Fig. 1. Principle of AFI. (a) System layout; (b) polarization design of optical path in ANC

Fig. 2. Spacing calibration method of ANC. (a) Positive wave-front propagation; (b) calibration system; (c) calibration method

Fig. 3. Simulation experiment. (a) Modelling; (b) RMS of final measurement results based on modelling of dDP errors

Fig. 4. Simulation results of spacing calibration of ANC under different situations. (a) Shift distance; (b) measurement number; (c) null fringe pattern in each shift; (d) null fringe number

Fig. 5. Experimental layout

Fig. 6. Null fringes obtained by experimental calibration

Fig. 7. Spacing calibration in two groups of experiments. (a)-(c) First group of experiments; (d)-(f) second group of experiments

Fig. 8. Test results of surface figure errors of two paraboloid mirrors after spacing calibration of ANC. (a)-(c) Three independent test results for first paraboloid mirror; (d) test result of first paraboloid mirror by Zygo interferometer; (e)-(g) three independent test results for second paraboloid mirror; (h) test result of second paraboloid mirror by Zygo interferometer