Research On Precoding Technology For Low-cost Metropolitan Optical Transmission

With the continuous development of emerging technologies such as cloud computing,big data,and virtual reality,the data traffic in the Internet is also increasing.With the continuous advancement of urbanization and the large-scale construction of data centers,the data traffic in urban optical transmission is also showing a trend of rapid increase.At the same time,due to the national policy of "increasing speed and reducing fees",the revenue of operators is difficult to match their cost expenses.Therefore,how to achieve low-cost urban optical transmission has become the focus of research.The intensity modulated direct detection(IM-DD)system based on pulse amplitude modulation(PAM)has the advantages of simple structure and low cost,among which PAM4 is selected as the standard modulation format of 400G optical module and widely used in metro optical transmission systems.This article studies low-cost IM-DD systems and elaborates on the bottlenecks that limit the development of low-cost IMDD systems.In response to the issues of insufficient bandwidth of optoelectronic devices,frequency selective fading caused by dispersion,and low resolution DAC quantization noise in low-cost urban optical transmission systems,precoding technology and quantization noise shaping technology are used to improve system performance.The specific research content is as follows:(1)To address the bandwidth limitation issue in the IM-DD system,a compensation scheme based on THP precoding technology was designed in the paper,and a simulation system was built to verify the proposed scheme.In the simulation system,the 3dB bandwidth of the transmitter and receiver is set to 25 GHz,and the system bandwidth is limited by increasing the signal baud rate.The simulation results show that the symbol rate of the transmitted signal after THP encoding can reach up to 77GBaud,with an increase of 20%compared to the uncoded signal;The symbol rate can only be increased to 68GBaud using traditional bandwidth pre compensation technology.The results indicate that THP has stronger bandwidth compensation ability.(2)A low-cost urban optical transmission system has been built,using THP encoding instead of dispersion pre compensation.This scheme uses single drive MZM modulation at the transmitting end to save one DAC;And use low resolution DAC to reduce the cost and power consumption of the transmitter,while using quantization noise shaping technology to compensate for the quantization noise caused by low resolution DAC.Using THP precoding technology and digital resolution enhancement technology,56GBaud PAM4 signal transmission was achieved under the condition of a DAC physical quantization bit of 4 at the transmitter and a transmission distance of 40km.This scheme has a simple structure and low cost,and has reference significance for the research of urban optical transmission systems.