为了测量分布反馈（DFB）单模半导体激光器线宽，采用一种新颖的基于马赫-曾德尔干涉结构的光纤自外差测量方案，设计了一套全光纤延时自外差法测量系统，并进行了理论分析。在此基础上搭建了延时光纤长度分别为900m，3000m和6000m的窄带线宽测量系统，对实验室一台中心波长为1550nm、标称线宽值为800kHz的DFB单模半导体激光器光源进行了测试，测得激光器线宽值分别为951.566kHz，832.471kHz和802.221kHz，并对所设计的方案进行了模拟仿真验证。结果表明，与模拟仿真结果作对比，延时光纤长度为6000m时的窄带线宽测量系统最优，其误差在3%之内，证明了所用自外差干涉原理的合理性和准确性。全光纤移频延时自外差法对测量DFB激光器线宽具有优越性和重要的实用价值。

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Line-width measurement of DFB laser based on frequency shift delay self-heterodyning method

In order to measure the line-width of distributed feedback(DFB) diode single mode semiconductor laser, novel optical fiber self-heterodyne measurement scheme based on Mach-Zehnder interference structure was adopted and a set of all fiber time-delay self-heterodyne measurement system was designed. After theoretical analysis, narrow band line-width measurement system with time-delay fiber length of 900m, 3000m and 6000m was set up. A DFB single mode laser source with center wavelength of 1550nm and nominal line-width of 800kHz was tested. The measured line-width values of laser were 951.566kHz, 832.471kHz and 802.221kHz respectively. The designed scheme is verified by simulation. The results show that, compared with the simulation results, narrowband line-width measurement system with the length of 6000m is optimal, and its error is within 3%, which proves the rationality and accuracy of self-heterodyne interference principle. All fiber frequency shift delay self-heterodyne method has advantages and practical value for measuring the line-width of DFB lasers.