基于光纤延时声光频移自差拍法快速测量激光线宽

Rapid Measurement of Laser Linewidth Based on Fiber-Delayed AOM-Shifted Self-Heterodyne Scheme

基于光纤延时声光调制器(AOM)频移自差拍法实验研究了不同线宽激光的功率谱特性,并作了相关的仿真分析;同时,提出了利用短光纤测量窄线宽激光器线宽的一种简单方法。当光纤延时时间小于激光器的相干时间时,自差拍频谱的3dB带宽不能直接用于标定激光线宽。理论分析和实验均表明,此时激光的线宽信息主要由自差拍频谱中两翼的周期性振荡成分决定,几乎不受中央尖峰的影响。根据最小二乘法理论,对实验所测的自差拍频谱进行理论拟合可获得待测激光的线宽。该方案基本不受延时自差拍系统最小分辨率的限制,可以用于激光线宽的快速测量,特别是窄线宽激光的测量。

The characteristics of laser power spectra under different laser linewidths are investigated experimentally based on the fiber-delayed acousto-optic modulator （AOM） shifted self-heterodyne scheme, and the relevant simulation analysis is performed. Meanwhile, a simple method is introduced that short fiber is used to measure the linewidth of a narrow-linewidth laser. When the delay time of the fiber is less than the coherence time of the laser, 3 dB width of the beat signal cannot be directly used for measuring the laser linewidth. The experimental and theoretical analysis shows that the measurement result is hardly affected by the narrow peak. Therefore, it should be considered that the oscillations of the wings of the power spectrum rather than the effects of the narrow peak when dealing with the data. Using the weighted least square method, the laser linewidth can be obtained by theoretically fitting the experimental heterodyne spectrum. The scheme is not affected by the limit of the minimum resolution of the system, and it is applicable to the laser iinewidth measurement, especially for narrow-Iinewidth lasers.