Shang Fan, Yu Yi, Ma Lina, Qi Yue, Song Junqiang
Opt Express. 2021 May 24;29(11):16118-16134. doi: 10.1364/OE.423895.
The random disturbance in the leading fiber is considered as a vital noise source in the practical interferometric fiber Bragg grating (FBG) sensor array, which is usually interrogated by periodic laser pulse pair. As the two interrogation laser pluses propagate through the leading fiber in a time-sharing manner, the leading fiber disturbance could cause undesired demodulated phase noises to both the polarization state and the pulse-interval, which are summarized as the polarization fading induced noise and the Doppler noise, respectively. This paper focused on the Doppler noise under the demodulation scheme of polarization switching (PS) and phase generated carrier (PGC) hybrid processing method. A model describing the transformation from arbitrary leading fiber stretching to sensor phase background was presented. The complexity was that the Doppler noise was coupled with the birefringence states, as verified by both simulation and experiment. In response to this issue, a two-stage Doppler noise suppression method was proposed, which is based on the PS and PGC hybrid processing and a reference sensor. A processing procedure was presented where the polarization synthesis must be performed before and the reference sensor was considered. Otherwise, the suppression algorithm will be completely invalid due to the mutual coupling of the Doppler noise and the birefringence. Experimental results showed that only after the first stage of polarization synthesis, identical Doppler noise in the two TDM channels could be obtained, with an amplitude error of 0.02 dB. The second stage involved non-sensitive reference sensor subtraction, which achieved a maximum suppression of about 30 dB, which was the highest to be best of our knowledge. The two-stage Doppler noise suppression method was tested for sinusoidal and wideband leading fiber disturbances, providing a solution for practical interferometric FBG array applications.
在实际的干涉式光纤布拉格光栅（FBG）传感器阵列中，前置光纤中的随机扰动被视为一个重要的噪声源，该阵列通常由周期性激光脉冲对进行询问。由于两个询问激光脉冲以分时方式在前置光纤中传播，前置光纤的扰动会给偏振态和脉冲间隔带来不需要的解调相位噪声，它们分别被总结为偏振衰落诱导噪声和多普勒噪声。本文聚焦于偏振切换（PS）和相位生成载波（PGC）混合处理方法解调方案下的多普勒噪声。提出了一个描述从任意前置光纤拉伸到传感器相位背景转换的模型。复杂之处在于多普勒噪声与双折射状态相互耦合，这在仿真和实验中都得到了验证。针对这个问题，提出了一种基于PS和PGC混合处理以及参考传感器的两阶段多普勒噪声抑制方法。给出了一个处理过程，其中必须在考虑参考传感器之前进行偏振合成。否则，由于多普勒噪声和双折射的相互耦合，抑制算法将完全无效。实验结果表明，仅在第一阶段偏振合成之后，两个时分复用（TDM）通道中可获得相同的多普勒噪声，幅度误差为0.02 dB。第二阶段涉及不敏感参考传感器减法，实现了约30 dB的最大抑制，据我们所知这是最高的。对两阶段多普勒噪声抑制方法进行了正弦和宽带前置光纤扰动测试，为实际干涉式FBG阵列应用提供了一种解决方案。
