光束在自由空间中传输时, 其偏振特性随传输距离和光源参数的改变显示出不同的变化规律。为了研究其变化规律, 以偏振相干统一理论为基础, 仿真分析了各向同性和异性光束在自由空间传输时的偏振度变化规律。结果表明, 光束在自由空间中传输时, 光谱总密度随着传输距离的增加而逐渐降低, 偏振度在经过长距离传输后会达到稳定; 波长及光斑影响偏振度达到稳定状态距离, 相干长度影响其到达稳定值的大小。对于非偏振和全偏振光束在自由空间传输时, 只在特定条件下光谱的偏振度会保持不变。

It is found that the polarization properties of the beam will change with the distance and affected by the beam parameters on propagation in free space. In order to study its variation, study was based on unified theory of coherence and polarization, derived the cross-spectral density matrix evolution and simulated the variation of the degree of polarization. The results show that the spectral density is gradually decreased with increasing transmission distance, degree of polarization will reach stable after a long-distance transmission. The wavelength and spot size affect the reach distance of the steady state, the coherence length affects the value of its steady state. For completely un-polarized and completely polarized beam, the degree of polarization of the spectrum will remain unchanged under certain conditions.