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.

In the work, characteristics of the erbium-doped fiber amplifier (EDFA) are investigated. The amplification and noise figure dependences on different EDFA parameters in a 2.5 Gbit/s one-channel WDM transmission system are simulated and measured. Additionally, simulation of a four-channel 2.5 Gbit/s WDM system containing in-line amplifiers of the type was done in order to investigate the EDFA performance in multichannel systems. Almost identical results obtained for both the simulation model and the experimental system are indicative of high accuracy of the simulation. It is shown that the EDFA amplification depends on such parameters as the signal power, wavelength, EDF length, and configuration of the pump laser.

An all-optical clock recovery has been demonstrated numerically with single and double ring microring resonators from 40 Gbit/s return-to-zero on-off keying optical signal. The influence of device cascadability on amplitude fluctuation caused by patterning effects of extracted clock values have been evaluated. Open source simulation toolbox Optilux was used for simulations. The results show that these fluctuations related to patterning effects are considerably reduced after processing with five cascaded single ring microring resonators.

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