在光纤通信系统中，光纤中传输的是二进制光脉冲"0"码和"1"码，它由二进制数字信号对光源进行通断调制而产生。而数字信号是对连续变化的模拟信号进行抽样、量化和编码产生的，称为PCM（pulse code modulation），即脉冲编码调制。这种电的数字信号称为数字基带信号，由PCM电端机产生。-In optical fiber communication systems, fiber-optic transmission of light pulses is a binary " 0"　code and " 1"　code, which is a binary digital signal to carry out on-off modulation source derived. The digital signal is a continuously variable analog signal sampling, quantization and coding generated is called PCM (pulse code modulation), or pulse code modulation. Such as digital signal power digital baseband signal by the PCM client machine generated electricity.