Researches On Multicarrier Source Used For Terabit/s Optical Fiber Communication System

With the development of data traffic, especially for the images and videos, the pursuit of large-capacity network results in the terabit/s optical transmission system being the main trend for the next generation optical network. Limited by the bandwidth of electronic components, the capacity of single-channel is hard to achieve the Tb/s transmission. To support the Tb/s transmission and improve the spectral efficiency, higher-order modulation formats and kinds of multiplexing technologies have been used.So far, the Tb/s superchannel transmission systems based on frequency-locked multicarrier which generated from a single laser source have gained a hot-point in research. So, the frequency-locked multicarrier is one of the key components. The recirculating frequency shifter (RFS) based on the single-side band (SSB) modulator is the one of the schemes to achieve the multicarrier sources.However, to meet the needs of the Tb/s superchannels, there are some problems of the RFS should be solved. Firstly, the output properties of output multicarrier under the ideal case, such as the stability, output optical signal-to-noise ratio (OSNR), have not been analyzed. Secondly, there are many factors which impact the output properties of RFS in the practical case. The influences of these factors are different from the ideal case. Thirdly, to improve the output quality of the multicarrier, the modified configuration of RFS has not been proposed. Additionally, due to the loop configuration of RFS, the polarization properties are also important while having also not been analyzed. Therefore, the potential application of multicarrier source based on RFS has been limited due to these factors.Concerning the first challenge, a simple model which the third harmonics are the main crosstalk components due to the IQ modulator can be used to get the transfer function. Based on this model, the output stability, OSNR, and the maximum OSNR and corresponding optimal RF drive voltages can be obtained. In addition, by using the OSNR penalty model, the penalty with different desired carrier number can also be obtained.For the second problem, it can be solved by setting the transfer function model under the practical case. Then, the analysis of the influence of different factors on the output properties can be achieved.By optimizing the output property of the SSB modulator, the output quality of the multicarrier source can be improved effectively. At the same time, by applying the configuration of multi-seed laser cascaded RFS, the OSNR and number of output carriers can be increased.When set up the polarization model of multicarrier source, the polarization properties of RFS can be analyzed. By adjusting the polarization controller properly, the output quality of multicarrier can also be improved.In this thesis, the focuses are the four issues mentioned above. Firstly, the analysis of RFS under the ideal case has been presented. Then, the other three issues have been analyzed consequently. It mainly consists of following parts,(1) Under the ideal case, where the third-order harmonics are the dominant crosstalk components, the output properties of multicarrier source based on RFS with SSB modulator have been analyzed theoretically. By using the numerical simulation, the output flatness, OSNR, maximum OSNR, optimal drive voltages and OSNR penalty have been obtained.(2) Under the practical case, the properties of the transfer function influenced by different impact factors have been analyzed. These factors include the asymmetric property of SSB modulator, the imbalanced DC bias voltages and the imbalanced RF drive signals. The simulation and experiment have been implemented. Both results have a good agreement with the theoretical analysis.(3) Simulation on the optimization of RFS under the ideal case has been carried out. By suppressing or eliminating the third-order harmonics, the entire output quality of RFS has been improved effectively. By applying the configuration of multi-seed laser cascaded RFS, the number of output carriers have been increased multiply.(4) Theoretical analysis and simulation results on the polarization properties of RFS have been implemented. The transfer function has been derived. The variation of polarization of different subcarrier has been simulated. In addition, the experimental demonstration of the impact of polarization has been carried out. The experimental results show a good agreement with the theoretical analysis.In summary, this thesis mainly focuses on the studies on the generation of frequency-locked multicarrier based on SSB modulator which used for the Tb/s superchannel transmission system. By starting at the basic physical model combined the mathematic formulas, the important results of multicarrier source based on RFS have been obtained by presenting some analysis methods. At the same time, the experiments have also been implemented. Additionally, could be used to make some contribution to the continuing studies is also the desire of this thesis.