Research On Impairments Analysis And Optimization Of Optical Orthogonal Frequency-division Multiplexing Transmission Systems

With the rapid development of communication technology, people become moreurgent to demand for communication quality. How to realize information transmissionwith high speed, large capacity and high quality at limited bandwidth draws greatattention of researchers. As an important modulation technique, optical orthogonalfrequency division multiplexing (OOFDM) with high spectral efficiency, and hightolerance of fiber optic dispersion and polarization mode dispersion (PMD) hasbecome a research hotspot. And the passive optical network (PON) based OFDMtechqnie combined the OOFDM technique with passive optical network (PON) withthe advantage of flexible dynamic bandwidth allocation, variable services transparenttransmission and compatible with the existing network, thus it is one of the keytechniques for optical access network in the next generation or near future.Under the knowledge of basic principle of OFDM technology in the wirelesscommunications, the key techniques, the advantages and disadvantages of OFDM arebriefly introduced. And a detailed description for the operation principle of a typicalintensity modulation with direct-detection optical OFDM (IM/DD-OOFDM)transmission system.An in-depth theoretical analysis of the effect of laser phase noise and the bias ofMach-Zehnder modulator (MZM) on the transmission performance. On this basis, thefollowing three parts of research work and related achievements are show below:(1) Implentment of the mathematical modeling of OFDM modulator anddemodulator, MZM, chromatic dispersion of fiber optic etc. in order to provide afeasible simulation platform to analyze the effects of laser phase noise and bias ofMZM in IM/DD-OOFDM transmission system.(2) The Laser phase noise with chromatic dispersion of fiber in IM/DD-OOFDMsystem is converted to intensity noise, and the higher frequency subcarrier, theinterference is larger, the orthogonality between subcarriers are subject to differentdegrees of damage. According to the mechanism of damaged effects, using adaptivepower and bit allocation or the pre-emphasis technique is proposed to reduce the effectof laser phase noise.(3) The study and analysis of the effects on the OFDM receiver sensitivity withMZM at different modulation index under various dc bias by employing the theories,numerical simulation and experiments respectively, then according to different modulation index to optimize bias of MZM to improve the sensitivity of receiver tosome extent.