Fig. 1. Schematic diagram of detection optical path of three-dimensional laser Doppler micro-vibration measurement system and off-axis signal light transmission. (a) Schematic diagram of detection optical path of three-dimensional laser Doppler micro-vibration measurement system; (b) schematic diagram of off-axis signal light transmission

Fig. 2. Schematic diagram of off-axis signal light propagation

Fig. 3. Light field distribution on each plane without mechanical deformation. (a)(b) Original plane; (c)(d) reference plane; (e)(f) fiber plane

Fig. 4. Relationship between coupling lens eccentricity and fiber coupling efficiency

Fig. 5. Tilt lens model

Fig. 6. Relationship between misalignment of optical fiber and coupling efficiency. (a) x-y plane; (b) z direction

Fig. 7. Schematic diagram of fiber angle misalignment

Fig. 8. Relationship between fiber misalignment angle and coupling efficiency

Fig. 9. Schematic diagram of mechanical form variables caused by out-of-plane vibration

Fig. 10. Relationship between out-of-plane vibration displacement and coupling efficiency