在光电振荡器(OEO)测距方法中,振荡频率与环路群时延关系的建立依赖于纵模阶数,纵模阶数测量误差直接影响测距精度。但是OEO频率稳定性较低,通过直接测量振荡频率和相邻纵模频率间隔所获得的纵模阶数误差较大。分析了频率漂移对纵模阶数测量的影响及测量过程中的频率漂移规律,提出一种新的纵模阶数测量方法,该方法在不改变OEO结构的基础上,利用OEO纵模等间隔分布的特点,分别测量振荡模到x阶高阶模和x阶低阶模的频率间隔后获取纵模间距,减小并补偿频率漂移造成的误差。随后建立了纵模阶数测量误差模型,并进行了1km光纤20GHz信号的纵模阶数测量对比实验,实验结果与误差模型相符。 In the OOO ranging method, the establishment of the relationship between the oscillation frequency and the delay of the loop group depends on the order of the longitudinal mode, and the measurement error of the ordinal order directly affects the accuracy of the ranging. However, the frequency stability of OEO is relatively low, and the errors of the longitudinal mode orders obtained by directly measuring the oscillation frequency and the adjacent longitudinal mode frequency intervals are relatively large. The influence of frequency drift on the measurement of the longitudinal mode number and the frequency drift in the measurement process are analyzed. A new method for the measurement of the longitudinal mode order is proposed. Without changing the OEO structure, the OEO longitudinal mode is used at equal intervals Distribution characteristics, respectively, the oscillation mode to the x-order high-order mode and x-order low-order mode frequency interval to obtain the longitudinal mode spacing to reduce and compensate for the frequency drift error. Then, the error model of longitudinal mode order measurement was established, and the comparison of longitudinal mode order measurements of 1GHz optical fiber 20GHz signal was carried out. The experimental results are consistent with the error model.