窄线宽光纤激光器的线宽作为相干光学系统的重要参数需要进行准确的测定，延时自外差法(DSHI)是测量窄线宽比较理想的方法。本文讨论了DSHI 测量线宽的基本原理，根据DSHI 的功率谱表达式，利用MATLAB 程序对不同光纤延迟线长度条件下的DSHI 功率谱进行了仿真，并分析和讨论了光纤延迟线长度对线宽测量结果的影响。建立了1 550 nm 波长的DSHI 线宽测量系统，对IPG 公司的光纤激光器线宽进行了测量。该系统用示波器代替频谱仪，并采用FFT 软件算法对示波器获取的光电流信号进行分析，测得该激光器的线宽约为16 kHz，在理想的精度范围内。

As an important parameter of the coherent optical system,the linewidth of narrow fiber laser must be measured accurately. Compared with other currently available linewidth measurement techniques, the Delayed Self-heterodyne Interferometer (DSHI) technique is the most promising one. In this paper, theory of the DSHI for determining the linewidth of lasers is described in detail. The MATLAB emulator is programmed to analyze the effects of fiber delay line on the results. Furthermore, an experimental setup based on the DSHI is constructed to measure IPG’s fiber laser linewidth. We substitute oscilloscope for the spectrum analyzer in this system, and the software algorithm is designed for the analysis of the photocurrent signal. From numerical analysis, the measured linewidth of the IPG’s fiber laser is about 16kHz, which is in the range of an ideal accuracy.