在长距离光通信系统中,采用高阶外调制和相干接收技术来提高系统总的传输容量。但是在短距离光通信系统中更倾向于使用低成本的直接调制-直接检测技术, 此时, 要实现高速、大容量传输就必须采用多电平调制。目前国际上主流的调制方案有三种: PAM(脉冲幅度调制)、DD-OFDM(直接检测-正交频分复用)调制和CAP(无载波幅度相位)调制, 文章对这三种方案的原理与性能进行了分析与比较, 希望以此作为未来短距离大容量光通信系统设计的依据。

High-order external modulation and coherent detection technology are generally used in long-haul optical communication systems to improve the overall system transmission capacity. However, a low-cost direct modulation-direct detection technology tends to be more used in short-haul optical communication systems. In this case, it is necessary to adopt advanced multi-level modulation to realize high-rate large-capacity transmission. Currently, there are three principal modulation schemes considered internationally, i.e. Pulse Amplitude Modulation (PAM), Direct Detection-Orthogonal Frequency Division Multiplexing (DD-OFDM) modulation, Carrierless Amplitude/Phase (CAP) modulation. This paper analyzes and compares their principles and performances, hoping to use them as the basis for the design of future short-haul large-capacity optical communication systems.