Research On The Method Of Eliminating Polarization Crosstalk In All-optical Wavelength Conversion System For PM-OFDM Signal

With the advent of the "Internet of Everything" era,the demand for the capacity and speed of optical transport networks has increased dramatically.In order to satisfy these demands,advanced modulation formats,such as orthogonal frequency division multiplexing(OFDM)technology and polarization multiplexing(PM)technology,are introduced into optical transmission network.The combination of OFDM technology which can resist optical fiber dispersion and polarization mode dispersion and polarization multiplexing technology can greatly improve the spectrum efficiency.The all-optical wavelength conversion(AOWC)technology is introduced in the transmission nodes of optical networks to improve the information exchange between optical networks and increase the capacity of WDM communication networks.The AOWC system based on the SOA-FWM has the advantages of fast response time,easy integration and transparency to signal conversion.Since SOA is a polarization-sensitive device,different phase changes between modes will cause polarization state rotation when PM-OFDM signals are transmitted in SOA.After wavelength conversion,crosstalk will occur to signals in two polarization directions.Therefore,in this paper,the AOWC of PM-OFDM signals based on the SOA-FWM effect is studied theoretically and emulation,and a crosstalk elimination scheme is proposed to solve the problem of polarization crosstalk in wavelength conversion system.The main innovations are as follows:Firstly,the polarization crosstalk in orthogonal dual-pump structure wavelength conversion system for PM-OFDM signal based on SOA-FWM effect is studied.And a new AOWC scheme based on polarization diversity structure for PM-OFDM signal to eliminate polarization crosstalk is proposed.The numerical simulation setups of conventional scheme and polarization diversity structure scheme are built,the system performance of the two schemes is compared by bit error rate.The simulation results show that the conventional structure system has polarization crosstalk,and the polarization diversity structure system can realize PM-OFDM signal direct receiving without polarization crosstalk.The simulation results verify the accuracy of the theoretical analysis.Secondly,a theoretical model of polarization crosstalk in conventional AOWC system for PM-OFDM signal with parallel dual-pump based on SOA-FWM effect is established.The scheme of AOWC based on orthogonal dual-pump polarization diversity structure for PM-OFDM signal is proposed to eliminate polarization crosstalk.The system simulation platform is built.The system performance of the conventional scheme and the crosstalk elimination scheme was compared under the factors of the power of signal,SOA injection current,laser linewidth at 16QAM/64 QAM modulation formats and so on.The results show that,compared with the conventional schemes,the AOWC system for PM-OFDM signal with using the proposed polarization diversity structure can reduce crosstalk elimination and has wider tunable range.