Publikace

Guidance mechanism in photonic crystal fibers

Přenosové prostředí, druhá generace ADSL a VDSL, měření na přípojkách

The multi-carrier modulation is used in many applications, primary for a wireless transmission, for example Wi-Fi and WiMAX networks or DVB-T. But the same physical principle can be used also for metallic lines in access or local networks, for example ADSL and VDSL. The multi-carrier modulation in these cases is called DMT. The methods for VDMT modulation and partial crosstalk cancellation are discussed and simulation results are presented.

This paper deals with Photonic Crystal Fibers (PCF) that is not sensitive to bending. On one hand, fiber bending may result in potential negative chromatic dispersion or coupling light from the fundamental mode into the cladding modes, which opens many possibilities to design microstructured optical components for all-optical PCF-based system (e.g. group velocity dispersion compensator) On the other hand, fiber bending is responsible for huge bending losses. The goal of this paper is to reduce bending losses in an operating range of the designed fiber. Reduction of bending losses could be considered in the fiber that would be single-mode for wide range of bending angles or bending radii, but the light is not being coupled into the cladding and the fiber is not sensitive to bending in an office environment.

This article deals with the problems of simulations and statistical evaluations of far end crosstalk between symmetrical pairs in metallic cable. The paper follows previous publications, gives new insights into questions associated with crosstalk evaluations based on theoretical assumptions, which resulting of metallic cable constructional arrangement. Paper also presents an idea of application these results in Generator of transmission functions to analyze the overall impact of Vectored DMT modulation on digital subscriber line traffic. To verify theoretical assumptions, several measurements were performed and proceedings of gained values of crosstalk are included in this article.

The new promising wireless networks based on multi-carrier modulations (MCM) and multiple-input multiple-output concept (MIMO) will soon offer high-speed digital connections. Their access points are mostly connected by fixed metallic lines to core data and telecommunication networks. That is why it will also be necessary to increase the transmission speed and overall performance of these fixed access networks adequately in order to meet the expected requirements of wireless connections. It would be possible to use VDSL2 digital subscriber lines and implement MIMO concept into the existing metallic networks for this purpose, but before that it will be necessary to solve several problems first. The transmission capacity of present VDSL2 digital lines is limited mainly by crosstalk occurring in metallic cables.

FEXT is the dominant source of disturbance in current digital subscriber lines (xDSL). One of the most promising solutions for far-end crosstalk cancellation is Vectored Discrete Multi-tone modulation (VDMT). New method for modeling of far-end crosstalk was developed and is presented in this paper. This advanced model is based on the capacitive and inductive unbalances between pairs in a cable and it also respects the cable's internal structure. The results of the model are subsequently used for the simulation of VDMT modulation and its impact on the FEXT cancellation.

This article proposes an innovative application of passive optical networks with optimized bus topology for local backbone data networks. We present mathematical apparatus for calculating of the maximum number of splits and the number of bridge taps in the passive optical network with the bus topology and an example of obtained results.