为了研究复合腔抑制超模噪声的问题，基于传输函数法建立了复合腔等效结构模型，从理论上分析了复合腔主动锁模光纤激光器的结构特性，论证了等效复合腔基频与两子腔腔长的关系。在1GHz射频调制频率下，给出了复合腔各参量与超模噪声的关系。结果表明，复合腔可以减小超模数目，超模噪声的抑制与单腔相比并不具有优势。该结果对复合腔主动锁模光纤激光器的实验研究有一定的参考意义。

In order to study the supermode noise suppression in a mode-locked fiber laser with composite cavity, an effective structure model of the composite cavity was built based on the transfer function. The characteristic of an active mode-locked ring fiber laser with composite cavity was investigated theoretically. The dependence of the effective basic frequency of the composite cavity on the length of two sub-cavities was demonstrated in detail. Setting the RF modulation frequency at 1GHz, the relation between the supermode noise and parameters of the composite cavity were listed in a table. It was shown that the number of supermodes was reduced; however, the reduction of overall supermode noise was not remarkable in comparison with the standard single-cavity configuration. The result is helpful for experimental study of supermode noise of active mode-locked ring fiber laser with composite cavity.