光纤器件尤其是光纤电光调制器(EOM)在简化PDH频率锁定装置的同时会诱发残余幅度调制(RAM)，该效应会使PDH误差信号出现一个受环境温度影响的直流偏置，同时线型也出现一定程度的扭曲，这不仅会使频率锁定点发生漂移，同时也会影响频率锁定的时间。对PDH误差信号中存在RAM的线型进行理论和实验分析，并利用Hnsch-Couillaud(HC)技术抑制RAM，在实验上获得了无偏置且信号对称的PDH误差信号。分别利用RAM抑制闭环和开环的误差信号，进行了激光到腔模的频率锁定，验证了RAM抑制方案可以极大地增加基于光纤EOM的PDH频率锁定技术的稳定性。

The structure of PDH technique is greatly simplified when the fiber components especially fiber electro-optic modulator (EOM) are applied to it. Since the key of this locking technique is frequency modulation, unaligned modulation process induces residual amplitude modulation (RAM), which produces a temperature dependent direct current (DC) offset and a lineshape distortion. This effect may induce the drifting of frequency locking point and shortening of locking time. A theoretical and experimental analysis of PDH error signal including RAM is given, and the symmetric PDH error signal of RAM reducing method based on Hnsch-Couillaud technique is obtained experimentally. The locking performance of the laser to the cavity is analyzed with and without RAM reducing feedback, and it is verified that the RAM reducing scheme greatly increases the stability of fiber EOM based PDH frequency locking technique.