基于扫频激光器和马赫-增德尔干涉结构的光纤传感系统, 针对扫频激光器的频率步进不够精细导致干涉臂长差解调结果不精确的问题, 提出了一种相似性解调方法.该方法通过在频率步进范围内进一步细分, 构造相应细分值的模拟函数, 与采集到的干涉信号进行相似性对比, 相似性最大时所对应的模拟干涉臂长差即为精确结果, 并通过仿真与实验验证了该方法的可行性.实验表明该系统中干涉臂长差的解调范围为2~17 mm, 该范围内解调结果最小分辨率为1 μm, 可以达到测试量程万分之一的分辨率, 且抗干扰能力强、精度高, 可实现信噪比大于6.87 dB时信号的解调.根据解调原理, 在不强调实时性的应用中, 可以通过提高细分的精细度, 进一步提高系统分辨率.

A new similarity demodulation method in fiber optic sensing system based on a frequency-swept laser and a Mach-Zehnder interference structure is proposed and demonstrated. The method is designed specifically to overcome the difficulty due to the finite frequency steps of the frequency-swept laser, which is not fine enough and will result in inaccurate demodulation result of the interference arm length difference. The method relies on the construction of a simulated function by finely subdivide in the frequency step range, and then compare it with the real interference signal, the simulated interference arm length difference corresponding to the maximum similarity is considered closest to the true result. The feasibility of the method is verified by simulation and experiments, which show that the demodulation range of the interference arm length difference of the system is 2~17 mm, and the minimum resolution of the demodulation result over this entire range is 1 μm, corresponding to a resolution of 1/10 000th of the full scale. In addition, the method also features high anti-interference ability, and can perform demodulation satisfactorily as long as the signal-to-noise ratio is greater than 6.87 dB. According to the principle of the new demodulation scheme, in applications that do not emphasize real-time performance, the resolution of the system can be further improved by increasing the subdivision.