Fig. 1. Principle diagram of laser interferometer ring

Fig. 2. Internal structure of typical circulator

Fig. 3. Relationship between displacement error and direction of circulator and its local magnification

Fig. 4. Point diffraction spatial light circulator

Fig. 5. Contrast test object of circulator displacement measurement

Fig. 6. Displacement measurement results of two circulators. (a) 1^st set of measurement; (b) 2^nd set of measurement; (c) 3^rd set of measurement; (d) local magnification of 3^rd set of measurement

Fig. 7. Displacement error of two circulators at different moments. (a) 3.000-3.010 s; (b) 5.000-5.010 s; (c) 7.000-7.010 s

Fig. 8. Displacement measurement data of two circulators in different target states. (a) State of rest; (b) state of motion