Fig. 1. Vibration direction changes of incident light after passing through polarizer and 1/2 wave plate

Fig. 2. Linearly polarized light becomes elliptically polarized light after passing through 1/4 wave plate

Fig. 3. Schematic of experimental device

Fig. 4. Process of locating fringe regions

Fig. 5. Process of finding fringe contrast

Fig. 6. Scatter plot of unpolarized light interference fringe contrast

Fig. 7. Curves of measured and theoretical values of interference fringe contrast at different polarization states

Fig. 8. Scatter plot of best fringe contrast in different vibration directions

Fig. 9. Scatter plot of best fringe contrast under different ellipticity