为了更好地实现远程光钟之间的高精度比对，对意大利Calosso小组所提出的光纤双向光学相位比对方案进行了拓展，提出了一种基于本地测量的双向光学相位比对方法。同源的两路光信号从同一光纤两端注入，其中一路光信号经光纤传输到远端后经反射原路返回本地端，另一路光信号从远端经光纤传输至本地端。两个信号均在本地端与参考光进行拍频，将拍频得到的两路拍频信号的相位进行比对。利用这种结构，系统不需要有源光纤相位噪声补偿也可以消除叠加在光纤链路上的共模相位噪声，该结构的最大优势在于拍频信号的采集和处理均可以在本地端完成，不需要引入额外的时间同步信号来保证两地拍频信号采集同步进行，简化了实验系统。计算分析了该方案的相位噪声极限，并建立了基于60 km缠绕光纤的示范系统来进行测试，测得其秒级频率稳定度为1.45×10-16，千秒稳定度达到 1.51×10-19。该方案有望用于远程光钟和其他原子钟之间更可靠的高精度频率比对。

In order to realize high precision comparison between remote optical clocks, the two-way optical phase comparison scheme proposed by the Calosso group in Italy is extended, and a two-way optical phase comparison method based on local measurement is proposed. Two optical signals which come from the same laser source are injected from two ends of the same optical fiber. One signal transmits to the far end through the optical fiber and then returns to the local end by reflection. The other signal transmits from the far end to the local end through the optical fiber. In this way, the two signals are beaten at the local end with the reference light to obtain the phases of the two beat signals. In this case, the common-mode phase noise induced by fiber links can be eliminated without the active fiber phase noise compensation. The most important advantage is that the acquisition and the processing for beat frequency signal can be done at the local end without adding extra time synchronous signal to ensure the synchronization of beat frequency signal acquisition, which simplifies the experimental system. The ultimate phase noise performance of the scheme is calculated, and a demonstration system based on 60 km spool fiber is established. The frequency instability are 1.45 × 10-16 for 1 s and 1.51 × 10-19 for 1000 s. The scheme is expected to be used for more reliable high precision frequency comparison among remote optical clocks and other advanced atomic clocks.