为获得尽可能大的差频转换效率，基于准周期极化铌酸锂(QPPLN)光学超晶格，提出了级联电光和差频理论，用于高效的差频转换。其方法是沿QPPLN光学超晶格的y方向施加一个外加电场，用来控制能量在抽运光、信号光、o偏振的差频光和e偏振的差频光四个光波之间的转移。计算结果表明，在一个100 ℃，40 mm长的QPPLN光学超晶格中，当1550 nm信号光与1064 nm抽运光光强比值r<0.324时，对光强超过特定值的任意抽运光都可以通过施加一个适当的外加电场将抽运光完全转化为1550 nm信号光和3393.4 nm 差频光；当r≥0.324，只当抽运光光强落在一定范围内时，才可以通过施加外加电场使抽运光完全转化为信号光和差频光；超过该范围，外加电场不能增加差频光转换效率。计算结果还表明，电光调制差频转换效率对温度和畴构造误差都不敏感。

In order to obtain as high efficiency of difference frequency conversion as possible, a method based on the cascaded electro-optic and difference frequency theory in the quasi-periodically poled LiNbO3 optical superlattice (QPPLN) is put forward. The idea is that an external electric field is applied along the y-axis of the QPPLN to control the energy conversion among the pump beam, signal beam, o-polarized difference-frequency beam and e-polarized difference-frequency beams. The numerical results show that, in a 40-mm long QPPLN at 100 ℃, when the ratio r of the intensity of the 1550-nm signal beam to that of the 1064 nm pump one, is less than 0.324, any pump light with an intensity higher than a specific value can be fully translated into the 1550-nm signal light and the 3393.4-nm difference-frequency light as long as a suitable electric field is applied. In the case that r is equal to or larger than 0.324, only in a fixed range can the pump light be translated into signal and difference-frequency ones completely under an appropriate applied electric field. Out of the range the applied electric field cannot increase the efficiency of difference-frequency conversion. The further investigation indicates that the difference-frequency conversion modulated by electro-optical effect is not sensitive to both temperature and domain structure error.