| With the rapid development of data center traffic,as the requirements of system capacity and bandwidth increase,it also needs to meet low-cost transmission requirement.To cope with this challenge,advanced modulation formats with simple structures and high spectrum efficiency have attracted more attentions.Several advanced modulation formats,such as Discrete multi-tone modulation?DMT?,Pulse amplitude modulation?PAM?and Carrier-less amplitude and phase modulation?CAP?formats have been extensively studied.DMT and PAM-4 are the first choices in the candidate modulation formats,which belong to the multi-carrier and single-carrier modulation formats,respectively.The essential distinction between these two formats leads to show a large number of differences in many scenarios.In intensity modulation and direct detection?IM/DD?systems,the bandwidth of the transmitter or receiver is frequently limited by device itself,and it seems to be even less than the baud rate of the signal.Also,some low-cost devices in IM/DD system cause frequency selective fading due to the rough packaging process and the interaction of the laser chirp and dispersion.The complexity of the transmission environment causes the diversity of system frequency characteristics,which results in a great influence on the signal transmission performance.This dissertation involves three aspects,research on improving modulation bandwidth technique by optical injection locking,transmission performance of DMT and PAM-4 signals in low-cost bandwidth limited optical fiber transmission systems,and comparison the differences between the two signals in different types of frequency response as well as detailed analysis of the computational complexity of digital signal processing.The main research work is as follows:Firstly,an IM/DD experiment system based on the optical injection-locked Fabry–Pérot laser has been set up through the experimental platform.The influence of injected optical power on the two signals is studied,and the power penalties of DMT and PAM-4 under B2B transmission are compared.Under the three conditions of B2B,transmission rate?10Gb/s?and bandwidth utilization?1.67bit/s/Hz?,which are satisfied at the same time,PAM-4 has a power penalty of approximately 2dB compared with DMT.However,when the bit rate is up to 20Gb/s,DMT adopts bit loading algorithm still has 0.5dB degradation compared with PAM-4 signal.This dissertation completed DMT in bandwidth limited system with 6d B bandwidth less than 1GHz,achieving26.5Gb/s transmission over 25km standard single-mode fiber,with3.6?10-3 BER.Secondly,the dissertation focuses on the differences in the frequency response of the system in the experiment and compares the effects of different frequency response characteristics on DMT and PAM-4 signals in bandwidth limited optical transmission system by numerical simulation.What is more,the dissertation quantitatively analyzes the impacts of system frequency response,signal-to-noise ratio?SNR?,and bit rate on the transmission capacity and power penalties of DMT and PAM-4 signals.When the SNR of the signal is large enough,special channel response curves have a significant impact on transmission performance in addition to the bandwidth.At the receiver,digital signal processing can be used to compensate the introduced distortion,but sacrificing computational complexity to optimize signal performance which inevitably increases the system cost.The computational complexity of DMT and PAM-4 signals in bandwidth limited system is analyzed in detail.Therefor,the overall performance and computational complexity need to be trade-off. |
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