A novel base station for microwave radio-on-fiber systems is proposed. It consists of an L-band electroabsorption modulator and a uni-traveling-carrier photodiode. We show it is applicable for bias-free operation and full-duplex transmission and demonstrate 100-Mbit/s bidirectional data transmission in the 5-GHz band.

The stateless-based cache invalidation schemes for wireless environments can be categorized into either asynchronous or synchronous cache invalidation according to the broadcasting way of invalidation report. However, if the asynchronous cache invalidation scheme attempts to support local processing of read-only transaction, a critical problem may occur; the asynchronous invalidation reports provide no guarantee of waiting time for mobile transactions requesting commit. To solve this problem, the server in our approaches broadcasts two kind of messages, asynchronous invalidation report to reduce transaction latency and periodic guide message to avoid the uncertainty of waiting time for the next invalidation report. This paper presents a simulation-based analysis on the performance of the suggesting algorithms. The simulation experiments show that the local processing algorithms of read-only transaction based on asynchronous cache invalidation scheme get better response time than the algorithm based on synchronous cache invalidation scheme.

785 nm (AlGaAs) laser diode (LD) with a window-mirror structure is demonstrated to be a potential candidate as a highly reliable light source of CD-R. The intermixing of a multi-quantum well structure by silicon implantation is used to form the window-mirror structure. Carbon is adopted as an acceptor because of its low thermal diffusion constant in crystals. As a result, the window-mirror-structure 785 nm AlGaAs LDs with ordinary far field patterns suitable for the actual CD-R drives have shown stable single lateral mode operation up to 250 mW. A mirror degradation level is significantly increased by the window-mirror structure. The pulsed operation current at 160 mW, 70 of the carbon doped LD is reduced by about 15% from that of zinc doped one. Highly reliable 160 mW pulsed operation is also realized at 70. This LD believed to be suited for the next generation high-speed (16-24x) CD-R drives necessitating 160 mW class LD.

The explosive growth of World Wide Web usage is causing a number of performance problems, including slow response times, network congestion, and denial of service. Web site that has a huge number of accesses and requires high quality of services, such as a site offering hosting services, or content delivery services, usually uses a cache server to reduce the load on the original server offering the original content. To increase the throughput of the caching process and to improve service availability, multiple cache servers are often positioned in front of the original server. This requires a switch to direct incoming requests to one of the multiple cache servers. In this paper, we propose a routing algorithm for such a switch in front of clustered multiple cache servers and evaluate its performance by simulation. The results show that our routing algorithm is effective when content has request locality and a short period of validity, for example, news, map data, road traffic data, or weather information. We also identify points to consider when the proposed algorithm is applied to a real system.

We propose a frequency stabilization system for laser diodes (LD's), in which the major parameters in the stabilization process can be controlled in respond to the monitored frequency noise characteristics in real-time basis. The performance of this system was also tested through stabilizing a 35 mW visible LD. The center frequency of the LD has been stabilized by negative electrical feedback based on Pound-Drever-Hall technique. The linewidth of the LD has been reduced by adapting optical feedback from resonant confocal Fabry-Perot (CFP) cavity. The controlling parameters, especially gain levels and frequency responses of the negative electrical feedback loop can be manipulated to remove the instantaneous frequency noise by monitoring power spectral density (PSD) of the frequency error signals in the real-time basis. The achieved PSD of frequency noise of a sample LD stabilized by the present system was less than 1105 Hz2/Hz for the Fourier frequency < 10 MHz. The reduced linewidth was estimated to be narrower than 400 kHz. The achieved minimum square root of the Allan variance was 3.910-11 at τ = 0.1 msec.

The thermal response of a tunable laser is analyzed by using a mode density method based on a Fourier-Laplace analysis. This method introduces a mode density function for mode distribution of the Fourier-Laplace transform and gives temperature time-dependency in an integral form instead of an infinite weighted summation. When symmetric structures are assumed, the mode density method gives the transient thermal response in a simple form: error functions (spherical-symmetry case) and exponential integral functions (cylindrical-symmetry case). The cylindrical-symmetry analysis was extended to the noncylindrical-symmetry model and the thermal response of the tunable laser was calculated by the mode density method. The result shows good agreement with a Fourier-Laplace analysis (deviation 2%) and experimental results. As a rough estimation, the thermal response of the laser is in proportion to the logarithm of time in some range that depends on the chip and tuning-section size of the laser.

Recent activities on ultrafast photonic device technology development in the Femtosecond Technology Project sponsored by NEDO are introduced. Topics include management and control of the higher order dispersions of optical fibers, ultrafast mode-locked semiconductor laser, symmetric Mach-Zehnder type all-optical switch, ultrafast serial-to-parallel signal converter and sub-picosecond wavelength switch. Challenges towards novel ultrafast switching material systems are also described.

In this paper, we propose an algorithm to calculate the higher moments of the busy period length of a discrete-time M/G/1 type queue with finite buffer. The queueing model has a level-dependent transition probability matrix. Our algorithm is given as a set of recursive formulas which are derived from the relationship among the generating function matrices of the fundamental period. As an example of our algorithm, we provide an approximate analysis of a HOL (Head Of Line) priority control queue.

Available statistical skew models are too conservative in estimating the expected clock skew of a well-balanced H-tree. New closed form expressions are presented for accurately estimating the expected values and the variances of both the clock skew and the largest clock delay of a well-balanced H-tree. Based on the new model, clock period optimizations of wafer scale H-tree clock network are investigated under both conventional clocking mode and pipelined clocking mode. It is found that when the conventional clocking mode is used, clock period optimization of wafer scale H-tree is reduced to the minimization of expected largest clock delay under both area restriction and power restriction. On the other hand, when the pipelined clocking mode is considered, the optimization is reduced to the minimization of expected clock skew under power restriction. The results obtained in this paper are very useful in the optimization design of wafer scale H-tree clock distribution networks.

This paper describes the recent progress in the device performance of the uni-traveling-carrier photodiode (UTC-PD). The UTC-PD utilizes only electrons as the active carriers and this unique feature is the key to achieving excellent high-speed and high-output characteristics simultaneously. The achieved performance includes a record 3-dB bandwidth (f3dB) of 310 GHz, a high output current over 180 mA with an f3dB of 65 GHz, a high linearity of up to 80 mA, and a zero-bias operation with an f3dB of 230 GHz and an output peak current of 6.8 mA.

A periodic approach introduced previously is applied to the TM wave scattering from a finite periodic surface. A mathematical relation is proposed to estimate the scattering amplitude from the diffraction amplitude for the periodic surface, where the periodic surface is defined as a superposition of surface profiles generated by displacing the finite periodic surface by every integer multiple of the period . From numerical examples, it is concluded that the scattering cross section for the finite periodic surface can be well estimated from the diffraction amplitude for a sufficiently large .

In this paper, a simple chaotic circuit using two RC phase shift oscillators and a diode is proposed and analyzed. By using a simpler model of the original circuit, the mechanism of generating chaos is explained and the exact solutions are derived. The exact expression of the Poincare map and its Jacobian matrix make it possible to confirm the generation of chaos using the Lyapunov exponents and to investigate the related bifurcation phenomena.

Negative differential conductance based on lateral interband tunnel effect is demonstrated in a planar degenerate p+-n+ diode (Esaki tunnel diode). The device is fabricated with the current silicon ultralarge scale integration (Si ULSI) process, paying attention to the processing damage so as to reduce an excess tunnel current that flows over some intermediate states in the tunnel junction. I-V characteristics at a low temperature clearly show an intrinsic electron transport, indicating phonon-assisted tunneling in Si as in the case of the previous Esaki diodes fabricated by the alloying method. In addition, a simple circuit function of bistable operation is demonstrated by connecting the planar Esaki diode with conventional Si metal-oxide-semiconductor field effect transistors (MOSFETs). The planar Esaki diode will be a promising device element in the functional library for enhancing the total system performance for the coming system-on-a-chip (SoC) era.

As a method of analyzing the wave scattering from a finite periodic surface, this paper introduces a periodic approach. The approach first considers the wave diffraction by a periodic surface that is a superposition of surface profiles generated by displacing the finite periodic surface by every integer multiple of the period . It is pointed out that the Floquet solution for such a periodic case becomes an integral representation of the scattered field from the finite periodic surface when the period goes to infinity. A mathematical relation estimating the scattering amplitude for the finite periodic surface from the diffraction amplitude for the periodic surface is proposed. From some numerical examples, it is concluded that the scattering cross section for the finite periodic surface can be well estimated from the diffraction amplitude for a sufficiently large .

This paper proposes two modes of the congestion control scheme to improve its behavior during the start-up period of networks in current TCP over ATM-UBR implementation. The proposed two modes are a single packet loss mode and a multiple packet losses mode. The proposed algorithm is to minimize the number of cell losses in the ATM switch during specially the start-up period. During the start-up period, multiple packet losses often happens because a TCP sender starts with default parameters. It often ends up sending too many packets and too fast, leading to multiple losses is packet burstiness which occurs right after fast recovery ends. We analyze the transition behavior during fast recovery algorithm and estimate the number of new packets sent when multiple packet losses detected. We present a simple simulation model and numerical results to investigate its performance of the proposed algorithms.

The analytic expression for the transmission spectrum of cascaded long-period fiber gratings is presented in a closed form. When several identical gratings are cascaded in-series with a regular distance, the transmission spectrum is revealed to have a series of regularly spaced peaks, suitable for multi-channel filters. The analytic solution is obtained by diagonalizing the transfer matrix of each grating unit that is composed of a single grating and a grating-free region between adjacent gratings. The spectrum of the device is simply described with the number of cascaded gratings and a single parameter that has the information of the phase difference between the modes. With the derived equation, the spectral behaviors of the proposed device are investigated. The intensity of each peak can be controlled by adjusting the strength of a single grating. The separation between adjacent gratings determines the spacing between the peaks. The finesse of the peaks can be increased by cascading more gratings. The derived analytic results are compared with the known results of paired gratings and phase-shifted gratings.

We will present the theoretical analysis of and experimental measurements on the transmission characteristics of multi-channel long period fiber gratings in terms of the physical parameters like the separation distance, grating length and number of gratings. These parameters can be used to control the spectral channel spacing, number of channels, loss peak depth, and channel bandwidth of multi-channel long period fiber gratings.

The analytic expression for the transmission spectrum of cascaded long-period fiber gratings is presented in a closed form. When several identical gratings are cascaded in-series with a regular distance, the transmission spectrum is revealed to have a series of regularly spaced peaks, suitable for multi-channel filters. The analytic solution is obtained by diagonalizing the transfer matrix of each grating unit that is composed of a single grating and a grating-free region between adjacent gratings. The spectrum of the device is simply described with the number of cascaded gratings and a single parameter that has the information of the phase difference between the modes. With the derived equation, the spectral behaviors of the proposed device are investigated. The intensity of each peak can be controlled by adjusting the strength of a single grating. The separation between adjacent gratings determines the spacing between the peaks. The finesse of the peaks can be increased by cascading more gratings. The derived analytic results are compared with the known results of paired gratings and phase-shifted gratings.

We will present the theoretical analysis of and experimental measurements on the transmission characteristics of multi-channel long period fiber gratings in terms of the physical parameters like the separation distance, grating length and number of gratings. These parameters can be used to control the spectral channel spacing, number of channels, loss peak depth, and channel bandwidth of multi-channel long period fiber gratings.

In an ideal fiber grating having a uniform refractive index modulation, the reflection or the transmission spectrum is symmetric with equal amount of side lobes on both sides of the resonant wavelength of the fiber grating. It is observed that a long-period fiber grating made by a non-uniform UV laser beam through a uniform amplitude mask has an asymmetric transmission spectrum. The asymmetric characteristic is explained with Mach-Zehnder effect in the long-period fiber grating. The non-uniform UV laser beam makes also a non-uniform index modulation along the fiber core. Therefore, a beam coupled to a cladding mode at a section of the grating can be re-coupled to the core mode after passing a certain distance. The re-coupled beam makes Mach-Zehnder-like interference with the un-coupled core mode. However, it is presented that the asymmetric phenomenon can be overcome by scanning the UV laser beam along the fiber over the mask. The beam scanning method is able to suffer the same fluence of the UV laser beam on the fiber. Finally, a linearly chirped long-period fiber grating was made using the non-uniform UV laser beam. Due to the asymmetricity the chirping effect was not clearly observed. It is also presented that the beam scanning method could remove the asymmetric problem and recover the typical spectrum of the linearly chirped fiber grating.