The Research Of The Movement Of Signal-Signal Beateing Interferece Of Optical Direct Detection OFDM Signal

Optical Orthogonal Frequency Division Multiplexing(Optical Orthogonal Frequency Division Multiplexing,OOFDM)modulation technique can effectively reduce the mode dispersion in optical fiber communication system,and has the advantages of high spectrum efficiency,flexible bandwidth allocation,which become a hot research topic to further enhance the capacity of optical communication.Applying it into the demand-growing modern communication network can upgrade the transmission rate smoothly;In addition,the modern optical network is moving toward along a highly adaptive and reconfigurable evolution direction,the features of OOFDM can greatly reduce equipment update caused system upgrades and artificial cost.Therefore,OOFDM is a potential for the future of technology.This dissertation first review the development process,reseach significance and basic principle of OFDM technology.Based on the analysis of double electrode lithium niobate-Mach mach-zehnder modulator(LiNb03 Mach-Zehnder Modulator,LN-MZM)OOFDM signals,we describe the two classical OOFDM receiving system,including direct detection optical orthogonal frequency division multiplexing(DD-OOFDM)and coherent optical orthogonal frequency division multiplexing(CO-OFDM)system.Since the optical carrier and the OOFDM signal come from the same laser with synthronous phase and frequency drift in DD-OOFDM system,the receiver does not need to estimate the carrier frequency and phase shift and the local oscillator laser.Therefore,the DD-OOFDM system has more simple,low cost of the implementation,which is an optimization scheme for bandwidth access network.The receiver consists of only one square-law photodetector(PD),which beats the OOFDM signal and optical carrier to electrical OFDM signal.However,in the same time the subcarrier-subcarriers beating produces the signal-signal beating interference(SSBI)in[0,B],which may overlap the desired OFDM signal.This dissertation will mainly study the influence of SSBI on DD-OOFDM system from two aspects below:(1)Research the joint influence of the optical carrier-to-sideband ratio and the reduced guard band on the signal-to-signal beat interference in a DD SSB-OOFDM system.Since OSNR and electric bandpass filter(EBF)have significant effect on the noise in the system,this dissertation derives the expression of SINR of DD SSB-OOFDM considering of OSNR and the bandwidth of EBF(Be);theoretically analyzes the joint influence of the CSR and GB on the system performance and SSBI when GB<B;sets up a 20 km 40 Gbit/s DD SSB-OOFDM system to verify the influence of the order and Be of EBF and OSNR on system performance and the optimum CSR,at last verify the radeoff between CSR and GB.The simulation results show that when GB=6 GHz an increased CSR=8 dB achieve the same EVM with the CSR=3 dB when GB=8 GHz,thus for the former the needed GB reduce 20%.This reseach reduces the influence of SSBI and the needed GB only by increasing CSR without increasing the complexity of the receiver.It has significant meaning of improves the spectral efficiency(SE)effectively in DD SSB-OOFDM system.(2)Propose Based on the advantage of eliminating the SSBI interference effectively of,this dissertation proposes a novel Multiband Optical Orthogonal Frequency Division Multiplexing Passive Optical Network(MB-OFDM PON)architecture based on balanced detection,set up a 40 Gb/s downstream OFDMA signal transmission and 30 Gb/s 3 bands upstream MB-OFDM signal simulated transmission link via only one wavelength.Since the beat interference cancellation receiver based on balanced detection(ICRBD)can eliminate the SSBI interference effectively,in both OLT and ONU the signal is detect by ICRBDs.Besides,the optical carrier of downstream OOFDM signal is made full use as upstream carrier modulation to realize the passive optic and no amplifier.,This proposed structure,which combines MB-OFDMA and PON,has the advantages of low cost,effective SE and large capacity.