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  • Author: S. Spolitis x
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Schemes for Compensation of Chromatic Dispersion in Combined HDWDM Systems

The authors seek best ways to realize chromatic dispersion (CD) compen-sation schemes for differently modulated optical signals in high-speed mixed data rate HDWDM systems. The research is based on OptSim 5.1. simulation software, which numerically solves nonlinear Schrödinger equation using the split-step Fourier method. It is shown that the CD compensation scheme is crucial for the performance evaluation in combined HDWM transmission channels. Therefore, a scheme of the type is proposed that is suited best for a very complicated combined fiber optical transmission system. It is also found that asymmetrical CD compensation schemes in pre- and post-compensation modules are the most efficient, allowing the best BER in a channel to be achieved.


The paper presents the improved method of noise immune Fibonacci counting in the minimal form of representation. The method was tested and investigated in the developed noise immune pulse counter based on a minimal form of Fibonacci code with a fractal decoding device. The proposed device, which is simulated in the NI Multisim software, possesses a homogenous structure, increased noise immunity, performance and detection of bit errors in the process of its operation.


In the paper, the authors compare efficiency of two physical dispersion compensation methods for single channel and 8-channel WDM fibre-optical transmission systems using return-to-zero (RZ) and non-return-to-zero (NRZ) line codes for operation within optical C-band frequencies by means of computer simulations. As one of the most important destructive effects in fibre optical transmission systems (FOTS) is chromatic dispersion (CD), it is very important to reduce its negative effect on a transmitted signal. Dispersion compensation methods that were implemented in the research were dispersion compensating fibre (DCF) and fibre Bragg grating (FBG). The main goal of the paper was to find out which dispersion compensation method (DCF or FBG) provided the highest performance increase for fibre-optical transmission system and provided the longest transmission distance after dispersion compensation was implemented at different locations in the fibre-optical line while RZ or NRZ line codes were used. In the paper the reference point of signal quality for all measurements, which were obtained at the receiver, was BER<10−12.


Considering the growing demand for broadband of access networks, in the present paper we investigate various modulation formats as a way of increasing the performance of optical transmission systems. Non-return-to-zero (NRZ) on-off keying, return-to-zero (RZ) OOK, carrier suppressed RZ (CSRZ) OOK, duobinary (DB), NRZ differential phase shift keying (NRZDPSK), RZ-DPSK and CSRZ-DPSK formats are compared using the maximal achievable reach with bit error rate less than 10−9 as a criterion. Simulations are performed by using OptSim software tool. It is shown that using the transmission system without dispersion compensation the best results are shown by duobinary and CSRZ-OOK modulation formats, but with the system using dispersion compensating fiber (DCF) the longest transmission distance is achieved by RZ-DPSK modulation format. By investigating the influence of channel spacing for best-performed modulation formats, network reach decrease for transmission systems with DCF fiber has been observed due to channel crosstalk.