Long-range fiber-based laser Doppler vibrometer using Faraday rotator for polarization-rotation compensation

In this paper, we report a method for extending distance of an optical fiber-based laser Doppler vibrometer system. This method uses a Faraday rotator (FR) to compensate polarization rotation in an installed long-range optical fiber. The construction of the proposed system is simple and achieved only by adding the FR to the sensing head unit, leading to stable and highly reliable vibration measurement even by using a long-range optical fiber exceeding kilometer. Experiments by using 100-m and 10-km long standard single mode fibers with emulated polarization rotation verified advantages of the proposed method; the system performances retained almost the same values even when the polarization state of reflected light was randomly rotated in installed optical fibers.