Verification of an Elasto-Piastic Earthquake Analysis Procedure

An effective stress based, finite element procedure of modeling earthquake soil and soil-structure interaction problems is described. Elasto-plastic constitutive models are used to describe the stress-strain behavior of soils. A fully-coupled finite element formulation is employed, which allows the pore pressure build-up and dissipation to be modelled simultaneously. Undrained behavior is modelled as a special case of this general formulation. In a previous study, the procedure was used to perform a “before the event” prediction of the liquefaction behavior of a 10-meter thick saturated sand deposit subjected to an earthquake loading. In the present paper, the predictions are compared with experimental centrifuge data. In a second study, an earthquake soil-structure interaction problem modelled in a centrifuge was analyzed and the results compared. The results of this study are also summarized in this paper

Cost efficient narrow linewidth laser transmitter for coherent detection

Authors present a cost efficient narrow linewidth laser transmitter for future coherent detection systems. The spectral purity of the laser allows the phase modulation of data signals at bit rates as low as 155 Mb/s

Experimental investigation of the impact of optical injection on vital parameters of a gain-switched pulse source

An analysis of optical injection on a gain-switched distributed feedback (DFB) laser and its impact on pulse parameters that influence the performance of the pulse source in high-speed optical communication systems is presented in this paper. A range of 10 GHz in detuning and 5 dB in injected power has been experimentally identified to attain pulses, from an optically injected gain-switched DFB laser, with durations below 10 ps and pedestal suppression higher than 35 dB. These pulse features are associated with a side mode suppression ratio of about 30 dB and a timing jitter of less than 1 ps. This demonstrates the feasibility of using optical injection in conjunction with appropriate pulse compression schemes for developing an optimized and cost-efficient pulse source, based on a gain-switched DFB laser, for high-speed photonic systems

Characterization of wavelength interleaving in radio-over-fiber systems employing WDM/SCM

A radio-over-fiber (RoF) distribution system incorporating both sub-carrier multiplexing and wavelength division multiplexing (WDM) technologies is presented. This signal is directly modulated onto three high-speed lasers. Bragg filters are employed at the receiver base station in order to both demultiplex the required optical channel, and ensure that the detected signal is single side band (in order to overcome dispersion limitations of the link). System spectral efficiency is optimised by wavelength interleaving. The channel spacing between the WDM channels is varied and the system performance for different values of channel spacing and spectral efficiencies is investigated. The results show that wavelength interleaving is a reliable technique that could be used to increase the spectral efficiency of RoF systems

Cyclic Loading Response of Cohesive Soils Using A Bounding Surface Plasticity Model

The concept of the bounding surface in plasticity theory has been used to develop a general three-dimensional constitutive model for cohesive soils within the framework of critical state soil mechanics. The present work focuses on the response of the above model under cyclic loading conditions. It is shown mainly qualitatively and partially quantitatively, that the model predicts in detailed form a material response which does agree with observed experimental behavior under undrained and drained loading conditions at any overconsolidation ratio and for different cyclic deviatoric stress amplitudes

Pulse source for 80 Gb/s systems using a gain-wwitched laser diode followed by a nonlinearly chirped grating

This work presents the generation of 3.5 ps pulses at a repetition rate of 10 GHz and the optimization of the pulse spectrum. The output pulses are near transform limited and have pulse pedestals that are virtually eliminated to 35 dB down from the peak of the pulse, thus providing a source suitable for use in 80 Gb/s OTDM systems

Optimized pulse source based on a gain-switched laser diode in conjuction with a non-linearly chirped grating for 40 Gbit/s systems

A technique based on the design of an optimized source of pico-second optical pulses, which exhibits excellent temporal and spectral purity, is presented. The procedure entails an initial complete intensity and chirp characterization of pulses, from an externally injected-gain switched laser (EI-GSL), using the technique of frequency resolved optical gating (FROG). This characterization yields the parameters that are required for the design of a non-linearly chirped fibre Bragg grating (NC FBG) with a chirp profile that is opposite to that measured across the pulse. By employing the tailor made NC FBG after the gain-switched laser, direct compression of the gain-switched pulses is achieved, to obtain pedestal-free, near transform-limited, 7 ps pulses. The system viability, characterized by simulations, portrays a 6 dB difference in performance between a pulse source with insufficient TPSR and one that exhibits adequate TPSR &(ge; 30 dB)

Inverse scattering approach to multiwavelength Fabry-Pérot laser design

A class of multiwavelength Fabry-Pérot lasers is introduced where the spectrum is tailored through a patterning of the cavity effective index. The cavity geometry is obtained using an inverse scattering approach and can be designed such that the spacing of discrete Fabry-Pérot lasing modes is limited only by the bandwidth of the inverted gain medium. A specific two-color semiconductor laser with a mode spacing in the THz region is designed, and measurements are presented demonstrating the simultaneous oscillation of the two wavelengths. The nonperiodic effective index profile of the particular two-color device considered is shown to be related to a Moiré or superstructure grating

Optimized pulse source employing an externally injected gain-switched laser diode in conjunction with a nonlinearly chirped grating

In this paper, we demonstrate the generation of transform-limited short optical pulses, which display excellent spectral and temporal qualities by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a nonlinearly chirped grating. Using this technique, 3.5-ps optical pulses exhibiting a time-bandwidth product (TBP) of 0.45 are generated, which are suitable for use in high-speed 80 Gb/s optical time-division multiplexing (OTDM) communications systems. The numerical integration of a set of rate equations using suitable parameters for the devices used in the experiments were carried out to further confirm the feasibility of the proposed method for developing an optimized pulse source for high-speed photonic systems

Analysis of bit rate dependence up to 80 Gbit/s of a simple wavelength converter based on XPM in a SOA and a shifted filtering

This paper provides the analysis of wavelength converted pulses obtained with a simple semiconductor optical amplifier (SOA)-based wavelength conversion scheme, which exploits cross phase modulation (XPM) in an SOA in conjunction with shifted filtering. The analysis includes experimental measurements of the back-to-back system performances as well as frequency-resolved optical gating (FROG) characterisations of the wavelength converted pulses. These measurements are implemented at different bit rates up to 80 Gbit/s and for both red and blue-shifted filtering, particularly showing different patterning effect dependencies of red and blue-shifting techniques. This analysis is developed by the addition of a numerical study which corroborates the experimental results. A further understanding of the different performances of red and blue filtering techniques, presented in the literature, can thus be proposed. The placement of the filter to undertake red-shifted filtering (RSF) allows us to achieve very short pulse widths but high bit rate operation is limited by pattern effects. The blue-shifted filtering (BSF) technique shows optimum performance as regards to patterning effects even if the wavelength converted pulses can be larger