Research On Real-Time Imdd Optical OFDM System

The techniques of Orthogonal Frequency Division Multiplexing (OFDM) have been widely used in Asymmetrical Digital Subscriber Loop (ADSL), Digital Audio Broadcast (DAB), Digital Video Broadcast (DVB), High Definition Television (HDTV), Wireless Local Area Networks (WLAN), and the Fourth Generation (4G) mobile communications. As the fast increasing of the traffic requirements of optical communications, the optical OFDM has also attracted extensive attentions nowadays and becomes one of the hot spots in the research area of optical transmission.However, the current global researches on optical OFDM techniques are mainly focused on offline digital signal processings, and there are rarely few researches on real-time optical OFDM realizations and system demonstrations. Different with the offline algorithm studies, the real-time optical OFDM processing is much more complicated, taking in to the consideration of various aspects such as computation resources, parallel processing speed, realization complexity of algorithms, as well as the limitations of accuracies of Analog to Digital and Digital to Analog Converters. This is the main reason that real-time optical OFDM studies is much fewer than the offline processings. This thesis focuses on the study and realizations of real-time digital signal processing for Intensity Modulated, Directed Detected Optical Orthogonal Frequency Division Multiplexing (IM-DDO-OFDM) systems, and the error-free transmission of such a system is also successfully demonstrated after240km fibers. Moreover, the thesis also proposes two novel configuration schemes of Optical Vector Network Analyzer (OVNA) for the transmission matrix measurements of optical components and link parameters of optical communication systems, with the advantage of tunable measurement accuracy as well as the no use of frequency swept lasers. The main achievements and innovations of this thesis include:(1) The basic principle of OFDM techniques is analyzed, as well the digital signal processing schemes of IM-DD-OOFDM systems, the correctness and effectiness of which are also substantiated by numerical simulations。(2) The real-time digital signal processing algorithms of the IM-DD-OOFDM transceivers are realized based on the Field Programable Gate Array (FPGA). The real-time transmission experiments demonstrate the good performance of these algorithms with the evidence of long-term successful transmissions of80M baud Quadrature Phase Shift Keying (QPSK) modulated signals after240km fiber links. (3) Two novel configuration schemes of OVNA are proposed. The theoretical derivation and numerical simulations proves the effectiveness of characterizing the optical components and transmission links, supporting the measurements of their transfer matrix. Compared to the traditional schemes, these novel configurations do not need the expensive frequency swept lasers and have the advantage of tunable measurement accuracy.