Performance Investigation Of Optical Orthogonal Frequency Division Multiplexing Transmission System In SSMF

Opitcal orthogonal-frequency-division-multiplexing (OFDM) has attracted much attention since the fiber chromatic dispersion (CD) and polarization-mode dispersion (PMD) can be electronically equalized through the receiver-end digital signal processing (DSP). In the simulation experiment of 10Gb/s, direct-detection (DD) OFDM and coherent optical (CO) OFDM transmission systems have been achieved in standard single mode fiber (SSMF). We use Optisystem to simulate transmitter, optical links, and receiver condition. Modulation and demodulation of OFDM signal have been finished offline in Matlab.Based on architecture of DD-OFDM and CO-OFDM systems, many research has been done in performance of optical filters in the DD-OFDM, the performance of optical signal to noise ratio(OSNR) and bit error rate(BER) have been analyzed by adjusting the bandwidth and order of the optical filters at transmitter and receiver. In CO-OFDM system, channel estimate algorithm for the fiber dispersion compensation is studied on the receiving end, the amendments and improvements to the algorithm are given.The mainly works are expressed as follows:1. We address direct detection OFDM transmission over the optical links, including transmitter, optical links and receiver. The paper simulates performance in different transmission distances of direct detection structure, and provides the constellation of 4QAM in receiver, BER of B2B and 320km, verifies the feasibility of DD-OFDM transmission system.2. In the simulation experiment of 10Gb/s DD-OFDM transmission over 640km standard single mode fiber (SSMF), the performance of optical signal to noise ratio(OSNR) and bit error rate(BER) have been analyzed by adjusting the bandwidth and order of the optical filters at transmitter and receiver. To achieve a BER of -3dB at receiver-end, OSNR of DD-OFDM can be improved 1dB by using high order optical filters instead of common single-sideband (SSB) filters, and then ultimate performance of the filter has been researched when filter order gets 8 orders. The equivalent relationship between FBG filter and Gaussian band-pass optical filter has been given in DD-OFDM. Meanwhile, the selection of radio frequency can influence the performance of DD-OFDM. Comparing the frequency efficiency with the system sensitivity, the result shows that an optimization performance has been obtained by varying bandwidth gap.3. In the simulation experiment of CO-OFDM transmission over 640km SSMF, we research on data processing demodulation and dispersion compensation algorithm. Formula and conditions of the algorithm is analyzed and deduced, advantages and disadvantages of LS algorithm and LMMSE algorithm have been analyzed, respective. The conclusion of data analysis in matlab is that the performance of LMMSE with the statistics in a stable light channel environment, is higher than 1.8dB compared with performance of based on the the pure observation of the LS algorithm.