Modeling And Equalization Of Polarization Effects In Fiber Channels In Special Scenarios

Since the advent of optical fiber communication technology,it has brought major changes in technology and society to the entire communication field,and has now become an important pillar of information transmission network.With the continuous arrival of various application technologies,people have put forward higher demand for network bandwidth.At present,optical fiber communication systems are developing rapidly in the direction of large-capacity,high-speed and long-distance transmission.Techniques such as high-order modulation formats and polarization division multiplexing(PDM)are often used in optical fiber communication systems to increase system transmission capacity.Since the influence of various impairments in the optical fiber link on the transmitted signal cannot be ignored,it is necessary to equalize the damaged signal at the receiving end,that is,coherent detection technology and Digital Signal Processing(DSP)technology have attracted much attention and are widely used in optical communication systems to recover damaged signals.When optical signals are transmitted in optical fibers,they are inevitably affected by various channel damages.This paper focuses on polarization-related channel damage,including polarization mode dispersion(PMD),rotation of state of polarization(RSOP),and polarization dependent loss(PDL).In recent years,the single-channel transmission rate has reached more than 110 Gbaud,and in laboratory research,the maximum baud rate can reach 220 Gbaud.With the increase of single-channel baud rate,the influence of polarization effect on the performance of optical fiber communication system cannot be ignored,especially in the polarization multiplexing system.The polarization effect largely limits the quality of signal transmission,so the polarization effect modeling and equalization research is very necessary,and at present,a variety of modeling methods have been proposed and achieved a more ideal equalization effect.However,in extreme scenarios,such as thunderstorms,ultrafast RSOP of up to several hundred krad/s or even Mrad/s will be generated in the optical fiber around the lightning,and traditional equalization algorithms are difficult to track,eventually leading to communication interruptions.In vlew of this problem,it is particularly important to establish a polarization effect model that can reflect the real lightning scene and find an equalization algorithm that can effectively combat the damage.In addition,PDL is also an urgent problem to be solved in optical fiber communication,which will cause the signal-to-noise ratios of the transmitted signals on the two quadrature polarization states to be different,which in turn will affect the transmission performance of the optical fiber communication system.PDL has become the main factor limiting the transmission of communication systems,so modeling and equalizing this impairment is of great significance to ensure the quality of communication systems.This paper focuses on the topic of polarization channel modeling and polarization damage equalization of optical fiber communication system in special scenarios.Based on the time-frequency domain evolution model of broadband PMD,the physical mechanism and mathematical model of polarization effect damage under lightning scenarios are deeply studied,the polarization effect model under lightning is established,the influence of lightning strikes on optical fiber communication systems is analyzed,and an effective equalization algorithm is proposed to alleviate polarization damage in channels.In addition,PDL,RSOP and PMD always exist at the same time in the actual optical fiber link,and this paper deeply studies the interaction and statistical characteristics between various polarization impairments,and explore the impact on system performance in the presence of multiple polarization impairments in fiber channels.The main research contents are as follows:(1)The polarization effect model under lightning is established to reflect the time and frequency evolution characteristics of the polarization effect in the real optical fiber link,and the influence of lightning on the optical fiber communication system is analyzed.For the proposed lightning model,we propose an improved Kalman Filter(KF)equalization algorithm,which is compared with the traditional Constant Modulus Algorithm(CMA).The results show that when the maximum speed of lightning strikes exceeds 5 Mrad/s,the traditional CMA fails,but the Kalman equalization algorithm shows good performance for the equalization of ultrafast RSOP and large PMD.(2)The transmission channel model under the coexistence scenario of PDL,PMD and RSOP was constructed,the interaction between polarization effects and the statistical characteristics of various polarization impairments under interaction were studied,and the influence of combined polarization effects on system performance was analyzed.The results show that the addition of PDL will reduce the equilibrium effect of CMA algorithm on PMD,and in turn,the addition of PMD will alleviate the damage caused by PDL to the system to a certain extent.