mask.

A newly developed hybrid-integrated Symmetric Mach-Zehnder (HI-SMZ) all-optical switch is reported. For integration, we chose the Symmetric Mach-Zehnder (SMZ) structure rather than the Polarization-Discriminating Symmetric Mach-Zehnder (PD-SMZ) structure which is similar to SMZ but more often used in experiments using discrete optical components. We discuss advantages and disadvantages of SMZ and PD-SMZ to show that SMZ is more suitable for integration. We also discuss about the use of SOAs as nonlinear elements for all-optical switches. We conclude that, although the ultrafast switching capability of SMZ is limited by the gain compression of SOAs, the very low switching energy is more important for practical devices. We then describe the HI-SMZ all-optical switch. This integration scheme has advantages which include low loss, low dispersion silica waveguides for high speed operation and ease in large scale integration of many SMZs with other optical, electrical, and opto-electrical devices. We show that a very high dynamic extinction ratio is possible with HI-SMZ. We also examine HI-SMZ with 1 ps pulses to show its ultrafast capability. Finally, we describe a 168 to 10.5 Gbps error-free demultiplexing experiment which is to our best knowledge the fastest experiment with an integrated device.

10-Gbit/s monolithic receiver OEIC's for 1.55-µm optical transmission systems were fabricated using a stacked layer structure of p-i-n photodiodes and HEMT's grown on InP substrates by single-step MOVPE. A receiver OEIC with a large O/E conversion factor was obtained by adding a three-stage differential amplifier to a conventional feedback amplifier monolithically integrated with a surface-illuminated p-i-n photodiode. The circuit configuration gave a preamplifier a transimpedance of 60 dBΩ. The receiver OEIC achieved error-free operation at 10 Gbit/s without a postamplifier even with the optical input as low as -10.3 dBm because of its large O/E conversion factor of 890 V/W. A two-channel receiver OEIC array for use in a 10-Gbit/s parallel photoreceiver module based on a PLC platform was made by monolithically integrating multimode WGPD's with HEMT preamplifiers. The side-illuminated structure of the WGPD is suitable for integration with other waveguide-type optical devices. The receiver OEIC arrays were fabricated on a 2-inch wafer with achieving excellent uniformity and a yield over 90%: average transimpedance and average 3-dB-down bandwidth were 43.8 dBΩ and 8.0 GHz. The two channels in the receiver OEIC array also showed sensitivities of -16.1 dBm and -15.3 dBm at 10 Gbit/s. The two-channel photoreceiver module was constructed by assembling the OEIC array on a PLC platform. The frequency response of the module was almost the same as that of the OEIC chip and the crosstalk between channels in the module was better than -27 dB in the frequency range below 6 GHz. These results demonstrate the feasibility of using our receiver OEIC's in various types of optical receiver systems.

File system buffers provide memory space for data being transferred to and from disk and act as caches for the recently used blocks, and the buffer manager usually reads ahead data blocks to minimize the number of disk accesses. However, if several multimedia files with different consumption rates are accessed simultaneously from the file system in which LRU buffer replacement strategy is used, the read-ahead blocks of the low rate file are unloaded from memory to be used for loading a data block of a high data rate file, therefore they should be reloaded again into memory from disk when these blocks are actually referenced. This paper proposes and implements a new buffer cache management scheme for a multimedia file system and analyzes the performance of the proposed scheme by modifying the file system kernel of FreeBSD. In this proposed scheme, initially, some buffers are allocated to each opened multimedia file, privately, then these buffers are reused for other data blocks of that file when they are loaded from the disk. Moreover, the number of private buffers allocated for the file is dynamically adjusted according to its data rate. An admission control scheme is also proposed to prevent opening of a new file which may cause overloads in the file system. Experimental results comparing proposed scheme with the original FreeBSD and a simple CTL-based model show that the proposed buffer management scheme could support the realtime play back of several multimedia files with various data rates concurrently without helps of a realtime CPU and disk scheduling.

Principle of a single shot demultiplextion by means of time-to-space conversion was investigated using femtosecond nonlinear optical response of absorption bleaching of squarylium dye (SQ) J-aggregates. Spincoated films of squarylium dye J-aggregates on glass substrates exhibit efficient and ultrafast transmittance change, which recovers 73% of its initial level (0 fs) within 1 ps. A simple method for time-to-space conversion was applied for this film. We took our attention to one of the characteristics of femtosecond pulse, which is the spatial thinness in its propagation direction. Femtosecond pulses of a single pump pulse and train of four probe pulses were illuminated to the same area (diameter of 10 mm) of the surface of the SQ J-aggregates film. Direction of the probe beam was normal to the surface of the film and that of the pump beam was oblique angle in horizontal plane. Caused by spatial delay of a pump pulse due to the illumination in oblique angle to the film, four probe pulses with interval time of 1 ps (1 THz) meet separate places on the film. Because of the fast response of the SQ J-aggregates, the film picked out part of each probe pulse, which has narrower shapes in horizontal direction compared to the initial circular one by transmittance change of the film. The spatially separated four lines were observed by a CCD camera for an image of the transmitted probe pulse train. These results suggest that the response time of SQ J-aggregate film, which determines the horizontal width of each line, to be enough for demultiplexing of 1 THz optical signals.

The 1 4 optical switch array for wavelength division multiplexing system has been demonstrated where four 14 waveguide digital optical switches have been integrated into one chip. Tape fiber is used as the connection between switch modules to avoid an interconnection fiber jungle. The architecture can be adapted to any number of wavelength channels. Redundant optical switch stage for crosstalk rejection has been used to attain a low crosstalk level. Electro-optic switching is used to attain low power consumption indispensable for routing large wavelength channels.

An architecture for a digital-to-RF converter for a software defined radio (SDR) transmitter is proposed. The ideal hardware architecture for an SDR is a digital-signal to RF-signal direct conversion transmitter. However no conventional digital-to-analog converter (DAC) has converted over 1-GHz RF signal with enough resolution, in the present condition. In this paper, a digital-to-RF direct converter architecture using a ΔΣ modulation technique is proposed for the amplitude-phase modulated signal. The experimental results show that the proposed direct converter outputs a sufficiently accurate signal.

The transmission performance of WDM transmission systems is influenced by many effects according to the type of optical fiber employed in the system. Japanese high-speed transmission systems use dispersion-shifted fiber (DSF). It is well known that the transmission distance of WDM systems employing DSF is restricted by fiber four-wave mixing (FWM). Unequally spaced channel allocation (USCA) was proposed to mitigate the FWM effect. However, if no FWM light is allowed to fall on any optical channel, the number of channels is limited. This paper proposes a new method to extend the number of USCA channels to more than 16 under the optical bandwidth limitation. This method determines channel allocation by considering the distribution of the zero-dispersion wavelength of the optical fiber. The transmission performance of a WDM transmission system employing the proposed USCA methodology is clarified by numerical simulation to confirm that the optical bandwidth requirements can be reduced without degrading transmission performance. As a result, for 16 2.5 Gbit/s, if the fiber input power ranges from -3 dBm/ch to 3 dBm/ch, the achievable transmission distance is 700 km; the fluctuation in zero-dispersion wavelength is assumed to have the standard deviation of 5 nm. For 16 10 Gbit/s, if the fiber input power ranges from 0 dBm/ch to 3 dBm/ch, the achievable transmission distance is 400 km.

A software antenna, which will be a key device realizing flexible and highly reliable wireless communications systems, is inherently matched with software defined radios (SDR). In this paper, first, key technologies on the software antenna are introduced. The technologies contain i) how to recognize the radio environment, ii) how to determine the optimum adaptive signal processing algorithm, and iii) how to reconfigure the digital beamforming circuit. Then, an image of a software antenna with reconfigurable eigenvector-beamspace configuration is presented. Finally, by assuming various propagation conditions, performance of the software antenna in terms of algorithm diversity is demonstrated.

This paper presents a constant-scale-factor radix-2-4-8 CORDIC algorithm for fast vector rotation and sine/cosine computation. The CORDIC algorithm is a well-known hardware algorithm for computing various elementary functions. Due to its sequential nature of computation, however, significant reduction in processing latency is required for real-time signal processing applications. The proposed radix-2-4-8 CORDIC algorithm dynamically changes the radix of computation during operation, and makes possible the reduction in the number of iterations by 37% for 64-bit precision. This paper also describes the hardware implementation of radix-2-4-8 CORDIC unit that can be installed into practical digital signal processors.

In this paper we propose a new lattice based second-order adaptive infinite impulse response (IIR) notch filter that uses a simplified adaptation algorithm. Steady-state analysis of the proposed structure is then studied based on the mean-squared error analysis of the steady-state variable coefficient fluctuations. The analysis is used to derive simple analytical expressions for steady-state variable coefficient variance and an upper bound for the step size adaptation constant. The results are shown to be useful in designing an FSK demodulator using the proposed structure. Computer simulation results are shown to confirm derived analytical expressions.

We present three-wave mixing devices useful for signal processing functions in WDM and TDM systems, including wavelength conversion, spectral inversion, and gated mixing. These mixers exhibit extremely wide bandwidth, low noise, high efficiency, and format transparency.

A new computational method for evaluating the reverse-link interference distribution in a cellular CDMA system is proposed. In particular, a positive feedback effect of the reverse-link closed-loop power control has been taken into account to precisely capture a realistic effect of unequal cell loading on system capacity. It subsequently facilitates computing the frequency reuse efficiency of the cellular CDMA system under unequal cell loading.

A new algorithm is proposed for improving the convergence of backpropagtion networks. This algorithm is obtained by combining the conjugate gradient method and the Kalman filter algorithm. Simulation results show that the proposed algorithm can perform satisfactorily in all cases considered.

This paper investigates the turbo equalization techniques for wireless cellular systems. Simulation results over three GSM channel models are presented.

Agent-based simulations are expected to enable analysis of complex social phenomena. In such simulations, one of the important behaviors of the agents is negotiation. Throughout the negotiations, the agents can make complex interactions with each other. Therefore, the ability of agents to perform negotiation is important in simulations of artificial societies. In this paper, we focus on price negotiations, in which the two sides have opposing interests. In the conventional price negotiation model, the process consists of an alternate succession of directly presented offers and counter-offers exchanging the desired prices. As an extended price negotiation model, we introduce virtual words to mimic the negotiation techniques of humans for indirectly presenting the desired price. The process of the proposed negotiation model consists of an alternate succession of offers of desired price and counter-offers of a word. The words represent the degree of the agent's demand. We propose agents with reinforcement learning who can acquire the ability to distinguish words and use them to negotiate. As a result, we will show that the virtual words became meaningful in the process of negotiations between agents whose negotiating strategies are acquired by reinforcement leaning.

PARAdeg has been defined to try to measure parallelism inherent in a program net. Studies on computation of PARAdeg have been done, but the quantitative evaluation, on how much PARAdeg fits parallelism of program nets, has not been studied. In this paper, we do the evaluation by applying genetic algorithm to measure firing completion times when PARAdeg processors, and less and more processors are provided for 400 program nets. Our experimental results show that the firing completion times decrease rapidly with increase of processors till PARAdeg and slowly when processors are increased to more than PARAdeg, which implies PARAdeg is a reasonable standard to measure parallelism of program nets.

A broadband and flexible receiver architecture is investigated for the handheld software defined radio (SDR). The proposed SDR architecture is based on the direct conversion and low intermediate frequency (low-IF) principle with digital channel filtering, which provides the receiver with flexibility for the multi-standard application. This architecture also enables analog-to-digital converter activating essentially in baseband or low frequency so that the clock jitter, which serves as an important subject in the well-known IF sampling method, can be reduced. Basic performance of the proposed architecture has been confirmed by the experimental model.

In this paper, we propose an idea of the generalization of threshold signature and authenticated encryption for group communications. The concept of the (t, n) threshold signature with (k, l) shared verification is implemented in group-oriented cryptosystems. In the system, any t members can represent a group to sign a message and any k verifiers can represent another group to authenticate the signature. By integrating the cryptographic techniques of data encryption, digital signature and message recovery, a group-oriented authenticated encryption scheme with (k, l) shared verification is also proposed. The message expansion and communication cost can also be reduced in our schemes.

We propose a new method for generating visual stereo images from the common two dimensional images without 3D reconstruction. The major novel contributions of this report are in two aspects. First, we address the detection of dominant motion presented in the given scenes, for doing so we borrow phase shift theorem and calculate the inverse Fourier transform of cross-power spectrum to find the maximum peak value whose position can be used to decide motion parameters. Secondly, unlike most of researchers study the stereo vision to recover 3D information for modeling and rendering, we address the visual stereo image generation without 3D reconstruction by applying the computed motion parameters to make decision of selecting two given images to form a stereo pair for left eye and right eye respectively. The proposed approaches can be employed for applications such as navigation in a virtual environment.