Research And Application Of Digital Signal Processing Algorithm In High Speed Coherent Optical Transmission System

With the development of coherent optical communication technology in recent 10 years,high-speed coherent technology has been widely used in backbone transmission network.From 2011,the single wave length technology of 100 Gbit/s has been commercial,and has become the most common line speed of transmission network.By 2018,200 Gbit/s and 400 Gbit/s technology has been gradually commercial,and the commercialization of800 Gbit/s or 1 Tbit/s technology has become an inevitable trend in the future.With the continuous development of network services and communication demands,coherent optical communication technology began to develop into other fields.However,due to the characteristics of different application network,traditional coherent optical communication technology still has some problems to be solved.In short-range network,such as access network,data center and so on,the demand of high-speed data services provides the development opportunity for coherent optical communication technology.However,due to the requirement of low cost and low power consumption in short distance network,the traditional coherent optical communication technology with high cost and high power is difficult to be accepted.In addition,in the field of ultra long span optical communication,coherent optical communication technology has become the best solution based on its higher receiving sensitivity and signal to noise ratio tolerance.However,due to the fiber in the natural environment,it is easy to be affected by some environment factors.The application of traditional coherent optical communication technology still faces many practical problems.At the same time,in the backbone network where coherent optical communication technology has been widely used,based on wavelength division multiplexing technology,the network bandwidth and node capacity are growing rapidly.With the continuous growth of Internet traffic,the demand for large bandwidth service scheduling is increasing rapidly.How to achieve wavelength channel management in the optical layer has become a new problem in the backbone network.In view of the above problems,this dissertation has carried out a series of research on signal processing algorithms related to digital coherent optical transmission system.The main achievements and innovations of this thesis are as follows:(1)Mainly for short-range applications such as access network and data center,to further reduce the complexity of coherent technology,a simplified digital signal processing algorithm is studied,and a new adaptive channel equalization algorithm structure is proposed.Then,according to the new algorithm structure,a new error calculation method is proposed to improve the performance of the algorithm.The new algorithm structure can reduce about 40% multiplier resource.Based on the real-time coherent transmission platform,the algorithm is implemented at the receiving side.The transmission experiment is carried out to verify the performance.In the back-to-back and 60 km transmission experiments,compared with the traditional algorithm,the performance penalty of the proposed algorithm is only about 0.2?0.3 d B.The proposed algorithm not only reduces the resource consumption,but also has the same requirement for the sampling wideth of analog to digital converter.And it has stronger polarization demultiplexing ability than the traditional algorithm.(2)Mainly for ultra long span transmission network,a novel adaptive filter algorithm structure with state of polarization monitoring and feedback is proposed to solve the problem of polarization state fast rotation caused by external environment interference.Firstly,by extracting the filter tap coefficients in adaptive filter,the Stokes vector is calculated to obtain the state of polarization rotation,which realizes the real-time monitoring of polarization state rotation.Then,the update coefficient of the filter is adjusted according to the change of polarization state,and the polarization tracking ability of the algorithm can be improved.The transmission experiment is carried out to verify the performance.The results show that the proposed algorithm structure can improve the polarization tracking ability of the traditional algorithm structure by more than 4 times.Compared with resources consumption of the traditional algorithm structure,the increased resource of the proposed algorithm is only 1%.(3)Mainly aiming at the requirement of wavelength channel management in optical layer in backbone network,a new optical label signal transceiver system based on pilot is proposed.Based on the optial subcarrier index modulation,the optical labelling signals of different wavelengths are loaded in different frequency bands.Therefore,the whole band optical labelling signals can be recognized by only one photo diode at the receiver.In terms of digital signal processing,the phase adjustment algorithm is used to reduce the signal peak to average power ratio at the transmitter side.At the receiver side,phase offset estimation and compensation algorithm,and the overlap summation algorithm in frequency domain,are implement to improve the signal to niose ratio.The relevant parameters are optimized through experiments,and the feasibility of the optical label scheme in 100 Gbit/s coherent wavelength division multiplexing optical network is verified.