Raman laser based on a fiber with variable mode structure

A Raman converter based on an active fiber with variable mode structure is experimentally and theoretically studied. It is demonstrated that a conventional telecommunication fiber with variable mode structure can be used to construct Raman converters © Pleiades Publishing, Ltd., 2011.

Effect of Rayleigh-scattering distributed feedback on multiwavelength Raman fiber laser generation

We experimentally demonstrate a Raman fiber laser based on multiple point-action fiber Bragg grating reflectors and distributed feedback via Rayleigh scattering in an ∼22-km-long optical fiber. Twenty-two lasing lines with spacing of ∼100 GHz (close to International Telecommunication Union grid) in the C band are generated at the watt level. In contrast to the normal cavity with competition between laser lines, the random distributed feedback cavity exhibits highly stable multiwavelength generation with a power-equalized uniform distribution, which is almost independent on power. © 2011 Optical Society of America.

Passive mode locking in erbium-doped fibre laser by carbon nanotubes

Passively mode locked fibre lasers have a variety of applications ranging from telecommunication to medical photonics. Carbon nanotubes (CNTs) have attracted recently a great deal of attention as a promising solution for saturable absorber elements required for laser mode locking (see e.g. [1-3] and references therein). CNTs can be used as a saturable absorber in passively mode locked fibre laser directly [1,2] or as a CNTs polymer composites [3]. An attractive feature of CNT-based solutions in fibre lasers is a possibility to maintain the compactness, robustness of all-fibre format and low cost through using all standard telecom compatible components. The two important technical challenges in such type of lasers are: (i) to achieve stable polarization properties of the generated radiation without using complex control elements, and, (ii) to avoid low frequency instabilities of the mode-locked pulse train. In this paper we report results of the experiments on mode-locked soliton fibre laser using the following standard components: 1m of highly doped erbium fibre (Liekki Er80-8/125) serves as the gain medium with nominal absorption of 80 dB/m at 1530 nm; a 976 nm laser diode providing up to 310mW power is used to pump the laser via a 980/1550 wavelength division multiplexing; an isolator is employed to ensure single direction oscillation; SMF-28 is used to create necessary amount of anomalous dispersion to form soliton pulse making the total cavity length around 7.83 m; the CNT-polyvinyl alcohol polymer saturable absorber sandwiched in the FC/PC connector is used as a mode-locker device (see [3] for details). © 2011 IEEE.

Generation of 1.7-μJ pulses at 1.55μm by a self-modelocked all-fiber laser with a kilometers-long linear-ring cavity

We report on the record-high pulse energy of nearly 1.7 μJ obtained directly from a self-mode-locked all-fiber erbium laser with a linear-ring cavity owing its extreme elongation up to several kilometers. Specially selected telecommunication fibers, providing large normal net cavity dispersion in the vicinity of 1.55 μm, have been used for this purpose. Along with compensation for polarization instability in the longer linear arm of the cavity, such approach has ensured stable wavebreaking- free mode-locked lasing with an ultra-low pulse repetition rate of 35.1 kHz. © 2010 by Astro Ltd.

Informatika, telekommunikáció és gazdasági stabilitás (Information technology, telecommunications and economic stability)

Fizikai példákon és matematikai modelleken bemutatjuk, hogy a rendszerek működésének hatékonyságnövekedése instabilitást eredményezhet. Megvizsgáljuk, hogy az informatika és a telekommunikáció fejlődése okozhat-e rendszerszintű instabilitást, illetve milyen gazdasági eszközök vannak a stabilitás fenntartására. / === / Using examples from physics and mathematical modeling, the paper shows that increasing efficiency in systems can lead to instability. The question thus arises whether the development of information and telecommunication technology can lead to instability in the economic system. The policy tools used to maintain stability are also discussed.

Kiigazítás recesszió nélkül. Esettanulmány a magyar stabilizációról = Adjustment without recession: A Case Study of Hungarian Stabilization

1995. március 12-én a magyar kormány és a központi bank szigorú kiigazítási és stabilizációs programot hirdetett meg. A cikk az első eredmények számbavételére tesz kísérletet. A program meghirdetése előtt Magyarország két egymást követő év- ben hatalmas fizetésimérleg-hiányt mutatott fel, és nemzetközi megítélése romlani kezdett. A program radikális intézkedései nyomán elkerülhetővé vált a mexikói vál- sághoz hasonló pénzügyi katasztrófa. Sok makrogazdasági mutató jól érzékelhető javulást jelez: lényegesen csökkent a kereskedelmi mérleg és a folyó fizetési mérleg hiánya, a költségvetés elsődleges egyenlege pozitív lett. Az ilyesféle stabilizációs programokat rendszerint súlyos visszaesés és a munkanélküliség nagy növekedése kíséri. Magyarország elkerülte ezeket a mellékhatásokat: a GDP drasztikus vissza- esés helyett valamelyest tovább növekedett, és a munkanélküliség változatlan ma- radt. A javulásnak nagy ára volt: az életszínvonal erőteljes csökkenése, az infláció felgyorsulása, bár a magyarországi infláció még mindig a kézben tartott, mérsékelt infláció sávjában maradt. A cikk ismerteti a program heterodox módszereit: 1. nagy leértékelés, az előre meghirdetett csúszó árfolyam rezsimjének bevezetése, valamint ideiglenes import- vámpótlék kivetése; 2. határozott jövedelempolitika, amely 12 százalékos reálbércsök- kenést kényszerített ki; 3. fiskális intézkedések, köztük jóléti jogosultságok csök- kentése (a program meghirdetése előtt ezek a jogosultságok tabuk voltak); 4. a hitel- kínálat átcsoportosítása a vállalati szektor javára, a jövedelmezőség növekedése; 5. feszített (bár nem mértéktelenül feszített) monetáris politika, amely lehetővé tette a sikeres vállalatok expanzióját; 6. a privatizáció felgyorsítása, nagy és sikeres lépé- sek egyes kulcsszektorok (energia, telekommunikáció) privatizációjában. Végezetül a tanulmány óva int a túlzott magabiztosságtól és felhívja a figyelmet a potenciális veszélyekre. A makrogazdasági javulás még törékeny. A magyar fejlődés legbiztatóbb sajátossága a termelékenység erőteljes és folyamatos növekedése. / === / On March 12, 1995 Hungary s government and central bank announced a tough program of adjustment and stabilization. This study is an attempt to asses the first results. Before the announcement of the program Hungary had a huge current account deficit for two consecutive years, and her international reputation started to decline. The program s radical measures made it possible to avoid a Mexico-style financial catastrophe. Many macroeconomic indicators show tangible improvement: the trade deficit and the deficit on the current account have been reduced significantly, the primary budget shifted to surplus. These kinds of adjustment programs are usually associated with deep recession and a large increase of unemployment. Hungary avoided these adverse side-effects: GDP instead of a drastic decline, continued to grow somewhat, and unemployment remained unchanged. There was a high price for the improvement: a sharp decline in the standard of living, and an acceleration of inflation, although Hungary is still in the range of controlled, moderate inflation. The paper describes the heterodox instruments of the program: (1) large devaluation, followed by a new exchange rate regime of pre-announced crawling peg, and a temporary import surcharge, (2) energetic income policy, enforcing a 12% cut in real wages; (3) fiscal measures, including cuts in welfare entitlements. That happened for the first time: before the program entitlements had been regarded as taboo ; (4) reallocation of credit supply in favor of the enterprise sector; increase of profitability; (5) tight (but not excessively tight) monetary policy, allowing the expansion of successful private busi- ness; (6) acceleration of privatisation, including large and successful steps in the privatisation of some key sectors (energy, telecommunication). Finally the paper warns against excessive self- confidence and draws the attention to potential dangers. The macroeconomic improvement is still fragile. The most reassuring feature of Hungary s development is the impressive and persistent improvement of productivity.

A társadalmi felelősségvállalás vállalati on-line kommunikációjának kritikai elemzése (Critical Analysis of Online CSR Communication in Hungary)

A vállalatok társadalmi felelősségvállalásával (CSR) kapcsolatos alapelvek, kezdeményezések és tevékenységek kommunikációja a vállalati kommunikáció egyik sarkalatos pontjává vált szinte az egész világon. A cégek CSR-kezdeményezéseik bemutatásához egyre többször az internetet is igénybe veszik. Az on-line média használatával párhuzamosan az elmúlt évtizedben egyre többen kutatják a CSR-kommunikáció elektronikus formáit, jóllehet ezek a kutatások többnyire leíró jellegűek, és a CSR-kommunikáció, valamint egyes vállalati jellemzők (méret, iparág és más magyarázó változók) között keresnek kapcsolatot. A szerzők e cikkben a társadalmi felelősségvállalással foglalkozó vállalati weboldalakat kritikai szemüvegen keresztül vizsgálják. Céljuk, hogy feltárják az on-line kommunikációt jellemző belső ellentmondásokat és a vallott és követett értékek közötti különbségeket. _______ Communicating corporate social responsibility (CSR) principles, initiatives, and activities has become a common practice of companies all around the world. It is quite apparent that firms use internet more and more often to communicate their CSR initiatives to their stakeholders. Parallel with the extensive use of the online media, more and more research has been elaborated on the field of online CSR communication in the last decade as well. However, these studies usually have a strong descriptive focus trying to reveal connections between the intensity of online communication of CSR values and activities, and company size, industrial background, and other explanatory variables. In contrast, the authors analysed corporate web pages dedicated to CSR through critical lenses. Their research was designed to explore any dissonances and contradictions within online communication and between communication and real activities of firms from construction, retail, and telecommunication industries in Hungary.

Az erősödő állami szerepvállalás értékelése a magyarországi elektronikus hírközlő hálózati fejlesztésekben (Evaluation of the increasingstate’s rolein the electronic communications network development in Hungary)

Az elektronikus hírközlő hálózat rohamszerű fejlesztésének igénye az elektronikus szolgáltatások széles körű elterjedésével az állami döntéshozókat is fejlesztéspolitikai koncepciók kidolgozására és azok végrehajtására ösztönzi. Az (információs) társadalom fejlődése és az ennek alapjául szolgáló infokommunikációs szolgáltatások használata alapvetően függ a szélessávú infrastruktúra fejlesztésétől, az elektronikus hírközlő hálózat elérésének lehetőségétől. Az állami szerepvállalási hajlandóság 2011-től kezdődően jelentősen megnőtt az elektronikus hírközlési területen. Az MVM NET Zrt. megalapítása, a NISZ Zrt. átszervezése, a GOP 3.1.2-es pályázat és a 4. mobilszolgáltató létrehozásának terve mind mutatják a kormányzat erőteljes szándékát a terület fejlesztésére. A tanulmányban bemutatásra kerül, hogy az állam milyen beavatkozási eszközökkel rendelkezik az elektronikus hírközlő hálózat fejlesztésének ösztönzésére. A szerző ezt követően a négy, jelentős állami beavatkozás elemzését végzi el annak vizsgálatára, hogy megfelelő alapozottsággal született-e döntés az állami szerepvállalásról. _____ With the widespread use of the Internet, the need for the rapid development of the digital communication networks has prompted government policy makers also to conceptualize and implement development policy. The advancement of the (information) society and the use of information communication technology as a prerequisite of it are fundamentally determined by the development of broadband infrastructure and whether broadband access to the digital telecommunication network is available. The propensity of the government to play a bigger role in the field of electronical communication has increased significantly from 2011. The setup of MVM NET Zrt. / Hungarian Electricity NET Ltd./, the realignment of NISZ Zrt. / National Info communication Services Company Limited by Shares - NISZ Ltd./, the GOP 3.1.2. tender and the plan to enable a new, i.e. the fourth mobile network operator to enter the market all indicate the robust intention of the government to develop this field. The study shows the tools of government intervention for the incentive of the development of the electronical communication network. Then the author analyses the four main government interventions to examine whether the decision on the role of the state was adequately well-founded.

E-learning Skill and Use in EU Countries – A Statistical Analysis

The article investigates the division between member states of the European Union considering the aspect of their level of information and communication technology (ICT) development focusing on e-learning. With the help of discriminant analysis the countries are categorized into groups based on their ICT maturity and e-learning literacy level of development. Making a comparison with a benchmarking tool, the ITU (International Telecommunication Union)’s ICT Development Index (IDI) the results are confirmed partly correct. The article tries to find economical explanations for the re-grouping of the countries ranking. Finally the author examines the reliability of Hungary’s ranking results and the factors which may affect this divergence from the real picture.

The importance of social embeddedness

This article argues the importance of social embeddedness at mobile providers by examining the effects of customers’ network topological properties on churn probability—the probability of a customer switching from one telecommunication provider to another. This article uses data from regional snowball sampling—the only practically feasible network sampling method—to identify groups with significantly different churn ratios for customers with different network topological properties. Clear evidence indicates that individual network characteristics (node-level metrics) have considerable impact on churn probabilities. The inclusion of network-related measures in the churn model allows a longer-term projection of churners and improves the predictive power of the model.With no possibility to carry out repeated sampling, sample stability was checked through simulation results. On the one hand, this article highlights the importance and effectiveness of the provider’s tailored marketing campaigns by showing that customers targeted by direct marketing campaigns are less threatened by churn than nontargeted customers. On the other, this article shows that social embeddedness blocks the impact of the very samemarketing efforts. This article forwards the idea that social embeddedness, also prevalent in vendor switching, can be extended to understanding the development of professional societies threatened by membership churn.

Traffic congestion control in communication networks

Next generation networks are characterized by ever increasing complexity, intelligence, heterogeneous technologies and increasing user expectations. Telecommunication networks in particular have become truly global, consisting of a variety of national and regional networks, both wired and wireless. Consequently, the management of telecommunication networks is becoming increasingly complex. In addition, network security and reliability requirements require additional overheads which increase the size of the data records. This in turn causes acute network traffic congestions. There is no single network management methodology to control the various requirements of today's networks, and provides a good level of Quality of Service (QoS), and network security. Therefore, an integrated approach is needed in which a combination of methodologies can provide solutions and answers to network events (which cause severe congestions and compromise the quality of service and security). The proposed solution focused on a systematic approach to design a network management system based upon the recent advances in the mobile agent technologies. This solution has provided a new traffic management system for telecommunication networks that is capable of (1) reducing the network traffic load (thus reducing traffic congestion), (2) overcoming existing network latency, (3) adapting dynamically to the traffic load of the system, (4) operating in heterogeneous environments with improved security, and (5) having robust and fault tolerance behavior. This solution has solved several key challenges in the development of network management for telecommunication networks using mobile agents. We have designed several types of agents, whose interactions will allow performing some complex management actions, and integrating them. Our solution is decentralized to eliminate excessive bandwidth usage and at the same time has extended the capabilities of the Simple Network Management Protocol (SNMP). Our solution is fully compatible with the existing standards.

A study of stock market fluctuations and their relation to business conditions

Most research on stock prices is based on the present value model or the more general consumption-based model. When applied to real economic data, both of them are found unable to account for both the stock price level and its volatility. Three essays here attempt to both build a more realistic model, and to check whether there is still room for bubbles in explaining fluctuations in stock prices. In the second chapter, several innovations are simultaneously incorporated into the traditional present value model in order to produce more accurate model-based fundamental prices. These innovations comprise replacing with broad dividends the more narrow traditional dividends that are more commonly used, a nonlinear artificial neural network (ANN) forecasting procedure for these broad dividends instead of the more common linear forecasting models for narrow traditional dividends, and a stochastic discount rate in place of the constant discount rate. Empirical results show that the model described above predicts fundamental prices better, compared with alternative models using linear forecasting process, narrow dividends, or a constant discount factor. Nonetheless, actual prices are still largely detached from fundamental prices. The bubblelike deviations are found to coincide with business cycles. The third chapter examines possible cointegration of stock prices with fundamentals and non-fundamentals. The output gap is introduced to form the nonfundamental part of stock prices. I use a trivariate Vector Autoregression (TVAR) model and a single equation model to run cointegration tests between these three variables. Neither of the cointegration tests shows strong evidence of explosive behavior in the DJIA and S&P 500 data. Then, I applied a sup augmented Dickey-Fuller test to check for the existence of periodically collapsing bubbles in stock prices. Such bubbles are found in S&P data during the late 1990s. Employing econometric tests from the third chapter, I continue in the fourth chapter to examine whether bubbles exist in stock prices of conventional economic sectors on the New York Stock Exchange. The ‘old economy’ as a whole is not found to have bubbles. But, periodically collapsing bubbles are found in Material and Telecommunication Services sectors, and the Real Estate industry group.

A thermally wavelength-tunable photonic switch based on silicon microring resonator

Silicon photonics is a very promising technology for future low-cost high-bandwidth optical telecommunication applications down to the chip level. This is due to the high degree of integration, high optical bandwidth and large speed coupled with the development of a wide range of integrated optical functions. Silicon-based microring resonators are a key building block that can be used to realize many optical functions such as switching, multiplexing, demultiplaxing and detection of optical wave. The ability to tune the resonances of the microring resonators is highly desirable in many of their applications. In this work, the study and application of a thermally wavelength-tunable photonic switch based on silicon microring resonator is presented. Devices with 10μm diameter were systematically studied and used in the design. Its resonance wavelength was tuned by thermally induced refractive index change using a designed local micro-heater. While thermo-optic tuning has moderate speed compared with electro-optic and all-optic tuning, with silicon’s high thermo-optic coefficient, a much wider wavelength tunable range can be realized. The device design was verified and optimized by optical and thermal simulations. The fabrication and characterization of the device was also implemented. The microring resonator has a measured FSR of ∼18 nm, FWHM in the range 0.1-0.2 nm and Q around 10,000. A wide tunable range (>6.4 nm) was achieved with the switch, which enables dense wavelength division multiplexing (DWDM) with a channel space of 0.2nm. The time response of the switch was tested on the order of 10 μs with a low power consumption of ∼11.9mW/nm. The measured results are in agreement with the simulations. Important applications using the tunable photonic switch were demonstrated in this work. 1×4 and 4×4 reconfigurable photonic switch were implemented by using multiple switches with a common bus waveguide. The results suggest the feasibility of on-chip DWDM for the development of large-scale integrated photonics. Using the tunable switch for output wavelength control, a fiber laser was demonstrated with Erbium-doped fiber amplifier as the gain media. For the first time, this approach integrated on-chip silicon photonic wavelength control.

Realization of Differentiated Quality of Service for Wideband Code Division Multiple Access Core Network

The development of 3G (the 3rd generation telecommunication) value-added services brings higher requirements of Quality of Service (QoS). Wideband Code Division Multiple Access (WCDMA) is one of three 3G standards, and enhancement of QoS for WCDMA Core Network (CN) becomes more and more important for users and carriers. The dissertation focuses on enhancement of QoS for WCDMA CN. The purpose is to realize the DiffServ (Differentiated Services) model of QoS for WCDMA CN. Based on the parallelism characteristic of Network Processors (NPs), the NP programming model is classified as Pool of Threads (POTs) and Hyper Task Chaining (HTC). In this study, an integrated programming model that combines both of the two models was designed. This model has highly efficient and flexible features, and also solves the problems of sharing conflicts and packet ordering. We used this model as the programming model to realize DiffServ QoS for WCDMA CN. ^ The realization mechanism of the DiffServ model mainly consists of buffer management, packet scheduling and packet classification algorithms based on NPs. First, we proposed an adaptive buffer management algorithm called Packet Adaptive Fair Dropping (PAFD), which takes into consideration of both fairness and throughput, and has smooth service curves. Then, an improved packet scheduling algorithm called Priority-based Weighted Fair Queuing (PWFQ) was introduced to ensure the fairness of packet scheduling and reduce queue time of data packets. At the same time, the delay and jitter are also maintained in a small range. Thirdly, a multi-dimensional packet classification algorithm called Classification Based on Network Processors (CBNPs) was designed. It effectively reduces the memory access and storage space, and provides less time and space complexity. ^ Lastly, an integrated hardware and software system of the DiffServ model of QoS for WCDMA CN was proposed. It was implemented on the NP IXP2400. According to the corresponding experiment results, the proposed system significantly enhanced QoS for WCDMA CN. It extensively improves consistent response time, display distortion and sound image synchronization, and thus increases network efficiency and saves network resource.^

Factors Affecting the Adoption of New Technology: the case of 311 Government Call Centers

Government call centers (311) were first created to reduce the volume of non-emergency calls that were being placed to emergency 911 call centers. The number of 311 call centers increased from 57 in 2008 to about 300 in 2013. Considering that there are over 2,700 municipal government units across the United States, the adoption rate of the 311 centers is arguably low in the country. This dissertation is an examination of the adoption of 311 call centers by municipal governments. My focus is specifically on why municipal governments adopt 311 and identifying which barriers result in the non-adoption of 311 call centers. This dissertation is possibly the first study to examine the adoption of 311 call centers in the United States. The dissertation study has identified several significant factors in the adoption and non-adoption of 311 government call centers. The following factors were significant in the adoption of 311 government call centers: managerial support, financial constraints, organizational responsiveness, strategic plan placement, and technology champion. The following factors were significant barriers that resulted in the non-adoption of a 311 government call center; no demand from citizens, start up costs, annual operating costs, unavailability of funding, and no obvious need for one.If local government entities that do not have a 311 government call center decide to adopt one, this study will help them identify the conditions that need to be in place for successful adoption to occur. Local government officials would first need to address the barriers in setting up the 311 call centers.