电磁波电场强度的取向和幅值随时间而变化的性质，在光学中称为偏振。如果这种变化具有确定的规律，就称电磁波为极化电磁波（简称极化波）。如果极化电磁波的电场强度始终在垂直于传播方向的（横）平面内取向，其电场矢量的端点沿一闭合轨迹移动，则这一极化电磁波称为平面极化波。电场的矢端轨迹称为极化曲线，并按极化曲线的形状对极化波命名。因此如果E的失端轨迹是圆，则此电磁波称为圆极化波。(The properties of the orientation and amplitude of the electric field intensity of electromagnetic waves vary with time, which are called polarization in optics. If this change has a definite law, the electromagnetic wave is called polarization electromagnetic wave (called polarization wave). If the electric field intensity of the polarized electromagnetic wave always orientations in the plane perpendicular to the propagation direction, the terminal point of its electric field moves along a closed path. Then the polarized electromagnetic wave is called the plane polarized wave. The vector end track of the electric field is called the polarization curve and is named for the polarized wave according to the shape of the polarization curve. Therefore, if the lost track of E is a circle, the electromagnetic wave is called a circular polarization wave.)