A novel method to generate carrier-suppressed return-to-zero (CSRZ) pulses by using a sampled fiber Bragg grating (FBG) is proposed, and the transmission characteristics of the CSRZ pulses are simulated and discussed. This CSRZ pulse has a duty cycle of 50%, narrower than conventional CSRZ pulse, which is due to the filtering and shaping of FBG, and leads to increase of nonlinearity and dispersion tolerance in high-speed transmission systems. Through proper design of FBG and adoption of short pulse source, this technique provides a promising way to modify the pulse shape and consequently improve system performance.
This paper focuses on the simulative optimization of modulation format, which is CS-RZ format with appropriate spectrum filtering, in a 42.7Gb/s spectrally efficient long-haul DWDM system. It is studied that the required bandwidth of the CS-RZ signal with spectrum pruning for channel spacing of 50GHz. The power loss and crosstalk are calculation under the Gaussian filter with various order and bandwidth. The influence on the CS-RZ waveform by the filter of various order and bandwidth was also investigated. Furthermore, the Q-value of the 42.7Gb/s CS-RZ signal was simulated before and after 640km fiber link transmission with 3 order Gaussian filter of various bandwidth, which simulative test system was designed as a 42.7Gb/s DWDM system with simultaneous C+L band discrete Raman amplifier by dispersion compensation fiber (DCF) as Raman medium. As a conclusion, the optimum filter bandwidth of 42GHz is obtained for the 42.7Gb/s 50GHz spaced DWDM system. Q-value of the signal is up to 8 and remains 6.7 after transmission of 640km fiber link, with the filter of the optimum bandwidth.