The improvement of Nyquist pulse shaping for all-optical OFDM system in multi-users network

The all-optical orthogonal frequency division multiplexing has a better spectral efficiency and a lower response requirement of modulators for high capacity transmission. In the system, the optical filter will degrade the performance of subcarriers which are far away from the center carrier. We proposed an improvement method of all-optical OFDM scheme using Nyquist pulse shape in the pulse source generator. Comparing a Nyquist shape pulse with a Gauss pulse in a 4 × 100 Gb/s DP-QPSK all-optical sampling OFDM system, the side lobe of transmitted spectrum can be effective suppressed, and the optical power will be more focused on the effective frequency band. By coherent receiver, the results show that the Nyquist pulse shaping can improve the OSNR and transmission performance of subcarriers which deviate mostly from the center frequency of optical filter. This improvement is of great benefit for multi-users system.