Analysis Of Nonlinearity Tolerance In DQPSK DWDM System

With an increase in the number of channels in dense wavelength division multiplexing(DWDM) system, the capacity of optical communication link has grown exponentially while the required signal-to-noise ratio of no error transmission has been bigger and bigger. But high signal-to-noise ratio will lead to severe nonlinear impairments. The most predominant non-linear effects arise from the intensity independent refractive index of optical fiber(Kerr effect). The interand intra-channel four wave mixing(FWM) is one of them. To evaluate the FWM effect and total nonlinear tolerance is an important issue.The main works are given as follows:Based on OptiSystem software, nonlinear separate model is suggested. By using the model, the impact of FWM noise is numerically obtained for co-polarization Dense WavelengthDivision Multiplexing(DWDM) systems with 33 channels. Compared with the traditional simulation model, this nonlinear separate model can analysis the degradation of Q value by four wave mixing noise.We simulate DWDM transmission systems with 33 channels and the channel spacing is 50GHz. In this simulation model, the channel of center frequency with differential quardrature phase shift-keying(DQPSK) is used for detection channel.Three modulation scenarios are given. The first one is that all channels are DQPSK modulated. The second one is that all even channels are DQPSK modulated and odd channels are differential phase shift-keying(DPSK) modulated. The third one is that all even channels are DQPSK modulated and odd channels are on-off keying(OOK) modulated.For simulation platform mentioned above, we study the transmission performance of two kinds of fiber link. One of them is traditional dispersion compensation link; the other one is novel dispersion-managed fiber link. By using the nonlinear separate model, the FWM-included system performance degradation and the total nonlinear tolerance are numerically obtained.