Nonlinear Effects Of Optical Fiber On The Transmission Of Optical CO-OFDM Signal Transmission System

With the widespread application of digital information technology and the in-depth development of related technologies,the Internet of Things' demand for information transmission rate and channel capacity has shown an exponential growth trend in recent years.For this reason,as the backbone optical fiber communication of the communication network,people have put forward a series of challenges to its communication capacity,especially the communication capacity of long-distance transmission.Therefore,research and development of new optical fiber communication technology to effectively increase the communication capacity has become a top priority.This thesis mainly focuses on the structure of a coherent optical orthogonal frequency division multiplexing(CO-OFDM)system over long-haul optical fiber.The aim is to explore the non-linear characteristics of the optical fiber and their impact to the CO-OFDM signal in terms of signal spectrum,base-band signal constellation and bit-error-rate.Furthermore,optical domain phase conjugate(OPC)technique is employed to compensate the fiber non-linear effects.The investigation in this thesis is carried by theoretical analysis and computer simulations.The major contributions of this thesis include:(1)The CO-OFDM transmission over optical fiber is discussed through theoretical analysis to investigate the key elements of a CO-OFDM transmission system,including the radio frequency OFDM transmitter,electro-optic modulation module,transmission link,photoelectric detection module and radio frequency OFDM receiver.Also,a simulation model to be implemented as an investigating platform of CO-OFDM transmission over optical fiber is studied.(2)Modeling and analysis of the non-linear effects of optical fiber,especially of the long-haul fiber and the impact of non-linear characteristics to CO-OFDM signal.The non-linear effects of fiber are mainly focusing on SPM(self-phase modulation effect),XPM(cross-phase modulation effect),and FWM(four(Wave mixing)effects.The effects of such non-linearcharacteristics on the performance of CO-OFDM signal as well as the extension to the base-band signal are the most important investigation in this thesis,which focuses on the signal spectrum,signal constellation and bit-error-rate.The experimental results show that the nonlinear effect has a great damage effect on the quality of the baseband signal and the performance of the system.(3)Study on the compensation of non-linear effects using OPC technique is another key issue to improve the performance of CO-OFDM over long-haul fiber.Simulation experiment is conducted to investigate the correlation function between Q factor,the transmission distance and transmit power for the system with/without OPC.The experimental results show that the OPC technology compensation system can effectively increase the maximum Q factor by about 3dB and the baseband signal error rate by nearly two orders of magnitude.It is verified that the OPC compensation method can effectively reduce nonlinear effects and improve system performance.