Research On Performance Analysis And Application Of High-speed All-optical OFDM System

In recent years, the huge growth of optical communication network demands an effective exploitation of the fiber channel capacity. In China, based on dual-polarization quadrature phase shift keying (DP-QPSK) coherent detection, a single-carrier100Gbit/s real-time processing system has been tested successfully.400Gbit/s is expected to be a possible data for the next generation long haul optical transmission after100GbE. Recently, optical OFDM brings the benefit of multicarrier parallel processing into the next generation400Gbit/s system. The all-optical orthogonal frequency division multiplexing (AO-OFDM) technology performs the multicarrier and the inverse fast Fourier transform and fast Fourier transform all-optically. It is proposed to overcome the limitation of electronic process and reduce power consumption.Sponsored by the National Basic Research973Program of China, the simple structures of OIFFT/OFFT modules are realized by optical passive devices. The main research achievements and contributions are summarized as followings:(1) A400Gb/s DP-QPSK AO-OFDM signal transmission system is simulated. Each channel is modulated with100Gb/s DP-QPSK signal. The AO-OFDM can operate with a lower OSNR than DWDM. The AO-OFDM has an advantage for sensitivity, when the BER reaches the10’3FEC limitation. For fiber transmission, the accumulated dispersion tolerance of this400Gb/s AO-OFDM system is about330ps/nm for the10-3BER. Transmitted over single-span80km SMF (G.655), the AO-OFDM system has a power penalty. Additionally, the central AO-OFDM channel is more susceptible to interference. With the increase of the incident optical power, the receiver sensitivity of AO-OFDM system is degraded obviously due to the fiber nonlinear effects, approximately3dB in channel1and2dB in channel4. At a same incident optical power, the central AO-OFDM channel shows greater weakness in the receiver sensitivity. In the12×80km fiber transmission, the BER performance becomes worse since the fiber nonlinearity becomes dominant at higher powers, and the nonlinear phase noise brings a severe deterioration to the BER performance. Fiber Kerr nonlinearities has a greater limitation on the performance of AO-OFDM system for long-distance transmission.(2) The AO-OFDM system based on the carrier-suppressed short pulse source has a better perforamce in the condition of dual-polarization modulation. The carrier-suppressed AO-OFDM system has a good tolrence to the increased mismatch of polarization alignment. For transmission, it has a certain tolerance to some linear dispersion and nonlinear impairments accumulated along a long-haul transmission. With the improvement of carrier-suppressed pulse source, the AO-OFDM system has a higher sensitivity.(3) A16X10Gb/s AO-OFDM system based on the pre-coded technology is simulated. The AO-OFDM system uses pre-coded method to balance and re-distribute the power distribution of optical sub-carriers signal for PAPR reduction. The simulation results show this method can reduce the PAPR value1.9dB, increase the Q value with2and improve the power impairment with3.8mW.(4) With simulations, we proposed an improvement method of AOS-OFDM scheme using Nyquist pulse shape in the pulse source generator. 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. In this way, it is of great benefit for multi-users system.(5) We propose and demonstrate a novel all optical orthogonal frequency division multiplexing passive optical network (AO-OFDM-PON) architecture in which all-optical flexible optical network units (ONUs) internetworking is enabled and ONUs share a source. Using the subcarrier bands allocation, we consider the intra-ONU and inter-ONU communications which correspond to two different cases:communication among ONUs in a same group and in different groups. The proposed scheme can not only provide the enhanced security and dynamic resource allocation for ONU-group users, but also decrease the inventory and provisioning complexity greatly for operators. All results verify that the proposed scheme is feasible.