相位调制是光纤中提高受激布里渊散射阈值、抑制受激布里渊散射效应的有效方法。理论分析了相位调制中调制幅度及调制频率的改变对受激布里渊散射阈值的影响，实验研究了25 MHz调制频率、不同调制幅度以及调制幅度为1.5，不同调制频率下受激布里渊散射阈值的变化情况。结果表明，受激布里渊散射阈值既随相位调制幅度的增大而增大，又随相位调制频率的增大而增大。当相位调制幅度为7.7，相位调制频率为25 MHz时，受激布里渊散射阈值提高约7 dB。当相位调制幅度为1.5，相位调制频率较小为5 MHz时，相位调制对受激布里渊散射阈值的影响不够明显。

Phase modulation is an effective method to increase the threshold of the stimulated Brillouin scattering. Effects of modulation amplitude and frequency on the threshold are analyzed in theory. Experiments at different modulation amplitudes and frequencies are conducted to investigate the variance of the threshold. It is shown that the threshold increases with not only the modulation amplitude but also the modulation frequency. When the modulation amplitude is 7.7 and the modulation frequency is 25 MHz, the threshold is improved by about 7 dB. When the modulation amplitude is 1.5 and the modulation frequency is as small as 5 MHz, the effect of phase modulation on the threshold is not obvious.