High-performance computing systems are of steadily growing interest to provide new levels of computational capability for an increasing range of applications. The growing use of and dependence on optical interconnects to meet these system's scaling bandwidth demands has given rise to “computercom” as a distinct market segment, alongside the traditional datacom and telecom markets. This paper discusses the trends, requirements, tradeoffs, and potential technologies for this market.

Optical Interconnects for High-Performance Computing

We have studied RF transmission over various multimode fibers (MMFs) and a standard single-mode fiber, targeting picocellular networks for voice, data, and video applications. Bandwidth requirements of MMF links that are based on vertical-cavity surface-emitting laser (VCSEL) have been extensively studied. The performance of the radio-over-fiber link is assessed in terms of the error vector magnitude. Also conducted was a full system analysis, including the investigation of an achievable dynamic range and a noise figure for different low-cost architectures. This was compared to coax-based RF transmission. The IEEE 802.11 a/b/g standard, as well as other applications like radio frequency identification tracking, was considered. For experimental investigations, we have used both commercial wireless access points and a vector signal generator as a signal source, with two types of directly modulated VCSELs - 850-nm sources and 1310-nm high-speed uncooled single-mode AlGaInAs/InP VCSELs. A robust system performance was demonstrated in both 2.4- and 5-GHz RF bands, and record multimode and standard single-mode fiber transmission distances were achieved. A transponder design that can meet system requirements in terms of sensitivity ( 95 dBldrHz2/3) for a dual-band wireless LAN (WLAN) fiber-radio picocellular network was developed. A full 14-cell experimental WLAN system with cells of 4-m radius was implemented to study networking issues such as handoff and cochannel interference.

Radio Over Fiber for Picocellular Network Architectures

The modal group delays (GDs) are a key property governing the dispersion of signals propagating in a multimode fiber (MMF). An MMF is in the strong-coupling regime when the total length of the MMF is much greater than the correlation length over which local principal modes can be considered constant. In this regime, the GDs can be described as the eigenvalues of zero-trace Gaussian unitary ensemble, and the probability density function (pdf) of the GDs is the eigenvalue distribution of the ensemble. For fibers with two to seven modes, the marginal pdf of the GDs is derived analytically. For fibers with a large number of modes, this pdf is shown to approach a semicircle distribution. In the strong-coupling regime, the delay spread is proportional to the square root of the number of independent sections, or the square root of the overall fiber length.

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Statistics of Group Delays in Multimode Fiber With Strong Mode Coupling

We present a detailed analysis of the modal properties, dispersive behavior, and nonlinear mode coupling in graded-index multimode fibers (GIMFs), and lay out a simplified form of a generalized nonlinear Schrodinger equation, which can be used to explore the rich nonlinear dynamics related to the propagation and interaction of light pulses in GIMFs in a tractable manner. We also briefly discuss an application of the presented formalism in the study of four-wave mixing in these fibers. While the reported formalism is fairly general, our presentation is mainly targeted at device applications in which short segments of GIMFs are used.

Pulse Propagation in a Short Nonlinear Graded-Index Multimode Optical Fiber

A novel optical signal modulation concept of adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) is proposed, and a comprehensive theoretical model of AMOOFDM modems is developed. Numerical simulations of the transmission performance of the AMOOFDM signals are undertaken in unamplified multimode fiber (MMF)-based links using directly modulated distributed feedback (DFB) lasers (DMLs). It is shown that 28 Gb/s over 300 m and 10 Gb/s over 900 m transmission of intensity modulation and direct detection (IMDD) AMOOFDM signals at 1550 nm is feasible in DML-based links using MMFs with 3-dB effective bandwidths of 200 MHz/spl middot/km. Apart from a higher signal capacity, AMOOFDM also has a greater spectral efficiency and is less susceptible to different launching conditions, modal dispersion, and fiber types, compared with all existing schemes. In addition, a large noise margin of about 15 dB is also observed. The bits of resolution of analog-to-digital converters (ADCs) and the cyclic prefix of AMOOFDM symbols are the main factors limiting the maximum achievable performance, on which the influence of DMLs is, however, negligible under the optimum operating condition.

High-speed transmission of adaptively modulated optical OFDM signals over multimode fibers using directly Modulated DFBs

This paper describes an advanced multimode-fiber-link model that was used to aid the development of Telecommunication Industry Association standard specifications for a next-generation 50-/spl mu/m-core laser-optimized multimode fiber. The multimode-link model takes into account the interactions of the laser, the transmitter optical subassembly, and the fiber, as well as effects of connections and the receiver preamplifier. We present models for each of these components. Based on these models, we also develop an efficient and simple formalism for the calculation of the fiber transfer function and the signal at the link output in any link configuration. We demonstrate how the model may be used to develop specifications on transmitters and fibers that guarantee any desired level of performance.

Modeling and simulation of next-generation multimode fiber links

This paper reports on the suitability of the simulated annealing (SA) optimization algorithm to equalize multimode fiber (MMF) links using linear equalizers through simulation tools and experimental validation. Several variations of the SA algorithm and the selection of initial tap weights through the use of a predefined set of tap weights were examined. The authors also experiment with several eye mask shapes that can be used as a cost function and found that the symoctagon offers the best performance. Transmission experiments and simulations at 10 Gb/s were carried out on a large number of 300-m-long MMF links with a feedforward equalizer at the receiver using both legacy (OM1 and OM2) and next-generation (OM3) fibers. Simulation and experimental results show that the SA algorithm in its various forms is well suited to equalize MMF links with a linear equalizer. The algorithm showed relatively fast convergence with a tradeoff between convergence speed and final value for the eye opening. The SA algorithm converges well even in the presence of noise, and the link performance is limited by the signal-to-noise ratio rather than the adaptation algorithm

Performance of Simulated Annealing Algorithm in Equalized Multimode Fiber Links With Linear Equalizers

Blockchain nowadays is finding great application in many areas, based on its security, decentralized mode of operation, however many things during its use remain challenging include the issue of data privacy, such as safe and effective data management, maintaining data integrity and data quality, etc. Through this paper we will try to make an overview of existing blockchain technologies, their use today and sublimating existing and future trends. We will briefly describe application of blockchain technology in various fields suggesting solutions, advantages and disadvantages of blockchain, cloud platforms for blockchain data storage. We will focus on data privacy by making a description of the strategies used in this regard. We will conclude the paper by giving the latest research regarding data storage, the importance of data storage and our views regarding the future of data management and storage.

Overview of Blockchain Data Storage and Privacy Protection

Blockchain technology, thanks to its characteristics which are being seen as indispensable in many fields, is also trying to find application in the field of education, especially in higher education institutions to prevent different types of misuse of data and falsification of diplomas. Although there are attempts for a wider application in all areas of higher education institutions, blockchain is encountering various difficulties, where we will try to describe some of them through this paper and clarify where are the problems based on the various researches that have been done in this direction. One thing is evident that the falsification of documents, especially diplomas in particular, is a phenomenon that even today exists, and methods must be taken to prevent such a phenomenon which is harmful to society. Part of the paper will also present some general models of how blockchain can be applied in higher education institutions and the same can be expanded with other institutions of the similar nature, forming a common chain for the protection against the possible falsification of diplomas. The paper describes the challenges that blockchain faces when applying to higher education institutions, and proposes a model for the protection against diploma forgery, theoretically offering a diploma management software based on blockchain. The practical implementation of blockchain in higher education institutions is encountering many difficulties, despite efforts, due to the immutability of data and the possibility of updating them.

Challenges of Blockchain in Higher Education Institutions for Protection Against Diploma Forgery

Blockchain technology is encountering many challenges during its application in the field of education, especially in higher education institutions. Above all, it can be used for the process of generating and verification of various academic documents, including diplomas and various certificates. Apart from the creation of several prototypes and pilot projects, recent research shows that there is no standard platform based on blockchain that has managed to show good results and is applicable in any higher education institution. Through the paper, we try to clarify the challenges of blockchain application in higher education institutions and we will propose a method for electronic generation through the blockchain system of academic documents. For faster and easier verification, we propose the method by generating a QR code during the generation of academic documents. Higher education institutions should cooperate with each other to reach a standard platform based on blockchain for the generation and verification of academic documents, as the only possibility to prevent various forgeries.

A. Risteski

Papers

Modeling and simulation of next-generation multimode fiber links

Performance of Simulated Annealing Algorithm in Equalized Multimode Fiber Links With Linear Equalizers

Overview of Blockchain Data Storage and Privacy Protection

Challenges of Blockchain in Higher Education Institutions for Protection Against Diploma Forgery

Identification During Verification Of Diplomas In The Blockchain System