The positive and negative frequency expressions of quasi - monochromatic optical fields of a pulse in fiber - optic communication and the positive and negative frequency forms of fourier transformations and nonlinear schr ? dinger ( nls ) equations are discussed 摘要讨论光通信中脉冲的准单色光光场的正负频表示,正负频形式的傅里叶变换,正负频形式的非线性薛定谔方程及它们之间的关系。