| We live in a highly information-oriented society,especially in recent years,the rapid development of the Internet,multimedia,and mobile communications,the number of users has increased dramatically,and higher requirements have been placed on optical fiber communication performance.Transmission media and technology improve communication quality to meet the needs of production and life.Among the many modulation methods,high spectral efficiency quadrature amplitude modulation(QAM)can make full use of bandwidth and has strong anti-noise capability,which has become a research focus in the field of optical communication.Dispersion-flattened fiber(DFF)has small second-order dispersion and flat dispersion over a wide range of wavelengths,which can be used as a better medium for information fiber transmission.Combining QAM technology with DFF and other optical fibers,we propose two transmission systems,and conduct research on some transmission characteristics measured experimentally and draw conclusions.The two transmission systems are as follows:We propose a dispersion flattened fiber(DFF)front-haul transmission system with high bitrate,polarization multiplexing(PM)and quadrature amplitude modulation(QAM)signal at low input optical power.The modulation format of the system is PM-16QAM,and the bitrate is 256Gbit/s.Three experiments were performed using the system.In the experiment,the transmission characteristics of the DFF link system were first studied,and compared with the transmission characteristics of a standard single-mode fiber(SSMF)link and a non-zero dispersion shifted fiber(NZDSF)link.Experimental results show that the EVM of a 256Gbps,PM-16QAM signal on a 25km DFF link is at least 0.75%better than a 25km NZDSF link,and the BER and Q factors are much better than NZDSF.The EVM and BER of the three links decrease with increasing input optical power,and the Q factor increases with increasing input optical power.Under the same conditions,the characteristics after 25km SSMF transmission are the worst.The greater the dispersion,the more the constellation points deviate from their respective centers,and the worse the constellation characteristics.The greater the attenuation of DFF,the smaller the input power,the more the constellation points deviate from their center,and the worse the constellation characteristics.This research provides new ideas and experimental support for the frontier propagation of mobile communications in special application scenarios.We propose an unrepeated long single-span front-haul transmission system based on dispersion-decreasing-like fibers.The modulation format is 160Gbps and PM-16QAM.We obtain that the dispersion and the optical power of signal decrease with the increasing of transmission distance by using dispersion-decreasing-like fibers.As a result,the dispersion and nonlinear effects of the transmission system are balanced and the system performance is improved.Because the total dispersion is low,the proposed system can effectively avoid the delay caused by dispersion compensation in the digital signal processing in the corresponding standard single-mode optical fiber transmission system.At lower input optical power,the first-order Raman amplification in this system can effectively compensate for attenuation impairment in signal transmission.Then the bit error rate(BER)of the system is better than 7%hard-decision forward error correction threshold(FEC)of3.8×10-3 in a wide range of input optical power.This system can be used in the long single-span front-haul transmission in special application scenarios.At higher input optical power,the nonlinear effect of optical fiber is the dominant factor affecting the performance of the transmission system,and nonlinear effect of optical fiber increases with the increasing of input optical power and Raman pump power,as a result,the system performance deteriorates.The improvement of system performance requires equalization of Raman amplification power and input optical power. |
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