| In recent years,with the rapid development of the society,the emergence of new data services and applications such as the Fifth-Generation mobile communication,Cloud Computing,Big Data,Artificial Intelligence,Internet of Things,intelligent mobile devices,ultra-high-definition video transmission,etc.,has led great demands on the traffic explosive growth.The rapid growth of data traffic demands drives the optical fiber communication system to directions of ultra-fast speed,ultra-large bandwidth,ultra-long distance and ultra-high capacity.However,the development of high-speed transmission systems leads to the appearance of various problems gradually,including the degradation of the spectrum efficiency,the performance’s ineffectiveness of the traditional polarization de-multiplexing algorithm,and the increase of algorithm power consumption in the coherent receiver.The research in this thesis can be summarized as "two systems,four directions",namely,the in-depth research on decoding scheme and systematic impairments eqaulization by influenced inter-symbol interference for Faster-Than-Nyquist system,polarization effect electrical-domain and optical-domain equalization for high-speed Nyquist system.The main research contents and innovations of this thesis are summarized as follows:(1)Research on decoding scheme and systematic impairments equalization for Faster-Than-Nyquist systemFor Faster-Than-Nyquist system,it can effectively promotes the system’s spectrum efficiency.The higher the signal compression is,the higher system’s spectrum efficiency is,but the higher the influence of inter-symbol interference is.For the serious inter-symbol interference problem caused by high signal compression,the thesis proposes a decoding scheme which combines Polybinary shaping and maximum likelihood sequence estimation,which can decode in Faster-Than-Nyquist system with signal compression factor varying in the range of 0.45～1.00,and it gets the relationship between different signal compression factors and different level Polybinary shaping to achieve the best decoding performance of the proposed scheme.In order to ensure the corresponding decoding performance of the proposed decoding scheme,the traditional polarization de-multiplexing algorithm and carrier phase recovery algorithm that are applicable to the Nyquist system have been modified,so that they can work in Faster-Than-Nyquist system.At the same time,a polarization de-multiplexing algorithm suitable for extreme polarization effects in Faster-Than-Nyquist system has been developed based on the Kalman filter algorithm,thus laying the foundation for practical deployment of the Faster-Than-Nyquist system.(2)Research on dynamic all-order polarization mode dispersion electrical-domain equalization for broadband systemThe increase of the speed of optical fiber communication system makes the signal’s bandwidth broaden,which makes the polarization effect in optical fiber link more complex than that in the narrowband system and shows the all-order polarization mode dispersion characteristics with both time and frequency evolution.For the polarization effect of optical fiber link in broadband system,the thesis establishes a 20-segment cascaded channel model,and through relevant verification,it has been proven that the channel model can accurately reflect the polarization impairment characteristics in broadband systems.Based on the rationality of the established channel model,the thesis proposes a two-stage time-frequency domain extended Kalman filter algorithm for dynamic and all order polarization mode dispersion and its algorithm’s complexity is analyzed.In the process of the simulated verification,the proposed two-stage time-frequency domain extended Kalman filter algorithm can effectively equalize the polarization effect with an average different group delay of 10 ps and an average rotation of state of polarization rate of 8 Mrad/s in the 100 GBaud-PDM-QPSK system and 100 GBaud-PDM-16QAM system.In the process of experimental verification,when the average different group delay is 88 ps and the maximum rotation of state of polarization rate is more than 6 Mrad/s in the 16 GBaud-PDM-QPSK system,the proposed two-stage time-frequency domain extended Kalman filter algorithm has better polarization de-multiplexing performance compared with constant module algorithm.The experiment further indicates the proposed two-stage time-frequency domain extended Kalman filter algorithm can effectively equalize.dynamic all-order polarization mode dispersion in broadband system.(3)Research on optical-domain compensation for channel polarization effectShort-range optical fiber communication system uses intensitymodulation direct-detection system,but with the continuous improvement for the capacity in the data center,the limitation of intensity-modulation direct-detection system is gradually reflected.Coherent detection system with high sensitivity and large capacity does not have the same limitation as the intensity-modulation direct-detection system.The algorithm power consumption of the receiver in coherent detection systems hinders the deployment of coherent detection systems in short-range systems.However,the proposed concept of "coherent-lite" makes the use of coherent detection technology in short range system become possible.While it is particularly crucial to reduce the power consumption of polarization de-multiplexing algorithms that account for up to 15%of receiver power consumption.To solve the above problems,the thesis proposes an optical-domain polarization de-multiplexing scheme that is suitable for short-range high-speed coherent systems.The characteristic parameter selected in the scheme isn’t affected by chromatic dispersion in the optical fiber link.Therefore,it can correctly reflect the change of the state of polarization in the optical fiber link.The simulation results show that the performance of the scheme has no connection with modulation format,namely,it is transparent to modulation format.Based on the scheme,the designed optical-domain polarization de-multiplexing device can effectively achieve the performance of polarization de-multiplexing when the rotation of state of polarization up to 10 krad/s in the 10 km-112 GBaud-PDM-QPSK and 10 km-112 GBaud-PDM-16QAM system.The performance of the designed optical-domain polarization de-multiplexing device is basically consistent with expected results during the sensitivity and long-term stability test.In addition,in order to effectively compensate for the influence of all-order polarization mode dispersion in the long-range high-speed system,the thesis also proposes the concept of optical-domain compensation scheme for the long-range high-speed system,and provides relevant explanations for the scheme’s principle and the selection of devices,so that it can provide an effective optical-domain compensation scheme for the compensation of polarization effects in the long-distance high-speed system.In conclusion,the thesis focues on Faster-Than-Nyquist systems and Nyquist systems.For Faster-Than-Nyquist systems,the thesis proposes decoding algorithm,polarization de-multiplexing scheme and carrier phase recovery algorithm by influenced inter-symbol interference.For short-range coherent systems,the thesis proposes optical-domain polarization de-multiplexing scheme.For long-range high-speed systems,the thesis proposes electrical-domain and optical-domain polarization de-multiplexing scheme.Thus,contributing to the development of high-speed optical communication systems. |
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