Multilevel Pulse Amplitude Modulation And System Testing For Next Generation Optical Interconnects

Compared with electrical interconnects,optical interconnects has advantages of high bandwidth,low power consumption,low latency,low transmission loss,no electromagnetic interference,parallel transmission,etc.It could not only solve some existed problems of electrical interconnects in network system,but also be the best means to overcome the bandwidth limitation of current data center.Multilevel modulation technology is considered as the most promising application of 400 G optical interconnects,and it is being explored and industrialized.The development and popularity of high-definition streaming media,mobile Internet,and cloud computing provide a broad market for optical interconnects and its applications.The researches about multilevel modulation method and system testing technology become more and more important in both academic field and industrial application.In order to improve the quality of PAM4 signals and its transmission rate / distance in a way with more practical value,based on dual-drive MachZehnder modulator,this study constructs simulation and experimental systems of PAM4 by optical synthesis.Using the characteristics of dualdrive Mach-Zehnder modulator modulation to achieve the full range of completely linear modulation in optical domain,the system not only reduces cost and power consumption,avoids electrical bandwidth limitations,but also achieves better modulation and transmission performance in a simpler way,which provides a feasible solution and research idea for the study of multilevel modulation method.On the basis of the research of system test technology,two sets of optical interconnects automatic test system are developed,which improve the efficiency of product line and process yield.This study optimizes the linearity and amplitude on the vertical axis of the modulator transfer function and realizes coding and decoding by controlling the amplitude and bias of the input signals.From the view of optical PAM4 signal's quality,this scheme has clearer eye diagrams,better effects of eye height,eye width,jitter and linearity than that by electric synthesis.Besides,the experiment further verifies the advantages of signal quality in the transmission system and obtains 1-dB receiver sensitivity improvement.In addition,linear mapping and demapping of PAM8 are realized by the expansion and innovation of the modulator structure.