Doppler vibration measurement with a miniaturized slant-ended fiber

Laser Doppler measurement technology, due to its high precision, is widely applied in the field of vibration detection. However, traditional Doppler vibrometers generally suffer from complex structures and bulky size, which limit their application in confined spaces. To address this limitation, this paper proposes a Doppler heterodyne measurement method based on a slant-ended fiber. The end face of the fiber is ground to form a specific inclination angle, which causes the reflected light from the end face to be coupled into the cladding for propagation. This design effectively suppresses the interference signals caused by end-face reflection, thereby enabling single-fiber direct measurement of object vibration. A prototype of fiber-optic vibrometer was constructed, with a metallic cylindrical resonator serving as the test object. The signal demodulation process was carried out using the Arctan algorithm. The measurements indicate that the amplitude of the resonator ranges from 0.22 to 973.6 nm, with a nonlinear error of 0.68% and a resolution of 0.2 nm/mV. In comparison with commercial vibrometers, the relative error across the full range is maintained within ±4%. The all-fiber Doppler vibrometer developed in this study ensures high measurement accuracy while realizing the miniaturization of the optical probe, which has a diameter of only 2.5 mm. The device's capabilities extend to applications such as aero-engine health monitoring, modal analysis of automotive components, and an optical microphone.