Spectral interferometry using frequency comb has become a powerful approach to absolute distance measurement. In this paper, we analyze the principle of spectral interferometry in detail. With the consideration of dispersion, pulse chirp and the power ratio of the reference pulse and the measurement pulse, we develop a Gaussian model, which can be used to determine distances. The frequency of the spectral interference fringe is of key importance. The distances can be directly determined by the frequency of the spectral interference fringe through one-step fast Fourier transform with no filters during the data processing. The simulation results show that the maximum deviation is 1.5 nm when the distance is 1.5 mm theoretically. The comb consists of hundreds of thousands of teeth in the spectral domain, and each tooth can be regarded as a cw laser. We propose a method based on the phases of two close modes. The principle is introduced, and the maximum deviation is 8.7 nm with a distance of 1.5 mm while the minimum deviation is 0.3 nm corresponding to distance of 0.5 mm. We theoretically show that the linear pulse chirp can be used for distance measurement. The measurement principle is analyzed, and the simulation shows that the maximum deviation is 5.3 nm when the distance is 1.2 mm.%详细分析了光学频率梳光谱干涉的原理，建立了较全面的光谱干涉的数学模型，为实现绝对距离测量提供理论分析基础.基于光谱干涉，指出通过光谱干涉条纹的振荡频率，即一次傅里叶变换，可以实现绝对距离测量，数值模拟结果表明，最大测量误差为1.5 nm；提出了一种等效的多波长并行零差干涉的方法，分析了多波长并行零差干涉法的测距原理.数值模拟结果表明，多波长并行零差干涉法的最大误差为8.7 nm；通过脉冲啁啾实现绝对测距，分析了基于脉冲啁啾实现绝对测距的原理，数值模拟结果表明，最大测距误差为5.3 nm.
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