| The early point to point communication methods have grown into complicated communication networks. One of the most famous communication networks is the Internet and the modern society can not live a normal day without it. Further more, the future Internet traffic will keep increasing. Therefore, the optical fiber communication system as the most important communication infrastructure is confronted with challenges and trends such as the evolution of 100Gb/s Ethernet, the emergence of dynamic reconfiguration network, and the trend of software defined optical transmission.Optical Orthogonal Frequency Division Multiplexing (OOFDM) technology can be used to gradually update the communication network in order to meet the continuing needs for higher transmission date rates. In addition, modern optical network are developed into a highly self-adaptive and reconfigurable way, which means that these features can greatly reduce the expensive cost of equipment replacement and manual intervention when communication systems are upgraded. OOFDM is a promising technology facing the future.This article first reviews the history of optical fiber communication as well as OFDM technology, including the later work when they merged together. Then the fundamentals of OFDM and features of single mode fiber (SMF) are theoretically and heuristically given, respectively. After that, the principle of electrical-optical linear conversion via dual electrode LiNbO3 Mach-Zehnder modulator (LN-MZM) is analysed. Based on that, two main OOFDM systems as Direct Detected OOFDM (DD-OOFDM) and Coherent OFDM (CO-OFDM) are introduced and their intrinsic advantages and defects are discussed. New scheme to improve the reception performance of each OOFDM system are introduced respectively:(1) The optimization for the reception in DD-OOFDM system. DD-OOFDM system has a lower spectral efficiency (SE) and its Signal-to-Signal Beat Interference (SSBI) can further degenerate the system performance. In order to improve the reception performance of DD-OOFDM, this article has introduced a beat interference cancellation receiver based on balanced detection (ICRBD) to eliminate the SSBI. Then we investigate the fiber transmission performance of the single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) signal with reduced guard band (GB) received by the ICRBD. The simulation results show that the error vector magnitude (EVM) of the 40Gb/s 16-QAM SSB-OOFDM with 2GHz GB remains below the forward error correction (FEC) limit even after 5 x 100km standard single-mode fiber (SSMF) transmission. The system has a good tolerance of both the laser linewidth and the linear channel imperfections.(2) The optimization for the reception in CO-OFDM system. CO-OFDM uses coherent detection in the receiving end, which is more sensitive to phase noise (PN). PN will cause common phase error (CPE) and inter-carrier interference (ICI) in OFDM system. Generally, pilots are used to compensate for the PN. Comb-type plot scheme is applicable in CO-OFDM system. However, the phase of the comb-type pilot subcarriers (PSs) also suffers the ICI from the adjacent data-bearing subcarriers in real situations. In terms of this issue, a novel comb-type pilot scheme is proposed in CO-OFDM system for testing the impact of the ICI by adding blank subcarriers, also known as guard subcarriers (GSs) at both sides of PSs. Thus clearer pilots can be obtained to mitigate the distortion caused by PN and channel distortion. The proposed pilot scheme with GSs is employed in a typical 20Gb/s QPSK CO-OFDM system, and the simulation results show that after 50km standard single-mode fiber (SSMF) transmission in conventional conditions, our scheme can reduce the error vector magnitude (EVM) of the receiving QPSK signal by about 3%. |
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