在对描述I类相位匹配倍频过程的耦合波进行分析的基础上,发现不同初始条件下倍频过程中基频光和倍频光强度变化情况不相同。当注入倍频光能量不为零,且初始相位满足一定条件时,能量会在基频光和倍频光中循环交换。利用倍频过程中的这个循环过程,提出在倍频过程中注入倍频种子光(简称倍频注入)以实现稳定的倍频能量输出,并用数值模拟计算结果证明了倍频注入方法的有效性。进一步的数值模拟研究结果表明：倍频注入方法中可以通过改变注入的倍频种子光强和倍频种子光与基频光之间的相对相位来调节实现稳定倍频输出所需的倍频晶体长度。

After analyzing the type I phased matched coupling equations for second harmonic generation (SHG) course, it is found that when the input 2ω signal intensity and the preliminary phase difference θ(0)=2(0)-21(0) change, the output 2ω intensity varies along with the length of SHG in different way. When the input 2ω signal intensity is not zero and θ(0)=2(0)-21(0)≠±π/2, part of the energy oscillates between 1ω and 2ω. It is proposed that this kind of phenomenon can be used to improve the stability of the output 2ω intensity. Simulation proves that the method of injecting 2ω signal can greatly improve the stability of SHG course. Further simulation shows that length of SHG crystal changes as the input 2ω intensity and phase difference between 1ω and 2ω changing.