针对已有线宽检测方法在窄线宽激光器测量中存在的缺陷,提出一种利用非平衡光纤干涉仪相位噪声测量并计算线宽的方法。理论分析了短程差非平衡干涉仪相位噪声与窄线宽激光器的光频噪声的关系,得到了激光器的光波功率频谱和线宽。利用臂差为10 m的光纤干涉仪对窄线宽分布反馈激光器进行测量,结果表明激光器光波功率谱有近似的洛伦兹线型且线宽为5.4 kHz,与5 kHz的理论值相近。窄线宽光纤环形腔激光器的线宽测量结果为0.75 kHz,比用零拍法测量到的同类型激光器低于1.5 kHz的结果更精确。 Aiming at the shortcomings of the existing linewidth detection method in the narrow-linewidth laser measurement, a method to measure and calculate the linewidth by using the unbalanced fiber-optic interferometer phase noise is proposed. The relationship between phase noise of short-range unbalanced interferometer and optical frequency noise of narrow-linewidth laser is analyzed theoretically, and the power spectrum and linewidth of laser are obtained. The narrow line width feedback laser was measured by a fiber interferometer with an arm difference of 10 m. The results show that the laser light power spectrum has an approximate Lorentzian linearity with a line width of 5.4 kHz, which is close to the theoretical value of 5 kHz. The narrow linewidth fiber ring cavity laser measures 0.75 kHz, which is more accurate than 1.5 kHz for lasers of the same type measured by the zero-beat method.