光电振荡器的振荡频率与环路延时密切相关，同时其光学谐振腔由超长的光纤构成，因此有潜力实现大尺寸高精度的距离测量。光纤作为光电振荡器的核心元件之一，其长度不但影响振荡信号的谱纯度，还决定着距离测量的灵敏度。通过分析光电振荡器的工作原理及其进行距离测量的方法，分别得到了光纤长度与光电振荡器的谱纯度以及距离测量灵敏度之间的关系，并使用不同长度的光纤进行实验，验证了分析结果。在振荡频率的测量分辨力为1 Hz时，综合考虑距离测量时对测量灵敏度、振荡信号谱纯度、测量范围的要求以及环境扰动引入的误差，光电振荡器的光纤长度应该在1 km左右。

The extra-long optical cavity of optoelectronic oscillator (OEO) and the relationship between oscillation frequency shift and the variation of cavity length open the possibility for high-accuracy distance measurements at long range. Optical fiber not only affects the spectrum purity of the output microwave, but also determines the sensitivity of distance measurement. Based on the theory of optoelectronic oscillator and the distance measurement method, the effects of optical fiber length on spectral purity of OEO and measurement sensitivity are analyzed respectively. Fiber loops with different lengths are used in experiments in order to verify the results of analysis. Considering the demands of the measurement sensitivity, the spectral purity and the measurement range, as well as the error introduced by the environment, the fiber length of OEO will be about 1 km when the resolution of frequency measurement is 1 Hz.