中文摘要：

为了深入研究Lyot型退偏器的退偏原理，利用光束叠加的方法，通过分析得到了该退偏器对复色线偏振光的退偏度表达式。利用该表达式及光束叠加思想，从新的角度分析了Lyot型退偏器的三个理想退偏条件：晶体光轴夹角为45°；每一片晶体的延迟量足够大；两片晶体的延迟量之差必须足够大。通过比较发现，早期研究结论的不同主要是由于选取的光源功率密度谱不同造成的。研究结果表明，光束叠加方法计算简单、意义清晰、退偏度表达式简洁，可以更加全面、细致地实现退偏性能的分析。

英文摘要：

In order to make a deep study the depolarization of Lyot depolarizer, the means of superposition of beams is used m get the formula of degree of depolarization for polychromatic linearly polarized light. From the formula and the idea of superposition of beams, a new discussion is given about three ideal depolarization conditions, which are （1）the angle between the crystal axes must be 45°, （2）the crystal retardances of both crystals must be large, （3）the difference between the two crystal must be large enough. It is found that the different conclusion of early researches are mainly caused by the different select of spectral-power distribution. It indicates that the method of superposition of beams is simple and clear, and the analysis of depolarization performance is realized in a meticulous and all-round way.