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当保偏光纤存在结构不均匀或者受到外部扰动时,将使其内部传输的一部分偏振光耦合到与其正交的偏振态上去。分析了保偏光纤内偏振光模式耦合的原理,给出了基于白光干涉法的偏振模式耦合检测方法,并用迈克尔逊干涉仪对保偏光纤的偏振模式耦合的耦合强度和耦合点发生的空间位置进行了测试。通过步进电机控制迈克尔逊干涉仪扫描臂的反射镜移动,改变干涉仪两臂之间的光程差,来补偿由于偏振耦合而形成的两偏振光从保偏光纤出射时的光程差,实现了对偏振耦合的测量。为提高检测系统的灵敏度,需提高输出信号的信噪比,对光源发出的光进行高频调制,通过频谱搬移和相干解调,有效地抑制了各种干扰和噪声,使输出信号的峰值信噪比提高了5.1 dB,耦合强度测试最小值也由-57.6 dB提高到-62.7 dB,增强了测试系统检测微弱偏振耦合的能力。
When the polarization maintaining fiber is unevenly distributed or externally disturbed, a part of polarized light transmitted inside the polarization maintaining fiber is coupled to the polarization state orthogonal to the polarization maintaining fiber. The principle of polarization mode coupling in polarization maintaining fiber is analyzed. The polarization mode coupling detection method based on white light interferometry is given. The coupling intensity of polarization mode coupling and the spatial position of coupling point of polarization maintaining fiber are analyzed by Michelson interferometer. taking the test. By controlling the movement of the mirror of the Michelson interferometer scanning arm by a stepping motor and changing the optical path difference between two arms of the interferometer to compensate the optical path difference of the two polarized lights due to the polarization coupling when exiting from the polarization maintaining fiber, A polarization-coupled measurement is achieved. In order to improve the sensitivity of the detection system, it is necessary to improve the signal-to-noise ratio of the output signal and to carry out high-frequency modulation on the light emitted by the light source. By spectrum shifting and coherent demodulation, various interferences and noises are effectively suppressed so that the peak signal The noise ratio is increased by 5.1 dB, and the minimum coupling strength test is also increased from -57.6 dB to -62.7 dB, enhancing the test system’s ability to detect weak polarization coupling.