Research On The Low-Cost And High-Speed IMDD PAM Optical Transmission System

With the coming of cloud computing and the popularity of big data centers, the data centers having high-capacity and high-speed gradually become the basis for a new generation of Internet services, as a result, the need of providing transmission support for data centers of short-distance and high-speed optical interconnects is urgent. Hence, the fiber transmission system with low-cost and high-speed has become the focus of attention. Given the issues about low-cost, low-power consumption and low complexity, nowadays, the method of combining intensity modulation and direct detection(IM/DD) with higher-order modulation format is more practical. However, as a result of the rise of rate and the increase of transmission distance, a number of problems in the optical fiber transmission system become a bottleneck restricting the development of optical communication, such as the bandwidth of the device, the fiber dispersion, and so on.In this paper, using electronic dispersion compensation technology, a low-cost scheme for PAM4 signal optical fiber transmission system based on the direct detection of the intensity modulation is proposed and experimentally demonstrated. As we all known, the bottlenecks of restricting the development of low-cost IMDD system majorly stems from the strict requirement on the bandwidth and inter-symbol interference produced by optical fiber dispersion. Electronic dispersion compensation technology can improve the receiver sensitivity, and then cut the cost by loosing these requirement. The main work of this paper has been completed are as follows:Firstly, it has built the simulation platform based on PAM4 signal IMDD optical fiber transmission system. The performance for suppressing the inter-symbol interference by the feed-forward equlization (FFE) and maximum likelihood sequence equalizer (MLSE) is investigated and compared. Moreover, the method of bandwidth of the pre-compensation in transmitter has also be considered to further improve the performance. The results shows that compared with FFE properties, MLSE performance is of 1.2dB promotion, and by introducing the bandwidth of the pre-compensation in transmitter, the receiver sensitivity is lifted 0.3dB and the complexity of receiver can be significantly reduced.Secondly, it has built IMDD optical fiber transmission system experiment platform based on PAM4 signal. And also, the experimentally demonstration about the system with back to back and optical fiber transmission are performed. In addition, the influence of the selection intensity modulation bias point, lack of system bandwidth and nonlinear problems on the performance of the system is also investigated. Moreover, as for the high complexity of maximum likelihood sequence equalizer, a combination of FFE and MLSE are proposed and demonstrated theoretically and experimentally. The experimental results show that the scheme can reduce system complexity and ensure system performance. Under the conditions that the error rate is not higher than at 2× 10-3, the rate of PAM4 signal on 25Gbaud, in 1310 nm, the longest distance of transmission fiber is 45km, the sensitivity of the receiver is-13.98 dBm, in 1550nm for transmission fibers 10km, the receiver sensitivity is-10 dBm. Finally, the experimental system established Volterra theoretical model.