基于方波信号的磁光调制具有优良的特性，但存在信号畸变的问题，从理论上研究了它的机理。将方波信号通过傅里叶级数展开成不同频率正弦信号叠加的形式。在此基础上用麦克斯韦方程组和贝塞尔方程对各个频率正弦信号的长螺线管空间磁场进行求解，再把经过处理的各正弦信号产生的磁场迭代运算，最终从理论上求解出方波信号驱动时的长螺线管磁场。

Magneto-optic modulation based on square wave signal has excellent properties, while it has the disadvantage of signal distortion. Theoretically, its mechanism is studied. Square wave signal is expanded into different frequency sine signal form by Fourier series. Magnetic fields of long solenoid driven by various frequency sinusoidal signals are calculated with Maxwell′s equations and Bessel′s equation. Various magnetic fields are added together and magnetic field of long solenoid driven by square wave is calculated in theory.