Research Of Outputting Stable Multi-Carrier Source Based On Polarization Control Technology

With the development of business in communication and internet industry, the requirements of message capacity and transmission quality increase day by day. In order to meet these requirements, many frontier studies on single-source Tb/s transmission have been conducted. Nowadays,100-Gb/s per-channel data rates have are now available in commercial systems, and data rate of1-Tb/s and beyond are under active research. In order to realize big capacity transmission and improve spectrum efficiency, some senior modulation formats and multiplexing have been used in modern optical transmission system.One promising method to realize per-channel data rates beyond1Tb/s is based on the multi-carrier superchannel architecture, in which multiple optical carriers are modulated and multiplexed together at high spectral efficiency, e.g., via orthogonal frequency-division multiplexing (OFDM) and coherent wavelength-division multiplexing (Co-WDM), and the multicarrier source is one of the key components. Multi-carrier source has the advantage of high spectral efficiency, and carrier interval fixed which OFDM requires. Research on multi-carrier source has become a popular research direction. The re-circulating frequency shifter (RFS) based on the single-side band (SSB) modulator is one of the schemes to achieve the multicarrier source. There is some research on this scheme these years, such as the impact analysis of I/Q modulator error on carrier flatness and signal-to-noise ratio (SNR), and optimization design of the multi-carrier source. However, to meet the needs of transmission systems, there are still some problems need to solve. Because of the polarization sensitive characteristics of the I/Q modulator, the SSB multi-carrier source is easily influenced by changes in the laser polarization state. Therefore, determining how the polarization state-of-light influences the output of multi-carrier source and how to control the polarization state to realize output stability is important. To solve this problem, the paper based on the existing research foundation of the SSB multi-carrier source, combine with the basic principle and polarization characteristics of the multi-carrier source devices, study the corresponding simulation scheme and solution. It mainly consists of following parts,1. Expound the development status and research significance of the multi-carrier source.2. Brief introducing relevant theoretical knowledge, including description of the polarized light, some representation methods of polarized light, and related introduction of polarization controller.3. Building polarization analysis model based on the SSB multi-carrier source system under ideal condition, including some models of the multi-carrier source components such as polarization controller, filter and I/Q modulator.4. Simulating transmission of the polarized light in RFS, tracking the change of the signal light polarization state in every circulation. Numerical simulation output spectrum of the multi-carrier source without polarization controller. Add polarization controller, obtain stable multi-carrier source output by adjust fast axial azimuth of three wave plates.5. Establish experiment system, verify the accuracy of the theoretical analysis. Get stable and flat multi-carrier output under the guidance of the theory.6. Based on working principle of the SSB multi-carrier source, theoretical analysis and simulation the impact of the third harmonic crosstalk on the flatness of the multi-carrier source under ideal condition. Introduce a multi-carrier source improvement scheme which could restrain third harmonic crosstalk.In summary, the paper does systematic research on the stability and polarization characteristics of the multi-carrier source which is suitable for terabit transmission system. Based on the mathematical model of the multi-carrier source, analyze polarization factor which influence the stability of light source by simulating transmission of the polarized light in RFS. Some important conclusions have been gotten, and the effectiveness and reliability of the conclusions have been verified by experiment.