A novel kind of optical fiber Raman amplifier was proposed in this paper.It employed low-power laser diode as pumping sources.A genetic algorithm was combined with the simulated annealing method to optimize the configuration of the pump wavelengths as well as pump powers.The optimization speed has been greatly accelerated in comparison with conventional methods.It can also avoid the results from being trapped in the local optimal points.Simulation results show that such a kind of Raman amplifier provides a gain profile of small in-band ripple and sharp out-of-band roll-off.Sharp roll-off feature can save the total pump power.

In this paper, amplified double Rayleigh backscattering noise (DRB) in the optical fibre Raman amplifier is analysed. Expressions are presented for both forward pumping and backward pumping schemes. Calculation is performed to show the effective suppression of DRB noise by employing an optical isolator. The optimal position for the isolator is determined and is found to be insensitive to the power levels of the signals and pumps. The results show that a reduction of the DRB noise by almost 2 to 3 orders can be reached.

Properties and performance for alloy and multilayer perpendicular recording media designs utilizing a soft magnetic underlayer are compared. Among samples considered here, grain size and grain size dispersion are more highly refined for alloy media deposited at high substrate temperature, and are beginning to approach those now available in longitudinal recording. Multilayer media made at ambient temperature typically sacrifice film density and surface smoothness for interface quality. Although microstructural development and the manufacturing process for multilayer media are less mature versus alloy, multilayer media remain attractive due to their high anisotropy potential and the ease with which H-n and H-c can be controlled. For thermally stable alloy media made on a pilot production sputtering machine, a spin-stand areal density of 61 Gb/in(2) has been demonstrated at 350 Mb/s data rate with an on-track bit-error-rate reference level of 1e-6. Using the same media, a working perpendicular drive has been demonstrated at 32 Gb/in(2) and 500-800 Mb/s data rate.

As the use of intranets becomes common in business environments and organizations, protecting such networks from intrusion is of critical importance. A security suite has been developed to achieve a high level of safety and security in preserving the integrity of intranet information. The various components of the suite fulfill different aspects of ensuring predefined security objectives: the Modified File Intrusion Detection System (mFIDS), the Security Log Processing and Analysis System (SLPA), and the Network Security Toolkit (NST). The mFIDS aims to target malicious intranet users, handle unauthorized file activities in real-time and constantly updates the central server. SLPA aims to capture all intranet file activities, provide historical and statistical analysis, and thus detect trends of attacks and malicious behavior. NST attempts to provide a systematic way in configuring and manipulating the properties of the network elements to suit an organization's security objectives.

Measurements and modeling of soft magnetic underlayer (SUL) materials for perpendicular magnetic recording application are carried out. The process dependent magnetic properties of FeCoB, CoZrNb, and FeAlN SUL materials on glass and aluminum disk substrates are studied and correlated with spin-stand noise performance. The SUL-induced do noise amplitude approaches the electronic noise floor for certain material combinations, e.g., FeCoB or CoZrNb on glass, when care is taken to relieve stress-induced perpendicular anisotropy by thermal annealing. Landau-Lifshitz-Gilbert micromagnetics, finite-element method calculations, and a micromagnetic recording model show that write field amplitude, write field gradient, and readback waveform are only slightly impacted by SUL moment in the 1-2 T range. Much more important are the head-to-SUL distance and the write head saturation moment. These results suggest that extremely high SUL moment may not be necessary, which can be leveraged to meet other key practical requirements such as corrosion resistance and manufacturability.

In this pape r,we analyze and simulate the temperature effect on electro-optical behavior of single quantum well laser diodes (SQW-LD) both in time and frequency domains.M odeling of SQW-LD based on three-level rate equations by means of Matlab Simul ink is given and various simulations are present.The results show that the SQW- LD has good temperature property and wide modulation bandwidth.When the temperat ure increases from 250 K to 350 K,the modulation bandwidth decreases only from 2 5.00 GHz to 21.72 GHz.

With the rapid proliferation of Internet technologies, accessing and operating engineering instruments remotely anytime anywhere is fast becoming a reality. This paper presents a new Web-based virtual laboratory on a frequency modulation experiment for the teaching of an undergraduate course on communication principles in the National University of Singapore (NUS). The laboratory requires only a common Web browser to access and incorporate schemes for reducing data traffic and authenticating users. It enables students to have a natural hands-on experience of using an expensive spectrum analyzer on a one-to-one basis and provides a solution for distant engineering education. The system uses a double client-server structure where access to the experiment is via two rounds of client-server processing. The virtual laboratory can be accessed at the Web site http://vlab.ee.nus.edu.sg/vlab/freqmod/index.html.

Article Comparison among RZ, NRZ, and CRZ Pulse Evolutions in Birefringent Nonlinear Fibers with Third-order Dispersion Effect was published on October 1, 2001 in the journal Journal of Optical Communications (volume 22, issue 5).

This paper presents the implementation of a web-based laboratory experiment on a `coupled tank apparatus', a MIMO system using the Transmission Control Protocol (TCP) for communication. The web-based laboratory has been developed to serve undergraduate students in the Department of Electrical Engineering at The National University of Singapore. The control strategies adopted include: manual control, the use of PID controllers, a general state-space controller, as well as fuzzy controllers. The implementation uses video conferencing to provide fast and point-to-point visual feedback to the client, on the events in the laboratory and also allows users to control the zoom and viewing angle of the video. This web-based remote labs can be accessed at vlab.ee.nus.edu.sg/vlab/control/

A novel technique for incorporating rapid thermal annealing into media sputter fabrication has facilitated the production of flyable media samples. Discs are fabricated with standard processing techniques to control physical grain size and crystallite texture. A CrMn caplayer ranging in thickness between 0.5 and 5 nm is subsequently deposited to provide the Mn-diffusant necessary to achieve post-treatment exchange decoupling. While still in-situ and before application of protective overcoats, the discs are exposed to temperatures between 200/spl deg/C and 350/spl deg/C compatible with most media production processes. A threefold increase in coercive force (peak reaching /spl sim/3800 Oe) and 10 dB improvement in medium signal-to-noise ratio is observed for the optimized process.

In this work, we have studied the effect of lubricant thickness on magnetic recording, specifically, its effect on head-media spacing (HMS). In the experiment, a series of disks were first lubricated to various thicknesses ranging from 20 to 60 /spl Aring/. Then, read/write recording tests were performed for each disk on one track near the disk OD with variable linear densities. Next, the lubricant was washed off from MD to OD using a solvent, so the thickness of lubricant at the OD track was reduced. The read/write tests showed that the read-back signal was enhanced after lubricant wash-off. Using Wallace's equation, the HMS change was calculated and found to be proportional to the change of the lubricant thickness. This result conclusively establishes that disk lubricant indeed takes up HMS and must be accordingly accounted for in HMS budgeting.

In this article, we present an overview on the web-based virtual laboratories currently available in the Department of Electrical and Computer Engineering, NUS (National University of Singapore). Two pilot web-based virtual laboratories have been developed and launched in the Faculty of Engineering at NUS. One laboratory is on an oscilloscope experiment and is aimed to serve over 1000 first year undergraduate engineering students in the Faculty. The other is on the control of a coupled-tank system and with the capability to implement and test various control strategies, is developed for both teaching and research. Rather than simulating what was happening in the real world on the client as is often done in other virtual laboratories, the system developed makes use of real time video and audio capture of actual instrument and apparatus. In addition, the use of the mouse to turn the control buttons and knobs of the instruments has been implemented so that a more realistic feel of the instrument is provided. The launch of the virtual laboratory on the oscilloscope experiment in early March 1999 has created a lot of interests, with numerous user feedback and comments received. Both laboratories can be accessed at http://vlab.ee.nus.edu.sg/vlab.

The effect of lubricant on flyability and read-write performance in ultra-low flying regime has been studied over the disks with lubricant on one half of disk surface thicker than the other half The dynamics of a slider was monitored using Acoustic Emission (AE) and Laser Doppler Vibrometer (LDV). An instability characteristic of a slider flying over the thick lubricant region has been observed and this instability intensifies as flying height decreases and the step thickness increases. After the slider flies over the disks, it has been found that lubricant re-distribution occurs as lubricant is "carried" by the flying slider from the thick lubricant region and deposited onto the thin lubricant region. Possible mechanisms were discussed to explain the observations. Finally, recording tests were performed and the magnetic spacing loss due to the lubricant steps was estimated.

The principle of single quantum well laser diode(SQWLD) was reviewed. Discussion was given on the functionality of the gateway state(quasi2 dimensional state) which was introduced to describe the transportation of carriers and photons between the separated confinement heterostructure(SCH) and the quantum well. A relative complete set of the equations was presented. By means of Simulink, which is a functional module of Matlab ○R , a mathematical model for digital analysis of SQWLD was proposed. The model is easy to use. It provides with the advantages of short computation time, realtime supervision and control, convenience for parameter modification. It was used to simulate the optoelectronic behaviors of SQWLD, such as carrier/photon establishment under step drive current, optical powerdrive current relationship, and frequency response to small signal modulation. The results are in good agreement with the reported data. The model can be used for the purpose of device technique improvement and for automatic design and performance simulation of optical fiber networks.

Mechanical texture and its impact on recording performance at high recording density have been studied experimentally in this paper. We found that texture noise has a negligible effect on the recording performance in modern disks, even at high density. Texture noise can well be explained by a band pass modulation model. Experimental evidence shows that texture caused amplitude modulation can appear as jitter, which proves statements from the modulation theory as suggested by V. Minhuin [J. Appl. Phys. April 1999],.